Uptake and accumulation of naphthalene by the oyster Ostrea edulis,in a flow-through system

A flow-through system was used to follow naphthalene and naphthalene metabolite accumulation in the seawater and in the tissue of the oyster Ostrea edulis. After 72 h, 82.5% of the naphthalene carbon was recovered from the system. Glucose was added to seawater to stimulate the pathways of glucose metabolism in the oysters. Streptomycin (100 ppm) reduced microbial oxidation of naphthalene and glucose, and reduced bacterial growth. However, even in the presence of streptomycin, microbial oxidation of naphthalene was considerable. The main oxidation product recovered from seawater was ¹⁴CO₂. Radioactivity was also associated with compounds which separated by TLC with 2- and 1- naphthol. The pattern of naphthalene uptake and accumulation in oyster tissues was relatively constant after only a few hours of exposure to naphthalene. The potential of tissues to accumulate naphthalene was shown to be a function of multiple variables such as nutritional state, lipid concentration, length of exposure to naphthalene, and the external naphthalene concentration. Carbon-14-labeled metabolites derived from ¹⁴C-naphthalene were consistently recovered from digests of the oyster tissues. Non-CO₂ alkaline-soluble substances were the primary metabolites. Hexane-extractable substances, which separated by TLC with known standards of 2- and 1- naphthol, were consistently recovered from seawater and tissue digests. It was not possible to conclude that these metabolites were a result of naphthalene metabolism by oyster enzyme systems.     

Mitochondrial cytochrome oxidase I gene sequences support an Asian origin for the Portuguese oyster Crassostrea angulata

The Portuguese oyster Crassostrea angulata (Lamarck, 1819) was long assumed to be native to the northeastern Atlantic, however, a number of lines of evidence now indicate that it is a close relative, or identical, to the Asian Pacific oyster C. gigas (Thunberg, 1793). Three hypotheses have been proposed to explain how this strikingly disjunct geographic distribution may have come about: ancient vicariance events, recent anthropogenic introduction to Asia and recent anthropogenic introduction to Europe. We have performed a molecular phylogenetic analysis of C. angulata based on mitochondrial DNA sequence data for a 579-nucleotide fragment of cytochrome oxidase I. Our results show that Portuguese oyster haplotypes cluster robustly within a clade of Asian congeners and are closely related, but not identical, to C. gigas from Japan. The mitochondrial data are the first to show that Portuguese oysters are genetically distinct from geographically representative samples of Japanese Pacific oysters. Our phylogenetic analyses are consistent with a recent introduction of C. angulata to Europe either from a non-Japanese Asian source population or from a subsequently displaced Japanese source population. Genetic characterization of Pacific oysters throughout their Asian range is necessary to fully reveal the phylogenetic relationships among Portuguese and Pacific oysters. Received: 15 April 1997 / Accepted: 12 February 1998     

The resistance of Crassostrea rhizophorae to starvation and asphyxia

Experiments were performed on the oyster Crassostrea rhizophorae in order to determine the degree of its resistance to conditions of starvation and asphyxia imposed by longlasting transportation. The most favorable results were obtained by lowering the environmental temperature to about 15°C, and keeping the oysters in air, with a daily bath in hypercalcic seawater (Ca content double that of seawater). In this way mortality decreases and energetic reserves are not impaired. Oysters kept in water at their normal environmental temperature, without nutrition, reveal a noticeable increase in mortality and a decrease of about 40% in the glycogen and lipid reserves, during a 15 day starvation period. The normal values of some metabolic and compositional indexes in this species are: oxygen consumption 104±6 cm³ O₂/kg living body weight/h; water content 81±1%; protein content 7.4±0.4%; lipid content 1.6±0.1%; glycogen content 6.0±0.5%. The glycogen is distributed almost uniformly throughout all visceral organs. The oxygen consumption shows no circadial or tidal rhythmicity.With the technical assistance of the students A. Areces, A. Olaechea, M. Oliva, A. Otaso, M. Rodríguez.     

