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Condition, reproductive activity, and gross biochemical composition of the Manila clam, Tapes philippinarum in natural and newly created sandy habitats of the southern coast of Korea.



ABSTRACT Sand was added to the mudflat Mudflats are coastal wetlands that form when mud is deposited by the tides or rivers, sea and oceans. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries.  in a small bay on the southern coast of Korea in an attempt to create a new habitat for the Manila clam (Tapes philippinarum) in the muddy intertidal zone The intertidal zone, also known as the littoral zone, in marine aquatic environments is the area of the foreshore and seabed that is exposed to the air at low tide and submerged at high tide, i.e., the area between tide marks. . To evaluate whether the newly created sandy habitat was functionally similar to natural ones, seasonal variations in condition, reproductive activity, and biochemical composition of clams in created and natural conditions were compared from May 2000 to October 2001. Clams reared in the newly created and natural habitats had similar patterns and levels with respect to condition and tissue dry weight. Standardized animal condition and tissue dry weight of clams peaked in spring, when protein and carbohydrate reserves were at maximum levels, and declined progressively throughout the summer-autumn period to October, as a result of continuous spawning. Condition and tissue weight were quickly restored during the winter-spring period, concurrently with accumulation of protein and carbohydrate reserves. Similar biochemical compositions and reproductive cycles reproductive cycle
n.
The cycle of physiological changes that begins with conception and extends through gestation and parturition.
 for the clam stocks in the two habitats are likely to be related to their similar environmental conditions, in particular food availability. Comparison of the isotopic signatures of T. philippinarum tissues and potential food resources suggested that food availability in the study area was mostly dependent on resuspension Noun 1. resuspension - a renewed suspension of insoluble particles after they have been precipitated
suspension - a mixture in which fine particles are suspended in a fluid where they are supported by buoyancy
 of microphytobenthos, along with seasonal dynamics of phytoplankton phytoplankton

Flora of freely floating, often minute organisms that drift with water currents. Like land vegetation, phytoplankton uses carbon dioxide, releases oxygen, and converts minerals to a form animals can use.
. These observations clearly show that newly created sandy habitats may provide habitat functions that enable Manila clams to have similar biological cycles to those in natural habitats.

KEY WORDS: Clam culture, Tapes philippinarum, condition, reproductive cycle, biochemical composition, created habitat

INTRODUCTION

The Manila clam, Tapes philippinarum (Adams & Reeve 1850), is a mollusc mollusc

members of the phylum Mollusca, which comprises about 50,000 species. Includes snails, slugs and the aquatic molluscs—oysters, mussels, clams, cockles, arkshells, scallop, abalone, cuttlefish, squid.
 species that lives in sand, sandy-silt, or muddy-gravel sediments from the intertidal in·ter·tid·al  
adj.
Of or being the region between the high tide mark and the low tide mark.



in
 to subtidal zones a few meters in depth. It is also one of the most widely exploited bivalve bivalve, aquatic mollusk of the class Pelecypoda ("hatchet-foot") or Bivalvia, with a laterally compressed body and a shell consisting of two valves, or movable pieces, hinged by an elastic ligament.  resources for human consumption. Because of its high productivity and commercial importance, it is now cultivated worldwide. Numerous studies, particularly for commercial production, have enhanced understanding of the growth, reproduction, and physiological ecology Physiological ecology (animal)

A discipline that combines the study of physiological processes, the functions of living organisms and their parts, with ecological processes that connect the individual organism with population dynamics and community structure.
 of the clam under different environmental conditions, and thereby enabled rearing outside its normal habitat (Bourne Bourne, town (1990 pop. 16,064), Barnstable co., SE Mass., crossed by Cape Cod Canal; settled 1627, inc. 1884. Bourne Bridge (1935), across the canal, made the town an entry point to Cape Cod and a resort and commercial center.  1982, Beninger & Lucas 1984, Xie & Burnell 1994).

In contrast to a progressive increase in T. philippinarum production in coastal areas where the clam was introduced, a steady trend of decreasing annual production has been observed in indigenous habitats on the Korean coast, from approximately 74,000 tonnes in 1990 to around 38,000 tonnes in 2000 (Ministry of Maritime Affairs and Fisheries The Ministry of Maritime Affairs and Fisheries, or MOMAF, is a cabinet-level division of the government of South Korea. It oversees a variety of government offices, including the marine police.  Republic of Korea 2005, National Fisheries fisheries. From earliest times and in practically all countries, fisheries have been of industrial and commercial importance. In the large N Atlantic fishing grounds off Newfoundland and Labrador, for example, European and North American fishing fleets have long  Research and Development Institute 2004). The major causes of this decline have long been recognized and include habitat loss through reclamation of tidal flats, habitat disturbance by marine pollution, overexploitation of the species, mass mortality (main causes are unknown yet), and predation predation

Form of food getting in which one animal, the predator, eats an animal of another species, the prey, immediately after killing it or, in some cases, while it is still alive. Most predators are generalists; they eat a variety of prey species.
 of mud shrimp The term mud shrimp is used for a number of different mud-dwelling crustaceans:
  • Infraorder Thalassinidea, including genera such as Callianassa and Upogebia
  • Corophium volutator, an amphipod of the North Atlantic
  • Species of
 on young clams (Chung et al. 1994, Chung et al. 2001). Of these, the loss of clam habitat caused by large-scale reclamation for intertidal flats in Korea has been extensive during the past few decades (Koh 2001). About 40% of a total of 2850 [km.sup.2] of intertidal area has been reclaimed during that period in South Korea. Clam growth is closely related to sediment type, with better growth occurring at low silt content (Goulletquer et al. 1999, Melia et al. 2004), so it may be feasible to create new Manila clam habitats on the muddy intertidal zone and develop clam-farming grounds by adding sand to mudflat areas. Detailed knowledge of the survival, growth, and reproduction of clam populations farmed in newly created sandy habitat is fundamental to improving cultivation of T. philippinarum.

The condition (flesh content) and biochemical composition of bivalves vary in time and space, because they are affected by exogenous Exogenous

Describes facts outside the control of the firm. Converse of endogenous.
 factors, such as water temperature and food availability, and endogenous endogenous /en·dog·e·nous/ (en-doj´e-nus) produced within or caused by factors within the organism.

en·dog·e·nous
adj.
1. Originating or produced within an organism, tissue, or cell.
 factors, such as energy demands for reproduction (Ansell & Trevallion 1967, Dare & Davies 1975, Newell & Bayne 1980, Navarro et al. 1989, Okumus& Stirling 1998, Kang et al. 2000). A close relationship has also been demonstrated between condition, the accumulation and utilization of nutrients, and the reproductive cycle in various bivalve species (Walne 1970, Gabbott 1975, Bayne 1976, Zandee et al. 1980, Ruiz et al. 1992, Ojea et al. 2004). Accordingly, seasonal variations in condition and biochemical composition of T. philippinarum can give a seasonal indication of its physiological or nutritional state under varying environmental conditions during the gametogenic cycle (Beninger & Lucas 1984, Robert et al. 1993, Marin et al. 2003, Meneghetti et al. 2004).

