Seed mussel stock assessments rely heavily on techniques similar to those used in seabed mapping and can involve both acoustic data collection and physical ground truthing. Optimum allocation analysis has recently shown value in using acoustic data variances as surrogates of seabed heterogeneity to allocate efficiently the ground-truthing effort that minimizes survey coefficients of variance. Using acoustic data from a single-beam ground discrimination system, optimum allocation analysis was used to direct ground truthing between seed mussel strata. The resulting stock assessment values and variances were compared with actual fished quantities and were found to be highly comparable when compared with random and expert judgment scenarios.

Poor nutritional condition of seed of the green-lipped mussel Perna canaliculus (Gmelin 1791) is a major cause of significant losses after seeding out onto mussel farms. Biochemical analysis of experimentally unfed seed mussels showed they preferentially depleted glycogen reserves versus lipid and protein during short periods of starvation (≤8 days). This knowledge allowed the use of a human diabetic glucose meter to assess quickly the levels of glycogen in seed mussels after they were first homogenized and then digested with α-amylase, which converted the glycogen to glucose and maltose. The assay was sensitive enough to detect significant differences between mussels that had been continuously fed (6.04 ± 0.24 (SE) mmol/L) compared with mussels that had been unfed for 4 days (1.71 ± 0.06 mmol/L) or 8 days (0.67 ± 0.02 mmol/L). These results were consistent with biochemical analysis of the actual glycogen content of the experimental groups (16.6 ± 1.8 mg/g dry mass vs. 6.2 ± 1.0 mg/g and 5.5 ± 0.7 mg/g, respectively). This novel assay has the potential for quickly assessing the nutritional quality of seed mussels, enabling the reduction of losses of seed in the mussel farming industry.

Brown ring disease (BRD) in the Manila clam is characterized by the formation of a brown deposit of conchiolin on the inner surface of the shell that gives the disease its name. The development of the signs of BRD may be favored by the entry of bacteria in the extrapallial compartments via mechanical disruptions of the periostracal lamina and/or chipping of the shell margin. To test this hypothesis, we conducted an experiment simulating clam handling under aquaculture conditions and we checked for prevalence of BRD signs. Our results assess that rough handling of Ruditapes philippinarum in presence of the bacterium Vibrio tapetis significantly increase the prevalence of BRD signs. As a consequence, our results show that minimizing manipulation and transfer of clams during culture is beneficial to avoid the development of BRD signs.

The grooved carpet shell clam Ruditapes decussatus (L. 1758) is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early 1990s. To understand the seasonality of its nutritional value, thus providing an improved basis for economic valuation of the resource, gross biochemical composition, percent edibility, and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam R. decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and nonprotein nitrogen covaried during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable with that shown by studies elsewhere at similar latitudes, and is underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.

Coquina clams (Donax variabilis) were sampled monthly at 2 sites in Pinellas County, Florida, to document recruitment and growth. Samples collected from the swash zone were counted, measured, and preserved. Histological staging of a subset of the preserved gonads was performed to assess patterns in reproduction. Peak spawning and recruitment were observed in early spring, and growth rates were calculated through the fall. Spawning and low densities of recruits persisted throughout the summer and fall. The presence of spawning D. variabilis during 21 of 23 mo indicates a continuous reproductive cycle. Multivariate analysis of length—frequency data and frequency of reproductive stages indicates a cycle of approximately 8 mo, suggesting a typical life span of less than 1 y, although some individuals survive longer.

Twenty-two large shells (>90 mm shell height) from a sample of live collected hard shell clams, Mercenaria mercenaria, from Buzzards Bay, Woods Hole, Cape Cod, MA, were subjected to sclerochronological analysis. Annually resolved growth lines in the hinge region and margin of the shell were identified and counted; the age of the oldest clam shell was determined to be at least 106 y. This age represents a considerable increase in the known maximum life span for M. mercenaria, more than doubling the maximum recorded life span of the species (46 y). More than 85% of the clam shells aged had more than 46 annual increments, the previous known maximum life span for the species. In this article we present growth rate and growth performance indicators (the overall growth performance and phi prime) for this record-breaking population of M. mercenaria. Recently discovered models of aging require accurate age records and growth parameters for bivalve populations if they are to be utilized to their full potential.

