Effects of freshwater release on oyster reef density, reproduction, and disease in a highly modified estuary.

Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for assessing the impact of altered hydrology on natural oyster reef (Crassostrea virginica) populations. The watershed has been highly modified and greatly enlarged by an artificial connection to Lake Okeechobee. Accordingly, to generate data to support water management recommendations, this study monitored various oyster biometrics over 15 years along the primary salinity gradient. Oyster reef densities were significantly affected by both prolonged high volume freshwater releases creating hyposaline conditions at upstream sites and by a lack of freshwater input creating hypersaline conditions at downstream sites. Low freshwater input led to an increase in disease caused by Perkinsus marinus and predation. Moderate (< 2000 cfs) and properly timed (winter/spring) freshets benefited oysters with increased gametogenesis, good larval mixing, and a reprieve from disease. If high volume freshets occurred in the late summer, extensive mortality occurred at the upstream site due to low salinity. These findings suggest freshwater releases in the late summer, when reproductive stress is at its peak and pelagic larvae are most vulnerable, should be limited to < 2000 cfs, but that longer freshets (1-3 weeks) in the winter and early spring (e.g., December-April) benefit oysters by reducing salinity and lessening disease intensity. Similar strategies can be employed in other managed systems, and patterns regarding the timing of high volume flows are applicable to all estuaries where the management of healthy oyster reefs is a priority.

A 13CO2 Enrichment Experiment to Study the Synthesis Pathways of Polyunsaturated Fatty Acids of the Haptophyte Tisochrysis lutea.

The production of polyunsaturated fatty acids (PUFA) in Tisochrysis lutea was studied using the gradual incorporation of a 13C-enriched isotopic marker, 13CO2, for 24 h during the exponential growth of the algae. The 13C enrichment of eleven fatty acids was followed to understand the synthetic pathways the most likely to form the essential polyunsaturated fatty acids 20:5n-3 (EPA) and 22:6n-3 (DHA) in T. lutea. The fatty acids 16:0, 18:1n-9 + 18:3n-3, 18:2n-6, and 22:5n-6 were the most enriched in 13C. On the contrary, 18:4n-3 and 18:5n-3 were the least enriched in 13C after long chain polyunsaturated fatty acids such as 20:5n-3 or 22:5n-3. The algae appeared to use different routes in parallel to form its polyunsaturated fatty acids. The use of the PKS pathway was hypothesized for polyunsaturated fatty acids with n-6 configuration (such as 22:5n-6) but might also exist for n-3 PUFA (especially 20:5n-3). With regard to the conventional n-3 PUFA pathway, Δ6 desaturation of 18:3n-3 appeared to be the most limiting step for T. lutea, "stopping" at the synthesis of 18:4n-3 and 18:5n-3. These two fatty acids were hypothesized to not undergo any further reaction of elongation and desaturation after being formed and were therefore considered "end-products". To circumvent this limiting synthetic route, Tisochrysis lutea seemed to have developed an alternative route via Δ8 desaturation to produce longer chain fatty acids such as 20:5n-3 and 22:5n-3. 22:6n-3 presented a lower enrichment and appeared to be produced by a combination of different pathways: the conventional n-3 PUFA pathway by desaturation of 22:5n-3, the alternative route of ω-3 desaturase using 22:5n-6 as precursor, and possibly the PKS pathway. In this study, PKS synthesis looked particularly effective for producing long chain polyunsaturated fatty acids. The rate of enrichment of these compounds hypothetically synthesized by PKS is remarkably fast, making undetectable the 13C incorporation into their precursors. Finally, we identified a protein cluster gathering PKS sequences of proteins that are hypothesized allowing n-3 PUFA synthesis.

Identification of Polyunsaturated Fatty Acids Synthesis Pathways in the Toxic Dinophyte Alexandrium minutum Using 13C-Labelling.

