Food chain: everything starts with plankton.

These microscopic little guys are at the bottom of the marine and freshwater food chains. Scoop up a litre of lake water and you might capture as many as 500 million planktonic organisms.

There are two main groups -- phytoplankton and zooplankton. Phytoplankton is photosynthetic organisms such as algae. For zooplankton, phytoplankton is the main menu item. Zooplankton consists of small crustaceans, jellyfish, worms, and mollusks, together with the eggs and larvae of the many animal species living in sea and fresh waters.

Fish such as sardines and anchovies eat zooplankton. Bigger fish eat smaller fish. Some of the biggest marine creatures, such as the blue whale, also eat zooplankton.

So, if something goes wrong with the organisms at the bottom of the food chain, all the organisms further up the chain are going to be affected. Unfortunately, something appears to be going wrong with plankton.

The ozone layer in the high atmosphere protects Earth from the Sun's ultraviolet radiation. Damage to the ozone layer, caused by the release of chlorofluorocarbons, poses dangers to all life on our planet. Humans counter this by slathering on sun-block creams. Plankton, of course can't do this. Now, scientists are finding evidence that ultraviolet radiation is harming the oceans' microscopic organisms, as well as juvenile anchovies. This damage is occurring not only in Antarctica, the site of the greatest ozone depletion, but also in shallow waters, including areas off the coast of Florida and the Bahamas. More ultraviolet radiation can penetrate to the seafloor in shallow water than in deep water.

Then, there's climate change. The world has warmed up over the last few decades and with it the temperature of the oceans. In 1995, scientists at the Scripps Institution of Oceanography in California released the disturbing results of a study. "The population of zooplankton in the waters off the coast of Southern California has declined by 70% in the last 42 years," they said.

While the Scripps scientists said the cause of the decline in zooplankton remains uncertain, they suspect the gradual warming of ocean surface waters over the last four decades may be to blame. And, plankton face yet another threat from human activity. Erosion from farms, logging, and construction operations is causing silt to cloud once-clear waters. Tiny particles of sand and clay floating in the water block sunlight needed by marine plants for photosynthesis.

At the same time, there seems to be a global shift in fisheries toward smaller, plankton-eating fish and invertebrates that are the prey species of larger, predatory fish such as tuna and swordfish. By removing larger volumes of fish that are lower down the food chain, the fish at higher levels are deprived of the prey they need to rebuild their populations. Also, because the interrelationships among fish species are not yet fully understood, there is a risk the fishing effort is disturbing an ecological balance millions of years in the making that is vital to many fish stocks.

The Plankton Net - http: //www.uoguelph.ca/ zoology/ocean/index.htm

Scripps Institution of Oceanography http://www.sio.ucsd.edu/

Marine Protected Areas http://www.wwfcanada org/en/cons_pgms/ cp_marine.asp

REFUGES

Former federal Fisheries Minister John Fraser has issued a warning that more and more marine species will become extinct if we don't take action -- and take it quickly. He says more "marine protected areas" must be created. The idea for setting up protected marine environments was put forward in 1962 at the first World Conference on National Parks. Since then, 1,300 such refuges have been created worldwide; the biggest and best known is Australia's Great Barrier Reef. The World Wildlife Fund is in the forefront of efforts to create more regions where unique ecosystems are protected. Its guidelines say that a marine protected area must be free of industrial activities of commercial resource extraction that might disturb habitats. Some limited fishing might be allowed, but there can be no dredging, mining, oil or gas development, drilling, bottom trawling, dragging, finfish aquaculture, or any other activity that severely jeopardizes the protected area's ecological balance.