The annual reproductive cycle of the Indo-Pacific tellinid clam Heteromacoma irus (Hanley, 1845) was investigated, using histology, for the first time in this study. The sex ratio of H. irus collected from a rocky intertidal area on the northern coast of Jeju Island, Korea, was found to be 1:1, indicating that H. irus is gonochoric. In January, most clams were in the resting phase, although a small number of females showed small oogonia on their follicular epithelium. From February to May, oocyte diameter increased rapidly, and fully mature eggs (44.8–56.8 μm) appeared in May. The first spawning males and females were observed in July, when the water temperature reached 18.0°C, and spawning activity continued until the end of August. During September and December, most clams were sexually in the resting stage. H. irus is considered to be a summer spawner, and annual gametogenesis was closely associated with the seasonal variation of the surface water temperature. Despite warm water temperatures in Jeju, the resting phase of female and male clams at the study site was prolonged from October to March, suggesting that food availability at this site could be poor and may act as a limiting factor in gametogenesis.

The Sydney rock oyster (Saccostrea glomerata) forms the basis of an important aquaculture industry on the east coast of Australia. During the 1970s, production of S. glomerata began to decline, in part as a result of mortalities arising from Queensland unknown (QX) disease. Histological studies implicated the paramyxean parasite Marteilia sydneyi in the disease outbreaks. Disease zoning was implemented to prevent the spread of M. sydneyi-infected oysters. This control measure hindered rock oyster farming, which historically has relied on transferring wild-caught spat between estuaries for on-growing to market size and has not prevented the subsequent occurrence of QX disease in the Georges and Hawkesbury rivers in central New South Wales. Management of QX disease has been hampered by the complicated life cycle of M. sydneyi, with outbreaks of QX disease likely to be regulated by a combination of the abundance of intermediate host of M. sydneyi, environmental stressors, and the immunocompetence of S. glomerata. The future of the Sydney rock oyster industry relies on understanding these factors and progressing the industry from relying on farming wild-caught seed to the successful commercialization of hatchery-produced QX-resistant S. glomerata.

Bindin is a major protein packaged as insoluble granules in sperm acrosomes. It may be responsible for speciesspecific recognition and binding of sperm to a glycoprotein receptor on the surface of eggs. The putative functional region of bindin is a fucose-binding lectin (F-lectin) domain. We cloned a novel bindin gene from the Kumamoto oyster Crassostrea sikamea by 3′ and 5′ RACE. The full-length cDNA of C. sikamea bindin was 1,134 bp, with a 774-bp open reading frame encoding 257 amino acids. The deduced amino acid sequence contained a putative signal peptide of 24 amino acids. The length of the bindin genomic DNA we obtained was 5,353 bp, containing 4 exons and 3 introns. We studied F-lectin repeats of the bindin gene from 3 species of Crassostrea to detect the relationship between them and found 11,2, and 5 haplotypes from C. sikamea, Crassostrea angulata, and Crassostrea gigas, respectively. Phylogenetic trees showed a closer relationship between C. gigas and C. angulata than between C. gigas and C. sikamea. Two haplotypes of C. angulata fell into 2 different clades, one in the C. gigas clade and the other in the C. sikamea clade. Deduced amino acid sequences and hydropathy plots were considerably similar among these species, indicating the close resemblance in the tertiary structure of bindin proteins. To test for selection, we compared the number of nonsynonymous substitutions and synonymous substitutions per nucleotide site among the 18 F-lectin haplotypes. This analysis identified 7 positively selected positions (P> 95%) among 18 haplotypes from the 3 species, all located on the F-lectin binding face around the 3 residues that are specifically involved in binding fucose (H37, R64, and R70). We hypothesize that these 7 clustered amino acids may be related to species recognition and thus could impose selective pressure on bindin divergence.

Although sea cucumbers have been successfully cultivated for restocking, very little is known about wild juvenile sea cucumber (JSC) settlement, recruitment, growth, population dynamics, natural mortality, or their ecological role. For fishery managers to develop management practices that accelerate the recovery of overfished areas and to increase the survival rate of restocked organisms, they need an understanding of spatial and temporal trends in JSC distribution and abundance, as well as cost-effective recruitment monitoring techniques. We show that wild juvenile giant red sea cucumber (Parastichopus californiens) can be collected using a commercial oyster cultch bag filled with Pacific oyster (Crassostrea gigas) shell. From the collection results, it is clear that location, depth, and substrate influence the settlement of JSC. Using JSC collectors will enable further identification of trends in sea cucumber recruitment and will give a better understanding of the distribution and behavior of JSC in various environments.