The synthetic pathways responsible for the production of the polyunsaturated fatty acids 22:6n-3 and 20:5n-3 were studied in the Dinophyte Alexandrium minutum. The purpose of this work was to follow the progressive incorporation of an isotopic label (13CO2) into 11 fatty acids to better understand the fatty acid synthesis pathways in A. minutum. The Dinophyte growth was monitored for 54 h using high-frequency sampling. A. minutum presented a growth in two phases. A lag phase was observed during the first 30 h of development and had been associated with the probable temporary encystment of Dinophyte cells. An exponential growth phase was then observed after t30. A. minutum rapidly incorporated 13C into 22:6n-3, which ended up being the most 13C-enriched polyunsaturated fatty acid (PUFA) in this experiment, with a higher 13C atomic enrichment than 18:4n-3, 18:5n-3, 20:5n-3, and 22:5n-3. Overall, the 13C atomic enrichment (AE) was inversely proportional to number of carbons in n-3 PUFA. C18 PUFAs, 18:4n-3, and 18:5n-3, were indeed among the least 13C-enriched FAs during this experiment. They were assumed to be produced by the n-3 PUFA pathway. However, they could not be further elongated or desaturated to produce n-3 C20-C22 PUFA, because the AEs of the n-3 C18 PUFAs were lower than those of the n-3 C20-C22 PUFAs. Thus, the especially high atomic enrichment of 22:6n-3 (55.8% and 54.9% in neutral lipids (NLs) and polar lipids (PLs), respectively) led us to hypothesize that this major PUFA was synthesized by an O2-independent Polyketide Synthase (PKS) pathway. Another parallel PKS, independent of the one leading to 22:6n-3, was also supposed to produce 20:5n-3. The inverse order of the 13C atomic enrichment for n-3 PUFAs was also suspected to be related to the possible ß-oxidation of long-chain n-3 PUFAs occurring during A. minutum encystment.

The sensitivity of the deepsea species northern shrimp (Pandalus borealis) and the cold-water coral (Lophelia pertusa) to oil-associated aromatic compounds, dispersant, and Alaskan North Slope crude oil.

This study investigated the sensitivity of two deepsea species using mortality of northern shrimp (Pandalus borealis) and polyp activity of stony coral (Lophelia pertusa) to dispersant, Corexit 9500 and aromatic hydrocarbons (toluene, 2-methylnaphthalene, phenanthrene) in 96-h tests. Resulting hydrocarbon toxicity data were fit to the Target Lipid Model to generate predictive models and determine species sensitivity. Toxicity of chemically enhanced water accommodated fractions of Alaskan North Slope crude oil (ANS-oil) was also investigated with shrimp using nominal loading, total petroleum hydrocarbons and biomimetic extraction (BE) as oil exposure metrics. Coral were more sensitive to dispersant than shrimp while similar sensitivity was observed for hydrocarbons. Study and literature findings indicate deepsea species exhibit acute sensitivities to dispersant, hydrocarbons and oil that are comparable to pelagic species. Results support use of passive sampling methods to quantify dissolved oil for interpreting oil toxicity tests and suggest models for predicting time-dependence of toxicity warrant re-evaluation.

Study of Synthesis Pathways of the Essential Polyunsaturated Fatty Acid 20:5n-3 in the Diatom Chaetoceros Muelleri Using 13C-Isotope Labeling.

: The present study sought to characterize the synthesis pathways producing the essential polyunsaturated fatty acid (PUFA) 20:5n-3 (EPA). For this, the incorporation of 13C was experimentally monitored into 10 fatty acids (FA) during the growth of the diatom Chaetoceros muelleri for 24 h.Chaetoceros muelleri preferentially and quickly incorporated 13C into C18 PUFAs such as 18:2n-6 and 18:3n-6 as well as 16:0 and 16:1n-7, which were thus highly 13C-enriched. During the experiment, 20:5n-3 and 16:3n-4 were among the least-enriched fatty acids. The calculation of the enrichment percentage ratio of a fatty acid B over its suspected precursor A allowed us to suggest that the diatom produced 20:5n-3 (EPA) by a combination between the n-3 (via 18:4n-3) and n-6 (via 18:3n-6 and 20:4n-6) synthesis pathways as well as the alternative ω-3 desaturase pathway (via 20:4n-6). In addition, as FA from polar lipids were generally more enriched in 13C than FA from neutral lipids, particularly for 18:1n-9, 18:2n-6 and 18:3n-6, the existence of acyl-editing mechanisms and connectivity between polar and neutral lipid fatty acid pools were also hypothesized. Because 16:3n-4 and 20:5n-3 presented the same concentration and enrichment dynamics, a structural and metabolic link was proposed between these two PUFAs in C. muelleri.

Sublethal effects of oil-contaminated sediment to early life stages of the Eastern oyster, Crassostrea virginica.

