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The frontiers between oceans and continents.

The tamarisk and the glasswort grow on the scorching plains and beyond the rushes and the village limits, and in fields of golden samphire where the steers live and the white horses roam freely, away from the waves, wet with the spray.

Frederic Mistral Mireia (1859)

1 Between the land and the sea

1. The geographic space of coastal systems

1.1 The changing coastline

The oceans have changed and are constantly changing, although very slowly in comparison with the age of modern civilization, and the coasts have changed and continue to change. The rate of change of the coasts is faster than the change in form of the oceans, although the most important changes are also slow from a human point of view. Variations in sea level and orogenic and tectonic processes may cause important alterations in the form and size of the coasts. It is easy to draw on a topographic map a hypothetical coastline 330 ft (100 m) higher or 330 ft lower than the current one, simply by following the corresponding contour lines. In rugged coastlines this might not change the form of the coastline, although it would change its length or the area of the dry land of the continent. But in flat coasts, rises in sea level of 330 ft (100 m) might lead to the disappearance of entire countries, or their appearance in the case of falls in sea level.

The sea's memory

In the last major glaciation (as in the preceding ones) a large part of the liquid water on the planet left the oceans and was deposited as ice in the glaciers covering much of the polar regions and the high latitudes. The icecaps reached their greatest area about 18,000 years ago. Sea level descended about 330 ft (100 m) and many continental regions, bearing the immense weight of accumulated ice (up to 2 mi [3 km]), sank into the mantle of deformable rock they float on. While sea level was low, wind and rain eroded and shaped the part of the continent exposed to the air, while rivers excavated new valleys and transported soil sediments downwards. After the withdrawal of the ice and during the warm period that followed the glaciation, the sea level again rose, and some continental areas that had been weighed down by the ice started to rise and gradually recover a new equilibrium, floating, as always, on the magmatic fluid. In the last 1.6 million years there have been about 30 glaciations with their interglacial periods, and they have shaped the coastlines that we know.

These processes left unmistakeable marks around almost all the world's coasts on a structure called the continental shelf. If a topographical profile is drawn from the continent to the bottom of the ocean, it can be seen that in most cases the slope is variable: The slope is slight in the first stretch to about 656 ft (200 m), and increases as it enters the continental slope, and then decreases as it merges into the abyssal plains thousands of meters below.

However, underwater relief has little to do with the relief of the continental surfaces, while the large oceanic trenches below 19,685 ft (6,000 m) are the expression of significant tectonic phenomena, reminders that the oceans are continually being made and destroyed. Ocean crust is created in the areas of expansion, large submarine mountain ranges where the oceans are widening, while in other places where there are deep trenches, the old ocean crust sinks beneath the neighboring continent and disappears for ever, forming volcanoes and causing earthquakes. This is why there is no ocean crust older than 200 million years on a planet 4,500 years old. Bearing in mind that there have been oceans more or less like the present ones since about 3,500 million years ago, one can calculate that the ocean bottoms have been made and destroyed more than 10 times since the planet's hydrosphere came into existence.

This means that the memory of the oceans is short. The most recent memories are on a shelf next to the coast (continental shelf) in the sediments that cover the basins, but the oldest events have mostly been lost. Some structures and sediments have been saved from definitive burial and are found as fossils on the continents. The fossils of marine organisms can be found in the Himalayas thousands of meters above sea level, and this is because the world's highest range of mountains is the "scar" of an ocean that closed forever in Asia's collision with India 50 million years ago. In fact, in many places there are the remains of former oceans, beaches, coral reefs, fine sediments and, together with these structures, the remains of the organisms that lived there.

Between the sea and the continent

There can be no doubt that of all current marine regions, the coast is and has been the most important for human beings. The reason is simply that it is the limit of the continental system humans belong to, and so humans lose one of the two degrees of freedom provided by the land surface. The coast is a frontier, but it is not a simple one-dimensional line. The coast should be considered from a functional point of view, as a system, in order to comprehend its landscape, its changes, its history, and to plan its future.

The coastline is defined by the line of contact between the surface of the sea and the land of the continent. The form of this line depends on the relief of the land, as it can be considered that the surface of the sea is in effect flat and adopts the form of its recipient. It is only necessary to introduce the complication that sea level varies with tides, but this is not a fundamental complication, except through its effect in creating a narrow strip that is intermittently submerged, the intertidal zone. The form of the coastline is not static, but is influenced by the action of the waves and ocean currents.

Waves are responsible for the erosion of the lower parts of cliffs, which in the long-term results in the fall of large quantities of rock. The forms generated by this action speak for themselves. Waves also have a complex effect on low and sandy coasts. They erode the beach but also produce a drift current along the beach that transports sediment laterally, not only from the coast towards the ocean floor. The losses to beaches caused by erosion tend to be compensated by the supply of sediments from rivers, but the effects of drift currents and the external supply of sediments are unequally distributed, and so there are places where sediments accumulate and others where the coast retreats. It should also be pointed out that regularization of the flow of rivers and seasonal rivers with irregular flow regimes, by means of channeling, floodgates, and reservoirs, reduces the quantity of sediments reaching the sea, causing continuous beach loss in several areas of the world. Coastal processes may be fast in a storm, for example, but if we bear in mind the average change over many years, it is observed that the results are relatively slow, although on a time-scale that can easily be grasped by human beings (decades to centuries). This dynamic is what causes the most visible changes to the coastlines, especially in deltas, forming sediment banks on capes, sandbanks that enclose coastal lagoons, changes in the location of river mouths, etc.

The general marine currents have little effect on the evolution of the form of the coastline. Tidal currents do, however, act on low and flooded coasts with effects comparable to those of drift currents, but in an area further inside the coastline system.

Another factor that changes the form of the coastline is biological activity. The clearest example is the coasts formed by coral reefs, but we must also remember the interaction between mangrove (and other plant) formations and the accumulation and redistribution of sediments on low coasts. Human activity may also be considered as a biological activity, although a very special one. Humans create artificial supports that locally modify coastlines to a great extent; protective breakwaters, barrages, and ports now form a substantial part of the world's coastal landscape.

Finally, volcanic activity also changes the form of the coastline in some areas.

Coastal landforms

Coastal landforms are the result of the interaction of two classes of process: immediate changes to form of the coast--waves, ocean currents, biological and volcanic activity--and slower geomorphological processes that occur on a larger scale. Both of these processes act upon a basic or specific style of coast. Thus coastlines may be low and sandy, tall and rugged, highly indented with many inlets and promontories, or they may follow a more-or-less straight line.

Irregular coastlines are usually present in areas where the continent is relatively sunken (or the sea level is relatively high). This is clearly shown by all the zones that sunk due to the effect of the weight of the ice during the last glaciation and still have not attained their definitive equilibrium height. On some of these coasts the sea water floods the valleys of the rivers or the former glaciers. On others, the low, flat, submerged coast has a different kind of form, although it is also irregular.

The coasts that are more-or-less straight or regular in form are usually present in relatively raised zones where the surface of the seawater bathes former submarine sedimentary deposits. In most cases the slope is gentle and one can talk of coastal plains, but in others the coast is a series of old cliffs and plains or raised reliefs, often cut at different levels by the action of the waves.

Finally, there are the special coastal landforms. Coral reefs are almost circular atolls around small volcanic islands in the middle of the ocean, or large barrier reefs along the coast, like the one off eastern Australia. River deltas, often similar in appearance to a sponge, occur where the waters of the river and the sea mix together in countless areas that vary in size and shape. Lava pillows are found on volcanic islands throughout the world's oceans. Perhaps the least stable coastal landforms are frozen coasts--the limits of the marine ice that form and break up, and the glaciers that flow into the sea sowing it with icebergs of all sizes, some many kilometers wide. These are genuine but short-lived drifting islands.

1.2 A sea that rises and falls

The presence of the coast limits the horizontal displacement of water and tends to redirect marine currents and make them flow in parallel to its main direction. However, if there is a convergence of waters towards the coast, as happens with the tidal waves, the obstacle forces the elevation of the sea level, and with the undercurrent, the level subsides.

As these oscillations of the water level are very frequent and have a certain periodicity, although their extent is limited, the geometric changes produced in the horizontal direction of the coastline might be included in what is, in effect, a coastline in the broad sense.

The form and outline of the coast significantly modulate the tide. Especially in semi-enclosed areas of sea, such as bays and estuaries, some periodic components of the tide may coincide with what is called the "oscillation mode" of the bay or estuary in question.

Tidal oscillations

To understand what a tidal oscillation means one can perform a simple experiment: move your hand to-and-fro in a bucket, sink, or bathtub. If you move your hand quickly, the water is agitated and the waves are smallish and chaotic in appearance. If you slow down the to-and-fro movement, a rhythm is produced and the water goes up and down at both ends of the container. In this case it feels as though the water flows over your hand with almost no friction, and only a little force is required to make a wave that will flow over the edge of the container. In this situation, the level of the surface in the container's center does not vary, while its variation is greatest at the edges. What you have found is the oscillation mode of the water surface in the container. If you perform this experiment in the three containers, you will see that the period (the frequency you move your hand) is shorter in the bucket of water than in the sink, and this in turn has a shorter period than the bathtub. Thus, when the period of the tide coincides with the mode characteristic of a bay or an estuary, there is resonance and this may greatly increase the tidal range.