Oysters have been an important resource in Washington state since the mid 1800s and are intimately associated with recent history of the Willapa Bay estuary, just as they have defined social culture around much larger U.S. east coast systems. The Willapa Bay oyster reserves were set aside in 1890 to preserve stocks of the native oyster Ostrea lurida in this estuary, but these stocks were overfished and replaced with the introduced Pacific oyster Crassostrea gigas during the late 1920s. Pacific oysters have spawned and set naturally in this estuary on a fairly regular basis since that time, and have formed the basis of a sustainable fishery established on state oyster reserves. The fishery is managed as an annual sale of oysters to private aquaculture interests. Oysters are harvested mostly by hand from intertidal tracts, usually moved to better growing areas closer to the estuary mouth, and shell is required to be returned to the reserves to perpetuate the fishery. Although oyster harvest for human consumption will remain an important social management goal, these bivalves have been shown to provide a suite of other ecosystem functions and services. A survey of the reserves suggests that they represent 11.2% of the intertidal habitat in Willapa Bay and cover substantial subtidal areas as well. A comparison with historical maps suggests that most of the low intertidal area in the reserves formerly populated by native oysters is now covered primarily with eelgrass (Zostera marina), which potentially serves as important habitat for numerous other organisms, including juvenile salmon, Dungeness crab, and migratory waterfowl like black Brant. Native oysters can still potentially be restored to some of these areas, but the value of both introduced oysters and eelgrass as habitat and ecosystem engineers also deserves attention, and the reserves provide an excellent place to elucidate the role of these additional conservation targets at the landscape scale.

Human activities since the beginning of the industrial age have greatly increased the amount of carbon dioxide in the atmosphere. Increased levels of atmospheric carbon dioxide have already caused a 0.1-U decline in global ocean pH, and a continuing decline of 0.3–0.5 U is predicted by the end of 2100. Acidification of the oceans has widespread effects on marine organisms, including reduced rates of calcification and interruptions to normal physiological functions. This study used gaseous carbon dioxide to maintain seawater at 2 treatment levels of pH: 7.8 and 7.6. When compared with controls held at pH 8.1–8.2, pearl oysters (Pinctada fucata, Gould) held at pH 7.8 and pH 7.6 showed no significant difference in the number of byssal threads produced or total distance traveled. Byssal threads produced by oysters in the pH 7.6 treatment were significantly thinner than those produced by oysters in the control. However, it is postulated that this was a result of the acute stress of transfer to treatment conditions and not a result of physiological stress caused by near-future levels of ocean acidification. The potential for P. fucata to adapt to near-future levels of ocean acidification is discussed.

Spat recruitment of the winged pearl oyster Pteria penguin, in relation to season, substrate type, and depth was investigated at Orpheus Island in north Queensland for 27 mo, from February 2008 to April 2010. Two substrate types (70% shade cloth and open-weave polypropylene mesh bags) were deployed at 2 depths (4 m and 6 m) and checked every 6 wk for 3 spawning seasons to determine any differences in quantity of spatfall between these factors. No significant difference was found in spat recruitment between substrate types (P = 0.158) or depth (P = 0.349), although there was a significant seasonal effect on spat recruitment (P < 0.001), with a peak in the quantity of spatfall in late summer, from February to March, and no spat collected in the winter to spring (July to October). Maximum settlement of spat was 10.2 spat per mesh bag collector in February 2008. Recruitment was significantly reduced (P < 0.001) during the 2010 spawning season as a result of disturbance from severe storms generated by tropical cyclone Olga in late January.

This is the first study of seasonal changes in gonad development and tissue biochemical composition of the cockle Fulvia mutica in Cheonsu Bay off the west coast of Korea. Gametogenesis commenced in December when the surface water temperature was 9.1°C. In May, the first discharge of oocytes was observed, and spawning continued until October. The condition index (CI), a ratio of tissue dry weight to shell dry weight, increased gradually from late May to July and declined dramatically in August and September, indicating that active discharge of gametes occurred in the bay during this period. Histology and the CI suggested that F. mutica spawning in Cheonsu Bay is continuous from early summer to early fall, with two spawning peaks in June and July, and September and October. All cockles examined in November were sexually inactive. The relatively low CI recorded in late fall to mid winter (November to January) coincided with high levels of ash and low levels of lipids and carbohydrates in the tissue, whereas protein levels remained unchanged. The observed spawning pattern of F. mutica in Cheonsu Bay suggests that the currently established timing for fishing closure, from July to September, should be expanded from June to October to protect earlyspawning broodstocks. This change may secure recruitment and lead to a subsequent increase of the wild cockle population in the bay.