In this study we evaluated seasonal variations in condition, reproductive activity, and biochemical composition of the Manila clam, T. philippinarum, in natural and newly created sandy habitats.

MATERIALS AND METHODS

Study Site and Field Experiment Design

Jinju Bay is a small (about 25 km long and 13 km wide), shallow bay located on the southern coast of Korea. with a mean water depth of 4 m (Fig. 1). It is well protected by islands to the south and the water is well mixed by strong tidal currents. The tide is semidiurnal sem·i·di·ur·nal  
adj.
1. Of, relating to, occurring, or performed during half a day.

2. Occurring or coming approximately once every 12 hours, as the tides.

3.
 with a maximum tidal range of 3.6 m on spring tide. Intertidal sediments in the bay are typically muddy sand, and about 411 ha have been developed for Manila clam culture. However, mud depth in the bay has increased up to 50 cm during the last two decades through sedimentation sedimentation

In geology, the process of deposition of a solid material from a state of suspension or solution in a fluid (usually air or water). Broadly defined it also includes deposits from glacial ice and materials collected under the effect of gravity alone, as in talus
 of suspended silt transported in intermittent freshwater pulses from the artificial dam on the Nam River, north of the bay. This has made the sediment muddier and thus reduced the area of clam habitat.

To assess if clam farming ground could be developed, sand of a total of 900 [m.sup.3] to a depth of 18 cm was added to the fine sediment surface of 5000 [m.sup.2] (50 m x 100 m) of a mudflat site on the west of the bay in March 2000. The sanded flat was tilled by raking nine months after addition of the sand. creating a silty silt  
n.
A sedimentary material consisting of very fine particles intermediate in size between sand and clay.

v. silt·ed, silt·ing, silts

v.intr.
 sand habitat. In May 2000, clam juveniles collected from natural beds were seeded onto three sites: the created silty sand habitat, a nonsanded mudflat area, and a natural habitat area. Juvenile clams of about 1500 kg were planted at each site. The period of immersion varied between 1 h (neap tides the lowest tides of the lunar month, which occur in the second and fourth quarters of the moon; - opposed to spring tides.

See also: Neap
) and 5 h (spring tides) per tidal cycle at the three sites. Water depth was approximately 2 m at high tide, depending on the neap-spring tidal cycle. Sediment characteristics of the experimental sites, and initial density, shell length, and final density of the clam are presented in Table 1. Initial clam density was 153 [+ or -] 8 (SE). 112 [+ or -] 10, and 112 [+ or -] 10 individuals [m.sup.-2] at the non-sanded mudflat area, created silty sand habitat, and natural habitat, respectively. At the end of experiment, the clam density was 34 [+ or -] 3 (SE) and 23 [+ or -] 1 (SE) individuals [m.sup.-2] at the created silty sand habitat and natural habitat, respectively. Survival rates were over 90% of the initial density at those two sites two months after seeding, but all the clams at the nonsanded mudflat area had disappeared during that period. Therefore, further monthly sampling was only conducted at the created silty sand habitat (the treatment site) and natural habitat (the control site).

[FIGURE 1 OMITTED]

Clam Collection and Biometric Measurement

Clams were collected monthly at the treatment and control sites from May 2000 to October 2001. Clams of similar size were sampled to minimize compositional variations because of age (size) class differences and to assess seasonal variation in clam activities (Fig. 2). About 60 individuals were collected at each site using a manual rake. Specimens were transported to the laboratory and placed overnight in filtered seawater seawater

Water that makes up the oceans and seas. Seawater is a complex mixture of 96.5% water, 2.5% salts, and small amounts of other substances. Much of the world's magnesium is recovered from seawater, as are large quantities of bromine.
 at in situ In place. When something is "in situ," it is in its original location.  temperature, to ensure gut evacuation and removal of fecal fecal /fe·cal/ (fe´k'l) pertaining to or of the nature of feces.

fe·cal
adj.
Relating to or composed of feces.



fecal

pertaining to or of the nature of feces.
 contents. After rinsing, the weight of each clam was determined and the shell length, width, and height were measured to the nearest 0.05 mm using Vernier calipers See Vernier.
- Knight.

a gauge with a graduated bar and a sliding jaw bearing a vernier, used for accurate measurements.

See also: Calipers Vernier
. The clams were then dissected dis·sect·ed  
adj.
1. Botany Divided into many deep, narrow segments: dissected leaves.

2. Geology Cut by irregular valleys and hills.

Adj. 1.
 and the sex of each determined by a smear. Tissue dry weight and biochemical composition was determined for 15-20 specimens of each sex, and a further 10 specimens of each sex were used for histological his·tol·o·gy  
n. pl. his·tol·o·gies
1. The anatomical study of the microscopic structure of animal and plant tissues.

2. The microscopic structure of tissue.
 analysis. The shell of each clam was dried at 60[degrees]C for approximately 72 h, and the shell weight recorded. Tissues dissected for biochemical analysis were freeze-dried and the tissue dry weight of each individual was determined by subtracting the water content mass from wet tissue mass. The dried tissues were ground to powder with a mortar and pestle A mortar and pestle is a tool used to crush, grind, and mix substances. The pestle is a heavy stick whose end is used for pounding and grinding, and the mortar is a bowl. The substance is ground between the pestle and the mortar.  and an aliquot aliquot (al-ee-kwoh) adj. a definite fractional share, usually applied when dividing and distributing a dead person's estate or trust assets. (See: share)  was heated at 450[degrees]C for 24 h to determine ash weight. The remaining dry tissue was stored at -30[degrees]C in a refrigerator for later biochemical analysis.

Environmental Conditions

On each sampling occasion at each site the temperature and salinity of surface and bottom waters were measured at high tide using a CTD CTD 1 Connective tissue disease, see there 2 Cumulative trauma disorder, see there  meter (Seabird Electronics, Inc.). For bottom waters, 5 L was pumped from 1 m above the bottom, screened through a 180 [micro]m Nitex mesh to eliminate zooplankton zooplankton: see marine biology.
zooplankton

Small floating or weakly swimming animals that drift with water currents and, with phytoplankton, make up the planktonic food supply on which almost all oceanic organisms ultimately depend (see
 and large particles, and collected in acid-washed plastic bottles. Water samples were kept on ice in the dark until filtered on pre-combusted Whatman GF/F glass-fiber filters (47 mm, 0.7 [micro]m pore size). Filters for chlorophyll a Noun 1. chlorophyll a - a blue-black plant pigment having a blue-green alcohol solution; found in all higher plants
chlorophyl, chlorophyll - any of a group of green pigments found in photosynthetic organisms; there are four naturally occurring forms
 analysis were stored at -80[degrees]C, and filters for suspended particulate matter particulate matter
n. Abbr. PM
Material suspended in the air in the form of minute solid particles or liquid droplets, especially when considered as an atmospheric pollutant.

