Modulatory effects of hard clam (Mercenaria mercenaria) tissue extracts on the in vitro growth of its pathogen QPX.

Quahog parasite unknown (QPX) is a fatal protistan parasite affecting cultured and wild hard clams Mercenaria mercenaria along the northeastern coasts of the USA and maritime Canada. Field investigations and laboratory transmission studies revealed some variations in the susceptibility of different hard clam stocks to QPX infection. In this study, we used in vitro QPX cultures to investigate the effect of plasma and tissue extracts from two different clam stocks on parasite survival and growth. Results demonstrated the presence of factors in clams that significantly modulate QPX growth. Extracts from gills and mantle tissues as well as plasma inhibited in vitro QPX growth, whereas foot and adductor muscle extracts enhanced parasite growth. Investigations of anti-QPX activities in plasma from two clam stocks displaying different susceptibility toward QPX disease in vivo demonstrated higher inhibition of QPX growth by plasma from New York (resistant) clams compared to Florida (susceptible) clams. Some clams appeared to be deficient in inhibitory factors, suggesting that such animals may become more easily infected by the parasite.

Cellular responses to in vitro exposures to ß-blocking pharmaceuticals in hard clams and Eastern oysters.

Increased consumption and improper disposal of prescription medication, such as beta (ß)-blockers, contribute to their introduction into waterways and may pose threats to non-target aquatic organisms. There has been rising concern about the impacts of these prescription drugs on coastal ecosystems, especially because wastewater treatment plants are not designed to eliminate them from the discharge. Few studies have characterized the sublethal effects of ß-blocker exposures in marine invertebrates. The overall aim of our research is to identify cellular responses of two commercially important filter-feeding marine bivalves, hard clams (Mercenaria mercenaria) and Eastern oysters (Crassostrea virginica), upon exposures to two ß-blocker drugs, propranolol and metoprolol. In vitro exposures with bivalve digestive gland and gill tissues were conducted where tissues were separately exposed to each drug for 24 h. Tissue samples were analyzed for cellular damage (lysosomal membrane destabilization and lipid peroxidation), total antioxidant capacity, and glutathione-s-transferase activity. Elevated damage and changes in enzyme activities were noted in the exposed tissues at environmentally relevant concentrations. Differences in species and tissue sensitivities and responses to exposures were also observed. These studies enhance our understanding of the potential impacts of prescription medication on coastal organisms. Additionally, this work demonstrates that filter-feeders may serve as good model organisms to examine the effects of unintended environmental exposures to ß-blockers. These studies are part of our ongoing work aimed at evaluation of sublethal biomarkers of pharmaceutical exposures and identification of key events that can contribute to the development of adverse outcome pathways (AOPs).

Brevetoxins, like ciguatoxins, are potent ichthyotoxic neurotoxins that accumulate in fish.

Brevetoxins and ciguatoxins are closely related potent marine neurotoxins. Although ciguatoxins accumulate in fish to levels that are dangerous for human consumption, live fish have not been considered as potential sources of brevetoxin exposure in humans. Here we show that, analogous to ciguatoxins, brevetoxins can accumulate in live fish by dietary transfer. We experimentally identify two pathways leading to brevetoxin-contaminated omnivorous and planktivorous fish. Fish fed with toxic shellfish and Karenia brevis cultures remained healthy and accumulated high brevetoxin levels in their tissues (up to 2675 ng g(-1) in viscera and 1540 ng g(-1) in muscle). Repeated collections of fish from St. Joseph Bay in the Florida panhandle reveal that accumulation of brevetoxins in healthy fish occurs in the wild. We observed that levels of brevetoxins in the muscle of fish at all trophic levels rise significantly, but not to dangerous levels, during a K. brevis bloom. Concentrations were highest in fish liver and stomach contents, and increased during and immediately following the bloom. The persistence of brevetoxins in the fish food web was followed for 1 year after the K. brevis bloom.

Inter- and intra-annual variations of Pb/Ca ratios in clam shells (Mercenaria mercenaria): a record of anthropogenic lead pollution?

In this study, we re-assess the use of bivalve shells as a proxy of lead pollution. Previous studies have stressed that shells display little variability compared to soft tissues and thus are better for pollution biomonitoring. However, in this manuscript we illustrate that there is large inter- and intra-annual Pb variability between shells of the clam Mercenaria mercenaria collected in North Carolina, USA. Therefore, year to year, as well as intra-annual variations in Pb/Ca ratios should be interpreted with caution. Despite this variability, we were able to obtain an annual Pb chronology from 1949 to 2002 using 11 shells collected at different times which clearly exhibited the late 1970's peak in Pb from leaded gasoline use. This indicates that when enough specimens are pooled together, bivalve shells can be used to reconstruct large, long term changes in environmental Pb concentrations. Our data compare well with other studies of aragonite clams from sites with low regional lead pollution. From this we conclude that the Cape Lookout region of North Carolina has not received extensive pollution over the 1949-2002 period. The Pb concentration in shells growing in the 1949-1976 period was not significantly different from those growing in the 1982-2002 period, although other proxies suggest that the 1949-1976 period should be considerably higher. Therefore, our data suggest that there is still a modern low-level source of Pb in the coastal North Carolina environment.

Effect of cooling rates and temperatures on quality and safety of quahog clams (Mercenaria mercenaria).