From the point of view of coastal ecosystems, not only the frequency of the movement and the range of the tide are important, but also the way these parameters are expressed in a specific location. In particular, the slope of the coast the tide acts on will be very important, since for the same range (vertical displacement), the area of land exposed to the ebb and flow will be greater the less the slope . On a vertical coast, a maximum tidal range of 3 ft (1 m) creates an intertidal zone of 3 ft (1 m). If the slope is 1% (one in a thousand), or 3 ft in 0.6 mi (1 m in 1 km), the same range creates an intertidal zone one kilometer wide. The gentler the slope of the coast, the greater the speed at which the tide front moves, and the greater the currents and the erosion of sediments.

Thus the organisms that live in the intertidal zone have to learn to anticipate if they are to avoid being swept away by the current or suffering excessive desiccation, but they can also use the periodicity of the tides as a clock to synchronize activities such as feeding and reproduction.

Catastrophic variations in sea level

The perfect periodicity of the tides means that it is easy to adapt to them so they cease to represent a danger, but can even be used in many ways. There are, however, variations in sea level that are unpredictable because they are not rhythmic and because they may combine with tidal movements to produce changes in the height of the sea that are much greater than normal.

Normally, differences in level of the sea due to variations in pressure or caused by wind (and the movement of water it involves) are no greater than those due to tides. In general, the interpolation of non-periodic variations on the tide only introduces a new factor that reduces the precision of tide prediction tables. However, if the causes of these variations are extreme (hurricanes, tsunamis, storms, and intense atmospheric depressions), and if they coincide with the moment of greatest differences in the height of the tides, they may have catastrophic effects. Some situations of this type have occurred frequently enough to require the construction of extremely expensive and complicated protective barriers (London, the Netherlands). The effectiveness of these protective systems is only optimal when they are combined with systems for predicting these phenomena. There is now a network of satellites that provides instantaneous meteorological information which can be combined with hydrodynamic models that can work quickly to make predictions, with sufficient time for floodgates to be operated or to warn civil defense services to alert the population of the zone at risk of flooding. Seismic observatories provide information on earthquakes, allowing prediction of the time of arrival of the wave of the tsunami at any of the affected coasts, and thus its probable coincidence with local tides.

On the coast other vertical changes are observed in sea level that differ in periodicity from the tides, and which may be locally important and should not be confused with tides. Seasonal variation in atmospheric pressure, for example, in semi-enclosed seas like the Mediterranean, provokes a rise or fall in sea level that may last for weeks (highs and lows). In this case, a seasonal situation occurs in the coastal ecosystem, as the populations of benthic organisms of the upper levels may be left exposed for so long they desiccate and die.

Some rhythmic nontidal movements show periods of a few minutes and a range of 3 ft (1 m) or more. In the Mediterranean they are due to internal waves near the coast provoked by high-frequency disturbances in the atmosphere. These internal waves have a short amplitude and generally pass unnoticed, but on some occasions their duration is similar to that of some bays, ports, and coves. In these cases then resonance may occur, and the sea may rise or fall more than a meter in a short time (such as ten minutes) and the phenomenon may last for an hour or so. In tideless seas, in which sea level is not expected to vary so much, these phenomena (which usually occur in summer, although they are unpredictable) cause damage to boats moored in small ports or at anchor in sheltered coves.

1.3 The boundaries between land and sea

From the ecological point of view, the limits of any system are frontiers, in principle arbitrary, through which there are exchanges and flows of materials and energy. In practice, ecologists studying a system try to ensure that the flow of materials, organisms, energy, or nutrients across the frontiers chosen are easy to quantify and check. Two types of boundaries are particularly useful for marking the limits to ecological systems from a functional point of view: those that are impermeable, in other words through which no flows occur, and those that can be considered symmetrical because the flows are identical in both directions.

In nature, these two types of boundaries never exist strictly speaking, but it is possible to choose the limits to the ecosystem so that flows are reduced to a minimum. This is true for hydrographic basins, which have natural limits in the form of watersheds; that is to say, where there are changes of slope, because water and the materials it carries cannot rise against gravity. In the open sea, for example, it is normally accepted that any vertical plane represents a symmetrical frontier because, unless there is a clear difference between the two sides of the plane or a significant current crosses it, it can be supposed that in pelagic ecosystems the level of exchanges across this boundary will be similar in both directions. This would be a symmetrical boundary.

The coast, a frontier area

The coast is a frontier area. Or in other words, if one seeks to mark its limits from functional point of view for practical purposes, it is necessary to place limits on a system that is itself a frontier. Flows occur across the coastline in both directions, although clearly the easiest and most important is in the direction of gravity, from land to sea. Anyway, the most substantial part of the flow occurs in limited areas, as if they were windows or doors.

The rivers are the most important of the passages between the land and the sea. The air is also a significant vehicle for transport of water, dissolved substances, and particles, both landward and seaward. In this case, the flows are asymmetric. Many organisms, like birds and fish, transport materials across the coastline using air or river water as a support. Finally, in "humanized" coasts, direct human transport is often the most important activity. Flows from land to sea include urban sewage; industrial or agricultural discharges; emissions from underwater outfalls or from rivers; solids or chemical products discharged by industrial, construction, or extractive activities, which may be transported by agents, air, lorries or boats, as well as oils and petrol. The flows from land to sea are smaller and are usually the result of extractive activities, whether of living resources (fish, seafood, seaweed, etc.) or minerals. These flows often take place through ports.

It is thus clear that the coast is the area where most flows occur between the interior of the continent and the sea, and between the sea and the land.

The relatively arbitrary nature of the delimitation

The coastal system should be understood as a strip more or less centered on the coastline, varying in width, including some land and some sea. The part of the sea that has to be considered as coast is the region most directly influenced by the inputs from the continent, the zone directly affected by human activities.

Although the limits vary in different coasts, it is considered that the seawater to a depth of 20 in (50 cm) forms parts of the coastal system, although it should be remembered that this is an arbitrary decision. In fact, this is almost always the emission depth for underwater sewage outfalls, or sludge from coastal sewage plants. The effect of the small rivers is also felt as far as a few miles from the coastline, while large rivers affect much larger areas, and in this case it may not be feasible to consider the entire area of influence as falling within the coastal system. It should also be pointed out that in most coasts there is a wider band of sea (about 30 miles or more) including the continental shelf, with its own characteristics distinct from those of the more oceanic water further from the shore. The water of the shelf, including the strictly coastal strip, does not mix easily or continuously with that of the oceanic region. A front arises between them (a physical frontier) that acts to oppose exchanges. The idea that everything discharged into the sea from the land rapidly disperses and disappears is incorrect, since pollution accumulates on the coasts and ends up returning to the land in one form or another.

The landward limits of the coastal strip are no easier to ascertain. There are physical and ecological criteria to define accurate enough limits. In coastal areas with mountain ranges that run more or less parallel to the coastline, it is useful to consider the crests of these mountain ranges as natural limits, thus including the smaller coastal watersheds. Where the coast is flat or in places where wide valleys open out to the sea, the limits should be set at the distance where the influence of the seawater can still be perceived. One possible criterion is to consider the height of the water table with respect to the sea level. The lower slopes and large valleys of rivers or deltas are frequently zones with important urban, industrial, and agriculture settlements that consume large quantities of fresh water extracted directly from rivers or wells that exploit underground water. Heavily exploited deltas often have problems of salinization of the water table, a clear sign of conflict and interaction between the sea and the continent.

Whatever the criterion chosen, it must be borne in mind that on the land, sociology and economics are also involved, and often politics, because on very "humanized" coasts the weight of human activity is often a determining factor.

1.4 Ecological criteria for classifying coastal systems

In order to analyze landscapes, in this case coastal systems, we must not ignore some key ecological concepts. The scientific study of natural systems provides a functional view of landscapes that helps us to understand and manage coastal systems. One good management criterion is not to request nature to do what is unnatural or impossible, but to rely on its way of functioning and changing to ensure that maintenance is as automatic and low-cost as possible. One must not go against nature, but adapt to its rhythm and its regeneration capacity. It should not be forgotten that the clearest and most important effect of human beings on nature is the acceleration of those processes that always implies simplification and the loss of stability. Far from equilibrium, structures (in this case those of the coastal system) can only maintain themselves through a considerable expenditure of material and energy, and also of information. In other words, with an economic cost proportional to the degree of disequilibrium incurred.

Historically, the most important human settlements in terms of development and culture have been close to rivers. Water and fertile land are the features most valued by human beings because they represent great potential for development, growth, and maintenance. The sea has sometimes played the role of a real frontier, but as humans mastered the skills of navigation, it has also represented a two-way cultural and economic doorway. Sites where rivers coincide with the sea are usually densely populated, although this depends on the type of river mouth and on the coast. Estuaries have been easier to colonize than deltas and marshes.

Production and productivity

The ecological concepts of production (increase in biomass per unit of space and time) and productivity (production per unit of biomass present) are basic in order to start to analyze the determining characteristics of any ecological system. The entire trophic functioning of an ecological system depends on primary production (by plants); this determines the maximum number of animals that can live in the system, including humans. Productivity is a good indicator of the rhythm of the system--in other words, the flow of energy it processes--because it reflects the rate of renewal of the biomass. Greater productivity means a faster rate of renewal. Production depends on the simultaneous presence in the same place of the factors that make it possible. These are light, mineral nutrients, and plants. Also important is the physical support for the producers (soil, or water in aquatic systems), since it determines the stability, the degree of oxygenation, etc.

Rivers bear sediments and nutrients to the sea, and they will form the edges of the valleys in their final, flattest stretches and in the deltas. The river water containing materials enters the seas and enriches the coastal waters. Thus the coast generally has a greater chance of being a rich, productive area than others in the interior of the continent, and this richness is not limited to the landward strip, but extends to the sea where plankton and fish communities, and benthic communities living on the ocean bottom, will flourish more near the coast than in areas further from the coast.

