V. Monica Bricelj

A POPULATION DYNAMICS MODEL OF THE HARD CLAM, MERCENARIA MERCENARIA: DEVELOPMENT OF THE AGE- AND LENGTH-FREQUENCY STRUCTURE OF THE POPULATION

Abstract An individual-based model was developed to simulate growth of the hard clam, Mercenaria mercenaria, in response to temperature, salinity and food supply conditions. Unique characteristics of the model are that: (1) length and tissue weight are related only by condition index, so that weight, up to a point, can vary independently of length, and (2) age is decoupled from length. Tissue weight changes result from the difference in assimilation and respiration. Changes in hard clam condition are determined from a standard length-weight relationship for average hard clam growth. Changes in hard clam length (growth) occur only when condition index is greater than zero, which happens when excess weight for a given length is attained. No change in length occurs if condition index is zero (mean case) or negative (less weight than expected at a given length). This model structure resolves limitations that accompany models used to simulate the growth and development of shellfish populations. The length-frequency distribution for a cohort was developed from the individual-based model through simulation of a suite of genotypes with varying physiological capabilities. Hard clam populations were then formed by the yearly concatenation of cohorts with partially independent trajectories that are produced by cohort- and population-based processes. Development and verification of the hard clam model was done using long-term data sets from Great South Bay, New York that have been collected by the Town of Islip, New York. The ability to separately track length and age in the simulations allowed derivation of a general mathematical relationship for describing age-length relationships in hard clam populations. The mathematical relationship, which is based on a twisted bivariate Gaussian distribution, reproduces the features of age-length distributions observed for hard clam populations. The parameters obtained from fitting the twisted bivariate Gaussian to simulated hard clam length-frequency distributions obtained for varying conditions yield insight into the growth and mortality processes and population-dependent processes, compensatory and otherwise, that structured the population. This in turn provides a basis for development of theoretical models of population age-length compositions. The twisted bivariate Gaussian also offers the possibility of rapidly and inexpensively developing age-length keys, used to convert length-based data to age-based data, by permitting a relatively few known age-length pairs to be expanded into the full age- and length-frequency structure of the population.

Domoic acid uptake and elimination kinetics in oysters and mussels in relation to body size and anatomical distribution of toxin.

Toxin accumulation by suspension-feeding qualifier depends on a balance between processes regulating toxin uptake (i.e. ingestion and absorption of toxic cells) and elimination (i.e. egestion, exchange among tissues, excretion, degradation and/or biotransformation) during exposure to toxic blooms. This laboratory study compares the size-specific uptake and elimination kinetics of domoic acid (DA) from Pseudo-nitzschia multiseries in two co-occurring bivalves, the oyster Crassostrea virginica and the mussel Mytilus edulis. Domoic acid concentrations were measured in visceral and non-visceral tissues of different-sized oysters and mussels during simultaneous long-term exposure to toxic P. multiseries cells in the laboratory, followed by depuration on a non-toxic algal diet. Mussels attained 7-17-fold higher DA concentrations than oysters, depending on the body size and exposure time, and also detoxified DA at higher rates (1.4-1.6 d(-1)) than oysters (0.25-0.88 d(-1)) of a comparable size. Small oysters attained markedly higher weight-specific DA concentrations (maximum=78.6 μg g(-1)) than large, market-sized individuals (≤ 13 μg g(-1)), but no clear relationship was found between body size and DA concentration in mussels (maximum=460 μg g(-1)). Therefore, differential DA accumulation by the two species was, on average, approximately 3-fold more pronounced for large bivalves. An inverse relationship between DA elimination rate and body size was established for oysters but not mussels. Elimination of DA was faster in viscera than in other tissues of both bivalves; DA exchange rate from the former to the latter was higher in oysters. The contribution of viscera to the total DA burden of mussels was consistently greater than that of other tissues during both uptake (>80%) and depuration (>65%) phases, whereas it rapidly decreased from 70-80% to 30-40% in oysters, and this occurred faster in smaller individuals. Residual DA concentrations (≤ 0.25 μg g(-1)) were detected at later depuration stages (up to 14 d), mainly in viscera of oysters and non-visceral tissues of mussels, suggesting that a second, slower-detoxifying toxin compartment exists in both species. However, a simple exponential decay model was found to adequately describe DA elimination kinetics in these bivalves. The lower capacity for DA accumulation in oysters compared to mussels can thus only be explained by the formers comparatively low toxin intake rather than faster toxin elimination.