Noun 1.
 were dried at 60[degrees]C overnight and then placed in a dessicator.

Chlorophyll a concentration was determined from acetone acetone (ăs`ĭtōn), dimethyl ketone (dīmĕth`əl kē`tōn), or 2-propanone (prō`pənōn), CH3COCH3  extracts using a fluorometric method according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 Holm-Hansen et al. (1965), using a fluorometer fluorometer /flu·o·rom·e·ter/ (fldbobr-rom´e-ter) the instrument used in fluorometry, consisting of an energy source (e.g., a mercury arc lamp or xenon lamp) to induce fluorescence, filters or monochromators for selection of the  (Turner Designs Model 10 AU 005). Total suspended particulate matter (SPM SPM - Sequential Parlog Machine ) was determined from filter weights before and after drying, following filtration of a known volume of water.

Condition and Reproductive Cycle

The condition index was calculated from the dry weight of tissue and shell according to the formula: Condition = [tissue dry weight (mg)/dry shell weight (mg)] x 100 (Lucas and Beninger 1985).

For 10 specimens of each sex, the gonads were fixed in Bouin solution, embedded in paraffin paraffin, white, more-or-less translucent, odorless, tasteless, waxy solid. It melts between 47°C; and 65°C; and is insoluble in water but soluble in ether, benzene, and certain esters. , sectioned at 5 [micro]m, and stained with iron hematoxylin-eosin (Humason 1962). The gametogenic stage was classified (Chung et al. 1994, Sbrenna & Campioni 1994), and scored on a 0-4 scale according to Mann's (1979a) scheme: stage 0 = inactive, stage 1 = early active, stage 2 = late active, stage 3 = ripe, stage 4 = spawning-spent). The arithmetic means (mathematics) arithmetic mean - The mean of a list of N numbers calculated by dividing their sum by N. The arithmetic mean is appropriate for sets of numbers that are added together or that form an arithmetic series.  of the individual scores of whole specimens were recorded as the gonadal gonadal

pertaining to or arising from a gonad. See also testicular, ovarian.


gonadal cords
cords formed by epithelial cells which migrate from the mesonephric tubules in the embryo to the gonadal ridge and establish the indifferent
 maturity index (GMI GMI Governance Metrics International (New York, New York)
GMI Giant Magneto-Impedance
GMI Global MSF Interoperability
GMI General Motors Institute
GMI General Mills, Inc.
) for each sampling occasion (see details in Meneghetti et al. 2004).

Biochemical Analysis

Powdered sample (5-10 mg) was used for biochemical analysis. Protein content was determined using the method of Lowry et al. (1951) after alkaline hydrolysis hydrolysis (hīdrŏl`ĭsĭs), chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds.  with 0.5 N NaOH at 30[degrees]C for 24 h. Carbohydrate and glycogen glycogen (glī`kəjən), starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals.  were extracted in 15% trichloroacetic acid trichloroacetic acid /tri·chlo·ro·ace·tic ac·id/ (tri-klor?o-ah-se´tik) an extremely caustic acid, used in clinical chemistry to precipitate proteins and applied topically in chemabrasion and to remove warts.  and determined as glucose following the phenol-sulfuric acid method (Dubois et al. 1956). Glycogen was quantified after precipitation with 100% ethanol. Extraction of total lipid was performed in a mixture of chloroform chloroform (klôr`əfôrm) or trichloromethane (trī'klôrōmĕth`ān), CHCl3  and methanol methanol, methyl alcohol, or wood alcohol, CH3OH, a colorless, flammable liquid that is miscible with water in all proportions. Methanol is a monohydric alcohol. It melts at −97.  (Bligh & Dyer 1959) and lipid content determined following the method of Marsh and Weinstein (1966).

[FIGURE 2 OMITTED]

Standard Animal

To evaluate the physiological state Noun 1. physiological state - the condition or state of the body or bodily functions
physical condition, physiological condition

wakefulness - a periodic state during which you are conscious and aware of the world; "consciousness during wakefulness in a sane
 of T. philippinarum independent of growth, absolute values for tissue dry weight were standardized to that of a clam (standard animal) of 31.5 mm in shell length (the mean of all specimens analyzed) and compared for each sampling occasion. Allometric al·lom·e·try  
n.
The study of the change in proportion of various parts of an organism as a consequence of growth.



al
 equations of tissue dry weight against shell length at each sampling were determined by linear regression Linear regression

A statistical technique for fitting a straight line to a set of data points.
 analysis following logarithmic logarithmic

pertaining to logarithm.


logarithmic relationship
when the logs of two variables plotted against each other create a straight line.
 transformation (base 10). The same analysis was used to relate the weight of biochemical constituents and ash to the tissue dry weight. All regressions were statistically significant (P < 0.01). Dry weights of biochemical constituents were then computed for a given shell length by substituting appropriate values of tissue weight in the regression equations Regression equation

An equation that describes the average relationship between a dependent variable and a set of explanatory variables.
 referred to above (see details in Navarro et al. 1989). The results of biochemical analysis were then expressed in mg per standard animal.

Stable Isotopes stable isotope
n.
An isotope of an element that shows no tendency to undergo radioactive breakdown.
 

The clam tissue [[delta].sup.13]C and [[delta].sup.15]N were measured for at least four individuals, sampled bimonthly bi·month·ly  
adj.
1. Happening every two months.

2. Happening twice a month; semimonthly.

adv.
1. Once every two months.

2. Twice a month; semimonthly.

n. pl.
 at each site as described above. Marine particulate par·tic·u·late
adj.
Of or occurring in the form of fine particles.

n.
A particulate substance.



particulate

composed of separate particles.
 organic matter (POM) and riverine riv·er·ine  
adj.
1. Relating to or resembling a river.

2. Located on or inhabiting the banks of a river; riparian: "Members of a riverine tribe ...
 POM were collected bimonthly at the bay mouth and downstream of the Nam River. For sampling POM at each site, about 20 L of water was prefiltered in situ with a 250-[micro]m screen to remove large particles and transported to the laboratory as soon as possible. The particulates in this prefiltered water were concentrated onto a precombusted Whatman GF/F filter in the laboratory, treated with 2-3 drops of 10% HCl, and then rinsed with distilled water Noun 1. distilled water - water that has been purified by distillation
H2O, water - binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade;
. For each POM sampling, microphytobenthos was collected by scraping the visible mat of benthic ben·thos  
n.
1. The collection of organisms living on or in sea or lake bottoms.

2. The bottom of a sea or lake.



[Greek.
 diatoms diatoms

a series of unicellular algae, microscopic in size, with cell walls containing silica. Members of the family Diatomaceae. Their remains accumulate as geological deposits and are mined. See diatomaceous earth.
 from the sediment surface. This was extracted and prepared for isotope analysis Isotope analysis is the identification of isotopic signature, the distribution of certain stable isotopes and chemical elements within chemical compounds. This can be applied to a food web to make it possible to draw direct inferences regarding diet, trophic level, and subsistence.  according to Couch's procedure (1989), as described by Riera and Richard (1996). These pretreated samples were kept frozen until analysis, freeze-dried at -70[degrees]C, and then loaded into tin capsules prior to isotope analysis.