Production depends to a large extent on the rate of entry of the energy (and materials) the ecosystem receives. These inputs in the form of mechanical energy, river or rain water, inorganic or organic nutrients strengthen the system and make it more productive--a system adapted to a specific regime of inputs processes and uses, with differing degrees of efficiency, this external energy. The coast, due to its nature as a boundary across which most flows from land to sea must pass, is a system that contains many particularly unnatural and productive landscapes. However, the rate of entry of external energy is inversely proportional to the system's efficiency. In other words, highly forced systems usually process the materials supplied with less efficiency and tend to export a substantial proportion of the inputs, only processing partially. These forced systems thus because systems that, in turn, force their closest neighbors below them in the cascade of material and energy transport.


Natural systems are subject to disturbances that make them, to some extent, unstable. The communities that develop in any location are the result of the intimate interaction between the physical medium and the biological medium. For a given level of external energy input, the most stable physical media ensure more permanent communities with organisms showing greater anticipation. This leads to greater complexity and maturity than in less-stable systems.

An unstable physical support implies greater renewal and, thus, less persistence. Natural communities tend to adapt to the existing regime of disturbances, as the organisms that form the community adapt their rates of reproduction and growth. The more unstable the community, the greater the rate of renewal or reproduction, the shorter the lifespan, and the smaller the organisms forming the community. The more stable the community, the larger the organisms, the slower they grow, and the lower the rate of reproduction. Thus, the most stable and constant systems lead to complex communities that are apparently not very variable over time, forming mosaics showing little repetition in space or which are very diverse. These systems develop slowly, process efficiently and, although they show high levels of production, they also show high levels of respiration. In fact, because their biomass is high, their productivity is low. In the sea these systems are exemplified by coral reefs, and on dry land by tropical rainforests. The stability of these systems is basically due to the stability of their physical support and the regularity of the regime of disturbances they are subject to, bearing in mind that these disturbances are sometimes catastrophic.

Many coastal systems, however, such as river deltas, are examples of systems naturally subjected to relatively intense, more-or-less recurrent disturbances like flooding that renew the system and supply new materials that enrich the medium. In fact, they cause things to "start again," implying the maintenance of a high level of productivity and renewal, and at the same time these disturbances prevent the establishment of longer-lasting communities.


From an ecological point of view a system is exploitable if, as a result of the regime of disturbances it is subject to, including the different types of input of external energy, it produces more than it can process in situ. In other words, if it has a surplus that neighboring systems can exploit. Every system showing high productivity is potentially exploitable. The deltas of rivers, together with coastal marshes and lagoons, can be considered exploitable systems, and this is why they are visited by migratory birds that make use of their surplus at the right moment. Marshes, mangroves, and other similar systems export part of their production to the sea and are not only a refuge for juveniles and adults, but also the trophic source feeding many of the organisms of the nearby marine system. The enriched sea is also exploited by terrestrial organisms, mainly birds that cross the physical frontier, helping to increase the efficiency of the flows between the two systems.

Humans are no different from other organisms in their use of the capacity to anticipate and make use of the surplus production of exploitable systems. In fact, what distinguishes humans is that they can modify natural systems by increasing their instability and their capacity to provide them with an excess of external energy. Human beings water and fertilize seeds they have sown, for example, something no other species does consciously. Furthermore, this exploitation maintains the system at a level of sustained rejuvenation that makes them even more exploitable. People are sometimes, or even often, unaware that their activities easily lead to these simplifying changes that accelerate the rate of renewal of the biological environment.

At the other end of the range of ecosystem types, the most stable, mature ecosystems are not very exploitable. The least exploitable seas are those with the most transparent blue waters, often with rich, diverse biological communities. These systems are often culturally appreciated. They are like living works of art and it is pleasant to observe them and to bathe in their warm, transparent waters. Leisure culture, strongly rooted in societies with stronger economies, has invented tourism, which depends on "excess" time, that which is not necessary for survival and can be used for play activities, travel, letting one's imagination soar, and doing nothing. Many of the world's coastlines have the environmental conditions that are culturally most appreciated for leisure, landscapes that correspond to unproductive ecosystems, with clear water and temperate or warm climates. In this sense, a new concept of exploitability has to be added to the more classically ecological one mentioned earlier. However, in this case a grave contradiction arises, namely that the greatest potential wealth in terms of tourism is in conflict with this form of exploitation (tourism itself). Tourists requires a degree of "humanization" to make life comfortable, but the mere act of going there rebounds against them, since they spoil the very landscape that attracts them. Humans destroy natural spaces to construct houses, even if they are only for seasonal use; we produce undesirable residues, some solid and others liquid, and these are then discharged into the sea. Water enriched with nutrients ceases to be transparent, even if it does not become a health risk. The disturbed communities become simpler and cease to be what they were, both in the sea and in the terrestrial strip of the coastline.

In fact, in the most developed countries there are now no ecosystems unmodified by humans in precisely the areas where they would be most desirable. What can be more agreeable than a landscape full of meadows and woodlands, with a great diversity of plants edging a river with clear water that opens out into a broad beach of clean sand,

The fractal coastline

Calculating the area of a country is easy with a good map. Things are more complicated if the country is mountainous, as maps do not show the real surface, only its projection on to a plane. As so often happens, very complex things are hiding behind something apparently banal. Even more difficult than calculating a country's area is calculating the exact length of its coastline. Theoretically, the problem is very simple and can be solved with a good map and a pair of compasses: Use the compass to measure a distance against the scale of the map, and then just count the number of times it is necessary to move the compass by this distance in order to go around the coastline. But what about a highly indented coastline, as in reality they always are?

Thus, after calculating the perimeter one is not very convinced, because if the dividers are opened too wide, many bays and capes will be ignored. To obtain greater precision, it is necessary to repeat the measurement with a smaller aperture, and thus a shorter unit of measurement that corresponds more closely to the real sinuous form. Naturally, repeating the calculations will give a different total length for the coastline. This second measurement may be insufficient, but a third measurement can be made using a more detailed map. And a fourth. And as many as desired. And with each measurement the coastline grows longer. What is happening?

A map of Iceland is used to perform this calculation, using the scale located on the meridian and centered on the island's latitude to minimize distortions derived from the cartographic projection used. As the map used is a nautical one, the separation between each two lines is 10 minutes of arc, 10 nautical miles (18.5 km). Using a pair of dividers, a typical sailor's instrument, the operation is repeated several times, decreasing the aperture to 100, 60, 20 and 10 mi (160, 96, 32, and 16 km). The results are surprising. Using measurements of (roughly) 62 mi (100 km), the island's perimeter is only 600 mi (1,110 km), but when the compass opening corresponds to 20 mi (37 km) the coastline is 960 mi (1,776 km), and if it is closed to the equivalent of 10 mi (18,5 km), the coastline of Iceland is 1,250 mi (2,312 km) long. If the perimeter was measured using in steps of only 100 m (0.054 miles), its would be 7,060 mi (13,061 km) long, almost 12 times longer than the first measurement!

In mathematical terms, any coastline tends to infinite length as the resolution of the measurements increases. Obviously in practice this explanation is not very useful. Evidently, decreasing the measurement unit to one centimeter or one millimeter, means measuring the outline of every pebble or grain of sand on the beach, supposing that their outlines continue to coincide with the map of the coast as a whole, which is not so. By increasing the size of the map successively, it can be observed that any part of the coastline at any scale is similar to any other part at any other scale. This property is called "self-similarity." It can be said the drawn form of the coastline is independent of the scale. This involves the apparent paradox of accepting that any coast, however straight or jagged, has the same indefinite length. Thus we must conclude that the coastline does not behave like the entities measurable with conventional systems, perhaps because it is not one. It is not measurable in this way, and geometric objects presenting this class of self-similarity were given the name fractal objects by Benoit Mandelbrot, the mathematician who studied this type of phenomenon during the 1970s.

In mathematical terms, any coastline tends to infinite length as the resolution of the measurements increases. Obviously in practice this explanation is not very useful. Evidently, decreasing the measurement unit to one centimeter or one millimeter, means measuring the outline of every pebble or grain of sand on the beach, supposing that their outlines continue to coincide with the map of the coast as a whole, which is not so. By increasing the size of the map successively, it can be observed that any part of the coastline at any scale is similar to any other part at any other scale. This property is called "self-similarity." It can be said the drawn form of the coastline is independent of the scale. This involves the apparent paradox of accepting that any coast, however straight or jagged, has the same indefinite length. Thus we must conclude that the coastline does not behave like the entities measurable with conventional systems, perhaps because it is not one. It is not measurable in this way, and geometric objects presenting this class of self-similarity were given the name fractal objects by Benoit Mandelbrot, the mathematician who studied this type of phenomenon during the 1970s.

Many other natural fractal forms show, on some scales, structures of a fractal nature. Like self-similar geometric figures, they maintain the same rules of generation at all scales, and they can be simulated mathematically in a computer. Computers and televisions sets now create images of objects and imaginary landscapes that appear real because they have the same fractal dimensions as the real landscapes they imitate.

2. The great planetary river

2.1 The flowing waters

It may seem out of place, in a volume dedicated to ocean and coastal systems, to make an incursion into limnology. Limnology is the multidisciplinary science studying the waters that flow over or stand on the continents (and therefore called continental waters), the best known ones being rivers and lakes. This work deals with these continental waters within each of the large terrestrial biomes of which they form a part, but continental waters also form part of a world-wide system of distillation and transport, and thus play a role in global or planetary ecology.

