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1.
The flux of ammonia, phosphate, silica and radon-222 from Potomac tidal river and estuary sediments is controlled by processes occurring at the sediment-water interface and within surficial sediment. Calculated diffusive fluxes range between 0·6 and 6·5 mmol m?2 day?1 for ammonia, 0·020 and 0·30 mmol m?2 day?1 for phosphate, and 1·3 and 3·8 mmol m?2 day?1 for silica. Measured in situ fluxes range between 1 and 21 mmol m?2 day?1 for ammonia, 0·1 and 2·0 mmol m?2 day?1 for phosphate, and 2 and 19 mmol m?2 day?1 for silica. The ratio of in situ fluxes to diffusive fluxes (flux enhancement) varied between 1·6 and 5·2 in the tidal river, between 2·0 and 20 in the transition zone, and from 1·3 to 5·1 in the lower estuary. The large flux enhancements from transition zone sediments are attributed to macrofaunal irrigation. Nutrient flux enhancements are correlated with radon flux enhancements, suggesting that fluxes may originate from a common region and that nutrients are regenerated within the upper 10–20 cm of the sediment column.The low fluxes of phosphate from tidal viver sediments reflect the control benthic sediment exerts on phosphorus through sorption by sedimentary iron oxyhydroxides. In the tidal river, benthic fluxes of ammonia and phosphate equal one-half and one-third of the nutrient input of the Blue Plains sewage treatment plant. In the tidal Potomac River, benthic sediment regeneration supplies a significant fraction of the nutrients utilized by primary producers in the water column during the summer months.  相似文献   

2.
Measurements were made of chlorophyll-a and phaeophytin-a in calcareous sediments along transects off the east coast of Florida (75–190 m) and the west coast of Grand Bahama Island (170–300 m). Solvent partitioning showed that chlorophyll-a concentrations never exceeded 0·1 mg m?2 at either location, most as degradation products. Total pigment concentrations (chlorophyll and phaeopigments) ranged from 0·18–1·83 mg m?2 in sediments off Grand Bahama Island and 2·50 to 20·65 mg m?2 off West Palm Beach. Pigments, expressed per gram dry weight of sediments, increased with depth across the Florida Continental Shelf. This is probably due to differences in sediment character between near-shore and off-shore sediments.  相似文献   

3.
The bivalve molluscs Mytilus californianus and Crassostrea gigas were exposed to filtered seawater containing the isotope 95mTc added as pertechnetate (TcO4?) to study the biokinetic behaviour of this element. Whole body concentration factors for both organisms at equilibrium were small (CF = 1·3–1·5); individual organ concentration factors were highest for the visceral mass in both. Loss rates determined both in the laboratory and under field conditions were biphasic for both molluscs; initial loss of Tc was rapid with slightly more than 50 % of the initial label being lost within 10 days. Thereafter, loss rates decreased and whole body biological half-lives ranged from 80 to 134 days. Neither I? nor IO3? affected the uptake of Tc by M. californianus even when concentrations of these anions exceeded those normally present in seawater by two orders of magnitude.  相似文献   

4.
Coastal environments with reducing waters and/or sediments represent potential sinks for 99Tc discharged to sea. Here, we have examined estuarine sediments from four geochemically distinct locations that have been exposed to 99Tc discharged from Sellafield. Both the relative uptake and the operationally defined sediment “component” that holds the Tc were investigated in order to establish whether particular biogeochemical processes are predominately responsible for reducing and binding Tc in sediments. Despite the artefacts that can pose problems for sequential extractions, this scheme [Int. J. Environ. Anal. Chem. 51 (1993) 187] appears to be robust with regard to Tc. The results show that relative uptake of Tc varied greatly between the sites, with the highest occurring at an almost permanently anoxic fjord (Mariager Fjord, Denmark), followed by a brackish, seasonally eutrophic fjord (Roskilde Fjord, Denmark), then a sub-oxic salt marsh (which receives particle bound radionuclides from a more reducing mud patch; Esk Estuary, UK) and finally sulfidic and iron-reducing muddy sandy sediments (Needle's Eye, Solway Firth, Scotland). High relative uptake at the fjords was explained by the greater mixing of Tc-labelled oxic seawater into the part of the system where reduction of TcO4− was possible. Uptake at Mariager Fjord was higher than at Roskilde Fjord, reflecting the highly reducing geochemical conditions in the water body. Low uptake at Needle's Eye may be related to the speciation of technetium at this site as the sequential extraction data suggest that Tc is associated with the carbonate phase here. Tc carbonates are largely soluble, and this is the first observation of Tc association with carbonate fractions in the natural environment. The other three sites showed that organic matter, in conjunction with reducing conditions, was very important for binding and retaining Tc in sediments. The specific role of sulfides in controlling Tc retention in sediments was unclear because sulfides and organic matter are leached simultaneously in the sequential extraction scheme we applied, but there was evidence that Tc was not associated with acid-volatile iron monosulfides.  相似文献   