Occurrence of the Kumamoto oyster Crassostrea sikamea in the Ariake Sea, Japan

The Kumamoto oyster Crassostrea sikamea is distinguished from the closely related Pacific oyster C. gigas by concordant differences in 16S rDNA, allozymes, and a one-way gametic incompatibility. After repeated failures to find this oyster in its native habitat, we speculated in 1994 that “the Kumamoto oyster may be extinct in Japan”. In September 1996, we sampled small, deep-cupped oysters from the Ariake Sea and typed these for 16S rDNA and ITS-1 DNA markers previously shown to be diagnostic for the three most common oysters in the Ariake Sea, C. gigas, C. sikamea and  C. ariakensis. Our earlier suggestion of the demise of  C. sikamea proved incorrect. Of the 256 oysters sampled, 181 (71%) were  C. gigas, 53 (21%) were C. sikamea, and 22 (9%) were  C. ariakensis; no interspecific hybrids were observed. The distributions of C. sikamea and  C. ariakensis are clumped in the Ariake Sea:  C. sikamea occurs on the eastern and northern shores,  C. ariakensis occurs only in the northern part. These results emphasize the value of molecular markers for discriminating these morphologically plastic species both in the field and in aquaculture. Received 6 July 1998 / Accepted 8 October 1998     

Time-course uptake and elimination of benzo(a)pyrene and its damage to reproduction and ensuing reproductive outputs of Pacific oyster, <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The time-course of uptake and elimination of benzo(a)pyrene (BaP) for the Pacific oyster, Crassostrea gigas and reproduction damage and reproductive outputs were studied. Sexually immature C. gigas broodstock were fed for 28 days with live algae grown in four BaP solutions of 0, 50, 500, and 5,000 μg L⁻¹ (hereafter, control, 50, 500, and 5,000 oysters) and were subsequently conditioned to maturation by a feeding with BaP-free live algae under temperature manipulation for another 28 days. The 5,000 μg L⁻¹ oysters gained a steady state concentration, around 30,000 ng g⁻¹ d.w. for digestive gland, a week earlier compared to the 500 μg L⁻¹ oysters. The earlier gain or longer persistence of the steady state concentration influenced elimination of BaP, with an eliminating trend for 500 μg L⁻¹ oysters, while no elimination for 5,000 μg L⁻¹ oysters. The maternal persistence of the steady state concentration resulted in significant damages in the reproductive success and their reproductive outputs in terms of the hatching rate and larval growth, survival, and settlement. The 50 μg L⁻¹ oysters remained far below the steady state concentration, and showed a manifest eliminating behavior during the subsequent BaP-free 28 day maturation period. The reproductive success and initial larval events of 50 μg L⁻¹ oysters were comparable to those of control. However, the damage potential of the 50 μg L⁻¹ oysters might be more significant if their maternal exposure continued beyond 28 days, since the accumulation profile at this dose was linear.     

纳米氧化镍颗粒对长牡蛎(Crassostreagigas)抗氧化防御体系的影响

纳米氧化镍(nNiO)作为一种广泛使用的纳米颗粒,其水生毒理效应研究还很有限。为探索n Ni O对海洋贝类的毒性机制,本研究将长牡蛎(Crassostrea gigas)置于不同浓度(0、1、10、100 mg·L~(-1))的n Ni O中暴露96 h,分别测定鳃和消化腺组织的丙二醛(MDA)含量和超氧化物歧化酶(SOD)、过氧化物酶(POD)以及过氧化氢酶(CAT)活性,并通过实时荧光定量PCR技术测定了鳃和消化腺中应激蛋白HSP70和AOX基因的表达变化。结果显示:在100 mg·L~(-1)n Ni O处理下,2种组织中MDA含量均显著性升高(P0.01),显示纳米颗粒造成了长牡蛎的脂质过氧化,并可能引起相应的氧化损伤。同时,n Ni O暴露也诱导了长牡蛎抗氧化酶(SOD、CAT和POD)活性的改变。其中,SOD和CAT活性在10 mg·L~(-1)浓度处理组达到最高,而POD活性在1 mg·L~(-1)浓度组即达最高值。在高浓度n Ni O(100 mg·L~(-1))胁迫下,3种抗氧化酶的活性均比低浓度(1和10 mg·L~(-1))处理组降低,表明抗氧化酶的保护作用在较低浓度暴露下更有效;而热激蛋白(hsp70)和交替氧化酶(aox)基因却分别在长牡蛎消化腺和鳃组织中上调表达(P0.01),并表现出一定的组织差异。说明高浓度纳米颗粒暴露中主要是应激蛋白发挥了作用。本文结果为纳米氧化镍对海洋双壳贝类的毒性机制研究及生态风险评估提供了基础数据。     