Rivers in the water cycle

The river has always been considered as the model for the flow of things, and more specifically as a model for human life. This is both expressed in the pre-Socratic paradox that it is impossible to bathe twice in the same river, and in the poetry of the 15th century Castilian poet Jorge Manrique, "Our lives are rivers flowing into the sea, which is death." This image of what comes to pass turns into a practical reality, with the result that rivers may be considered more important than lakes, which after all only slow down the drainage system. Rivers and lakes focus landscapes, beautifying and harmonizing them. Lakes are also kind enough to accumulate sediment, including minerals, pollen, and other materials that form very useful historical records. Lakes are classified as oligotrophic (not very productive) or eutrophic (more productive), more frequently due to external fertilizers than to accelerated recycling. Eutrophic lakes have greenish water and oxygen is scarce in deeper layers, meaning the water may smell bad and attack iron or cement, undesirable properties for humans, but typical of the current general eutrophication of many continental waters.

Rivers make global circulation more visible and through them we can figuratively take the pulse of the biosphere. The lower stretches of rivers contain an extract of the materials, whether natural or added by humans, gathered over the entire watershed. The composition of the water lets us deduce the state of (ecological) health of the watershed, in the same sense that the urine informs us about the health of the human body.

It is essential to understand in quantitative terms the water cycle, the features underlying the continuous observed changes in the distribution of cloudiness, rainfall, and the flow of the rivers. Fluctuations are observed at all levels, and within these fluctuations it is difficult or impossible to distinguish sustained tendencies from regular cycles. Bearing in mind that there is a more or less repeated annual cycle, the natural thing is to compare some years with others. The result is to confirm the difficulty of explaining the annual fluctuations in the volume of flow in rivers and in the level of their associated lakes. Exceptional events, such as floods called the "flood of the century" are followed by years of drought or rain in sequences that lack definition. It has been said that there are similarities between the characteristics of consecutive years, and it has also been said that the similarity is greater between alternate years. Time sequences showing rainfall distribution in a given area always give food for thought, and also frustrate statisticians seeking to force idiosyncratic nature into a straightjacket.

Apparently capricious fluctuations are largely due to the weak buffering of the cycle, as the quantity of water retained in the form of water vapor in the atmosphere is small (between 10,000-15,000 [km.sup.3] of liquid water) and fluctuates very irregularly; it functions as an almost chaotic machine. On the other hand, it must also be borne in mind that the water of the atmosphere turns over in only 9-10 days, and any fluctuation, however small, is important on both a global and a local scale. Uncertainty is shown in the passing of atmospheric fronts and in weather conditions. The planet's annual rainfall (and evaporation) is estimated at 500,000 [km.sup.3]. Comparing this figure to the ones above, it follows that the water contained in the atmosphere turns over 30-40 times a year. It is a highly sensitive system. The quantity of "fresh" water retained and visible on the surface of the continents is estimated at 230,000 [km.sup.3], but only 0.5% of this quantity corresponds to what is visible in rivers.

It is very difficult to evaluate, on the one hand, the water retained under the earth in soils and in the aquifers occupying cavities between the solid materials of some sediments, and on the other hand, the solid fresh water retained above sea-level in the two polar regions; it may exceed 36 million [km.sup.3]. This is a very large reserve mass and is already showing signs of chemical attack by humans, signs that will be hard to remove given the aquifers' slow turnover. One of our most urgent tasks is to adopt (and fulfill) measures to protect subterranean water reserves. Aquifer contamination is a generalized risk. While a river cleans itself thoroughly because the water is rapidly renewed, any serious contamination of aquifers is as undesirable as dispersing hidden spots of radioactive materials with a long half-life.

Evaporation and its return in the form of rain represents a annual global average of about 33 in (1,000 mm) of water, equal to 1,000 litres per square meter. Of course local and seasonal differences exist. On land almost one third of the evaporation circulates through plants, in the process of evapotranspiration. Recall that in terrestrial systems between 53-132 gal (200-500 l) of water evapotranspirated per square meter per year corresponds to a primary production of about one kilogram dry weight. The rain that falls on the continents is equivalent to what evaporates from the land plus a large quantity of water evaporated from the oceans. This explains the difference of about 40,000 [km.sup.3], the annual surplus carried by rivers from the land to the sea.

Relief and the river network

Rivers adjust to the restrictions imposed by relief and substrate, but the river imposes its own, rationally explicable, dynamic on them. Rivers frequently start in abrupt landscapes rich in potential energy. The tributaries flow together and transport rocky materials that progressively fragment. On the plains they use their energy in redistributing the sediments they bear and continuously creating and modifying mobile meanders, expressions of the continuous dialogue between the water and the substrate. They are important agents in restarting succession and agents for reciprocal influence between life in the water and life on the continent. In the lower part of the river, in relation to the existence or not of tides on the neighboring coastline (if there is one) and their characteristics, the convergence of the tributaries gives way to a subdivision of the river into often sinuous drainage channels that form interesting landscapes of great beauty. Most of these landscapes are now endangered, except where there has been a determined effort to protect them, or one is made soon. In the confluence of the estuary, many materials are precipitated as a result of complex physical and chemical processes, contributing to the fertility of the marshes.

Different fluvial forms, such as confluences, branching, and meanders are repeated on several scales, and considerations derived from the science of fractal objects can be applied to them. The intermittent and to some extent unpredictable interaction between the river and the floodable areas often gives rise to biological production that is often abundant and almost always highly random, and that is used by large roaming or migratory animals, including the many birds that enrich riverside systems, especially those closest to the sea. These animals, depending on the annual but never synchronous fluctuations in biological production in each location, preferentially exploit one region or another. Marshes not only fluctuate but also show a notable capacity to regenerate if they are left alone. There are also migratory aquatic animals, mainly fish. The behavior of salmon and eels has often been contrasted, although they are comparable in many aspects. The common denominator of their behaviors is that in both cases the eggs hatch in the most productive and fluctuating part of the two ecosystems that they combine: upriver in the case of the salmon, and in the pelagic environment in the case of the eel.

The river network, in addition to its obvious significance, has other less-known features, such as forming the setting for evolution and successional phenomena, and serving as a support for highly productive ecosystems. The successive tributaries that combine downstream mix their waters, making them physically and chemically more uniform and enriching their biological populations, which will then be subject to selection. Depending on the position of the tributary watersheds in relation to the areas of more or less abundant or regular rainfall, the rivers may either join up, making the flow downstream more regular, or they may exaggerate the irregularity of its flow. Rivers act as conveyor belts transporting sediments that are broken down little by little and deposited according to the current. In the upper stretches, they are pebbles and rounded stones, and downstream they are sands that become finer and finer the further one goes down. Each seasonal flow, or torrent, introduces a sudden transition clearly visible in sediments (as long as their sequence is not totally disrupted) as a rapid change from fine materials to coarser ones overlying them. In a torrent, the distribution on the plane of the flow may also change, wandering across the entire width of a broader or narrower bed, whose history also includes its occupation by vegetation or disturbances by humans or other animals, such as beavers, which are famous for their building activities.

Our civilization, with its obsession for straightening and damming watercourses, extracts part of the energy that the river formerly invested in reorganizing nature and that it might otherwise have continued to invest. Furthermore, water is beginning to be considered as a good that can be easily piped on a large scale from one watershed to another. And this is in fact how it is transported, with a lack of concern comparable to the piping of gas or electricity, which in the case of water is less innocent, because in ecological terms, it is sacrificing or mortgaging the future of some watersheds.

Flows under river beds and underground water

Normally, the course of the river continues underground with more permeable materials, through which the water flows more slowly than in the open air. Life, often abundant, has adapted to these conditions and can easily be found by digging wells next to a river bed, and by looking for it in water pumped from the water flowing under the river bed. Underground waters dissolve carbonates, opening karstic cavities and conduits through which it flows, eventually covering the old cavities and caves with diverse, often breathtakingly beautiful concretions--stalactites. The theory of fractal forms is applicable here, both in describing the characteristics of water percolation and its movement between the sediments, and in describing the characteristics of the forms of the calcareous concretions.

Systems of underground cavities excavated by flowing water form what are known as karst, a name derived from the name of a region of Slovenia near the Adriatic Sea where spectacular examples of these formations are found. Whether with water or not, the cavities are colonized by organisms of terrestrial or aquatic origin that have undergone notable evolutionary differentiation. These include prolongation of lifespan, increase in size, lessening of metabolism, reduction in number of offspring, and often the loss of vision, depigmentation, and the elongation of body appendages. Generally they are small animals, but in certain areas, there are many fish and crabs, and in the Slovene karst, there is a famous amphibian, the olm (Proteus anguinus). Some terrestrial animals find temporary refuge in these cavities. Bats and birds (such as the South American oil bird [Steatornis caripensis]), for example, introduce alien food with their excrement, favoring later colonization by saprophagous organisms, fungi, many insects, and other animals.

2.2 The river system

Life in rivers may be difficult to understand and interpret within a relatively static framework, such as the one applicable to terrestrial or lake ecosystems. For this very reason the study of life in rivers allows us to extend the idea of the ecosystem to conditions of heterogeneous flow. Seen in this light, it illustrates and complements the study of plankton, which also raises a series of similar but even trickier problems.