The explosion of the Deepwater Horizon (DWH) oil drilling rig resulted in the release of crude oil into the Gulf of Mexico. This event coincided with the spawning season of the Eastern oyster, Crassostrea virginica. Although oil bound to sediments constitutes an important source of polycyclic aromatic hydrocarbon (PAH) exposure to benthic organisms, toxicity of sediment-associated DWH oil has not been investigated in any bivalve species. Here, we evaluated the sublethal effects of acute exposure of gametes, embryos and veliger larvae of the Eastern oyster to different concentrations of unfiltered elutriates of sediment contaminated with DWH oil. Our results suggest that gametes, embryos and veliger larvae are harmed by exposure to unfiltered elutriates of contaminated sediment. Effective concentrations for fertilization inhibition were 40.6 µg tPAH50 L-1 and 173.2 µg tPAH50 L-1 for EC201h and EC501h values, respectively. Embryo exposure resulted in dose-dependent abnormalities (EC20 and EC50 values were 77.7 µg tPAH50 L-1 and 151 µg tPAH50 L-1, respectively) and reduction in shell growth (EC2024h value of 1180 µg tPAH50 L-1). Development and growth of veliger larvae were less sensitive to sediment-associated PAHs compared to embryos. Fertilization success and abnormality of larvae exposed as embryos were the most sensitive endpoints for assessing the toxicity of oil-contaminated sediment. Bulk of measured polycyclic aromatic hydrocarbons were sediment-bound and caused toxic effects at lower tPAH50 concentrations than high energy water accommodated fractions (HEWAF) preparations from the same DWH oil. This study suggests risk assessments would benefit from further study of suspended contaminated sediment.

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.

The sensitivity of a deep-sea fish species (Anoplopoma fimbria) to oil-associated aromatic compounds, dispersant, and Alaskan North Slope crude oil.

A predominant concern following oil spills is toxicity to aquatic organisms. However, few data are available on effects in deep-sea cold water fishes. The present study had 3 major objectives. The first was to investigate the relative sensitivity of the deep-sea species Anoplopoma fimbria (sablefish) to acute effects of 3 aromatic compounds (toluene, 2-methylnaphthalene, and phenanthrene), dispersant alone, and chemically enhanced water accommodated fractions (CEWAFs) of Alaskan North Slope crude oil. The second was to determine the critical target lipid body burden (CTLBB) for sablefish by fitting aromatic hydrocarbon toxicity data to the target lipid model (TLM), which then allowed expression of CEWAF exposures in terms of dissolved oil toxic units. The final aim was to apply a passive sampling method that targets bioavailable, dissolved hydrocarbons as an alternative analytical technique for improved CEWAF exposure assessment. The results indicate that sablefish exhibit sensitivity to Corexit 9500 (96-h median lethal concentration [LC50] = 72.2 mg/L) within the range reported for other fish species. However, the acute CTLBB of 39.4 ± 2.1 µmol/goctanol lies at the lower end of the sensitivity range established for aquatic species. The utility of both toxic units and passive sampling measurements for describing observed toxicity of dispersed oil is discussed. The present study is novel in that a new test species is investigated to address the uncertainty regarding the sensitivity of deep-sea fishes, while also employing modeling and measurements to improve exposure characterization in oil toxicity tests. Environ Toxicol Chem 2018;37:2210-2221. © 2018 SETAC.

Evaluation of toxicity of Deepwater Horizon slick oil on spat of the oyster Crassostrea virginica.

The 2010 explosion of the Deepwater Horizon (DWH) oil rig generated the largest marine oil spill in US history with millions of barrels of crude oil released in the Gulf of Mexico (GoM). The eastern oyster, Crassostrea virginica, is an ecologically and economically important species in the northern GoM. Due to its biological characteristics (sessile, filter feeding), juvenile oysters may have been affected. This study investigated the effects of surface-collected DWH oil prepared as high-energy water-accommodated fraction (HEWAF) on the survival of 2-month-old oyster spat, and evaluated the potential impacts of HEWAF on particle clearance rate and spat tissue. Exposure of oysters to a range of oil/HEWAF (0-7-66-147-908-3450 µg tPAH50 (sum of 50 polycyclic aromatic hydrocarbons) L-1) resulted in non-dose-dependent mortalities and reduced clearance rates of algal food (Tisochrysis lutea). A morphometric study of the digestive tubules (DGTs) indicated a dose-dependent response to oil exposure on lumen dilation, on epithelium thinning of the DGT, and a significant change in DGT synchrony (LOEC = 66 µg tPAH50 L-1). This finding suggests that structural changes occurred in the digestive gland of exposed oysters most likely due to an oil-related stress. In addition, histological observations showed that tissues in contact with HEWAF (gills, palp, connective tissue, digestive gland) were adversely impacted at ≥ 7 µg tPAH50 L-1, and exhibited pathological symptoms typical of an inflammatory response (e.g., hemocyte diapedesis and infiltration, syncytia, epithelium sloughing).