The influence of irradiance on the biochemical composition of three phytoplankton species and their nutritional value for larvae of the Pacific Oyster (Crassostrea gigas)

Three species of phytoplankton grown at high (HL) or low light (LL) were fed as saturating rations to laboratory-reared larval Crassostrea gigas. Larval C. gigas fed diets of HL grown Chaetoceros gracilis and HL grown Isochrysis aff. galbana grew faster than those fed LL grown cells of the same phytoplankton species. Faster growth of C. gigas larvae was consistently associated with increases in the percent composition of short chain saturated fatty acids (FA) 14:0+16:0 in the HL grown cells. There were no consistent and significant differences between HL and LL grown phytoplankton cells in their content of carbon, nitrogen, protein, lipid or carbohydrate. Intraspecific increases in percent composition of essential fatty acids (EFAs), 20:53 and 22:63, in the phytoplankton were not associated with improvements in the growth or survival of the oyster larvae. Oyster larvae fed diets of Phaeodactylum tricornutum with a relatively high proportion of EFAs grew more slowly than those fed C. gracilis. In this experiment the proportion of dietary EFA 20:53 was negatively correlated with oyster growth rates. The faster growing oyster larvae contained relatively more of the FAs 14:0+16:0 which may be useful as measures of larval oyster condition. After a diet of one phytoplankton species for ca. 10 d, oyster larvae acquired distinctive FA profiles resembling that of their phytoplankton prey.     

Stable isotopes (δ13C, δ15N) and modelling as tools to estimate the trophic ecology of cultivated oysters in two contrasting environments

Food sources for cultivated marine bivalves generally are not well identified, although they are essential for a better understanding of coastal ecosystems and for the sustainability of shellfish farming activities. In addition to phytoplankton, other organic matter sources (OMS), such as microphytobenthos and detritus (of terrestrial or marine origins), can contribute significantly to the growth of marine bivalves. The aim of this study was to identify the potential food sources and to estimate their contributions to the growth of the Pacific oyster (Crassostrea gigas) in two contrasting trophic environments of Normandy (France): the Baie des Veys (BDV) and the Lingreville area (LIN). Two sites were studied in the BDV area (BDV-S and BDV-N) and one in the LIN area. To estimate the contribution of each type of OMS, we used a combination of stable natural isotope composition (δ¹³C, δ¹⁵N) analysis of OMS and oyster tissue together with a modelling exercise. Field sampling was conducted every 2 months over 1 year. The sampled sources were suspended particulate organic matter from marine (PhyOM) and terrestrial (TOM) origins, microphytobenthos (MPB), detrital organic matter from the superficial sediment (SOM), and macroalgae (Ulva sp., ULV). A statistical mixing model coupled to a bioenergetic model was used to calculate the contributions of each different source at different seasons. Results showed that isotopic composition of the animal flesh varied with respect to the potential OMS over the year within each ecosystem. Significant differences were also observed among the three locations. For instance, the δ¹³C and δ¹⁵N values of the oysters ranged from −20.0 to −19.1‰ and from 6.9 to 10.8‰ at BDV-S, from −19.4 to −18.1‰ and from 6.4 to 10.0‰ at BDV-N, and from −21.8 to −19.4‰ and from 6.3 to 8.3‰ at LIN. The contributions of the different sources to oyster growth differed depending on the ecosystem and on the period of the year. Phytoplankton (PhyOM) predominated as the principal food source for oysters (particularly in the LIN location). MPB, TOM, and ULV detritus also possibly contributed to oysters’ diet during summer and autumn at the BDV-S and BDV-N sites. SOM was not considered an OMS because it was already a mix of the other four OMS, but rather a trophic reservoir that potentially mirrored the trophic functioning of marine ecosystems.     