Feeding mechanics as the basis for differential uptake of the neurotoxin domoic acid by oysters, Crassostrea virginica, and mussels, Mytilus edulis

The neurotoxin domoic acid (DA), produced by diatoms Pseudo-nitzschia spp., is transferred to humans via consumption of contaminated bivalves. This study examines feeding mechanisms, namely reduced filtration, pre-ingestive rejection and poor absorption, that might explain the comparatively low DA levels commonly found in oysters during toxic Pseudo-nitzschia blooms. Clearance rate (CR), absorption efficiency (AE) of organic matter and selective rejection in pseudofeces of oysters (Crassostrea virginica) and mussels (Mytilus edulis) were investigated in relation to the DA levels accumulated during 2-wk, simultaneous exposure to toxic Pseudo-nitzschia multiseries. Effects of temperature and P. multiseries cell size were also tested to identify conditions, if any, under which oysters can accumulate unsafe DA levels. Oysters accumulated 3.0-7.5x less DA than mussels from a short-celled P. multiseries clone (length=24microm) at 12 degrees C. This was related to the 7.4-8.5x lower CRs determined for oysters relative to mussels at this temperature. Exposure to a longer-celled P. multiseries clone (81microm) resulted in up to 70x lower toxin levels in oysters compared to mussels, which was attributed to differential feeding selectivity. Mussels were unable to discriminate between long- and short-celled P. multiseries clones from a mixed suspension, whereas oysters were previously shown to preferentially reject long cells (>70microm) in pseudofeces. Both bivalves selectively rejected P. multiseries cells from mixed suspensions containing a flagellate but not another diatom. AE of organics from P. multiseries cells by oysters and mussels was comparably low (42 and 39%, respectively) and thus unlikely to explain their differential DA accumulation. CR and DA uptake by oysters were negligible at <or=4 degrees C but increased with increasing temperature up to 18 degrees C, although mean DA levels barely attained the regulatory limit (20microg g(-1)) when oysters were exposed to long P. multiseries cells. The maximum DA levels accumulated by mussels (320microg g(-1)) and oysters (44microg g(-1)) exposed to short P. multiseries cells in our study support the inter-specific differences in toxicity during Pseudo-nitzschia blooms, which are expected to be exacerbated at lower temperatures and when long cells or chains are dominant. Additionally, when alternate, non-diatom phytoplankton species are present, both bivalves can feed selectively and thus accumulate much lower DA levels than those predicted from their overall CRs. Our results provide support for the evaluation of species-specific management of DA-contaminated shellfish and need to be considered in modeling DA toxin kinetics of the two target species.

Effects of the red tide dinoflagellate, Karenia brevis, on early development of the eastern oyster Crassostrea virginica and northern quahog Mercenaria mercenaria

The brevetoxin-producing dinoflagellate, Karenia brevis, adversely affects many shellfish species including the commercially and ecologically important bivalve molluscs, the northern quahog (=hard clam) Mercenaria mercenaria and eastern oyster Crassostrea virginica, in the Gulf of Mexico, USA. This study assessed the effects of exposure of these bivalves to K. brevis during their early development. In separate experiments, embryos of 2-4 cell stage of M. mercenaria and C. virginica were exposed to both whole and lysed K. brevis cells isolated from Manasota Key, Florida. Low bloom concentrations of 500 to 3000 cells mL(-1) were simulated for 96 h. Shell length, percent abnormality (and normality), and percent mortality of resulting larvae were measured. Percentages were recorded after 6, 24, and 96 h of exposure; larval shell length was measured at 24 and 96 h. For both quahogs and oysters, the effects of exposing embryos to K. brevis on all larval responses were generally dose- and time-dependent. Percent mortalities and abnormalities of both clam and oyster embryos increased significantly after only 6h of exposure to whole cells of K. brevis. For clams, these parameters were significantly higher in whole and lysed treatments (at 3000 cells mL(-1)) than in controls. Percent mortalities of oysters were significantly higher in the whole-cell treatment (3000 cells mL(-1)) than under control conditions. After 24h of exposure, mean larval shell length of both bivalve species was significantly reduced relative to controls. This was evident for clam larvae in both the lysed treatment at 1500 cells mL(-1) and in whole and lysed treatments at 3000 cells mL(-1), and for oyster larvae in the lysed treatment at 3000 cells mL(-1). After 96 h, both species exposed to the lysed cell treatment at 3000 cells mL(-1) had significantly smaller larvae compared to those in the control. Overall, lysed cells of K. brevis had a more pronounced effect on shell length, percent abnormality, and mortality in both clams and oysters than did whole cells. Given the fact that blooms of K. brevis overlap with the spawning periods of these two bivalves, and that cells of this naked dinoflagellate are readily lysed by wave action, these results suggest that exposure to K. brevis during the early life history stages of clams and oysters could adversely affect their population recruitment. Further, the presence of whole or lysed cells of K. brevis in hatcheries could have a major negative impact on production.