5.
The number of bacteria in sediments, interstitial water and overlying tidal water of an oligohaline marsh system are about 109, 106 and 106 cells cm?3, respectively. Average cell size in the overlying water (about 0·06 μm3), is much smaller than that in sediments and interstitial water (about 0·18 μm3). Most bacterial cells in sediments are bound to sediment particles and less than 1% of the cells were displaced by percolating water through sediment columns. Concentration of bacteria in flooding tidal waters is generally higher than that in ebbing waters. Movement of bacterial biomass does not appear to be a significant mechanism of particulate organic transport in marsh sediments and marsh sediments do not appear to be a source of suspended bacteria for estuaries.  相似文献   

6.
ABSTRACT

Phosphorus (P) stores in gravel-bed rivers are released for uptake by periphyton when pH levels exceed 8.5. The Tukituki River has low alkalinity water and frequently experiences periphyton blooms, and daytime pH?>?9 during summer low-flows. We measured dissolved reactive P (DRP) and EPC0, the water concentration of DRP at which no net release or sorption from the river bed occurs, in sediment samples from the Tukituki River subject to controlled pH levels before (2014) and after (2017) changes to two wastewater discharges that reduced P release to the river by 95%. DRP released from 2014 sediments at pH 8.5–10 were 30?±?10?mg/m3 above background (pH 8) whereas those released from 2017 sediments were 5?±?3?mg/m3 above background. EPC0 levels in 2014 and 2017 were 11?±?6 and 7?±?2?mg/m3, respectively. Field estimates of released DRP calculated from continuous pH and the Redfield equation suggested that most of the readily available DRP released from sediments at elevated pH is derived from material attached to recently deposited sediment. Subsequently, a reduction in wastewater inputs or agricultural runoff should reduce sediment DRP stores, and hence sediment fluxes, within a few years and mitigate periphyton blooms in addition to directly lowering water column concentrations.  相似文献   

7.
Juvenile coho salmon, Onchorynchus kisutch, were exposed to 95mTc in both saltwater and freshwater to study the biokinetic behavior of this element in an anadromous fish. In freshwater, equilibrium whole-body concentration factors (CF5) ranged from 28 to 32 in two separate experiments, in sharp contrast to an equilibriumCF of < 5 in saltwater. While the uptake kinetics were unimodal in saltwater, in freshwater, biomodal uptake kinetics were observed.Technetium-95m retention was biphasic in freshwater depuration experiments, an initial rapid loss of 21% to 26% of the steady-state activity with an elimination half-life of 3 to 5 days was followed by a slower loss rate, with a whole-body elimination half-life ranging from 23 to 33 days. In saltwater, retention was monophasic with an elimination half-life of 5–16 days. Dramatic decreases in 95mTc body burdens when freshwater-labeled fish are transferred to Tc-labeled saltwater indicate that the changes in physiology accompanying saltwater acclimation lead to the loss of 95mTc.  相似文献   

8.
Total, chemical and biological oxygen demand of intertidal sediment cores from 12 stations in a mangrove swamp in southern Africa were measured under mean temperature and salinity conditions. In addition to measuring oxygen removed from water overlying cores, the uptake of oxygen from air overlying sealed cores was also determined. Total oxygen consumption ranged from 2·9 to 37·0 ml O2 m?2 h?1 in water and from 22·1 to 81·6 ml O2 m?2 h?1 in air. Chemical oxygen demand usually equalled or exceeded the total, underlining problems in the measurement of this parameter. Since oxygen is not present below a few millimeters in the sediment, it is concluded that oxygen diffusing from the overlying water or air is rapidly utilized at the surface and its uptake rate does not give any measure of metabolic activity deeper down. The oxygen content of the overlying water present during high tide may drop to relatively low levels due to this demand.  相似文献   