Toxic dinoflagellates (Alexandrium fundyense and A. catenella) have minimal apparent effects on oyster hemocytes

The possible effect of Alexandrium spp. containing paralytic shellfish poisoning (PSP) toxins on the hemocytes of oysters was tested experimentally. In one trial, eastern oysters, Crassostrea virginica Gmelin, were exposed to bloom concentrations of the sympatric dinoflagellate, Alexandrium fundyense Balech, alone and in a mixture with a non-toxic diatom, Thalassiosira weissflogii (Grun) Fryxell et Hasle. Subsequently, another experiment exposed Pacific oysters, Crassostrea gigas Thunberg, to a mixed suspension of the sympatric, toxic species Alexandrium catenella (Whedon et Kofoid) Balech, with T. weissflogii. Measurements of numbers of oyster hemocytes, percentages of different cell types, and functions (phagocytosis, reactive oxygen species (ROS) production, and mortality) were made using flow-cytometry. During and after exposure, almost no significant effects of Alexandrium spp. upon hemocyte numbers, morphology, or functions were detected, despite observations of adductor-muscle paralysis in C. virginica and measured toxin accumulation in C. gigas. The only significant correlation found was between toxin accumulation at one temperature and higher numbers of circulating live and dead hemocytes in C. gigas. The PSP toxins are known to interfere specifically with sodium-channel function; therefore, the finding that the toxins had no effect on measured hemocyte functions suggests that sodium-channel physiology is not important in these hemocyte functions. Finally, because oysters were exposed to the living algae, not purified toxins, there was no evidence of bioactive compounds other than PSP toxins affecting hemocytes in the two species of Alexandrium studied.     

Comparing the effect of elevated pCO2 and temperature on the fertilization and early development of two species of oysters

This study compared the synergistic effects of elevated pCO₂ and temperature on the early life history stages of two ecologically and economically important oysters: the Sydney rock oyster, Saccostrea glomerata and the Pacific oyster, Crassostrea gigas. Gametes, embryos, larvae and spat were exposed to four pCO₂ (375, 600, 750, 1,000 μatm) and four temperature (18, 22, 26, 30°C) levels. At elevated pCO₂ and suboptimal temperatures, there was a reduction in the fertilization success of gametes, a reduction in the development of embryos and size of larvae and spat and an increase in abnormal morphology of larvae. These effects varied between species and fertilization treatments with S. glomerata having greater sensitivity than C. gigas. In the absence of adaptation, C. gigas may become the more dominant species along the south-eastern coast of Australia, recruiting into estuaries currently dominated by the native S. glomerata.     

Molecular phylogenies help resolve taxonomic confusion with Asian <Emphasis Type="Italic">Crassostrea</Emphasis> oyster species

Identification of oyster species is still largely based on phenotypic characters that are highly plastic. Prompted by the proposed introduction of the Asian oyster species Crassostrea ariakensis into the Chesapeake Bay region of the U.S.A., this study uses molecular genetic information to understand the taxonomic framework surrounding C. ariakensis and to confidently distinguish among various sympatric oyster species. Putative samples of C. ariakensis and other species of cupped oysters from across Asia were collected and phylogenetic analyses were conducted on DNA sequences of both nuclear (ITS-1) and mitochondrial (COI) regions. Trees generated based on the two independent molecular datasets were highly congruent, and indicate that many oysters collected for this study as C. ariakensis were originally misidentified. Results also indicate that C. ariakensis, C. hongkongensis and C. nippona are distinct, but closely related species. There is strong support in both analyses for a close relationship between C. gigas and C. sikamea, as well as between C. belcheri and C. gryphoides, and between C. iredalei and C. madrasensis. The parsimony analyses based on these DNA markers, however, did not provide evidence to support C. angulata as a distinct species from C. gigas. Overall, the results emphasize the need for rigorous species identification, and additional extensive and intensive sampling to more accurately determine relationships among Crassostrea species, define their geographic distributions, and establish existing sympatry patterns.     