Values for [[delta].sup.13]C and [[delta].sup.15]N were obtained using a CHN CHN China
CHN Chain
CHN Canadian Health Network
CHN Coalition on Human Needs
CHN California Homeschool Network
CHN Cleveland Housing Network
CHN Center for Human Nutrition
CHN Carbon, Hydrogen, Nitrogen
CHN Community Health Nurse
 elemental analyzer (EuroVector 3000 Series, Italy) combined with a continuous-flow isotope ratio mass spectrometer spectrometer

Device for detecting and analyzing wavelengths of electromagnetic radiation, commonly used for molecular spectroscopy; more broadly, any of various instruments in which an emission (as of electromagnetic radiation or particles) is spread out according to some
 (GV Instruments, IsoPrime, UK). All isotope ratios were expressed as the relative per mill ([per thousand]) difference between the sample and conventional standard reference materials (PeeDee Belemnite bel·em·nite  
n.
A cone-shaped, fossilized internal shell of any of an extinct genus of cephalopods related to the cuttlefish.



[New Latin belemn
 carbonate and [N.sub.2] in air) as follows: [delta]X = [([R.sub.sample]/[R.sub.standard]) - 1] x [10.sup.3], where X is [sup.13]C or [sup.15]N, and R is the corresponding ratio of [sup.13]C:[sup.12]C or [sup.15]N:[sup.14]N. A laboratory internal standard (peptone peptone /pep·tone/ (pep´ton) a derived protein, or a mixture of cleavage products produced by partial hydrolysis of native protein.pepton´ic

pep·tone
n.
, Merke) was run every sixth sample. Measurement precision based on the standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.

(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers.
 of 20 replicates of the internal standard was within 0.2[per thousand] for both isotope pairs. Two replicates were analyzed from each sample of ground clam tissue.

Statistical Methods

Commercially available software was used to analyze the experimental results (SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance.  package, Chicago, IL). Data were tested for normality normality, in chemistry: see concentration.  using the Shapiro-Wilk procedure. Leven test was used to check the homogeneity Homogeneity

The degree to which items are similar.
 of variance among data. A paired sample t-test for paired comparisons was used to test the significance of variations in environmental parameters between sites and to determine differences in condition index, tissue dry weight, and biochemical components between sexes or sites during the study period. The arcsine transformation was applied to percentage data, such as condition index, prior to analysis. Analysis of variance (ANOVA anova

see analysis of variance.

ANOVA Analysis of variance, see there
, two-way) with Tukey multiple comparison test was performed to determine differences in [[delta].sup.13]C and [[delta].sup.15]N values of the Manila clam tissues between sites and among sampling months.

RESULTS

Temperature, Salinity, and Potential Food

Monthly mean water temperature showed a seasonal cycle typical of temperate zones, with maximum temperatures (22.6[degrees]C to 25.1[degrees]C) in July-September and minimum temperatures (7.4[degrees]C to 8.0[degrees]C) in January-February (Fig. 3). Salinity varied inversely with a summer minimum of less than 30 PSU PSU - power supply unit  in 2000 and 31 PSU in 2001, according to the monsoonal climate and constant values at around 33 PSU for the major part of the year. No differences in temperature and salinity were found between sites (paired t-test, P = 0.798 and 0.067).

Monthly mean SPM concentration fluctuated between 6.9 and 19.0 mg [L.sup.-1] (Fig. 4A). Although relatively high concentrations of more than 16 mg [L.sup.-1] were recorded during May to July 2001, concentrations were highly variable. Although chlorophyll a concentration peaked in summer in 2000, coincident co·in·ci·dent  
adj.
1. Occupying the same area in space or happening at the same time: a series of coincident events. See Synonyms at contemporary.

2.
 with the period of salinity minima, its seasonal trend was not clear (Fig. 4B). Rather, chlorophyll a concentration was also characterized by irregular peaks as shown in variations of SPM concentration. Both SPM and chlorophyll a values did not differ significantly between sites (P = 0.422 and 0.559).

[FIGURE 3 OMITTED]

Condition and Reproductive Cycle

Because of the possibility of sexual differentiation sexual differentiation See Hermaphroditism, hirsutism, Müllerian ducts, Precocious puberty, Pseudoprecocious puberty, Tanner staging, Testis-determining factor, Virilization, Wolffian ducts, XXX, XXY, XXXY, XYY syndromes, Y Chromosome.  in biochemical composition, as shown in the clam Ruditapes decussates (L.) (Perez Camacho et al. 2003), all analyses in this study were carried out separately for each sex. Seasonal variations in condition index were very similar between control and treatment sites, and the data showed a clear seasonal pattern (Fig. 5) that was very similar between sexes. The maximum values in condition index occurred in May 2000 and were followed by a progressive decline throughout the summer-autumn period to minimum levels in October. After November a subsequent increase was observed, which peaked in March to April 2001. This spring peak was followed by a summer decline. No statistical difference in condition index was found between females and males of each population (P = 0.583 and 0.113 for control and treatment sites, respectively) or between sites (P = 0.466 and 0.791 for female and male, respectively).

Values for GMI also exhibited clear seasonality that was similar between control and treatment sites (Fig. 6). This was attributed to sexual maturation of the clams. In both years, the Years, The

the seven decades of Eleanor Pargiter’s life. [Br. Lit.: Benét, 1109]

See : Time
 development of gonadal tissue was initiated in both sexes in January and peaked during May to July, when the condition index values started to decline. Gametogenic stage 4 can be used as the criterion for the beginning and end of spawning. The appearance and disappearance of stage 4 coincided with the period of condition decline, indicating that spawning began in May and continued until October. Spawning was followed by a sexual resting period in November to December.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

Tissue Dry Weight

The tissue dry weight of a standard animal was calculated for each sex in the control and treatment groups (Fig. 7). There was a remarkable seasonal variation in tissue dry weight in both groups, the patterns being similar to those of the condition index. The dry weight of soft tissues decreased steadily from maximum levels in May 2000 to minimum levels in October, coincident with the spawning period, and increased progressively to spring 2001, when values peaked. This was followed by a gradual decrease to the end of the experiment in October 2001. Differences in tissue dry weight of standard animals were not statistically significant between females and males of each population (P = 0.150 and 0.727 for control and treatment sites) or between sites (P = 0.145 and 0.877 for female and male).

Gross Biochemical Composition

Seasonal variations in gross biochemical composition of standard animals showed similar patterns between sexes of each population or sites, with clear seasonal trends (Fig. 8). Seasonal patterns in absolute values for all biochemical components (protein, carbohydrate, and lipid) were very similar and followed those of tissue dry weight of standard animals and the condition index for each population.