9.
Cellulose levels in the sediments of Loch Linnhe and Loch Eil were measured over a period of years following the introduction of pulp mill effluent to system. Cellulose levels in experimental sediment systems subjected to pulp fibre inputs at levels simulating various possible loch input levels were measured and compared. No permanent build up of cellulose in either the loch systems or the experimental systems was observed, even at high input levels.Pulp fibre degradation rates were measured experimentally using two different techniques. No difference was found between the degradation rates of wet and predried fibre.Degradation rates equivalent to 0·2 g dry fibre m?2 day?1 were found in areas of low fibre input and 0·5 g dry fibre m?2 day?1 in areas of high input were recorded. These rates were of the same order as, but somewhat lower than, the probable input rates to the sediments in Loch Eil. Speculations as to possible reasons for this are advanced.  相似文献   

10.
The number and size of bacteria at four depths (0–1, 5–6, 10–11 and 20–21 cm) in a North Carolina salt marsh were minotored by direct counts for 13 months. The number of bacteria reached a maximum of about 1·4 × 1010 cells cm?3 at the sediment surface in October, corresponding to the period of Spartina alterniflora die-back. Cell numbers were lowest and most consistent throughout the year at the 20 cm depth of sediment. Cell volumes averaged 0·2 μm3 at the marsh surface and decreased with depth. Mean standing crop of bacteria to a depth of 20 cm of sediment was about 14 g bacterial carbon m?2. In surface sediments bacteria contribute up to 15% and algae up to 10% of total living microbial biomass as estimated by adenosine triphosphate (ATP). Bacteria were the major biomass component at sediment depths of 5, 10 and 20 cm. At all depths the microbial community contributes < 4% total organic carbon and < 8% of total nitrogen.  相似文献   

11.
Concentrations of tributyltin (TBT), dibutyltin (DBT), inorganic and total tin have been measured in water, sediments and deposit feeding clams, Scrobicularia plana, from 25 estuarine locations in England and Wales, in order to compare the bioavailability of different forms of the element. Abnormally high tin values in Scrobicularia from harbours and areas of high boating activity testify to the high bioaccumulation potential of organotins, notably TBT derived from anti-fouling paints, relative to inorganic tin.Infaunal deposit-feeding bivalves consistently contain higher concentrations of TBT than other benthic organisms indicating that sediments may be an important route for uptake. Significant correlations between sediment TBT values and residues in clams such as S. plana (r = 0·81, p < 0·001) support this hypothesis. Direct evidence of the bioaccumulation of sediment-bound TBT is provided from laboratory experiments in which Scrobicularia were exposed to TBT in water and in sediments, either separately or in combination. The results of these experiments clearly demonstrate a predominantly particulate component for TBT uptake in clams.The kinetics of TBT accumulation and elimination were studied in Scrobicularia exposed to sediments containing 0·3 and 1·0 μg/g TBT (as tin). Equilibrium concentrations in tissue are approached after 40 days.Sediments containing 10 μg/g TBT are acutely toxic to S. plana, although such concentrations are only likely to occur close to dockyards and large marinas. Preliminary laboratory and field observations suggest however, that clam populations could be affected at TBT concentrations in sediments of 0·3 μg/g and possibly lower.  相似文献   

12.
An in situ chamber of volume 3881 and bottom area 0·64 m2 was used to determine the flux of oxygen and inorganic nutrients across an estuarine sediment-water interface over a 65-day period. Over the first 7 days, oxygen uptake was 378 mg m?2 day?1 and the rates of ammonium and phosphate release were 2·22 and 0·34 mg at. m?2 day?1, respectively. The water became anoxic in 14 days.The rates of flux in a similar chamber containing only detritus recently settled from the water column were 371 mg m?2 day?1 (oxygen), 1·66 mg at. m?2 day?1 (ammonium) and 0 12 mg at. m?2 day?1 (phosphate), demonstrating that detritus contributes substantially to exchange across the sediment-water interface.The evolution of the two chambers was similar over the latter part of the experimental period. A third chamber containing only water exhibited very minor changes.The role of detritus in nutrient recycling at the sediment-water interface is discussed in relation to the productivity of shallow water bodies such as the estuary in which the experiment was conducted, which itself undergoes periodic deoxygenation during prolonged stratification. The measured flux of nitrogen across the interface was found to represent approximately 31% of the mean daily phytoplankton requirement.  相似文献   