Importance of refractory plant material to the carbon budget of the oyster Crassostrea virginica

The ability of the oyster Crassostrea virginica (Gmelin) to filter, ingest and assimilate ¹⁴C-labeled Spartina alterniflora as a carbon source was investigated under laboratory conditions. The oyster assimilated crude-fiber carbon extracted from S. alterniflora with an efficiency of approximately 3%. Enteric bacteria did not enhance this process. The annual average (April 1984 to November 1985) of crude fiber in the Choptank River sub-estuary of the Chesapeake Bay, Maryland, USA, from which the oysters were collected, was 15.7 g l^-1 (range 4.3 to 34.3 g l^-1). The potential food value of crude fiber to oysters in this system was estimated to be less than 1% of their carbon demand. However, the potential contribution of crude fiber to the carbon requirements of other oyster populations, such as those in southeastern USA, may be as great as 20%, due to higher crudefiber concentrations in the seston.     

Persistence of atrazine impact on aneuploidy in Pacific oysters,<Emphasis Type="Italic"> Crassostrea gigas</Emphasis>

Widespread use of the herbicide atrazine has incited much research on its toxicity in aquatic systems, where it is routinely detected due to runoff from cultivated fields. Moreover, the determination of the genotoxic effect of such pollutants in the marine environment has become a major requirement for ecosystem protection. In the Pacific oyster, Crassostrea gigas, hypodiploid aneuploid cells have regularly been reported. There is a negative correlation between this phenomenon and growth, as well as evidence for a genetic basis. A positive relationship between atrazine and aneuploidy has previously been demonstrated in C. gigas adults and juveniles. To evaluate the persistence of this impact, our study examined the offspring of the same adult population previously treated with different atrazine doses (10 µg l^–1, representing a peak value found in a polluted environment and 100 µg l^–1), and a seawater control. We observed that these offspring exhibited significantly higher aneuploidy levels when their parents had been exposed to atrazine (14.9–16.9% in comparison with the control where the levels ranged from 11.4% to 12.8%). In addition, the present study examined the aneuploidy level of a sample of juveniles, previously exposed for 3.5 months to the same doses of atrazine, then transferred to non-polluted conditions for an additional period of 2.5 months; this aneuploidy level remained significantly different between the treatments applied. These results demonstrate the persistence of an atrazine impact on Pacific oyster aneuploidy in time, within and between generations, indicating that this widely used compound may represent an important factor causing at least medium-term damage to genetic material.Communicated by S.A. Poulet, Roscoff     

Influences of environmental salinity on the structure and function of gill mitochondrial membranes of an osmoconforming invertebrate,Crassostrea virginica

The influence of salinity acclimation on the lipids of gill mitochondrial membranes was investigated in the osmoconforming oyster Crassostrea virginica. Commercially obtained oysters were maintained at 300 or 1000 mOsm for 1 mo at 10°C and fed identical diets of cultured algae. Salinity exposure induced an increase in some of the negatively charged phospholipids. This response may be a mechanism to bind accumulated cations which would otherwise interfere with intracellular metabolism. Lower levels of n6 fatty acids were also observed at high salinities, compared to oysters in dilute seawater and are consistent with the established marine versus freshwater n6 pattern. Arrhenius plots of membrane-bound carnitine palmitoyl transferase activity failed to display a shift in breakpoints, indicating the changes observed did not influence the properties of the membrane.     