Oyster reproduction is compromised by acidification experienced seasonally in coastal regions.

Atmospheric carbon dioxide concentrations have been rising during the past century, leading to ocean acidification (OA). Coastal and estuarine habitats experience annual pH variability that vastly exceeds the magnitude of long-term projections in open ocean regions. Eastern oyster (Crassostrea virginica) reproduction season coincides with periods of low pH occurrence in estuaries, thus we investigated effects of moderate (pH 7.5, pCO2 2260 µatm) and severe OA (pH 7.1, pCO2 5584 µatm; and 6.7, pCO2 18480 µatm) on oyster gametogenesis, fertilization, and early larval development successes. Exposure at severe OA during gametogenesis caused disruption in oyster reproduction. Oogenesis appeared to be more sensitive compared to spermatogenesis. However, Eastern oyster reproduction was resilient to moderate OA projected for the near-future. In the context of projected climate change exacerbating seasonal acidification, OA of coastal habitats could represent a significant bottleneck for oyster reproduction which may have profound negative implications for coastal ecosystems reliant on this keystone species.

Potential impacts of blooms of the toxic dinoflagellate Karenia brevis on the growth, survival and juvenile recruitment of the non-native green mussel Perna viridis in southeastern United States.

Red tide blooms formed by Karenia brevis are frequent along the Gulf coast of Florida and it is unclear what tolerance the green mussel Perna viridis, a recently introduced species to coastal waters, has toward these events. Established populations of P. viridis were monitored along the coastal waters of Estero Bay, Florida before, during and following two consecutive red tide blooms to assess the potential effects on growth, survival and juvenile recruitment. Upon onset of the bloom, growth rates fell from 6 to 10 mm month(-1) (March 2011-November 2011) to less than 3 mm month(-1). In the succeeding years, K. brevis blooms were present, and average growth of individually tagged mussels remained below 3 mm month(-1). During growth monitoring the use of calcein as an internal marker was tested with positive staining results and no observed effect on growth or survival. In March 2012, following the first red tide bloom, a population-wide mortality event was observed. Following this event, increased mortality rates were observed with peaks during onset of the bloom in the fall of 2012 and 2013. Juvenile recruitment was also limited during years in which blooms persisted into the spring spawning period suggesting gamete and/or larval sensitivity to K. brevis. Although it cannot be conclusively determined that the cause of reduced growth and survival is due to red tide events, the parallels observed suggest that K. brevis is a factor in the observed changes in population structure.

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.

Susceptibility of gametes and embryos of the eastern oyster, Crassostrea virginica, to Karenia brevis and its toxins.

The bivalve mollusc, Crassostrea virginica, is frequently exposed to blooms of Karenia brevis along the west coast of Florida during periods of spawning and early larval development. A continuous 4-day exposure of gametes and 2-4 cell stage embryos of C. virginica to whole-cell and culture filtrate of K. brevis at 500 and 5000 cells mL(-1), was followed by a 4-day 'recovery' period. Larval growth, percent of normal, abnormal and dead larvae, and the presence of food in the larval gut were measured throughout the exposure period. Results suggest that negative effects mainly occur during embryogenesis and early development. Damage to feeding apparatus/gut may occur during embryonic development or exposure to toxins may act as a feeding deterrent on non-toxic algae. Following 2-h in vitro exposure of gametes, differences in oocyte and sperm cell parameters were investigated using flow cytometry. The reduced sperm viability in the whole-cell 5000 cells mL(-1) treatment suggests the involvement of extracellular brevetoxins (PbTx) and perhaps other harmful, uncharacterized compounds associated with the K. brevis cell membrane. The cumulative effects of reduced sperm viability, fertilization success, embryonic and larval survival, and the near-annual exposure to blooms of K. brevis could cause significant bottlenecks on oyster recruitment.

Uptake and elimination of brevetoxin in the invasive green mussel, Perna viridis, during natural Karenia brevis blooms in southwest Florida.