13.
The response of a sub-arctic, deep-sea macrofaunal community to a simulated food sedimentation event was studied by means of a stable isotope “pulse-chase” experiment. A food pulse was simulated by adding 500 mg C m−2 of 13C-labelled diatoms, Chaetoceros radicans, to sediment cores retrieved from 1080 m in the Faroe-Shetland Channel. Carbon uptake by specific macrofaunal groups was quantified after 3 and 6 days of incubation. The carbon uptake of the dominant taxon (Polychaeta) was quantified at the genus-, and where possible, species-level, representing a data resolution that is rare in deep-sea tracer studies. The macrofaunal community reacted rapidly to the diatom addition, with 47% and 70% of the animals illustrating 13C-enrichment after 3 and 6 days, respectively. Approximately 95% of C uptake was located in the upper 2 cm due to the particularly shallow vertical distribution of the macrofaunal community and the nonexistent tracer subduction by burrowing species. Polychaetes of the families Ampharetidae and Cirratulidae were among the most heavily labelled with above background enrichment reaching 1300‰. Approximately 0.8 and 2.0 mg C m−2 were processed by the macrofauna after 3 and 6 days, representing 0.2% and 0.4% of the added carbon, respectively. It was not possible to differentiate sub-surface deposit-feeding polychaetes from predator/scavenger- and omnivorous polychaetes using their natural ??15N signatures. However, the combination of natural abundance ??15N data and 13C-labelling experiments proved to be useful for elucidating trophic relations in deep-sea food webs. This study confirms that macrofauna play an active role in the short-term carbon cycling at bathyal depths even at sub-zero temperatures and highlights the need for detailed knowledge of the community structure in understanding carbon processing patterns and early diagenesis of organic matter in marine sediments.  相似文献   

14.
Macoma inquinata, a detritus feeding clam, was exposed for 60 days to coarse-grained, and Abarenicola pacifica, a burrowing polychaete, to fine-grained, sediment. Each sediment contained 14-C-labelled phenanthrene, chrysene or benzo(a)pyrene. Over 70% of the chrysene and benzo(a)pyrene, but only 8% of the phenanthrene, remained in the coarse sediment during the exposure. Essentially all of the chrysene and benzo(a)pyrene and 70% of the phenanthrene remained in the fine sediment. The concentrations of chrysene and benzo(a)pyrene in the clams rose steadily, reaching levels 11·6 and 5·2 times as high as those in the sediment. The tissue phenanthrene concentration rose for 3 days, then fell to one-eighth of the initial concentration. The concentrations of each of the aromatic hydrocarbons in Abarenicola tissue increased for 2 weeks to four to six times the sediment levels. The tissue concentration of chrysene remained constant thereafter, but the levels of phenanthrene and benzo(a)pyrene fell to three-quarters of their peak values. No intermediate degradation products of any of the hydrocarbons were identified in extracts of sediment from either exposure system, or in solvent extracts of tissue or of tissue digestates.Significant 14C-activity, associated with non-solvent extractable compounds, remained in tissue digestates of individuals of both species exposed to phenanthrene.  相似文献   

15.
Seasonal dynamics of elemental sulfur in two coastal sediments   总被引：1，自引：0，他引：1  
A spectrophotometric method for elemental sulfur (S0) analysis without interference from other reduced sulfur compounds was adapted for the use in reducing sediments. The S0 distribution in two coastal sediments was studied regularly from summer to winter and compared to factors regulating the S0 accumulation, such as redox potentials, the rate of bacterial sulfide production and the general sulfur chemistry. Dense coatings of sulfur bacteria developed on the sediment surface of a sulfuretum which had an S0 concentration of up to 41 μmol S cm?3. The 2·5-mm thick bacterial coating contained 40% of all S0 in the sediment. A more typical marine sediment with a few cm thick oxidized surface layer had an S0 maximum of 1–3 μmol S cm?3 at 2–4 cm depth. The S0 maximum in both sediments increased from summer to winter as the sediments gradually became more oxidized. The deeper layers maintained a low S0 concentration. Most of the S0 in the upper few mm of a laboratory sulfuretum was present inside sulfur bacteria and actively migrated up and down with the bacteria depending upon the changing light and oxygen conditions.  相似文献   