River dynamics

Most ecological models start by expressing the geometrical growth of a population N of the species i: [dN.sub.i] /dt = [r.sub.i], where [r.sub.i] is the intrinsic rate of increase of the species or group i. The river continuously moves and disperses populations, and reason leads us to choose between two approaches. One can define a small volume in a geographical location and study the changes within it over time. This would be what is called an Eulerian approach to the problem. What is known as a Lagrangian current measurement would be to follow the changes in a single volume of water as it moves. However, as the volume deforms over the length of its path, its molecules separate and previously peripheral molecules come between them, the difficulties increase and, in short, Euler's model is more convenient.

When considering what is occurring in a fixed position within the river, not only are local population dynamics in operation, but also the current, which modifies the population according to the speed of the water, V, and the population gradient in the direction of flow, dN / dx. So:

[dN.sub.i] / dt = [r.sub.i] [N.sub.i] - [Vp.sub.i] ([dN.sub.i] / dx)

where [p.sub.i] is the probability that a member of the species i will be swept away by the current. Clearly [p.sub.i] = 1 if i is a species that lives suspended in water (potamoplankton) sand [p.sub.i] would be close to zero for any organism so tightly attached to the stones that it could only be detached with great difficulty, or one capable of swimming against the current. It can be seen that the interplay between reproduction and being swept away, between r and p, explains very well the adaptive evolution of organisms to life in rivers. Reducing the probability of being swept away also allows a reduction in the rate of reproduction necessary to ensure that the species can persist at the site. The same mechanism explains the persistence of a rich gene bank of all types on the riverbanks, at several heights. A prodigious quantity and variety of organisms can be found there. It is like a Noah's ark that ensures the unbroken colonization of the river ecosystem with species already preadapted to changes, such as the river drying out in the summer or a seasonal downpour.

From the clouds to the great planetary river

Even before it circulates on the surface of the earth, rainwater is active in the transport and interaction mechanism. Rainwater is slightly acidic (pH=5.65) because it contains dissolved carbon dioxide, which combines with the water to form carbonic acid. This partially dissociates and makes the water slightly acidic, although the quantity of ions is very small. Its acidity is greater if the rain contains other acids (mainly nitric and sulphuric acids) derived from combustion and several industrial processes, and this is the cause of acid rain. To some extent, they are the same elements (C, N, S) that plants absorbed and reduced and that on their return (mainly through combustion of fossil fuels), are once more oxidized.

One of the greatest alterations in global cycles, and one of the most serious, is the acceleration of this return as a consequence of all the different types of combustion, mainly burning fossil fuels, and the destruction of wood and soil humus. The increase in atmospheric C[O.sub.2] cannot be separated from acid rain. Nowadays, rainwater composition is usually measured in small high mountain lakes located in watersheds formed of old, insoluble rocks, which are excellent antennae for detecting atmospheric quality through the precipitation of rain and snow. Tree damage attributed to acid rain is not a simple phenomenon: In addition to the acidity of the rain, there are other factors, such as the loss of cations (Ca, Mg, K, Na) from the soil, partly due to the exploitation for wood of unfertilized forests, as a result of which the elements extracted from the ecosystems with the cut trees are not returned.

A condensed drop in a cloud starts very small and gradually increases in size and speed until it falls as rain. In the meantime it gains acidity and incorporates such diverse materials as terpenes, pheromones, or particles of soluble salts (near the coastline small crystals of sodium chloride are very frequent, especially if the wind is strong). They may also encounter in their path spores, bacteria, pollen, mineral particles, spiders, mosquitos, airplanes, and their corresponding excretions.

Before it reaches the soil, the rain wets the surfaces of the plants and flows down them. In forests there is a distinction between the water that drips off the trees and the water that flows down the trunk, dissolving and washing away a range of materials and usually enriched with potassium and nitrogenous compounds. On the surface of wet leaves, as well as on tree trunks or stones, and on the soil, the water is colonized by bacteria, fungi (yeasts), microscopic algae, rhizopods, flagellates, and ciliates (formerly called infusarians because they are found in infusions). Many organisms are only active during the few hours the humidity lasts, divide rapidly, and the resulting cells encyst and prepare for the next favorable episode.

The locations that are most frequently wetted, or where the water stands for longer, accumulate "biodiversity" in the form of a richer gene bank. Pavement often has puddles of rainwater, which are of great use in studying the relationship between the wealth and variety of accumulated life and the frequency and duration of water retention in each puddle. The sheaths at the base of the leaves of grasses, the small pools that form in the center of epiphytic bromeliads, holes in tree trunks opened by animals or through the decomposition of the wood, and the traps of many "carnivorous" plants often contain interesting, varied life-forms including noxious species such as mosquitos. The chemical composition of the water they contain may vary greatly, according to the secretions of their supports or the activities of the colonizing organisms.

The water that reaches the soil moves more or less horizontally over the surface of the soil through its profile. Changes of all kinds occur. It is well known that there is a distinctive smell of "wet earth" after a rainfall, the result of the activities of fungi and actinomycetes and the substances they consequently release. Compounds of nitrogen respond quickly and are more abundant in the runoff immediately after a storm starts. The succession of materials that are released and circulated in the soil takes place as a kind of soil chromatograph, with gradual ionic changes. A storm is not such a simple thing. Fungi immediately increase the capacity for transport and for several chemical reactions. The soil fauna contains a large number of organisms that are strictly aquatic (rhizopods, ciliates, rotifers, bdelloids, and tardigrades) that live in the water present in the soil in the form of a fine film on the solid granites, and that are especially active in the rain, or are reactivated by it, or are dispersed by it and then return to a passive life.

Water also acts on compact rocks: On calcareous (soluble) rocks, parallel dissolution grooves form that look like tracks left by scraping the fingertips along the rock: lapies. The effects of the dew may substitute or add to the effects of the rain. Desert roses are an example of the reconstruction of materials as a consequence of excess water circulation. What is often the most visible final result is due to the action of several organisms. In the deserts of Israel and North America, there has been detailed study of the formation of a fine layer of organisms (algae, fungi) on the rocks which gradually penetrates them. If the chlorophyll present is measured, there is often a very respectable amount present per unit area, more than in the Mediterranean, for example, which is surprising. In these conditions, the organisms create a reduction-oxidation gradient perpendicular to the surface of the rock, reducing and dissolving some minerals below the surface, which then migrate to the surface where they are oxidized forming the well-known desert patina, which is often very dark due to its content of iron and manganese. In loose blocks, the lower part that the light does not reach does not experience this migration or the consequent change in color. If some stones are turned over, they are lighter in color and contrast with the untouched ones. This is one way of making images on a large scale, that can only be seen by gods and astronauts, such as the well-known ones found in the high, arid regions of Peru. In their way, even the deserts form part of the great planetary river.

Interactions between rivers and their surroundings

The interactions between soil, water, and vegetation is of great importance in the systems that are occasionally flooded, such as savannah or the periodically flooded forests occupying much of the Amazon Basin, where fluctuations in water levels may range from 10-33 ft (3-10 m). The annual pulsation generated by flooding affects the entire local biology, and the water is a very important factor of horizontal transport (dispersing seeds, etc.) and, indirectly, of vertical transport (insect migrations, etc.).

The fertility of rivers (and other things derived from them, such as the production of fish) depends on the surfaces that are flooded. The periodic change in situation prevents the ecosystems from reaching a high level of maturity, keeping them "rejuvenated" and more open to evolution. The river is not only a basic transport mechanism, but also a very effect dynamic agent in past and present day tropical plains.

The area occupied by humans is increasing all the time (streets, sheds, airports, main roads, houses, artificially maintained lawns, etc.), as are cultivated and fertilized fields. The details of changes in composition of the rain falling on these areas are not known with sufficient precision, nor are their overall effects on the local and global water cycles. There is a clear difference between waters that have circulated slowly through forest soils, which are more uniform and less mineralised, and runoff water from human-managed areas, which contains more dissolved materials and differs more from one sample to another.

Rivers have a natural tendency to transport waste: they perform net transport of organic material downstream, part of which is reused by the river organisms. Humans abuse rivers' "goodwill" with excessive discharges, and this is nothing new. For a long time the degree of impurity of the water used has been measured by the microorganisms present (the saprotroph scale). Their presence shows this type of situation has always occurred and has been a stage for natural evolution. Yet much has changed: Our civilization is synthesising and dispersing thousands of new compounds (such as medicines, pesticides, herbicides, and plastics), many of which might represent some risk in and of themselves. And almost all of them might represent some risk through their decomposition products, whether in water, by fire, or in the soil due to the action of organisms, as their decomposition may give rise to many types of molecule with unknown or unexpected properties. This new scenario hides many unknowns, leads us to suspect possible new hazards and sometimes causes accidents. Heavy metals can be detected in river deposits, but apart from those related to industrial uses (cadmium, lead, etc.), they still mainly reflect the nature of the regional geological substrate.

The techniques developed to purify sewage do no more than use and enhance the effectiveness of natural biological processes, such as by introducing oxygen and by separating sediments and flocculated material. Apparently the fastest treatments, with a vigorous physical or chemical intervention, may give worse results or produce excessive quantities of sludge. Nowadays, in response to growing demand (often exaggerated) from cities, water supply has become one of technological civilization's most serious problems. Humans are more and more firmly connected to the great planetary river.

3. Coastal bacterial landscapes

3.1 Water, land, and bacteria

The biosphere's coastlines have been altered by bacteria since the most remote past. These tiny but diverse organisms live there in prodigious quantities, organized into distinctive macroscopic communities, and they have been responsible for making the coastlines habitable for other living organisms, whose presence often hides the role of bacteria in many ecosystems. However, in some special coastal landscapes bacteria leave very clear traces of their presence.