Pteria penguin is an important commercial bivalve species that is used in the production of half pearls known as mabè. Expansion of this industry in places with low natural spatfall is reliant on hatchery production of juvenile oysters, which begins with the incubation of fertilized eggs. This study addresses the issue of mortality during egg incubation by examining the effects of egg stocking density and the application of antibiotics. A factorial experimental design was implemented combining 3 egg densities (10, 50, and 100/mL) and 3 antibiotic treatments (control, no antibiotic; 5 mg/mL streptomycin—sulfate; 5 mg/mL tetracycline—erythromycin 2.5:2.5 mg/mL). Antibiotics were added to the culture medium as a single dose and fertilized eggs were incubated for an industry standard period of 24 h. Despite a 23% increase in mean survival during incubation, aquaria treated with tetracycline—erythromycin (1:1) yielded an average of only 9% more veliger larvae than control aquaria as a result of interference with development during the transition of trochophore to shelled larvae (D-stage). Application of the antibiotic streptomycin—sulfate improved mean survival by 16% compared with control aquaria, without significantly compromising development. A high egg density of 100/mL did not significantly reduce survival, but resulted in a 5% reduction in normal development to D-stage. The results of this study show that if tank space is limited during egg incubation, utilizing a high stocking density of 100 eggs/mL will provide the greatest number of D-stage larvae. However, if the supply of eggs is limited, we recommend stocking P. penguin eggs at a density ≤50/mL and minimizing mortality by treating the culture medium with the antibiotic streptomycin—sulfate.

Argopecten irradians concentricus has been cultivated along the southern coast of China for about 16 generations since its first introduction in 1991. To determine the effects of self-fertilization on the production traits of this isolated bay scallop population, 12 self-fertilized families and a mass-spawned group were produced and studied. The hatching success and survival at larvae, juvenile, and adult stages of the offspring of the mass-mated group were all significantly greater than that of 10 of the 12 self-fertilized families examined, and not significantly different from that of other 2 self-fertilized families. For newly hatched larvae on day 1, no significant difference in size was found among the self-fertilized families and the mass-spawned group. The shell length of the mass-mated group on days 9, 30, 75 and 230, and the live weight on days 75 and 230 were always significantly larger than that of 9 of the 12 self-fertilized families, and not significantly different from that of the other 3 self-fertilized families. In addition, a significant difference in survival, shell length, and live weight was seen among the 12 self-fertilized families at all development stages. The current study demonstrated the occurrence of inbreeding depression for production traits in the closed population of A. irradians concentricus and the necessity of avoiding inbreeding when creating a breeding production, although not all families are significantly affected by inbreeding.

The bivalve genus Spondylus, with its large and magnificent shells, has played an important cultural and economic role in coastal Ecuador that reaches back to Valdivian and Incan times. At least 2 of the 3 occurring species lately faced exploitation rates that the populations could not sustain, and a fishing ban for Spondylus calcifer and Spondylus princeps was announced in October 2009. The objective of this study is to evaluate the recovery potential of the stocks that are still present. We analyzed the reproductive cycle of 5. calcifer in the area of Ayangue (Santa Elena Province), and its relation to temperature and food abundance. In addition, we calculated fecundity values for the two threatened species. Our results show that S. calcifer in Ayangue reproduces year-round, although with a peak in October to December, when temperature is low and chlorophyll concentration is high. The total fecundity increases with soft body mass and is significantly higher in S. calcifer than in S. princeps. The individual fecundity levels in our study range from 2.2–8.3 million eggs in S. princeps, and from 2.9–35 million eggs in S. calcifer, which is in the range of better studied oyster and scallop species. With the latest observations on current densities of both species, we conclude that these have long fallen below the reproduction thresholds for other broadcast spawning invertebrates, and possibly for positive net recruitment rates. Because broadcast spawners are susceptible to mate limitation (which is the dominant cause of Allee effects in aquatic invertebrates), the reproductive asynchrony we found in Spondylus populations in Ecuador further increases the significance of potential depensatory mechanisms and of nearest neighbor distance.