16.
ABSTRACT

Macrofaunal communities of the Central Indian Basin (CIB) were sampled with a spade before (June 1997), and immediately after (August 1997), and 44 months (April 2001) after a simulated benthic disturbance for polymetallic nodule mining. The average density recorded down to a sediment depth of 40 cm ranged from 89 to 799 ind·m?2 (mean: 373 ± 221 SD; n = 12) and 178–1066 ind·m?2 (mean: 507 ± 489 SD; n = 3) in the test and reference area, respectively. Most of the macrobenthic animals (64%) were concentrated in the upper 0 to 2 cm sediment layers, whereas, sizeable fauna (6%) inhabited the 20–40 cm sediment section and the deepest 5 cm section from 35–40 cm contributed only about 2% to the total population density. The fauna, comprised of 12 groups, were dominated by the nematodes, which constituted 54% of the total population. The macrofaunal density in the test site showed a significant increase (x:400 ind·m?2) in the 44 months postdisturbance sampling (x:320 ind·m?2). The population of nematodes and oligochaetes was nearly restored after 44 months, but the polychaetes and crustaceans did not reach the baseline populations measured in June 1997. The top 0–2 cm sediment layer was severely affected by the disturber, and the study suggests that physically disturbed deep-sea macrofauna may require a longer period for restoration and resettlement than normally believed.  相似文献   

17.
Application of a simple model describing regional variations in the contents of manganese and associated minor metals in deep-sea sediments suggests that solid manganese phases are being removed from the <0.5 μm fraction of seawater at ～1–7 · 1012g yr?1 in excess of the rate of stream-supplied manganese. This flux is consistent with: (1) the relative rates of sediment accumulation in the Atlantic and Pacific Oceans; (2) the contrast between the oceanic residence time of manganese calculated from stream-supply data (14 · 103 yr) and from the flux of manganese precipitating in marine sediments or as manganese nodules (0.38–2.4 · 103 yr); (3) the surplus mass of manganese revealed by geochemical balance calculations (22.9 · 102g). On this basis excess manganese is accumulating in deep-sea sediments at 0.2–2.0 · 10?6 g cm?2yr?1. Manganese supplied to the upper layers of marine sediments by diagenesis has been evaluated with the aid of vertical advection—diffusion—reaction models. The calculated diagenetic flux of manganese at the sediment surface in a near-shore environment is in agreement with the known accretion rate of manganese deposits (1.7 · 10?2 g cm?2 10?3 yr?1) and the regionally variable flux over the area assessed is consistent with the presence or absence of manganese nodules at or near the water-sediment interface. The diagenetic flux at the surface of deep-sea sediments has been calculated at 0.7 · 10?4 g cm?2 10?3 yr?1 when the upper, oxic, zone of the sediment is ～20 cm thick. A limiting factor on the in situ production flux of dissolved manganese in deep-sea sediments appears to be the availability of reducing agents for manganese dissolution rather than the rate of downward transport of manganese-rich sediment to a reaction boundary where dissolution takes place. Various estimates of the rate of upward-migrating manganese suggest that manganese precipitates in the oxic zone with a rate constant of ～10?7 sec?1 with the result that diagenetic processes cannot supply the flux of excess manganese through more than ～0.25 m of oxic sediment. However, estimates of the flux of manganese to the oceans by submarine volcanic processes (0.79–1.1 · 1012g yr?1) are similar to the surplus mass of manganese detected by geochemical balance calculations (0.7 · 1012g yr?1). If submarine hydrothermal solutions provide only 10% of this excess then their computed discharge rate (39 g cm?2 yr?1) and residence time in the upper layer of oceanic crust (130,000 yr) agree well with these parameters for continental thermal springs.  相似文献   

18.
The soft sediment fish communities below 20 m depth were studied at two sites on the west coast of Scotland (Irvine Bay, Firth of Clyde and the Lynn of Lorne) using small meshed beam trawls. In both cases the emphasis was on the small demersal fish (<15 cm) within these communities. The Irvine Bay community was studied between May 1978 and December 1979 and the Lynn of Lorne community between February 1975 and October 1976.Twenty-seven fish species were recorded in Irvine Bay and 32 in the Lynn of Lorne. In both communities four species constituted more than 78% of the total annual abundance, two gobies (Lesueurigobius friesii and Pomatoschistus norvegicus) were high in the dominance ranking for both sites. The species abundance lists were similar for both sites (0·62 level of similarity) but the species lists for each site were different (0·36 level of similarity). The overall mean density of small demersal fish was similar for both sites (Irvine Bay = 0·045 individuals m?2 and the Lynn of Lorne = 0·047 individuals m?2). There were two periods of high abundance for both communities (late autumn to winter and late spring). There was, however, a low repeatability between successive years. The species richness (D) was relatively high (Irvine Bay = 1·5-3·08, Lynn of Lorne = 1·4-3·34) as was the species diversity (H′) (Irvine Bay = 1·17-1·97, Lynn of Lorne = 1·23-1·95). The proportional representation (J′) of each species within the community was greater in Irvine Bay (J′ = 0·57-0·77) than in the Lynn of Lorne (J′ = 0·50-0·72). Therefore these two communities of small demersal fish appeared to be similar at the community level but the way in which this was achieved was different.  相似文献   