Mortality of newly metamorphosed eastern oysters (Crassostrea virginica) in mesohaline Chesapeake Bay

 Stocks of eastern oysters, Crassostrea virginica (Gmelin), in mesohaline Chesapeake Bay, USA, exhibit a high degree of inter-annual and spatial variability in recruitment. We found that cumulative oyster spatfall on off-bottom collector plates, measured throughout the summer in 14 years over a span of three decades, was highly positively correlated (r ² = 0.8) with juvenile oyster recruitment on adjacent oyster bars. Total abundances of juvenile oysters on these bars were, however, generally 99.7% lower than predicted from cumulative seasonal larval settlement on collector plates. We propose that although the number of larvae metamorphosing was the key factor in determining the gross annual pattern of recruitment to these mesohaline oyster bars, the actual magnitude of recruitment was governed by post-settlement processes, such as competition for limited resources and predation. We tested the hypothesis that predation may be partly responsible for high post-settlement juvenile oyster mortality. We performed a series of 3-d field investigations over two summers (1989, 1990) at a mesohaline site, employing cages of various mesh sizes (400, 800, 1500 μm) to protect hatchery-reared spat of 0.5 to 4.0 mm shell height. Mortality rates for spat held for 3 d in the estuary (17.8%) were significantly higher (P = 0.0001) for the smallest spat (0.5 to 2.0 mm) compared with those of 2.01 to 4.0 mm (4.2%). In 1990, but not in 1989, enclosure within 400 and 800 μm mesh cages significantly (P = 0.004) increased survival during 3-d deployments (9.4 and 10.1%, respectively) compared with spat unprotected by mesh cages (21.9%). In a series of laboratory predation studies that used the entire community of invertebrates that could penetrate the cages, microscopic juvenile polyclad flatworms, Stylochus ellipticus, were the only organisms that we observed crawling into living oysters and feeding on oyster tissue. Large flatworms (50 to 200 mm²) are known to be important predators on oysters, but this ability of flatworms that were so small (<ca. 5 mm²) and translucent as to be almost invisible without magnification to feed on immediate post-metamorphic oysters has not been documented previously. Our results suggest that the rate of mortality due to predation in mesohaline Chesapeake Bay is much reduced once spat survive for 2 to 3 weeks post-metamorphosis. Thus, it is likely that predation in the 1 to 2 week period immediately after settlement may be a crucial factor in the structuring of eastern oyster populations. Received: 21 December 1998 / Accepted: 2 December 1999     

Effects of a phycotoxin,okadaic acid,on oyster heart cell survival

Okadaic acid (OA) is a dinoflagellate toxin which accumulates in shellfish producing diarrhetic shellfish poisoning (DSP) in humans. It was found that OA is a highly selective inhibitor of protein phosphatase types 1 (PP1) and 2A (PP2A) which produces a marked increase in phosphorylation of several proteins, including p38 mitogen-activated protein (MAP) kinase. The cytotoxicity attributed to OA and the effects on p38 MAP kinase and calcium current were examined in the oyster Crassostrea gigas in this study. Data showed that p38 MAP kinase is strongly expressed in oyster heart and that OA bioaccumulated in cultured heart cells. Hence the effects of OA was tested in vitro and in vivo on oysters. OA was found to (i) exert a positive chronotropic effect on cultured atrial cardiomyocytes which is related to an increase in calcium current via PKC as shown by patch clamp measurements, (ii) produce an activation/phosphorylation of MAP kinase as shown by Westernblot while the non-phosphorylated p38 remained constant during treatment, (iii) did not induce a pro-apoptotic effect. Data suggest that OA may also stimulate the anti-apoptotic pathway by phosphatase inhibition.     

Influence of the parasite worm <Emphasis Type="Italic">Polydora</Emphasis> sp. on the behaviour of the oyster <Emphasis Type="Italic">Crassostrea gigas</Emphasis>: a study of the respiratory impact and associated oxidative stress