In vivo Effects of Brown Tide on the Feeding Function of the Gill of the Northern Quahog Mercenaria mercenaria (Bivalvia: Veneridae)

The in vivo response of adult northern quahogs, Mercenaria mercenaria, to Aureococcus anophagefferens (brown tide) at the level of the gill was determined using video-endoscopy. Feeding activity, particle-approach velocities, and ventral-groove–transport velocities were documented after the quahogs were exposed to Isochryis galbana (baseline observations) supplemented with either toxic or nontoxic A. anophagefferens at two bloom concentrations (8 × 105 or 2 × 106 cells ml–1). Externally, there was no evidence of adverse effects of brown tide on feeding, as siphons remained extended and dilated. Toxic brown tide at both concentrations elicited gill muscular contractions, intermittent cessation of water flow, and decreased particle loading within the pallial cavity. The 8 × 105 cell ml–1 toxic treatment had no significant effect on approach velocities or ventral-groove–transport velocities after 2 h, although time-averaging showed significant reduction of the latter during the last 30 min of exposure. The higher concentration of toxic brown tide caused a significant decrease in these velocities after only 1 h. Nontoxic brown tide produced none of these effects. Thus, A. anophagefferens compromised quahog feeding by stimulating contractions of the branchial musculature and interfering with lateral and ventral groove ciliary beating. These effects were both time- and concentration-dependent and could be caused by either a dopaminergic or a serotonergic toxic factor.

PREPARATION OF LARGE BIVALVE SPECIMENS FOR SCANNING ELECTRON MICROSCOPY USING HEXAMETHYLDISILAZANE (HMDS)

Abstract Treatment with hexamethyldisilazane (HMDS) for drying specimens for Scanning Electron Microscopy (SEM) is described for relatively large (>20 mm shell height, SH) individuals of two scallop species, Placopecten magellanicus and Argopecten irradians. The traditionally used method of critical point drying (CPD) has been applied successfully for smaller specimens (~350 μm up to 15 mm SH); however, occasional rupture of the mantle occurred in these specimens. Furthermore, size limitation of the CPD chamber did not permit preparation of larger individuals. An alternative experimental protocol using HMDS was tested, which successfully preserves the morphology of the bivalve feeding organs, mantle surface and the cilia of the two scallop species with negligible shrinkage and few artifacts. Another benefit of this method is that the number of specimens and sample size is not restricted.

Effects of field and laboratory exposure to the toxic dinoflagellate Karenia brevis on the reproduction of the eastern oyster, Crassostrea virginica, and subsequent development of offspring