To investigate the influence of environmental pollution on the population genetics of Dreissena polymorpha, we developed five new polymorphic micro satellite loci for the zebra mussel. This mussel is widely distributed and is a common bioindicator in the field of ecotoxicology. The amplification of the microsatellite loci was tested on a single population of 24 individuals. In this population, the number of alleles per locus ranged from 3–14, and the observed heterozygosity ranged from 0.545–0.909 (mean, 0.772). All loci followed Hardy-Weinberg expectations, suggesting no evidence for null alleles. There was no significant genetic linkage disequilibrium, neither between the aforementioned loci nor between aforementioned loci and five previously published microsatellites for this species. All loci are valuable to investigate the influence of anthropogenic stressors on the bioindicator Dreissena polymorpha, and therefore on freshwater ecosystems in general.

Physa acuta (left-handed shell) have strong natural growth activity not only in lentic waters but also in eutrophic environments. Therefore, it has been considered one of the candidate species that could evaluate the degree of water pollution by physiological and biochemical methods. In this study, we constructed a P. acuta cDNA library using the 5′ oligo capping method, and determined the sequences of 2,282 clones by 5′ end-single path sequencing. After trimming, clustering, and assembling these sequences, we finally obtained 575 distinctly available transcripts that were 718 bp in average length. These transcripts were annotated using the BLASTX search and were classified by function using KOG analysis. After comparison with biomarker genes already known in several organisms, we identified 27 potential biomarker candidates that were categorized into two groups strongly related to stress and defense genes by their functions. To the best of our knowledge, this is the first report of massive profiling of cDNA sequences and the characterizing of potential biomarker genes in P. acuta. Our study offers valuable information to scientists for developing new environmental biomonitoring markers, and for scientists studying the physiology, growth and development, immunity, genetic identification, and evolutional diversity in P. acuta.

Diets microencapsulated with gelatin and ethyl cellulose for larval shrimp Penaeus japonicus were produced using a fluidized bed coating process. The two microencapsulated diets were within a broad size range. The size of the diet microencapsulated with ethyl cellulose was smaller than that of the diet microencapsulated with gelatin. Scanning electron microscopy micrographs showed that the microencapsulated diets had a dense film with a superior physical quality. Despite the less amount of wall material used, the diet microencapsulated with ethyl cellulose had a better performance with regard to lipid encapsulation efficiency and nitrogen retention efficiency compared with the diet microencapsulated with gelatin. Ten days after hatching, the mysis II larvae (P. japonicus) were fed two different microencapsulated diets for 20 days and grew significantly more than the control larvae fed with Artemia and shrimp flake. The growth and survival of the larvae confirmed that the microencapsulated diets had good digestibility. There were significant differences in growth and survival, trypsin activity, and amylase activity of the larvae between the two microencapsulated diet groups and the control (P < 0.05), but there was no significant difference in alkaline phosphatase activity in the larvae of each group (P > 0.05). There were significant differences in total length and trypsin activity of the larvae between the two microencapsulated diet groups (P < 0.05). The results showed that the larval digestive enzymes adapted to the feed composition, and the wall materials had no significant effect on the digestive enzymes activity of the larvae.

Populations of the world's largest freshwater invertebrate Astacopsis gouldi (tayatea, or giant Tasmanian freshwater crayfish) have declined because of land use changes and poaching. The species is endemic to northern Tasmania and is listed as “vulnerable” under the Commonwealth of Australia Environment Protection and Biodiversity Conservation Act of 1999 and the Tasmanian Threatened Species Protection Act of 1995. Mark-recapture models were tested for their suitability in estimating survival of a population of A. gouldi in a remote river. Tayatea were marked with passive integrated transponder (PIT) tags during a 7-mo period. Catchability of tagged and untagged A. gouldi was size and sex specific. Larger animals and females were more readily trapped throughout the sampling period, which spanned the austral autumn/winter. Catchability of male tayatea increased during May, and was strongly influenced by environmental conditions such as water temperature and river level. Results suggest that PIT tagging combined with mark-recapture methods are a feasible approach for estimating survival in tayatea, given sample sizes that can be achieved with reasonable effort. Precision of estimates could be improved by concentrating sampling around peak catchability during spring and autumn, and minor flood conditions during winter. This method provides a tool to estimate A. gouldi mortality as a result of illegal fishing and detrimental land use practices, thus providing better information for management. This strategy is essential to monitor progress toward the milestone of reducing their “vulnerable” classification under the Commonwealth and Tasmanian legislation within 14 y (1 generation) from the implementation of the plan.