Protein peaked at the beginning of the study in May 2000 and in April 2001. Sharp declines occurred in June 2000 and from August to October, when minimum values were detected. Loss in protein content correlated with spawning. Values then increased gradually to peak in March to April 2001, followed by a sudden decline in May and July to October. No statistical difference was found in the protein value of standard animals between females and males of each population (P = 0.148 and 0.811 for control and treatment sites) or between sites (P = 0.121 and 0.182 for female and male).

A similar seasonal pattern for carbohydrate and glycogen indicated that carbohydrate content of the clams depends on glycogen mobilization. Similar to protein, a carbohydrate peak occurred in May 2000 and was followed by a sudden decrease from June until October to November. Carbohydrate (glycogen) reserves were quickly restored during the winter to spring and decreased again through the summer to a minimum in October 2001. A paired t-test showed no significant difference in carbohydrate and glycogen values between females and males of each population (P = 0.693 and 0.820 for carbohydrate for control and treatment sites); 0.123 and 0.135 for glycogen) or between sites (P = 0.827 and 0.727 for carbohydrate for females and males; 0.199 and 0.142 for glycogen, respectively).

Lipid values were lowest in October to November and highest in spring, displaying a similar seasonal pattern to protein and carbohydrate. There was no difference in the lipid value of standard female and male clams between each population (P = 0.094 and 0.331 for control and treatment sites) or between sites (P = 0.389 and 0.341 for female and male).

Although peak values of ash content were observed in spring, its seasonal pattern was less pronounced than other biochemical variables. No significant difference in ash value of standard animals was found between females and males of each population (P = 0.141 and 0.191 for control and treatment sites) or between sites (P = 0.210 and 0.090, for females and males).

Stable Isotope Ratios for Clams and Potential Food Sources

Values for [[delta].sup.13]C in muscle tissue of clams averaged -17.4 [+ or -] 0.6[per thousand] (SD, n = 26) and -17.6 [+ or -] 0.6[per thousand] (n = 25) at the control and treatment sites, respectively (Table 2). There were no significant differences in [[delta].sup.13]C values between sites and among the sampling months (two-way ANOVA, [F.sub.(1, 39)] = 0.059, P = 0.809 for site; [F.sub.5, 39] = 2.318, P = 0.062 for month). Values for [[delta].sup.15]N averaged 10.8 [+ or -] 0.8[per thousand] (n = 23) and 10.5 [+ or -] 0.8[per thousand] (n = 23) at the control and treatment sites, respectively (Table 2), with no significant difference between sites (two-way ANOVA, [F.sub.5, 34] = 20.186, P < 0.001). However, the [[delta].sup.15]N values showed significant seasonal differences, being about 2[per thousand] more depleted de·plete  
tr.v. de·plet·ed, de·plet·ing, de·pletes
To decrease the fullness of; use up or empty out.



[Latin d
 in June 2001 than in August, October, and December 2000 for both sites ([F.sub.5, 39] = 2.318, P = 0.062; Tukey HSD HSD Human Services Department
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 test, P < 0.05). Although significant seasonal changes in both [[delta].sup.13]C and [[delta].sup.15]N values for microphytobenthos, marine POM, and riverine POM were detected, the stable isotope compositions of these three potential food sources were clearly distinguished: the average values (n = 12) were, respectively, -14.5 [+ or -] 1.6[per thousand], 21.1 [+ or -] 1.1[per thousand], and -27.8 [+ or -] 2.7[per thousand] for [[delta].sup.13]C, and 8.9 [+ or -] 0.9[per thousand], 5.7 [+ or -] 1.3[per thousand], and 9.0 [+ or -] 0.8[per thousand] for [[delta].sup.15]N (Table 2; Fig. 9).

According to a dual plot of [[delta].sup.13]C and [[delta].sup.15]N deviations measured for the clams and their potential food sources (Fig. 9), the dietary components of the clams appeared to be primarily composed of microphytobenthos and marine POM throughout the year. Figure 10 presents the relative biomass contributions of the three dietary sources, calculated from a linear mixing model based on mass balance equations using [[delta].sup.13]C and [[delta].sup.15]N values (the IsoSource model, Phillips & Gregg 2003). The results confirmed that a major part of clam biomass for both sites was derived from microphytobenthos and marine POM. Microphytobenthos contribution tended to be relatively constant from August 2000 to April 2001, and then sharply decreased to June. Conversely, the contribution of marine POM progressively increased from October 2000 to June 2001. The dietary contribution of riverine POM ranged between 11% and 17% in August and October 2000, but it was negligible throughout the rest of the year.

[FIGURE 6 OMITTED]

DISCUSSION

The condition index of marine bivalves summarizes the physiological activity of the animals under given environmental conditions, and its fluctuation has important implications for cultivation and harvesting strategies for bivalves (Lucas & Beninger 1985, Okumus& Stirling 1998). The primary objective in this study was to compare the condition of Manila clams (T. philippinarum) reared in natural and artificially created habitat in relation to gametogenic processes, and accumulation and mobilization of reserve materials, as well as to evaluate habitat functions of the created farming grounds for this species. The condition index had a seasonal cycle at both the treatment and the control site, with minimum values in autumn (October to November) rising to peak levels in early spring (May 2000 and March to April 2001) (Fig. 5). No difference was evident in the index level between clams from the natural and created habitat. As the condition of bivalves reflects changes of physiological status dependent on environmental factors including food supply and temperature, this result indicates that clam stocks from created silty sand habitat can have biological traits similar to those from natural clam habitat and provide a good quality product for market.

In this study, marine sand transported by a large barge was sprinkled on the muddy sediments during the high slack water slack water
n.
1. A period of cessation in the strong flow of a current of water, especially at high or low tide.

2. An area in a sea or river unaffected by currents; still water.

Noun 1.
 period and then flattened flat·ten  
v. flat·tened, flat·ten·ing, flat·tens

v.tr.
1. To make flat or flatter.

2. To knock down; lay low: The boxer was flattened with one punch.
 during the ebb tide ebb tide
n.
The receding or outgoing tide; the period between high water and the succeeding low water.



ebb tide  

The period between high tide and low tide during which water flows away from the shore.
. Adding sand made the muddy substrate coarser (Table 1). Monthly monitoring of the sediment characteristics showed that chemical oxygen demand (7.53-11.80 mg [g.sup.-1]), hydrogen sulfide hydrogen sulfide, chemical compound, H2S, a colorless, extremely poisonous gas that has a very disagreeable odor, much like that of rotten eggs. It is slightly soluble in water and is soluble in carbon disulfide.  (0.00-0.08 mg [g.sup.-1]), and organic content (1.0-7.7%) of coarser sediments in the created habitats were much lower than those (9.27-32.58 mg [g.sup.-1], 0.00-0.10 mg [g.sup.-l], and 7.0-8.1%, respectively) in muddy sediments (data not shown in Results). Clam-farming ground exposed to environmental conditions similar to those of natural clam habitat was created by adding sand to the muddy substrate, and none of the hydrological hy·drol·o·gy  
n.
The scientific study of the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere.
 and sedimentary parameters evaluated showed significant differences between the natural and created habitats (Figs. 3 and 4, Table 1). Although most differences were caused by reproductive and physiological characteristics of clams rather than regional differences in environmental conditions, environmentally stressful conditions can result in differences in physiological status of marine bivalves in time and space (Navarro et al. 1989, Robert et al. 1993, Kang et al. 2000, Marin et al. 2003). Accordingly, the comparable environmental conditions between the natural and created habitat were probably responsible for the similarity in timing and level of the maximum and minimum values for the condition index of clams in this study.