Blooms of the brevetoxin-producing dinoflagellate, Karenia brevis, are a recurrent and sometimes devastating phenomenon in the Gulf of Mexico. The eastern oyster, Crassostrea virginica, is exposed regularly to these blooms, yet little is known about the impacts of K. brevis upon this important species. The present study considered the effects of exposure to both a natural bloom and cultured K. brevis on the reproductive development of C. virginica. Oysters had been exposed to a bloom of K. brevis that occurred in Lee County, Florida, from September 2012 through May 2013, during a period of gametogenesis and gamete ripening. Ripe adult oysters were collected from this bloom-exposed site and from a site 200 miles north which was not exposed to any bloom. In addition, responses to two 10-day laboratory exposures of either unripe or ripe adult oysters to whole cells of K. brevis at high bloom concentrations (1000 and 5000cellsmL-1) were determined. Both field- and laboratory-exposed adult oysters accumulated PbTx (attaining ∼22×103ngg-1 and 922ngg-1 PbTx-3 equivalents in the laboratory and the field, respectively), and significant mucal, edematous, and inflammatory features, indicative of a defense response, were recorded in adult tissues in direct contact with K. brevis cells. Laboratory-exposed oysters also showed an increase in the total number of circulating hemocytes suggesting that: (1) new hemocytes may be moving to sites of tissue inflammation, or, (2) hemocytes are released into the circulatory system from inflamed tissues where they may be produced. The area of oyster tissue occupied by gonad (representative of reproductive effort) and reactive oxygen species production in the spermatozoa of oysters exposed to the natural bloom of K. brevis were significantly lower compared to oysters that were not exposed to K. brevis. Additionally, following 10-day exposure of ripe oysters, a significant, 46% reduction in the prevalence of individuals with ripe gametes was obtained in the 5000cellsmL-1K. brevis treatment. Brevetoxin (PbTx) was recorded within the spermatozoa and oocytes of naturally exposed oysters and was estimated to be 18 and 26% of the adult PbTx load, respectively. Larvae derived from gametes containing PbTx showed significantly higher mortalities and attained a smaller larval size for the first 6 days post-fertilization. These negative effects on larval development may be due to the presence of PbTx in the lipid droplets of the oocytes, which is mobilized by the larvae during embryonic and lecithotrophic larval development. Provision of a non-contaminated food source to larvae however, appeared to mitigate the early negative effects of this neonatal PbTx exposure. Results herein show that adult eastern oysters and their offspring are susceptible to exposure to K. brevis. Caution should therefore be exercised when identifying oyster reef restoration areas and in efforts to establish aquaculture in areas prone to red tides.

Phytoplankton Community Structure Based on Photopigment Markers in a Mid-Atlantic U.S. Coastal Lagoon: Significance for Hard-Clam Production

ABSTRACT Fantasia, R.L.; Bricelj, V.M., and Ren, L., 2017. Phytoplankton community structure based on photopigment markers in a mid-Atlantic U.S. coastal lagoon: Significance for hard-clam production. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay-Little Egg Harbor, New Jersey. Phytoplankton community structure at four contrasting sites in the Barnegat Bay-Little Egg Harbor (BB-LEH) Estuary was determined microscopically and by photopigment-CHEMTAX analysis. It was related to temperature, salinity, and weekly growth rates of juvenile hard clams, Mercenaria mercenaria, deployed at these sites during the summer in 2012 and 2013, pre- and post-Hurricane Sandy. Results indicated distinct differences in phytoplankton composition among sites, with a greater contribution of chlorophytes and cyanobacteria at the northernmost site, Island Beach State Park (IBSP). Photopigment analysis was useful in improving upon the taxonomic assessment of pico-coccoid (<3 μm) algae that are difficult to identify microscopically. The presence of the brown tide alga, Aureococcus anophagefferens, was confirmed by immunofluorescence during both years, with peak densities of 4.4 × 105 cells ml−1 in June 2013 at Sedge Island, in a Marine Conservation Zone that supports clam seeding. Concentrations of 19′but-fucoxanthin and A. anophagefferens showed a strong linear relationship, suggesting that this pigment is a good indicator of this pelagophyte in BB-LEH. The occurrence of brown tide was important to consider in CHEMTAX analysis as it affected the estimated contribution of diatoms to chl a, given that A. anophagefferens is also characterized by a relatively high fucoxanthin:chlorophyll a ratio. Generally, hard-clam tissue-growth rates were greatest at Sedge Island and Tuckerton, LEH, and least at IBSP, a lower salinity site, and off Harvey Cedars, a more developed site along a bulkheaded shoreline. Significant linear relationships were found between clam growth rate and diagnostic photopigments, with positive relationships for indicators of diatoms and negative relationships for those of cyanobacteria and chlorophytes.

