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Abstract: Within estuaries of New York, USA, recurrent harmful brown tides (Aureococcus anophagefferens) have contributed toward the collapse of two major bivalve fisheries (bay scallop, Argopecten irradians and northern quahog or hard clam, Mercenaria mercenaria), while populations of the Atlantic slipper limpet Crepidula fornicata have persisted in the presence of these blooms. Rates of suspension feeding by C. fornicata and M. mercenaria in the presence of different strains of A. anophagefferens and wild brown tide blooms were quantified to assess the potential impact of brown tides on slipper limpet and hard clam populations. Slipper limpets were capable of clearing all strains of A. anophagefferens at biomass-specific rates similar to an ideal food source (Isochrysis galbana), whereas clearance rates of M. mercenaria fed toxic clones of A. anophagefferens were significantly lower than when fed I. galbana or non-toxic clones of A. anophagefferens (p <0.01). During brown tide blooms (104–106 cells mL −1) on the south shore of Long Island during 2008 and 2009, clearance rates of C. fornicata when fed bloom water were an order of magnitude greater than those of M. mercenaria (p <0.001). Finally, during mesocosm experiments, C. fornicata reduced bloom densities of A. anophagefferens (106 cellsmL−1) by an order of magnitude in 3–4 days, whereas densities of A. anophagefferens in mesocosms stocked with equal or greater biomasses of M. mercenaria were unchanged. These results demonstrate that C. fornicata can actively feed in the presence of A. anophagefferens and suggest that this species could serve as a top-down control of blooms in shallow, poorly flushed estuaries. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The hard clam is an economically important bivalve and is abundant along the East Coast of the US. The goal of this research was to evaluate the sensitivity of this test species as compared to that of other benthic and epibenthic organisms. Toxic effects of cadmium (inorganic metal), DDT (organochlorine pesticide), and fluoranthene (polycyclic aromatic hydrocarbon) exposure in sediments (10-day) and seawater (24-h) on juvenile (212–350-μm) hard clams Mercenaria mercenaria were determined. The aqueous 24-h LC50 values were 0.42mg/L cadmium (95% CL=0.35–0.45mg/L), 0.61mg/L DDT (95% CL=0.40–0.95mg/L), and 0.65mg/L fluoranthene (95% CL=0.44–1.23mg/L). Results of sediment toxicity tests indicated that the 10-day LC50 values were 1.66mg/kg cadmium (95% CL=1.21–2.28mg/kg), 5.8mg/kg DDT (95% CL=4.8–8.3mg/kg), and 1.75mg/kg fluoranthene (95% CL=1.38–2.09mg/kg). Based on comparisons to toxicity data for other marine species, these findings suggest that the juvenile clam is one of the more sensitive species to a variety of contaminants and may be a valuable indicator for potential sediment toxicity. [Copyright &y& Elsevier]

The fossil record of the interaction between the predatory whelk Sinistrofulgur and its dangerous hard-shelled bivalve prey Mercenaria in the Plio-Pleistocene of Florida was examined to evaluate the hypothesis that coevolution was a major driving force shaping the species interaction. Whelks use their shell lip to chip open the shell of their prey, often resulting in breakage to their own shells, as well as to their prey. Mercenaria evolved a larger shell in response to an intensifying level of whelk predation. Reciprocally, an increase in attack success (ratio of successful to unsuccessful attacks) and degree of stereotypy of attack position by the predator suggest reciprocal adaptation by Sinistrofulgur to increase efficiency in exploiting hard-shelled prey. A decrease in prey effectiveness (ratio of unsuccessful to total whelk predation attempts) and an increase in the minimum boundary of a size refuge from whelk predation for Mercenaria may indicate that predator adaptation has outpaced prey antipredatory adaptation. Evolutionary size increase in Sinistrofulgur most likely occurred in response to prey adaptation to decrease the likelihood of feeding-induced shell breakage and unsuccessful predation when encounters with damage-inducing prey occur, coupled with (or reinforced by) an evolutionary response to the whelk's own predators. Predator adaptation to Mercenaria best explains temporal changes in whelk behaviour to decrease performance loss (shell breakage) associated with feeding on hard-shelled prey; this behavioural change limits attacks on prey to when the whelk's shell lip is thickest and most resistant to breakage. Despite evidence of reciprocal adaptation between predator and prey, the contribution of Mercenaria to Sinistrofulgur evolution is likely only a component of the predator's response to dangerous bivalve prey. This study highlights the importance of understanding the interactions among several species in order to provide the appropriate context to test evolutionary hypotheses about any specific pair of species. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 409–436. [ABSTRACT FROM AUTHOR]

Development of coastal areas in Cape Cod has increased nitrogen (N) loading to the region''s estuaries. Nitrogen supply limits phytoplankton, the major food source of many filter-feeding bivalves living in the estuaries, including quahogs (Mercenaria mercenaria) and soft-shell clams (Mya arenaria). N enrichment may therefore affect growth rates of these shellfish by altering their food supply in the water column. In this study, food quantity, as measured by chlorophyll a as a proxy for phytoplankton, was found to be higher in estuaries subject to higher N load. The food quality in these estuaries, measured by the ratio of C to N, remained constant. Results of growth rate experiments on quahogs and soft-shell clams planted in three estuaries of different N load revealed that the shellfish grew fastest in estuaries where phytoplankton abundance was highest. Nitrogen stable isotope analysis confirmed that shellfish were consuming food from within their own estuaries, rather than food from an outside source. Therefore, it appears N load affected the growth rates of the shellfish primarily through causing changes in the quantity, rather than the quality, of the food supply. [Copyright &y& Elsevier]