[FIGURE 7 OMITTED]

Spring maxima in condition found during this investigation have also been observed in European populations (Beninger & Lucas 1984, Marin et al. 2003). Biometric data revealed that the maximum condition value was considerably greater in both stocks in the spring of 2000 than in 2001. Similar results were obtained by Beninger and Lucas (1984) in T. philippinarum from the north Atlantic coast of France. This may be explained by the diminishing growth rate with size (age) in marine bivalves (Ohba 1959, Beninger & Lucas 1984, and references therein). The spring maxima in condition were followed by a progressive decline during summer and autumn caused by spawning, after which clam condition recovered rapidly in parallel to accumulation of energy the storing of energy by means of weights lifted or masses put in motion; electricity stored.

See also: Accumulation
 reserves in late autumn to winter 2000. The timing of condition minima recorded during this study appeared to be somewhat different from those observed in European clam populations. In Brittany (France), Beninger and Lucas (1984) observed only a partial condition recovery in spring because of physiological stress during the autumn and winter. In the Lagoon of Venice, Marin et al. (2003) also found condition recovery from February throughout spring to summer, because of the decrease in water temperature and food availability in autumn to winter. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke"
put differently
, minimum values in condition index were recorded during winter in European waters. These differences in timing of condition minima and recovery suggest that the clams at the study sites had a positive energy balance during late autumn and winter, as indicated by the accumulation of energy reserves after spawning.

Strong positive correlations between condition index and GMI values (control: r = 0.752 and 0.780 for female and male, P < 0.001 for both; treatment: r = 0.748 and 0.724, P < 0.001) indicated a close relationship between the gametogenic cycle and condition. There was no apparent difference in stages of gonadal maturation between sites (Fig. 6). After a brief inactive period in late autumn (November to December), gametogenesis Gametogenesis

The production of gametes, either eggs by the female or sperm by the male, through a process involving meiosis. In animals, the cells which will ultimately differentiate into eggs and sperm arise from primordial germ cells set aside from the
 was initiated in January. Ripe stage was reached in spring and was followed by spawning, which began in May and lasted throughout summer until October. Mean water temperature was 7.6[degrees]C in January 2001 and 14.3[degrees]C in May, comparable to minimum temperatures of 8[degrees]C for gonadal activity and 14[degrees]C for spawning of T. philippinarum (Mann 1979b). The reproductive cycle of T. philippinarum observed during this investigation is very similar to that of Mediterranean populations (Sbrenna & Campioni 1994, Meneghetti et al. 2004) and a Japanese population (Ohba 1959). However, the onset of gametogenesis and gamete gamete (găm`ēt): see reproduction.  ripening ripening

said of meat. See curing.
 in northern European populations (Beninger & Lucas 1984, Xie & Burnell 1994) and Vostok Bay populations of the northwestern part of the East/Japan Sea (Ponurovsky & Yakovlev 1992) is delayed compared with populations in warmer climates. Xie and Burnell (1994) speculated that this time lag could be explained by a time to temperature effect.

Continuous or multiple spawning during summer has been observed worldwide (Ponurovsky & Yakovlev 1992, Sbrenna & Campioni 1994, and references therein). In the present investigation, it is difficult to determine the precise timing and intensity of spawning from a monthly sampling strategy. The seasonal cycles of gametogenesis and the amplitude of seasonal fluctuations of standard animal tissue dry weight was quite similar between the natural and created habitat. The loss of tissue weight observed during the spring-summer period appeared to coincide with spawning time as seen in the seasonal variations in the sexual maturation process and the GMI values (Figs. 6 and 7). The rapid decrease in standard animal tissue dry weight during the spring to summer period suggests two spawning events. The spawning pattern of the Manila clam is known to be highly variable, with one spawning period reported in Washington State and Ireland (Holland & Chew 1974, Xie & Burnell 1994, respectively); two spawning peaks in Japan (Tanaka 1954, Ohba 1959), France (Beninger & Lucas 1984) and Italy (Sbrenna & Campioni 1994, Meneghetti et al. 2004); and three spawning events in southwest Spain (Sarasquete et al. 1990). The timing and intensity of gonadal development and spawning is known to vary locally, seasonally, and interannually (Beninger & Lucas 1984, Navarro et al. 1989, Sbrenna & Campioni 1994, Kang et al. 2000, Meneghetti et al. 2004). These studies demonstrated that temperature is not the only factor acting on gonad gonad /go·nad/ (go´nad) a gamete-producing gland; an ovary or testis.gonad´algonad´ial

indifferent gonad  the sexually undifferentiated gonad of the early embryo.
 development and the beginning of spawning, and that local or temporal variations in gonadal maturation of bivalves are closely related to variations in nutritional conditions (that is, food availability). Therefore, the gametogenic cycle observed during this investigation appears to be explained by a seasonal cycle in accumulation and mobilization of reserve materials in clams in relation to variability in trophic trophic /tro·phic/ (tro´fik) (trof´ik) pertaining to nutrition.

troph·ic
adj.
Of, relating to, or characterized by nutrition.
 conditions.

[FIGURE 8 OMITTED]

Seasonal patterns and levels of tissue dry weight and biochemical components in clams were quite similar in the natural and created habitat (Figs. 7 and 8), indicating that clams reared in created habitats can have the same physiological characteristics as those in natural habitats. Seasonal variations in the absolute values of biochemical components paralleled those of tissue dry weights in clams at both sites. Seasonal cycles in tissue dry weight of standard animals seemed to reflect the reproductive cycle, with weight being maximal prior to the spring to summer spawning, and then decreasing simultaneously with spawning. Protein constitutes the major organic component of gametes in T. philippinarum (Beninger & Lucas 1984). Somatic somatic /so·mat·ic/ (so-mat´ik)
1. pertaining to or characteristic of the soma or body.

2. pertaining to the body wall in contrast to the viscera.


so·mat·ic
adj.
 proteins are also mobilized during gametogenesis, acting as the predominant respiratory substrate during this period (Mann & Glomb 1978, Adachi 1979; see also Beninger & Lucas 1984, Marin et al. 2003). As expected from these studies, the absolute values for protein in clams in this study peaked during the spring-summer spawning period (Fig. 8). A sharp decline in May to June 2000 and April to May 2001 indicated the first spawning during these periods. After this first spawning, there was a rapid recovery in protein content and then a slow decrease until October, indicating the second spawning event.