Marine Molluscs in Nearshore Habitats of the United Arab Emirates: Decadal Changes and Species of Public Health Significance

ABSTRACT Grizzle, R.E.; Bricelj, V.M.; AlShihi, R.M.; Ward, K.M., and Anderson, D.M., 2018. Marine molluscs in nearshore habitats of the United Arab Emirates: Decadal changes and species of public health significance. This paper describes the results of three qualitative surveys of marine molluscs conducted in December 2010 and May 2011 and 2012 in nearshore benthic habitats along the Arabian Gulf and Gulf of Oman coasts of the United Arab Emirates. Findings are compared with historical studies, focusing on extensive surveys from the 1960s and 1970s. Molluscan species of public health significance are identified on the basis of their potential as vectors of algal toxins in light of the recent occurrence of harmful algal blooms (HABs) in the region. Habitats sampled included intertidal sand or gravel beaches, rocks and jetties, sheltered soft-sediment flats and mangroves, and shallow subtidal coral reefs. The present study showed differences in taxonomic composition and decreased species richness of gastropods compared with a previous mollusc survey conducted in the early 1970s, reflecting the probable impacts of extensive, ongoing coastal development activities, although other environmental stressors may play a contributing role. The major habitat change found in the current survey was replacement of natural “rocky” substrates with man-made jetties and breakwaters. Of the 27 live gastropod species collected, seven predatory or scavenging species were identified as potential biotoxin vectors: Thais savignyi, T. tissoti, T. lacera, Murex scolopax, Nassarius persicus, Hexaplex kuesterianus, and Rapana sp. Of the 22 live bivalve species collected, the following 11 suspension feeders were deemed to be potential vectors of HAB toxins on the basis of their body size and feeding mode: three venerid clams (Circenita callipyga and Tivela ponderosa, which are consumed locally, and Amiantis umbonella); the widespread encrusting rock oyster, Saccostrea cuccullata, also consumed locally; two pearl oyster species; Pinctada spp.; the prickly pen shell Pinna muricata; the scallop Chlamys livida; the cockle Acrosterigma lacunosa; and the facultative suspension-feeding tellinids Asaphis violascens and Hiatula rosea.

Impacts of exposure to the toxic dinoflagellate Karenia brevis on reproduction of the northern quahog, Mercenaria mercenaria

The Gulf of Mexico, including the southwest Florida coast, USA, experience recurrent blooms of the brevetoxin (PbTx)-producing dinoflagellate, Karenia brevis. Northern quahogs (hard clams) Mercenaria mercenaria, are an important commercial species in this region. This study examined the effects of field and laboratory exposure of adult clams to K. brevis during their reproductive period, and effects on their subsequently produced offspring. Ripe adult clams were collected from a site which had been exposed to an eight-month natural bloom of K. brevis and an unaffected reference site. Ripe adult clams were also exposed to bloom concentrations of K. brevis for 10 days in the laboratory. Clams exposed to K. brevis accumulated PbTx at concentrations of 1508 (field exposure), 1444 (1000 cells mL-1 laboratory treatment) and 5229 ng g-1 PbTx-3 eq (5000 cells mL-1 laboratory treatment). Field-exposed clams showed histopathological effects: a significantly higher prevalence of mucus in the stomach/ intestine (23.3%), edema in gill tissues (30%) and presence of the cestode parasite, Tylocephalum spp. in whole tissue (40%), compared to non-exposed clams (0, 3.3 and 6.7% respectively). These clams also showed reduced gonadal allocation (23% gonadal area) and a higher prevalence of clams of undetermined sex (20%) compared to those sampled from the non-exposed site (43% and 0%, respectively). It is hypothesized that less energy may be channeled into reproduction as more is allocated for homeostasis or tissue repair. The fertilization success of gametes obtained from both field and laboratory-exposed adults was significantly lower in clams that had been exposed to K. brevis and development of these offspring was negatively affected at Days 1 and 4 post-fertilization (in field- and laboratory-exposed clams at the higher K. brevis concentration and in laboratory-exposed clams at the higher K. brevis concentration, respectively). Negative effects may be due to toxin accumulation in the gametes of field-exposed clams (244 ± 50 ng PbTx g-1 and 470 ± 82 ng g-1 wet weight in oocytes and sperm, respectively). Adverse effects in M. mercenaria are compared to those previously reported in oysters, Crassostrea virginica, under similar conditions of exposure. This study provides further evidence of the impacts of K. brevis and its associated toxins on the adults and offspring of exposed shellfish. Site-selection for the collection of broodstock and aquaculture grow-out efforts should therefore consider the local occurrence of K. brevis blooms.