Planets without seas

Coasts exist wherever the land meets the sea. It would not make sense to think of a coast on a planet without water. Although it appears that 4,000 million years ago the inner planets (Mercury, Venus, Earth, and Mars) ejected vast quantities of water from their interiors, most of it was lost into space. Neither on the Moon or on the neighboring planets, Venus and Mars, is there any water, lakes, rivers, or pools; there is never even drizzle. Yet all these satellites of the Sun enjoy a loose rocky covering called regolith, made of particles that range in size from dust particles to boulders.

The origin of the surface regolith of these planets must be sought in the first 1,000 million years of their history (between 4,500 and 3,500 years ago). Since their formation, and especially during the first thousand million years, Mercury, Venus, Earth, and Mars suffered millions of spectacular collisions with meteorites which, when they crashed and broke up, formed, together with volcanic emissions, the surface regolith. Were it not for the presence of life, especially bacterial life, the earth would now be in the same situation as the other inner planets and their satellites, since these bodies all share a common history and common location in the universe. Unaltered regolith, not affected by living beings, is loose and open. Bacteria not only bind and precipitate regolith into sedimentary rock, but retain water, produce gases, remove carbon dioxide, precipitate metals, and alter surface in so many ways that, in the case of Earth, the regolith has been transformed. Without bacterial action the surface of our world would be covered, like Mars and Venus, by dry, fine dust and sand.

The interfaces of life

The environments with the greatest possibilities for life are those where the water flows over the land into the sea, and the three faces--air, water, and land--combine to provide intricate surfaces for growth. Subvisible life, the tiny photosynthetic and energy- and food-generating bacteria that first evolved 3,500 million years ago (long before any animal or plant colonised initial coastline), have maintained their stronghold ever since.

Three types of coastal features are distinguishable: initial coasts, depositional coasts, and erosional coasts. Initial coasts form directly by tectonic processes that make igneous rocks emerge (such as when volcanoes or the rims of meteoritic impact craters rise to the sea surface). Depositional coasts include all beaches, sand dunes, river deltas, spits, or bars where the sediments form the interface between land and sea, as well as biogenetic structures such as reefs or guano islands. Erosional coasts are produced by the encroachment of the sea, such as sea cliffs, caves, platforms, and fjords.

In initial coastline, such as the new Hawaiian islands, or Surtsey formed by volcanic eruption off the southern coast of Iceland, the inhabitants of newly exposed regolith are the same today as during the Archaean period: purple and greenish sulphur-reducing bacteria. These photosynthetic sulphur bacteria are bathed in sulphurous fumes in the regoliths of recent volcanos. With oxygen-producing cyanobacteria above them and oxygen-avoiding green sulphur bacteria and fermenters below, the phototrophs form a fine coat over the rocks and slowly, but tenaciously, establish their expanding colonies.

Since its very beginning, this bacterial life has colonized all initial and depositional coastal landscapes. Only coasts made by recent life forms, such as coral reefs formed since the Palaeozoic period by chalky coral animals and coralline algae, and the guano islands formed in the Cenozoic period, were not colonized by bacteria in the first 3,000 million years of life.

The pioneer life form that thrives wherever energy and an interface of lithosphere, seawater, and atmosphere exists is bacterial. As long as a source of external energy is present, airborne and waterborne autotrophic bacteria will set up house in this interface. If habitat remains available and the energy supply continues, bacterial communities will grow, expand, and complexify.

Energy sources

There are only two sources of energy useful to life: light and some chemical compounds. Solar radiation in the visible, infrared, and ultraviolet parts of the electromagnetic spectrum powers phototrophs. Reduced compounds of carbon (such as methane), of sulphur (such as sulphide), of nitrogen (such as ammonia), or iron (the bivalent ferrous form) present in the lithosphere or in water can be oxidized and power chemotrophs.

Since sunlight is by far the most abundant source of energy for the biosphere, throughout the history of life most primary production has been by photoautotrophs. Only some forms of bacteria, some protoctists (all are algae), and plants can perform photosynthesis.

This means that the photosynthetic bacteria, most of them living on the ocean's coasts, energized the entire biosphere through all of its early history. By the late Proterozoic eon, productive bacterial coastal communities were replaced in this task by algae, and by the late Paleozoic Era, by different groups of flowering plants, also.

However, even in places where dense local populations of marine flowering plants such as Zostera marina or Thalassia grow, bacterial communities still abound on their leaves, on neighboring rocks and cliffs, or in the intertidal zone of nearby pools. Productive coastal communities of bacteria were not replaced, but only supplemented, by the diversity of algae, and eventually by the plants and lichens that greened the world.

3.2 Bacteria as a geological force

Because they are at the base of the food web, supplying food and energy for the rest of coastal life, landscapes dominated by photosynthetic bacteria deserve special attention. These most productive organisms derive all their C[O.sub.2] from the atmosphere and what is dissolved in water. This means that if supplied with simple compounds--salts of nitrogen, phosphorus, sulphur, and a dozen or so trace elements--these colonizers can, in principle, establish themselves in just about any wet, or periodically wet, well-lit habitat. Bacteria "fix" carbon; that is they convert gaseous carbon into all the components of living cells: carbohydrates, proteins, nucleic acids, lipids, and cell-wall peptidoglycans. They never make their cell walls from cellulose as plants do, or from chitin as fungi do.

The types of coastal bacterial communities

Although only a few of the bacterial groups found along the world's coastlines have been studied in detail, some of these powerful bacterial communities have had such an impact that they can be analyzed as geological forces. They exist as mats, scums, epilithic, chasmolithic, endolithic, or epibiotic communities.

Bacterial mats are communities of benthic (bottom-dwelling) bacteria living below, between, or above the water level. In tidal coasts, if they do not remain below the low tide level they become flooded as the tides ebb and flow or are exposed at low tide. Scums are bacterial communities that separate from the bottom and float on the water's surface. They are easily destroyed and reformed by the force of the waves, but are established better in stiller waters where they rise and fall with the tide.

Epilithic communities live on the surfaces of rocks, while endolithic communities actively bore into the rock surfaces, perforating them and forming characteristic patterns of tunnels and tubes in calcareous rocks. Chasmoliths live in cracks and crevices made by physical forces, not by their own activity.

Lastly, epibiotic communities are those that form on the surface of other organisms. They are now a major field of study, as almost every seaweed or marine animal is a habitat for its own characteristic bacterial communities, on both its external and internal surfaces.

Bacterial mats

Bacterial mats are layered communities in which the surface organisms are generally cyanobacteria underlain by a variety of purple and green sulphur bacteria that are photosynthetic (and thus primary producers), but do not produce oxygen. Below them and intertwined with them are sulphate-respiring and fermenting microbes. They all interact with each other, recycling materials to form an interwoven structure called the microbial carpet or mat.

Since they often peel off the underlying sand or muddy sediment in a carpet-like thickness, the name microbial mat is apt. The cohesiveness of the structure and its rich and colorful texture makes these living fabrics a source of delight.

No one has a complete list of the organisms that comprise a microbial mat, although it seems logical that cyanobacteria and purple sulphur bacteria are the most effective in removing and displacing the sediments.

Microbial mats were not studied in detail until the 1970s and later, that is after the development of micropalaeontology and electron microscopy. However Charles Darwin, during his voyage on the Beagle, hinted at their existence, although he referred to the outdated group, the Confervae. The genus Conferva was a Linnaean genus of supposedly green algae, which included all kinds of unicellular organisms that were more or less green in color.

When the error was realized and these organisms (including cyanobacteria and chlorophyta) began to be classified correctly, the genus was removed from the literature. Darwin's remarkable intuition led him to realize the role of the subvisible microbes in salt formation, and even sense the presence of ciliates (called infusarians in the early days of microscopy).

Two of the best known dynamic coastal bacterial communities are sebkha and stromatolite communities. They serve as a model, not just because they are well researched but because the communities are the dominant form of life on the shores where they occur.

Microbial communities of coastal sebkhas

The arabic word sebkha means wide salt-flat lacking vegetation. On the Abu Dhabi coast (United Arab Emirates), the threat of desiccation is extreme and rainfall is so scarce that even the halophytic plants and algae most resistant to hot, dry climates are excluded by this harsh environment. Only cyanobacteria and associated microorganisms thrive, as long as there is light and water, however salty it is.

The rate of evaporation at low tide can be extremely rapid and the common ions contained in sea water tend to form salts and then precipitate from solution, in a specified order that depends on their solubility. The first is usually CaCO3 (calcium carbonate), then Ca[SO.sub.4] x 2[H.sub.2]O (gypsum) and, finally, the most soluble, NaCl (sodium chloride).

The organisms are under great stress, and respond in different ways. Some produce mucus and gel that help them to retain water. Others reduce their metabolic rate and enter into dormant stages. The high intensity of sunlight affects each of the bacterial populations differently, depending on the color and intensity of their pigmentation. To some the oxygen of the air is a necessity, while others are indifferent to it, and some are actually poisoned by it.

The consequence of different physiological responses to the major environmental factors of light and air is a distinctive zonal distribution of mat types. From the deeper waters moving towards the shallower within the intertidal realm, we can trace the growth and behavior of the different types of mat. In the deeper parts, soft, gelatinous, dome-shaped layered structures some tens of centimeters across are made by Phormidium hendersoni, a filamentous cyanobacterium whose tubular-sheathed threads are about one micrometer in diameter. In the daytime the filaments glide up towards the sunlight, to which they are attracted, although it is not known how they move as they have no organelles of motility. At night they move horizontally, wriggling out and abandoning their mucus sheaths. They lead an alternating circadian pattern of horizontally, then vertically oriented layers.