Perna viridis is a recently introduced species to US coastal waters and have vigorously spread throughout the southeastern seaboard since their invasion. Little information regarding their response to local environmental factors has been reported including responses to the local HAB species, Karenia brevis. This study monitored the tissue toxin concentration of brevetoxins in P. viridis from existing populations throughout two consecutive natural K. brevis blooms. The results showed P. viridis to rapidly accumulate PbTx upon exposure to the bloom, far exceeding the peak tissue concentrations of oysters, Crassostrea virginica, sampled during the same period, 57,653 ± 15,937 and 33,462 ± 10,391 ng g(-1) PbTx-3 equivalent, respectively. Further, P. viridis retained high PbTx concentrations in their tissues post bloom remaining above the regulatory limit for human consumption for 4-5 months, significantly longer than the depuration time of 2-8 weeks for native oyster and clam species. In the second year, the bloom persisted at high cell concentrations resulting in prolonged exposure and higher PbTx tissue concentrations indicating increased bioaccumulation in green mussels. While this species is not currently harvested for human consumption, the threat for post bloom trophic transfer could pose negative impacts on other important fisheries and higher food web implications.

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.

Mercury accumulation in sharks from the coastal waters of southwest Florida.

As large long-lived predators, sharks are particularly vulnerable to exposure to methylmercury biomagnified through the marine food web. Accordingly, nonlethal means were used to collect tissues for determining mercury (Hg) concentrations and stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N) from a total of 69 sharks, comprising 7 species, caught off Southwest Florida from May 2010 through June 2013. Species included blacknose (Carcharhinus acronotus), blacktip (C. limbatus), bull (C. leucas), great hammerhead (Sphyrna mokarran), lemon (Negaprion brevirostris), sharpnose (Rhizoprionodon terraenovae), and tiger sharks (Galeocerdo cuvier). The sharks contained Hg concentrations in their muscle tissues ranging from 0.19 mg/kg (wet-weight basis) in a tiger shark to 4.52 mg/kg in a blacktip shark. Individual differences in total length and δ(13)C explained much of the intraspecific variation in Hg concentrations in blacknose, blacktip, and sharpnose sharks, but similar patterns were not evident for Hg and δ(15)N. Interspecific differences in Hg concentration were evident with greater concentrations in slower-growing, mature blacktip sharks and lower concentrations in faster-growing, young tiger sharks than other species. These results are consistent with previous studies reporting age-dependent growth rate can be an important determinant of intraspecific and interspecific patterns in Hg accumulation. The Hg concentrations observed in these sharks, in particular the blacktip shark, also suggested that Hg may pose a threat to shark health and fitness.

Simulation of potential oyster density with variable freshwater inflow (1965-2000) to the Caloosahatchee River Estuary, southwest Florida, USA.

Oyster beds are disappearing worldwide through a combination of over-harvesting, diseases, and salinity alterations in the coastal zone. Sensitivity of oysters to variable discharge and salinity is particularly acute in small sub-tropical estuaries subject to regulated freshwater releases. South Florida has sub-tropical estuaries where watershed flood control sometimes results in excessive freshwater inflow to estuaries during the wet season (May-Oct) and reduced discharge and increased salinities in the dry season (Nov-Apr). The potential to reserve freshwater accumulated during the wet season could offer the capacity to regulate freshwater at different temporal scales, thus optimizing salinity conditions for estuarine biota. The goal of this study was to use simulation modeling to explore the effects of freshwater inflows and salinity on adult oyster survival in the Caloosahatchee River Estuary (CRE) in southwest Florida. Water managers derived three different freshwater inflow scenarios for the CRE based on historical and modified watershed attributes for the time period of 1965-2000. Three different salinity time series were generated from the inflow scenarios at each of three sites in the lower CRE and used to conduct nine different oyster simulations. Overall, the predicted densities of adult oysters in the upstream site were 3-4 times greater in seasons that experienced reduced freshwater inflow (e.g., increased salinity) with oyster density in the lower estuary much less influenced by the inflows. Potential storage of freshwater reduced the frequency of extreme flows in the wet season and helped to maintain minimum inflow in the dry season near the estuarine mouth. Analyses of inflows indicated that discharges ranging from 0 to 1,500 cfs could promote favorable salinities of 10-25 in the lower CRE depending on wet versus dry season climatic conditions. This range of inflows is similar to that derived in other studies of the CRE and emphasizes the value of simulation models to help prescribe freshwater releases which benefit estuarine biota.