[FIGURE 9 OMITTED]

Seasonal variation in absolute values for lipid was very similar to those of protein. It is commonly accepted that glycogen reserves are converted into lipids, which are a major component of bivalve oocytes (Holland 1978, Gabbott 1983, Beninger & Lucas 1984, Marin et al. 2003). Accordingly, the maximum values detected prior to spawning, and the minimum after, may be explained by the above hypothesis. As observed in the seasonal variation in protein, there was a rapid recovery in lipid content after the first spawning. Somatic proteins and lipids also serve as energy reserves in T. philippinarum under conditions of nutritional stress and energy imbalance (Beninger & Lucas 1984, Marin et al. 2003). After the spawning period in this study, tissue dry weight began to increase without a period of decrease during inactive gonadal phase (no oocytes) in winter, in contrast to European populations (Beninger & Lucas 1984, Marin et al. 2003). Because the absolute values of all biochemical components also increased during this period, it is difficult from this study to confirm the role of proteins and lipids as maintenance energy reserves.

Seasonal patterns of carbohydrate in clams from the sampling sites could be explained by glycogen patterns. Carbohydrate and glycogen peaks in May 2000 were followed by a sudden decrease as a consequence of spawning. In contrast to protein and lipid, glycogen recovery was not detected after the first spawning in both 2000 and 2001. Glycogen has long been considered to be the main energy reserve for both the formation of gametes and the maintenance of adult bivalves during periods of nutritional stress (see Beninger & Lucas 1984). The results presented here support this conclusion and also the conversion of glycogen into lipids, as previously discussed. The absolute values for glycogen were lowest at the end of spawning and then quickly recovered throughout winter to spring. In general, the recovery and accumulation of glycogen in bivalves is related to good conditions of food availability (Ansell & Trevallion 1967, Newell & Bayne 1980, Navarro et al. 1989, Okumus& Stirling 1998, Kang et al. 2000). Beninger and Lucas (1984) showed that a failure to constitute energy reserves in autumn after spawning, and the exhaustion of reserves caused by energy imbalances in winter, resulted in a delay in the recovery of condition and the maturation of gonads in Brittany (France) populations of T. philippinarum. On the other hand, Sbrenna and Campioni (1994), and Meneghetti et al. (2004) suggested that high accumulation of reserve materials, because of high food availability from late winter to early spring, leads to gamete development in winter and spawning in May in lagoon systems of Italy. Thus, the recovery of glycogen reserves throughout winter--spring in this study indicates that the Manila clams had sufficient food supply to enable resumption of gonadal maturation and spawning in May.

[FIGURE 10 OMITTED]

Comparison of isotopic signatures of T. philippinarum tissues with those of potential food resources confirmed the contribution of microphytobenthos to the clam diet in both the natural and the created habitat (Fig. 10). The POM and chlorophyll a data did not show any seasonal trend, indicating no apparent seasonality in the trophic conditions of ambient waters. Irregular peaks in SPM and chlorophyll a values, as well as the isotopic data. suggest that the nutritional conditions of waters were strongly influenced by resuspension caused by tide and wind. Therefore, despite an important role of phytoplankton in the clam diet throughout the year, food availability to meet energy requirements in this study area might be maintained by resuspension of microphytobenthos, even during the winter to spring period. The high availability Also called "RAS" (reliability, availability, serviceability) or "fault resilient," it refers to a multiprocessing system that can quickly recover from a failure. There may be a minute or two of downtime while one system switches over to another, but processing will continue.  of food because of the summer phytoplankton blooms may have provided energy requirements for the rapid recovery of reserve materials after the first spawning as well as for the second spawning in summer. The isotopic signatures of clam tissues showed that the dietary contribution of organic matter from marine POM (largely phytoplankton) increased markedly in late spring to summer 2001. Phytoplankton blooms caused by heavy rain and nutrient input, which are concentrated during late spring to early summer, are well-known phenomena in coastal regions with a monsoonal climate, as occurs on the Korean peninsula (Kang et al. 2000, Park et al. 2001). Although limited to late summer, a dietary contribution from riverine POM was detected. This is consistent with the conclusion of Kasai et al. (2004) that Manila clams select marine POM (phytoplankton and microphytobenthos) from the organic matter available in their habitat, and the contribution of terrestrial material increases temporarily during rainfall. Finally, our biochemical and isotopic data indicated that food availability in the study area was mostly dependent on resuspension of microphytobenthos, along with seasonal dynamics of phytoplankton.

In summary, clams reared in newly created or natural habitats had similar patterns and levels in condition and tissue dry weight. The similar biochemical compositions and reproductive cycles for clams in the two habitats are likely to be a consequence of similarities in environmental conditions, and thereby food availability. The results show that the newly created sandy habitats may provide habitat functions that enable Manila clams to have biological cycles similar to those in natural habitats. These results confirm the conclusion of Melia et al. (2004) that rearing sites with high sand content are preferable in terms of growth and maximum attainable size of Manila clams. This initial experiment primarily tested whether Manila clams can adapt to created sandy habitats. For commercially sustainable exploitation and better yield of T. philippinarum in the future, more detailed studies of the effect of stock density and deposition rate of silt modifying the substrate are needed.

ACKNOWLEDGMENTS

The authors thank H. J. Park, J. H. Kwak, and E. J. Jang for their technical assistance and the anonymous referees for their reviewing and critical comments on the manuscript. This work was supported for two years by Pusan National University History
Pusan National University (PNU) was founded on May 1946 in Pusan, Korea's second largest metropolis, by Korean government,which has been established five months earlier than Seoul National University in Seoul.
 Research Grant.

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CHANG-KEUN KANG, (1) * YANG SOON KANG, (2) EUN EUN Egyptian Universities Network
EUN Laayoune, Morocco - Laayoune-Hassan I Morocco (Airport Code)
EUN Endogenous Urinary Nitrogen
EUN External Update Notification
EUN End User Network
 JUNG CHOY, (1) DONG-SUN KIM, (3) BONG-TAEK SHIM (4) AND PIL-YONG LEE (2)

(1) Department of Biology, Pusan National University, Busan 609-735, Republic of Korea; (2) Department of Oceanography oceanography, study of the seas and oceans. The major divisions of oceanography include the geological study of the ocean floor (see plate tectonics) and features; physical oceanography, which is concerned with the physical attributes of the ocean water, such as , National Fisheries Research and Development Institute, Busan 619-900, Republic of Korea; (3) Research Center for Ocean Industrial Development (RCOID), Pukyong National University Pukyong National University is one of the 10 large-scale national universities in Busan, South Korea. University has two campuses - Daeyeon-dong and Yongdang-dong. These campuses are situated near coastal district of Nam-gu. , 608-737 Busan, Republic of Korea; (4) Goseong Maritime and Fisheries Office, Masan Regional Maritime Affairs & Fisheries Office. 638-805 Gyeongnam, Republic of Korea

* Corresponding author. E-mail: ckkang@pusan.ac.kr
TABLE 1.
Sediment characteristics of the experimental sites, and initial
density, shell length, and final density of the clam. Data are from
May 6 2000, when the sites were seeded with clams, except for final
density (October 30 2001). Data are means (ranges in parentheses).