Phormidium cells are confined to the deeper parts of the lighted zone of their coastal lagoons because of their poor tolerance of oxygen. They do not form coherent mats but "jelly biscuit"--like structures, and within one or two months the activities of cerithid snails and various burrowing worms obliterate any record of their past.

Far more resistant and sturdy structures are made by Enthophysalis major, a coccoid cyanobacterium that colonizes the large sand ripples, as much as a meter wide, made in lagoons and channels by frequent changes in current direction. Found just above low tide, the gelatinous colonies produce the millimeter-sized warts or nipples that give this microbial carpet its name: mamillate mat.

The cosmopolitan low, flat mat found in the mid-intertidal zone is more complex than the Phormidium biscuits and the Enthophysalis mamillae. These low, flat mats are found not only in Abu Dhabi, but in many other places on the East Coast of the United States from Halifax to North Carolina. The surface cyanobacterium, Lyngbya aestuari, is a large filamentous brownish cyanobacterium that has cells stacked like coins in a firm, tough sheath. This organism is named Lyngbya after the Danish city of Lyngby between Copenhagen and the Helsingore marine station where it was first studied.

Almost everywhere below Lyngbya one finds another, very attractive cyanobacterium Micro-coleus chthonoplastes (the generic name means "small sheath" and the specific name means "coming from the earth"). This is a vigorously growing organism in which many filaments are packed, like copper insulating wire, in a common sheath. Shading itself by moving under the darkly pigmented Lyngbya, Microcoleus enjoys alternate exposure and covering by water in the lower parts of stagnant pools, moving and growing laterally until it carpets the entire floor. Below Microcoleus are the red and green sulphur bacteria, including salmon-colored colonies of Thiocapsa, pink swimming Chromatium, and the strictly anaerobic green Chlorobium.

In the fourth type of bacterial mat, those forming small tents or pinnacles, Schizothrix splendida replaces Microcoleus beneath Lyngbya. Schizothrix requires more oxygen and better drainage than Microcoleus and tends to grow forming small conical tents or pinnacles, the result of a series of convolutions on a contiguous cover of mat that folds and traps gas in the folds. As the mat surface thrives with Schizothrix above and Microcoleus below, the convolutions become more pronounced holding water in the concave part and providing a well-drained surface in the convex part. As they desiccate, the convolutions perforate, trapped water becomes briny, and further evaporation leads to gypsum precipitation. If drying continues, Schizothrix replaces Microcoleus and mat growth slows, continuing only on the damp under surface.

Eventually, drying leads to the mat cracking and breaking up. However, especially in the coastal mats, where organisms glide up out of sticky sheaths to find sunlight, a mixing with the particles of the sediment occurs, which traps and binds them, leaving their mark on the landscape. With every tidal cycle, sand--whether quartz in Baja California, or carbonate in Abu Dhabi, or both--is dumped on the mat, stimulating the filaments to grow up out of the sediment. The structure acts as a coarse filter that traps the tiny (and not so tiny) particles transported by the tides that penetrate the mat when they are trapped in the sticky mesh, which helps to bind and harden the matrix of the mat.

During the Gulf War in 1990, beaches along the Arabian Gulf were covered with spilled oil. Although the effects were devastating on fish, burrowing worms, and all other animals, microbial mats continued to thrive and grew up over the oil patches. Like any natural sediment that tended to block the light, the spill was a stimulus to the growth of Microcoleus and other gliding filaments. Because the oil contained food sources for mat organisms, luxurious growth followed. Certainly one being's poison is another being's meal. Both microbial mats and oil spills were present long before people and are likely to persist long after we become extinct.


A different model of coastal community dominated by bacteria are the communities dominated by stromatolites. Hamelin Pond and Carbla Point, two neighboring localities in Shark Bay (a sheltered deep embayment off the west coast of Australia), are among the few places where there are bacterial communities that construct stromatolites. These are large stone structures uncannily similar to a type of laminar structure that dominated the fossil record in the oldest known rocks with traces of living organisms.

The discovery in the 1950s of living stromatolites on the coast of northwestern Australia allowed scientists to study structures thought to have disappeared 500 million years ago, making it possible to study in vivo processes that might have occurred during Earth's first 3,000 million years. Stromatolites are formed by microbial carpets that live in submerged hypersaline media that are supersaturated in dissolved minerals. Precipitation of calcium carbonate around the particles of sediment trapped by the carpets cements them together, leading to lithification. Researchers found that lithification of microbial carpets occurred suddenly over a short period of time at the hottest part of the summer. They also noticed that stromatolites undergoing lithification not only hardened but also changed color, from dark brown to bluish-black.

Amorphous carbonate, a poorly known type of carbonate mineral, precipitates within the enveloping gel of the cyanobacterium Enthophysalis major, the most important organism involved in building the abundant and robust, mamillate mats of these stromatolites. When lithification starts suddenly, it begins in the polysaccharide gel surrounding the coccoid cells of Enthophysalis major. Beginning on the inside, the mat becomes completely encrusted with a smooth and compact form of calcium carbonate (identified by scanning electron microscopy as the amorphous type of calcium carbonate formed only by living cells), while on top, on the outside of the mat, a secondary crust of pure aragonitic calcium carbonate crystals forms. On top of the crust certain black microorganisms (Hormathonema) colonize what is left of the Enthophysalis mat, and form the first stage in the succession that will lead to the formation of a new layer of microbial carpet. Then a precipitate forms as a mineral lining on the inside of the mat cavities, and lithification continues with the formation of large magnesium calcite crystals. Lithification signals the death of the Enthophysalis mat: The cells die suddenly, so suddenly that some have been caught in the process of cell division.

What is most surprising is that the mat-building-lithification process has been going on all over the world for at least 1,800 million years, the age of the rocks in Belcher Island in eastern Hudson Bay, where lithification was caught in the act. Eoentophysalis fossils very similar to Enthophysalis have been found in fossil stromatolites in rocks 1,600 million years old in Australia, and in more recent rocks in China (1,200 million years old) and Greenland (700 million years). Enthophysalis is thus the oldest living fossil known, as it has preserved its form and function for more than 1,500 million years.

Other bacterial landscapes

It is important to recognize how similar these Arabian and Australian bacterial landscapes are to many others around the world, although most such landscapes are found in very saline coastal areas due to high evaporation, but some occur in very cold water. Examples of this are the benthic bacterial communities growing beneath the Antarctic ice and the astounding calcium carbonate columns discovered in the late 1980s in waters with a strong undertow off Lee Stocking Island, Exuma Sound, in the Bahamas. Similar structures were later found in enclosed lagoons near Adelaide in Southern Australia and Kiritimati (Christmas Island) in the middle of the Pacific and on the big island of Hawaii. Nor is the sebkha in the Arab Emirate of Abu Dhabi unique: Similar bacterially-dominated scenes thrive on many other parts of Southwestern Asia, such as the coasts of the other Arab Emirates, of Saudi Arabia or of Kuwait, Solar Lake in the Sinai Peninsula, and various bays along the Red Sea.

The most efficient way to find conspicuous green and pink coastal bacterial landscapes is to seek out commercial saltworks: At Guerrero Negro in the Baja California Sur, 16,000 tons of salt are moved each day, mostly to Japan. Adjacent to the evaporation pans are well developed bacterial mats and scums. Further north at Laguna Figueroa at San Quentin Bay, the same phenomenon occurs, but on a smaller scale. Mexican people collect salt from microbial-laden evaporite flats as they have for at least 300 years, since the Spaniard Sebastian Vizcaino first saw them when he sailed up the coast.

On the Alfaques (meaning sandbar) Peninsula in the Ebro Delta, bacterial mats of Microcoleus extend along the shore beyond the Salicornia salt marsh vegetation. The setting is similar to that described for Abu Dhabi, but the wetter, colder Catalan climate and the unimportance of the tides means the bacterial mats are far less extensive and show discontinuities. Over the last years, considerable effort has been put into studying these mats, possibly the largest and most stable in Europe.

204 Marine and terrestrial worlds merge at the coast in such a way that the ecotone, or boundary, between these two regions is quite visible and more permeable than might be thought. These southern elephant seals Mirounga leonina, for example, resting on a Pacific beach on Campbell Island (New Zealand) spend part of their time on land and part at sea. Meanwhile, the nearby vegetation has developed mechanisms that cope with the continual salt spray. Between land and sea throughout the world there are a whole series of organisms that lead double lives.

[Photo: Jean-Paul Ferrero / Auscape International]

206 The steep and rocky coastline of Cape of Good Hope at the southernmost tip of Africa, at the confluence of the Atlantic and Indian Oceans. This type of coastline, normally irregular and jagged, surrounded by fallen rocks and great blocks torn from the cliffs, is the result of a furious struggle between the waves and the hard substrate.

[Photo: Jaume Altadill]

207 The long, low coastline at Platypus Bay on the Coral Sea within the Great Sandy (Fraser Island) National Park, Queensland, Australia. Low sandy coasts tend to be straight or gently curved and very regular.

[Photo: Jean-Paul Ferrero / Auscape International]

208 High tide and low tide in the Bay of Fundy, Nova Scotia (Canada), the area of the world with the greatest tidal variation. When the Bay's mode of oscillation coincides with those of the tides, the tidal range can reach 53 ft (16 m). [Photo: John Lythgoe / Planet Earth Pictures]

209 The disastrous effects of the tsunami that hit Japan in June 1993. The photograph shows the scene half a kilometer inland with a fishing boat stranded after the floods had subsided.