The economic feasibility of culture of the giant barnacle Austromegabalanus psittacus (Molina, 1782) in southern Chile is analyzed. This species is traditionally exploited on a small scale by local fishermen, with average landings of 200 t/y. Cultures on a semi-industrial scale have been undertaken, from settlement of competent larvae present in the water column, through grow-out. Growth sustained by seston filtration produces specimens of a commercially viable size in a maximum of 24 mo. To determine the economic feasibility of cultures of these species, the investments required, production costs, yields, and the potential market prices of two products were evaluated: canned products and frozen meat, with the latter including opercular plates. To this effect, cultures were undertaken in suspended systems in Metri Bay (41°36′ S; 72°43′ W), and the following parameters were evaluated: average spat density in the artificial collector; mortality; gross annual production per longline; average gross weight per specimen, including shell; period from spat collection to harvest; operational costs; and labor requirements. Loss through processing and packaging, in addition to product yield and costs, were evaluated for both products in an industrial processing plant. To carry out market studies, a visit was undertaken to the Aomori Prefecture in Japan, where a similar species, Balanus rostratus or “mine fujit subo,” is commercialized. Prices of other species of crustaceans were also considered as a reference. Based on technical and economic findings, cash flows were budgeted and economic profitability indicators (net present value (NPV), internal rate of return (IRR), discounted payback period (DPBP), and economic profitability index (EPI)), were calculated. To incorporate risk and its effects on economic performance, a local sensitivity analysis was undertaken, considering a range of possible values for six critical variables and their influence on NPV and IRR. Elasticity measures, which express the percent change in NPV given a percent change in a variable, were estimated for each critical variable in both products. Furthermore, business viability limits were calculated, determining critical values for each variable separately, all others being held constant. Evidence and results indicate that culture of the giant barnacle is economically viable, with attractive economic indicators for both processed products (NPV above US$490,000, IRR above 36%, DPBP from 3–5 y, and EPI above 1.7 times). Projected income, profits, estimated cash flows, and economic indicators are higher in canned products, resulting from differences in product yields and market prices. For both products evaluated, the greatest capital investment corresponds to marine culture systems (longlines and spat collectors), and the most significant operational cost is labor used during the culture process. Sensitivity analysis indicates that, in general, this culture can withstand important changes in each critical variable, maintaining a positive NPV, especially in canned products. Comparing elasticity values among products, frozen meat presents a higher sensitivity level with greater elasticity for every critical variable. In both products, the variable with lowest incidence on NPV is processing and packing costs, and the most relevant variables are gross weight at harvest and sale price FOB. Results indicate that giant barnacle culture is technically and economically feasible. Thus, interesting possibilities emerge for the diversification of Chilean aquaculture as well as for other barnacle cultures, such as the “craca” of the Azores Islands, Portugal, and the “fujit subo” in Japan.

From December 2004 to November 2006, we monitored monthly the growth and gonad development of the sea urchin Hemicentrotus pulcherrimus in relation to an algal standing crop in an Undaria pinnatifida and Saccharina japonica kelp bed in Matsushima Bay, Miyagi Prefecture, Japan. The algal standing crop increased markedly from January or February to a maximum in July. U. pinnatifida was predominant until May or July, then S. japonica predominated until August or September. The sea urchins grew significantly from January to April 2005. The gonad index (gonad wet weight × 100/body wet weight) was lowest (∼10) as a result of spawning from December to February, rose rapidly to more than 20 in April, and then remained high until November. The nutritive phagocytes in the lumen of the gonad were rapidly renewed and surrounded relict gametes for long periods from March to June or July. High gut content index values (gut content wet weight × 100/body wet weight) from January to May suggest that the test growth and marked rise in gonad index after spawning were caused by high food availability (U. pinnatifida). It is likely that subsequent sustained high gonad index values until maturation were ensured by the abundance of S. japonica.