                                                          Organic
                       % Mud        Median Grain          Content
Site                <63 [micro]m   Size ([micro]m)   (% Ignition loss)

Nonsanded mudflat        83               23           7.5 (7.0-8.2)
Created habitat          17              193           2.5 (1.0-7.7)
Natural habitat          20              185           2.6 (1.0-8.0)

                    Initial (seed)
                        Density                          Final Density
                    (individuals       Initial Shell     (Individuals
Site                  [m.sup.-2])       Length (mm)       [m.sup.-2])

Nonsanded mudflat    153 (138-164)    25.3 (18.0-33.9)         0
Created habitat      112 (100-131)    24.8 (17.6-41.2)    34 (22-39)
Natural habitat      100 (92-123)     24.5 (20.0-38.1)    23 (20-28)

TABLE 2.
[[delta].sup.13]C and [[delta].sup.15]N values (mean [+ or -] SD) for
microphytobenthos, marine POM (particulate organic matter), riverine
POM, and clams collected in Jinju Bay. Figures in parentheses are the
number of analyzed samples.

                                                August
                         Sample                  2000

[[delta].sup.13]C   Microphytobenthos   -13.7 [+ or -] 1.6 (2)
                    Marine POM          -22.0 [+ or -] 1.3 (2)
                    Riverine POM        -28.2 [+ or -] 1.1 (2)
                    Clams (control)     -17.9 [+ or -] 0.2 (4)
                    Clams (treatment)   -17.8 [+ or -] 0.5 (4)
[[delta].sup.15]N   Microphytobenthos     8.9 [+ or -] 1.6 (2)
                    Marine POM            4.6 [+ or -] 1.6 (2)
                    Riverine POM          9.5 [+ or -] 0.6 (2)
                    Clams (control)      11.3 [+ or -] 0.3 (4)
                    Clams (treatment)    11.4 [+ or -] 0.5 (4)

                         Sample                 October

[[delta].sup.13]C   Microphytobenthos   -13.8 [+ or -] 0.5 (2)
                    Marine POM          -21.9 [+ or -] 0.8 (2)
                    Riverine POM        -30.4 [+ or -] 2.1 (2)
                    Clams (control)     -17.8 [+ or -] 0.9 (5)
                    Clams (treatment)   -17.8 [+ or -] 0.3 (4)
[[delta].sup.15]N   Microphytobenthos     9.7 [+ or -] 0.1 (2)
                    Marine POM            5.6 [+ or -] 0.5 (2)
                    Riverine POM         10.0 [+ or -] 0.9 (2)
                    Clams (control)      11.3 [+ or -] 0.6 (4)
                    Clams (treatment)    11.2 [+ or -] 0.3 (4)

                         Sample                December

[[delta].sup.13]C   Microphytobenthos   -13.9 [+ or -] 0.1 (2)
                    Marine POM          -20.7 [+ or -] 0.9 (2)
                    Riverine POM        -31.3 [+ or -] 0.3 (2)
                    Clams (control)     -16.9 [+ or -] 0.8 (4)
                    Clams (treatment)   -17.9 [+ or -] 0.3 (4)
[[delta].sup.15]N   Microphytobenthos     8.9 [+ or -] 0.7 (2)
                    Marine POM            5.6 [+ or -] 1.0 (2)
                    Riverine POM          8.3 [+ or -] 0.2 (2)
                    Clams (control)      11.0 [+ or -] 0.7 (4)
                    Clams (treatment)    11.0 [+ or -] 0.2 (4)

                                               February
                         Sample                  2001

[[delta].sup.13]C   Microphytobenthos   -14.9 [+ or -] 0.8 (2)
                    Marine POM          -20.2 [+ or -] 0.9 (2)
                    Riverine POM        -26.4 [+ or -] 1.1 (2)
                    Clams (control)     -17.3 [+ or -] 0.3 (5)
                    Clams (treatment)   -17.0 [+ or -] 0.7 (5)
[[delta].sup.15]N   Microphytobenthos     9.7 [+ or -] 0.8 (2)
                    Marine POM            7.0 [+ or -] 0.4 (2)
                    Riverine POM          8.3 [+ or -] 1.0 (2)
                    Clams (control)      11.0 [+ or -] 0.4 (4)
                    Clams (treatment)    10.1 [+ or -] 0.6 (4)

                         Sample                  April

[[delta].sup.13]C   Microphytobenthos   -17.4 [+ or -] 0.6 (2)
                    Marine POM          -20.7 [+ or -] 1.5 (2)
                    Riverine POM        -24.4 [+ or -] 0.2 (2)
                    Clams (control)     -17.2 [+ or -] 0.3 (4)
                    Clams (treatment)   -17.5 [+ or -] 0.2 (4)
[[delta].sup.15]N   Microphytobenthos     7.6 [+ or -] 0.7 (2)
                    Marine POM            6.7 [+ or -] 0.1 (2)
                    Riverine POM          8.6 [+ or -] 0.3 (2)
                    Clams (control)      10.7 [+ or -] 0.4 (3)
                    Clams (treatment)    10.3 [+ or -] 0.4 (4)

                         Sample                  June

[[delta].sup.13]C   Microphytobenthos   -13.2 [+ or -] 1.1 (2)
                    Marine POM          -20.8 [+ or -] 0.2 (2)
                    Riverine POM        -26.0 [+ or -] 0.1 (2)
                    Clams (control)     -17.4 [+ or -] 0.7 (4)
                    Clams (treatment)   -18.0 [+ or -] 0.6 (4)
[[delta].sup.15]N   Microphytobenthos     8.4 [+ or -] 0.5 (2)
                    Marine POM            3.7 [+ or -] 0.1 (2)
                    Riverine POM          9.1 [+ or -] 0.2 (2)
                    Clams (control)       9.2 [+ or -] 0.7 (4)
                    Clams (treatment)     9.3 [+ or -] 0.3 (3)

                         Sample                  Total

[[delta].sup.13]C   Microphytobenthos   -14.5 [+ or -] 1.6 (12)
                    Marine POM          -21.1 [+ or -] 1.1 (12)
                    Riverine POM        -27.8 [+ or -] 2.7 (12)
                    Clams (control)     -17.4 [+ or -] 0.6 (26)
                    Clams (treatment)   -17.6 [+ or -] 0.6 (25)
[[delta].sup.15]N   Microphytobenthos     8.9 [+ or -] 0.9 (12)
                    Marine POM            5.7 [+ or -] 1.3 (12)
                    Riverine POM          9.0 [+ or -] 0.8 (12)
                    Clams (control)      10.8 [+ or -] 0.8 (23)
                    Clams (treatment)    10.5 [+ or -] 0.8 (23)
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Author:Kang, Chang-Keun; Kang, Yang Soon; Choy, Eun Jung; Kim, Dong-Sun; Shim, Bong-Taek; Lee, Pil-Yong
Publication:Journal of Shellfish Research
Date:Aug 1, 2007
Words:8733
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