[Photo: K. Kurita & M. Batsu / Gamma]

210 Oscillations in sea levels over the period of a year in Castellon de la Plana (Spain) and during two periods of a few hours in Estartit on the Costa Brava (Spain). The first graph shows the direct measurements for a whole year in the port of Castellon de la Plana (and those corrected for atmospheric pressure). The greatest oscillations coincide largely with the equinoxes, while least oscillation was observed in summer. The other two graphs represent the oscillations measured minute-by-minute in the port of Estartit on the night of September 16-17, 1975, and on the afternoon of July 2, 1981. It can be noted that on the first of these dates, in little over three hours, many of oscillations in the sea level of more than half a meter and some of almost a meter were recorded, and the figures recorded on the second date were even greater.

[Graph: Editronica, from data provided by the author]

211 Lighthouses are dotted along coastlines and act as important landmarks and guides for sailors keen to reach solid ground but afraid of shipwreck. The photograph shows Bell Rock near Arbroath (Scotland), surrounded by gulls, rising above the stormy North Sea.

[Photo: Jeni Bain / NHPA]

212 The fertilizing effect of rivers on the sea, as well as on coastal areas, is clearly shown in these two photographs. The upper is a photo of the Atlantic area that receives water from the Orinoco and Amazon (warm tones in the MSS or "multispectral scanner" image in false color taken by a satellite in October 1979). The lower photograph shows the waters of the Adriatic fertilized by the Po (true color photograph taken from the Columbia space shuttle in October 1984). In the latter example it is interesting to note the intensive agricultural exploitation of the alluvial plain and delta, made possible by the fertility accumulated over many centuries (see also figure 370).

[Photo: courtesy of Global Change Data Center, NASA Goddard Space Center]

213 Human transformation of coastlines has been underway for centuries and has become more intense in the last few decades as swimming in the sea and the coastline have become recreational areas. As a result, many coastlines are occupied by groups of second homes and permanent sports instal-lations, as this photograph of the Atlantic coast of South Africa shows.

[Photo: Jaume Altadill]

214 The global circulation of seawater as if the seas were a single, huge river, the largest on Earth, is a scientific concept that can also be expressed in literary terms. A suggestive and rhetorical literary metaphor would convert the seas into a single, immense river with an infinite number of sources turning the continents into mere islands within the very river they themselves create. Land, seas, and rivers would be but manifestations of a single entity, as this Arab text from the mid-14th century preserved in the National Library in Paris seems to suggest.

[Photo: Archiv fur Kunst und Geschichte, Berlin]

215 Apparently capricious fluctuations in river levels are the result of variations in rainfall patterns. Although rainfall levels vary from one year to another everywhere in the world, in some areas, such as those with Mediter-ranean-type climates, annual fluctuations can be very marked. The graph shows annual rainfall figures recorded by the Seville weather station between 1870 and 1990 (annual average was 22 in [561 mm]), as well as the accumulated deviations for the same period of time. Neither of the two variables seems to show any pattern or regularity.

[Graph: Editronica, from various sources]

215 Apparently capricious fluctuations in river levels are the result of variations in rainfall patterns. Although rainfall levels vary from one year to another everywhere in the world, in some areas, such as those with Mediter-ranean-type climates, annual fluctuations can be very marked. The graph shows annual rainfall figures recorded by the Seville weather station between 1870 and 1990 (annual average was 22 in [561 mm]), as well as the accumulated deviations for the same period of time. Neither of the two variables seems to show any pattern or regularity.

[Graph: Editronica, from various sources]

216 Idealized model of a river. Three stages can be identified in the dynamics of the continuous dialogue between water and the substratum that creates rivers. First, in the river's upper course, a number of streams rise in high or very high areas with steep slopes (and thus rich in potential energy) and their upper courses (1,2,3,...) flow together, forming the main river in any particular river basin. During its second stage, the middle course, the river flows over the plains towards its mouth, expending its energies by depositing the sediment carried in its waters, creating and transforming short-lived meanders, favored areas where succession is continuously being restarted and of interaction between aquatic and terrestrial life. In the third stage, the lower course, the river once again branches as it did in its headwaters, but in the opposite way. This is the opposite of the confluence of different courses, as it is the river's division into a number of often sinuous drainage channels that forms deltas or marshes, according to the characteristics of the sea they flow into and the coastal areas they flow through.

[Drawing: Editronica, from various sources]

217 Rivers are difficult, unstable environments where the probability of being washed away is high. Life in these environments permits the concept of ecosystems to be extended to areas with heterogeneous flow. The objective difficulties involved in surviving in fluvial ecosystems has stimulated the evolution of river life with many adaptations, some designed to increase levels of reproduction, while others try to diminish the possibility of being swept away by the current. [Drawing: Jordi Corbera, from data provided by the author]

218 The return of evaporated water to the sea may occur via rivers or more directly in the form of rain falling on the sea, as in this morning downpour on the Pacific coast of Australia.

[Photo: Hans & Judy Best / Auscape International]

219 A series of torrential storms and resulting changes in an area of Mediterranean woodland in the Montseny (Spain) at the beginning of October 1987. After rains, and above all after prolonged periods of drought, changes occur in river volumes and the composition of their waters. The example illustrates the history of a series of nine torrential storms in early October 1987 (9 in [221 mm] in little more than 10 days) after a prolonged drought during which only 0.9 in (24 mm) of rain had fallen in two months. Water volumes peaked during each storm and then gradually diminished. After each storm, alkalinity dropped and then gradually recovered until the next storm occurred. Calcium and sodium behaved differently during the first and last storms: during the two first storms concentrations of these two elements did not change significantly (there was a slight increase in the amount of calcium), yet during the rest of the storms concentrations were considerably diluted. Nitrate and potassium levels increased after each storm, although much more significantly (above all the nitrate) in the first.

[Diagram: Editronica, from data produced by Anna Avila and collaborators]

220 The world's great river basins. The situation and some relevant data from river basins of over a half million square kilometers. The study of the chemical composition of the waters of the world's mightiest rivers gives us an idea of the material that is transported globally by rivers from the continents to the sea and, above all, enables us to calculate that approximately 1% of the organic carbon synthesized on the continents flows into the seas. In comparison, the part played by human contamination is modest quantitatively, although not necessarily qualitatively. Taking into account the fact that organic matter produced by terrestrial vegetation and fungi is very resistant to destruction, it is quite plausible that a relatively high percentage of all the organic matter dissolved in the sea is, albeit remotely, of continental origin.

[Drawing: Editronica, from various sources]

221 Bacterial landscape in a coastal sebkha in Abu Dhabi on the Persian Gulf where no other life form can exist. The extreme conditions that occur in these sebkhas enable communities reminiscent of other geological eras to establish themselves.

[Photo: Stjepko Golubic]

222 Coastal limestone formation perforated by endolithic cyanobacteria (Mastigocoleus testarum and Kyrtuthrix dalmatica). The electron micrograph shows the fine perforations in the rock surface.

[Photo: Stjepko Golubic]

223 A cyanobacterial carpet of Microcoleus chthonoplastes split by winter drying-out in salt pans on the Adriatic Sea (Piran, Slovenia). In this area, salt is still extracted by the same archaic method (the incrustation of salt crystals in gypsum by bacterial action) as Darwin described in Patagonia in August 1833 in his Journal of Researches into the Geology and Natural History of the various countries visited by H.M.S. Beagle (1832-1836) (published in 1839). "The border of the lake is formed of mud: and in this numerous large crystals of gypsum, some of which are three inches long, lie embedded whilst on the surface others of sulphate of soda lie scattered about. The gauchos call the former 'padre de sal' and the latter the 'madre.' They state that these progenitive salts always occur on the borders of the salinas, when the water begins to evaporate. The mud is black and has a fetid odour (sulphuretum). I could not at first imagine the cause of this, but I afterwards perceived that the froth which the wind drifted on shore was colored green, as if by confervae; I attempted to carry home some of this green matter, but from an accident failed. Parts of the lake seen from a short distance appeared of a reddish color, and this perhaps was owing to some infusorial animalculata." The Gaucho's explanation given by Darwin very probably refers to the "pairing" of the "father" or gypsum (Ca[SO.sub.4] x 2[H.sub.2]O) with the "mother," sodium sulphate (Na[S.sub.O4]), which produces the "son," common salt or sodium chloride (NaCl).

[Photo: Stjepko Golubic]

224 Vertical structure of a bacterial carpet on the North American coast, consisting of a surface layer of the cyanobacteria Lyngbya aestuari, a further, deeper layer of another cyanobacterium Microcoleus chthonoplastes, and a final, pink basal layer formed of purple sulphur bacteria and other bacteria. Sulphate reduction takes place in this final layer and often gives rise to a new, black layer.

[Photo: Stjepko Golubic]

225 A rich and well-formed bacterial carpet in Guerrero Negro in the Pacific coastal marshes of Baja California. The thickness and gelatinous texture of the layer is obvious.

[Photo: Stjepko Golubic]

226 Large stromatolitic formations uncovered at low tide in Shark Bay (Western Australia). These stromatolites are rocky structures resembling coral reefs formed by the building ability of bacteria.

[Photo: Reg Morrison / Aus-cape International
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Publication:Encyclopedia of the Biosphere
Geographic Code:1USA
Date:Oct 1, 2000
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