Contamination of bivalves with yessotoxins (YTXs) has been reported since 1987 in several coastal environments. In our study we investigated the accumulation and the metabolism of YTXs in 2 bivalve species important to German fisheries and aquaculture. Mussels and oysters, Mytilus edulis and Crassostrea gigas, were exposed to the YTX-producing dinoflagellate Protoceratium reticulatum isolated from the North Sea. Toxin profiles from algae and bivalves were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). It was evident that 45-hydroxy YTX (45-OH YTX), carboxy YTX (COOH YTX), and the putative 45-hydroxy-carboxy YTX (45-OH-COOH YTX) were the dominant YTX analogues in M. edulis. The oyster C. gigas displayed a different toxin profile. YTX, 45-OH YTX, and 45-OH-COOH YTX were also present, but COOH YTX was not detectable. Furthermore, 2 unidentified analogues with the same MS/MS transition ([M-H] > [M-H-SO₃]) occurred in both bivalve species. Homo YTX and 45-hydroxy-homo YTX, which are regulated together with YTX and 45-OH YTX in 2002/225 EC were not detected. In general, we confirmed former field investigations on accumulation and metabolism of YTXs in M. edulis; however, this is the first study on accumulation and metabolism of YTXs in the oyster C. gigas.

The effects of the toxic dinoflagellate Heterocapsa circularisquama on the activity rate, development rate, prevalence of damage, and survival rate of trochophore and D-shaped larvae of the pearl oyster Pinctada fucata martensii were studied in relation to H. circularisquama cell densities and exposure duration. In addition, larvae were regularly processed via scanning electron microscopy to investigate morphological damage. The activity rate of both larval stages was significantly decreased after 3–6 h of exposure to H. circularisquama at densities ranging from 100 to 2 × 10⁴ cells/mL. The prevalence of damage was significantly high after 3–6 h of exposure to H. circularisquama at densities of 100 to 2 × 10⁴ cells/mL and 5 × 10³ to 2 × 10⁴ cells/mL for trochophores and D-shaped larvae, respectively. Cytoplasmic discharge, mass mucus production, irregular shape, delayed or inhibited mineralization of the shell, mantle protrusion, the appearance of abnormal masses in the velum, and the exfoliation of the larvae cilia coupled with epithelial desquamation were frequently observed. The activity rate of D-larvae transformed from trochophores exposed to H. circularisquama for 12–48 h at densities ranging from 10 to 2 × 10⁴ cells/mL was significantly reduced. The survival of D-shaped larvae plummeted to less than 0.013 for densities ≥ 5 × 10³ cells/mL. The results indicate that H. circularisquama blooms have detrimental impacts on bivalves at early life stages. Blooms of H. circularisquama occurring during the spawning periods will influence the natural recruitment in P. fucata martensii and will have profound impacts on its population biology. Therefore, shellfish farms should not be built in coastal areas where H. circularisquama occurs, or genitors should be relocated during potential blooming periods.

The purpose of this study was to determine the ability of the cownose ray, Rhinoptera bonasus (Mitchill, 1815), to manipulate oysters and clams, to test for relative prey preference, and to investigate whether susceptibility to cownose ray predation changes with bivalve ontogeny. We investigated patterns of predation for captive adult and young-of-year cownose rays on 4 species of bivalves, including Crassostrea virginica (Gmelin, 1791), Crassostrea ariakensis (Fujita, 1913), Mercenaria mercenaria (Linnaeus, 1758), and Mya arenaria Linnaeus, 1758. In oyster (C. virginica) trials, predation probabilities by adult rays were highest at shell heights of 30–70 mm and shell depths of 8–22 mm. The rates of predation by adult rays in trials in which samesize oysters were used were higher than rates in most comingled trials. Adult rays showed no differences in predation between native oysters (C. virginica) and nonnative oysters (C. ariakensis; P > 0.05). Adult rays selected hard- and soft-shell clams (Manly-Chesson index M. mercenaria, α = 0.736 ± 0.002, electivity = 0.473 ± 0.007; M. arenaria, α = 0.742 ± 0.003, electivity = 0.485 ± 0.013) over oysters (C. virginica, α = 0.263 ± 0.002, electivity = -0.473 ± 0.007; α = 0.257 ± 0.003, electivity = -0.485 ± 0.003). In young-of-year feeding trials, oysters with a shell height of 10–35 mm and a shell depth of 3–12 mm had the highest probability of predation. Native oyster and hard clam peak force or load crush tests resulted in forces of 200–1,500 N and 400–1,400 N across shell depths of 10–35 mm and 21–34 mm, respectively, before valve failure. The results of this study indicate that cownose ray predation on shellfish is limited by shell size and is likely related to ray jaw gape and bite force.