Host-parasite interactions: Marine bivalve molluscs and protozoan parasites, Perkinsus species.

This review assesses and examines the work conducted to date concerning host and parasite interactions between marine bivalve molluscs and protozoan parasites, belonging to Perkinsus species. The review focuses on two well-studied host-parasite interaction models: the two clam species, Ruditapes philippinarum and R. decussatus, and the parasite Perkinsus olseni, and the eastern oyster, Crassostrea virginica, and the parasite Perkinsus marinus. Cellular and humoral defense responses of the host in combating parasitic infection, the mechanisms (e.g., antioxidant enzymes, extracellular products) employed by the parasite in evading host defenses as well as the role of environmental factors in modulating the host-parasite interactions are described.

Flow cytometric characterization of hemocytes of the sunray venus clam Macrocallista nimbosa and influence of salinity variation.

Sunray venus clam Macrocallista nimbosa is a native bivalve mollusc of Florida, USA, currently evaluated as a potential new aquaculture species. Very little is known about the physiology and hemocyte characteristics of this species. Bivalve hemocytes are generally involved in various physiological functions including nutrition, tissue repair, detoxification and immune defense. Understanding hemocytes of M. nimbosa and their response to environmental variations is crucial. In estuarine Florida areas, salinity is probably the most important factor potentially affecting clams physiology since wide variations can occur within few days. In the present work, using flow cytometry, hemocyte types and cellular parameters (oxidative activity, lysosomal content, phagocytosis capacity) were first characterized in sunray venus clams, in relation with endogenous variables (i.e., size, body weight, gender). Clams were then transferred from salinity 30 psu to 18, 21, 25, 30, 35 and 38 psu. After 7 days, impact of salinity variations was determined on hemocyte parameters, along with estimation of physiological status of clams (mortality, valve closure, filtration activity). Hemocytes of sunray venus clam appeared as a unique population, both in terms of morphology (FSC vs. SSC) and intracellular parameters, but displayed high inter-individual variability. Allometric relationship was only described for intracellular oxidative activity. Transfer of clams to 18 psu and, at lower extent, 21 psu resulted in valve closure, mortality and decreased filtration activity. Low salinities resulted in reduction of the number of circulating hemocytes, potentially reflecting infiltration in tissues as part of an inflammatory response or to optimize nutrient distribution. Low salinities also highly impacted hemocytes as depicted by increased cell and lysosomal compartment volumes, decreased phagocytosis capacity as well as increased oxidative stress and mortality. Salinity drops depress physiology and immune defense capacities of sunray venus clams, potentially threatening survival in case of concomitant pathogen encounter or secondary stress.

Bioaccumulation and depuration of brevetoxins in the eastern oyster (Crassostrea virginica) and the northern quahog (= hard clam, Mercenaria mercenaria).

The eastern oyster (Crassostrea virginica) and northern quahog (= hard clam, Mercenaria mercenaria) are two species of economic and ecological significance in east coast waters of the United States and the Gulf of Mexico. Commercial industries for these species, especially within the state of Florida, are significant. The current study was undertaken to build upon the already established body of knowledge surrounding effects of the toxic dinoflagellate Karenia brevis on shellfish, to provide an understanding of the kinetics of brevetoxins within shellfish tissues, and to provide an estimate of brevetoxin retention times in these shellfish after a bloom event. Individual clams and oysters were exposed to the toxic dinoflagellate, K. brevis at a bloom concentration of 5 × 10(5) cells·L(-1) for eight days and then transferred to filtered water for depuration. Individuals were sampled periodically to determine depuration rates. Concentrations of brevetoxins (and/or their metabolites measured as PbTx-3 equivalent) in tissues were determined using an Enzyme Linked Immunosorbent Assay (ELISA). After five days of exposure, brevetoxin levels in tissues of both species reached concentrations well above the regulatory limit of 800 ng g(-1) (Pb-TX3 equivalent). Averaged concentration of brevetoxins in clams was 1000 ng g(-1), while the oysters averaged 1986 ng g(-1). After two weeks of depuration, tissue concentrations in both species were below regulatory levels with clams averaging ~204 ng g(-1) and oysters averaging ~437 ng g(-1). Toxins (or their metabolities) remained detectable in both clams (139 days) and oysters (82 days) for the duration of the experiment.