19.
To investigate the factors controlling lead (Pb) concentration and identify the sources of Pb in Yellow Sea sediments along the Korean coast, the concentration of Pb and Pb isotopes in 87 surface and 6 core sediment samples were analyzed. The 1 M HCl leached Pb concentrations had a similar geographic distribution to those of fine-grained sediments, while the distribution of residual Pb concentrations resembled that of coarse-grained sediments. Leached Pb was presumed to be associated with manganese (Mn) oxide and iron (Fe) oxy/hydroxide, while residual Pb was associated with potassium (K)-feldspar, based on good linear relationships between the leached Pb and the Fe/Mn concentrations, and the residual Pb and K concentrations. Based on a ratio–ratio plot with three isotopes (207Pb/206Pb and 208Pb/206Pb) and the geographic location of each sediment, sediments were categorized into two groups of samples as group1 and group2. Group 1 sediments, which were distributed in Gyeonggi Bay and offshore (north of 36.5°N), were determined to be a mixture of anthropogenic and natural Pb originating from the Han River, based on a 208Pb/206Pb against a Cs/Pbleached mixing plot of core and surface sediments. Group 2 sediments, which were distributed in the south of 36.5°N, also showed a two endmembers mixing relationship between materials from the Geum River and offshore materials, which had very different Pb concentrations and isotope ratios. Based on the isotopes and their concentrations in core and surface sediments, this mixing relationship was interpreted as materials from two geographically different origins being mixed, rather than anthropogenic or natural mixing of materials with the same origin. Therefore, the relative percentage of materials supplied from the Geum River was calculated using a two endmembers mixing model and estimated to be as much as about 50% at 35°N. The spatial distribution of materials derived from the Geum River represented that of fine-grained sediments originating from the Geum River. It was concluded that Pb isotopes in sediments could be used as a tracer in studies of the origin of fine-grained sediments along the Korean Yellow Sea coast.  相似文献   

20.
The distribution of the Manila clam Ruditapes philippinarum, which is often dominant in intertidal zones, is influenced by both environmental and biological conditions. However, there have been few comprehensive studies on the interactive effects of these two groups of factors. The present study examined the environmental and biological parameters determining the population dynamics of the clams that is a dominant component of the intertidal communities of Euhangri and Padori on the west coast of Korean peninsula. We collected R. philippinarum and other members of the macrobenthos (> 1 mm long) monthly from 0.25 m2 quadrats deployed in the intertidal zones at Euhangri, Taean, and Padori during the period from August 2013 to January 2015. Physicochemical parameters of the water and sediment were measured at the same time. Water temperature and salinity is high and low in the summer to winter, respectively. While mean grain size of the sediment was higher at Euhangri than at Padori, total mean density of R. philippinarum was higher at Euhangri (325 ind./ 0.25 m2 at Padori vs. 194 ind./0.25 m2 at Euhangri). Settled spat (< 10 mm in length) density was much higher at Euhangri than at Padori (132 vs. 12 individuals/0.25m2, respectively). R. philippinarum spats settled down on the sediment at Euhangri in October and grew continually until the following May, when they reached adult size. Spats that settled down at Padori between March and April were not able to reach the adult stage. As the density of the adult population increased, the condition index of individual clams decreased, but as the population density of the spat increased the body condition index increased. The chlorophyll a content of the sediments at Padori exceeded that at Euhangri and decreased as the population of R. philippinarum increased. The shapes of R. philippinarum shells at Euhangri were more prolate than those at Padori, and the condition index at Euhangri exceeded that at Padori, indicating better growth conditions at Euhangri. The condition index and density of R. philippinarum were affected by the amount of chlorophyll a in the water column and in the sediment. The recruitment success of spats was negatively influenced by spat density. We suggest that regulation of habitat conditions for R. philippinarum, including the food supply, will optimize production of these commercial clams.  相似文献   

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