The aim of this study was to investigate how the worm Polydora sp., which induces oysters into creating mud blisters in response to an irritation within their shells, could interfere with the oyster Crassostrea gigas physiology and ethology. The impact was characterized by studying two groups of oysters (non-parasitized and parasitized) during a 30 days period: (1) the animal behaviour by analysing their valve activity (valvometry), and (2) the animal respiratory physiology by measuring in vivo the oxygen partial pressure and the specific oxygen consumption in selected tissues (heart, fast and slow adductor muscle). We also researched a putative impact on the expression of several oxidative stress genes at the heart level. Our results show that Polydora sp. is clearly an oyster’s parasite as it induces a decrease in oyster growth according to the infestation intensity. Moreover, it modifies the behaviour and the respiratory physiology of the molluscs. Infested animals opened more frequently but for less time and their level of blood oxygenation was systematically higher than healthy molluscs. These high levels of oxygenation had no effect on the oxidative metabolism of the tissues studied but they induced oxidative stress. Indeed, the superoxide dismutase gene showed a threefold increase in expression in the heart of infested oysters. A putative scenario of the weakening mechanism is proposed.     

The rock oyster Saccostrea glomerata as an indicator of trace metals in Hong Kong

An urgent need for a sub-tropical and tropical indicator organism for use in the biological monitoring of pollutants is recognised. To this end, preliminary studies have been undertaken to test the indicator ability of the rock oyster Saccostrea glomerata (=Crassostrea glomerata Gould) for monitoring the trace metals cadmium, copper, iron and zinc. A survey of these trace metals in rock oysters from 54 sites in Hong Kong waters revealed elevated levels of metals in several areas. Profiles of metal abundance in S. glomerata agreed substantially with the distribution of industrial and domestic discharges in Hong Kong, and also with patterns of contamination found in studies of the Pacific oyster Crassostrea gigas and of sediments. Application of POLYDIV statistical analysis to these data has aided their interpretation and confirmed the relationship between known areas of contamination and elevated metal levels in S. glomerata. This oyster, which exhibits an unusually great capacity to accumulate a range of elements from the ambient environment, thus appears to be a reliable indicator organism, and may be of great value in global monitoring studies.     

Response of Asterias vulgaris to bivalves and bivalve tissue extracts

The sea star Asterias vulgaris was observed in aquaria and in a flow tank in the presence of oysters, oyster tissue, and extracts of four shellfish species. Oysters were approached after varying delays, opened, and consumed; oyster tissue was rapidly approached and eaten. Dilute (ppb) shellfish extracts were approached in a flow tank. High concentrations of extracts elicited posturing and stomach eversion responses. Some suspended materials in flowing seawater inhibited the approach of A. vulgaris to oyster extract. The behavior of A. vulgaris and A. forbesi to food stimuli are compared. Asteroids appear to distinguish between intact and injured tissue, and exhibit variable responses. These tendencies provide a possible mechanism for forming feeding aggregates.Contribution No. 2703 of the Woods Hole Oceanographic Institution, USA     

Delivery of dietary components to larval shrimp (Penaeus vannamei) by means of complex microcapsules

Efficient delivery of nutrients is necessary for the successful study of aquatic larval nutrition. Conventional artificial food particles for larval shrimp (Penaeus vannamei) have poor water stability and poor nutrient retention or both. We developed a novel food particle type that retained low-molecular weight, water-soluble nutrients (vitamins and glucose) within lipid-wall microcapsules embedded with dietary ingredients in particles of gelled alginate-gelatin. The combination of lipid-wall microcapsules (LWMs) embedded in gelled food particles was termed complex microcapsules (CXMs). Eighty-five percent of ¹⁴C-activity associated with encapsulated ¹⁴C-glucose was retained by CXMs (after 18 h of suspension in seawater). Bioavailability of CXM-encapsulated molecules was demonstrated by release of encapsulated dye marker into the gut lumen of larval shrimp, and by uptake of ¹⁴C from encapsulated ¹⁴C-glucose. Minimum ingestion rates, calculated from ¹⁴C-uptake for larval shrimp (Mysis-1 through Postlarva-2) fed CXMs, ranged from 48 to 99 g dry wt larva^-1 d^-1, and were similar to literature values reported for ingestion of live rotifers by penaeid larvae. Complex microcapsules described in this study will be a valuable new tool for studying nutrition of suspension-feeders in that both micro-and macronutrients can be delivered to these animals by one particle type.