The model ordinance in the National Shellfish Sanitation Program's Guide for the Control of Molluscan Shellfish was initially established for oysters; however, the clam industry also follows the protocol. Rapid cooling during periods when the growing waters exceed 80 °F (26.7 °C) results in cold shock, which causes unacceptable mortalities in clams. The clam industry was looking for a procedure to lower the clams to the standard temperature while minimizing shell shock mortalities during the warm summer months. Three tempering treatments were examined, and total aerobic plate counts (APCs) and most-probable-number (MPN) counts of Vibrio, V. parahaemolyticus, and fecal coliforms were enumerated. In treatment 1 (control), clams were harvested, held for 5 h at 90 °F (32.2 °C), and then moved to 45 °F (7.2 °C) for storage. In treatment 2, clams were harvested and held for 5 h at 90 °F (32.2 °C), followed by 12 h at 65 °F (18.3 °C) and 12 h at 55 °F (12.8 °C), and then were moved to 45 °F (7.2 °C) for long-term storage. In treatment 3, clams were harvested and held for 5 h at 90 °F (32.2 °C), followed by 24 h at 55 °F (12.8 °C) before being moved to 45 °F (7.2 °C) for long-term storage. Three replicate trials were performed with triplicate analyses during late June through early to mid-August. The current National Shellfish Sanitation Program standard is treatment 1; it contained statistically (P ≤ 0.05) higher total APCs than treatments 2 and 3 throughout the 21-day storage period. APCs ranged from 2.3 × 10(4) immediately after harvest to 2.7 × 10(6), 1.6 × 10(5), and 4.8 × 10(5) for treatments 1, 2, and 3, respectively, after 14 days of storage. A statistical analysis showed that treatments 2 and 3 had significantly lower total MPN per gram Vibrio than treatment 1 on day 7 but were equal to treatment 1 on days 1 and 14. MPN per gram for V. parahaemolyticus was statistically lower in treatments 2 and 3 than in treatment 1 on storage days 1 and 7. However, on day 14, treatment 3 was significantly lower than treatments 1 and 2. There was no statistical difference for fecal coliforms. The greatest mortality occurred in treatment 1 (87.4%), followed by treatment 2 (83.3%) and treatment 3 (66.0%). The outcome of this research clearly shows that treatments 2 and 3 can cool clams to a temperature of 45 °F (7.2 °C) without compromising quality or safety and can reduce the number of dead clams introduced into the marketplace.

Short-term acute hypercapnia affects cellular responses to trace metals in the hard clams Mercenaria mercenaria.

Estuarine and coastal habitats experience large fluctuations of environmental factors such as temperature, salinity, partial pressure of CO2 ( [Formula: see text] ) and pH; they also serve as the natural sinks for trace metals. Benthic filter-feeding organisms such as bivalves are exposed to the elevated concentrations of metals in estuarine water and sediments that can strongly affect their physiology. The effects of metals on estuarine organisms may be exacerbated by other environmental factors. Thus, a decrease in pH caused by high [Formula: see text] (hypercapnia) can modulate the effects of trace metals by affecting metal bioavailability, accumulation or binding. To better understand the cellular mechanisms of interactions between [Formula: see text] and trace metals in marine bivalves, we exposed isolated mantle cells of the hard clams (Mercenaria mercenaria) to different levels of [Formula: see text] (0.05, 1.52 and 3.01 kPa) and two major trace metal pollutants - cadmium (Cd) and copper (Cu). Elevated [Formula: see text] resulted in a decrease in intracellular pH (pHi) of the isolated mantle cells from 7.8 to 7.4. Elevated [Formula: see text] significantly but differently affected the trace metal accumulation by the cells. Cd uptake was suppressed at elevated [Formula: see text] levels while Cu accumulation has greatly accelerated under hypercapnic conditions. Interestingly, at higher extracellular Cd levels, labile intracellular Cd(2+) concentration remained the same, while intracellular levels of free Zn(2+) increased suggesting that Cd(2+) substitutes bound Zn(2+) in these cells. In contrast, Cu exposure did not affect intracellular Zn(2+) but led to a profound increase in the intracellular levels of labile Cu(2+) and Fe(2+). An increase in the extracellular concentrations of Cd and Cu led to the elevated production of reactive oxygen species under the normocapnic conditions (0.05 kPa [Formula: see text] ); surprisingly, this effect was mitigated in hypercapnia (1.52 and 3.01 kPa). Overall, our data reveal complex and metal-specific interactions between the cellular effects of trace metals and [Formula: see text] in clams and indicate that variations in environmental [Formula: see text] may modulate the biological effects of trace metals in marine organisms.

Microbial safety and consumer acceptability of high-pressure processed hard clams (Mercenaria mercenaria).

UNLABELLED: Littleneck hard clams (Mercenaria mercenaria) harvested from New Jersey coastal waters in the United States were high-pressure processed (HPP) in their shells using a 10 L high-pressure processing unit. A response surface (RS) methodology approach was used to optimize the pressure and time parameters for microbial inactivation caused by the high-pressure application. The total surviving microbial load in the hard clams was enumerated after processing at each experimental condition. The results indicated that log reduction in total plate count (TPC) due to high-pressure processing of hard clams was primarily a function of pressure. Pressure of at least 480 MPa was needed to achieve 1-log reduction in TPC in hard clams harvested from special restricted waters. In a parallel study, a panel of 60 regular raw clams consumers tasted both raw and processed hard clams that were harvested from approved waters and HPP at 310 MPa for 3 min. The consumers showed equal preference for processed and raw hard clams. Two subgroups of hard clam consumers were revealed; 1 group preferred the plumpness of the HPP clam and the other group preferred aroma of the unprocessed clam. Thus, plumpness and aroma may influence consumer acceptance of HPP hard clams. PRACTICAL APPLICATION: High-pressure processing has gained momentum as a processing technique that aids in retention of fresh appearance in foods. It holds promise as a method to process premium value food products while retaining quality attributes. Quantification of its impact on safety and consumer acceptance is critical for its acceptance and use in the food industry.