Effects of the dinoflagellate Karenia brevis on larval development in three species of bivalve mollusc from Florida

Abstract

The effects of Karenia brevis (Wilson clone) on larval survival and development of the northern quahog, Mercenaria mercenaria, eastern oyster, Crassostrea virginica and bay scallop, Argopecten irradians, were studied in the laboratory. Larvae were exposed to cultures of whole and lysed cells, with mean total brevetoxin concentrations of 53.8 and 68.9 μg L⁻¹, respectively. Survival of early (3-day-old) larvae was generally over 85% for all shellfish species at K. brevis densities of 100 cells ml⁻¹ or less, and not significantly different between whole and lysed culture. At 1000 cells ml⁻¹, survival was significantly less in lysed culture than whole culture for both M. mercenaria and C. virginica. Survival of late (7-day-old) larvae in all three species was not significantly affected by K. brevis densities of 1000 cells ml⁻¹ or less. At 5000 cells ml⁻¹, however, survival was reduced to 37%, 26% and 19% for A. irradians, M. mercenaria and C. virginica, respectively. Development of C. virginica and M. mercenaria larvae was protracted at K. brevis densities of 1000 cells ml⁻¹. These results suggest that blooms of K. brevis, and particularly their associated brevetoxins, may have detrimental consequences for Florida's shellfisheries by disrupting critical larval processes. Special attention should be paid to blooms of K. brevis where these shellfish occur naturally or where aquaculture and restoration activities are either ongoing or planned.

Introduction

Recurring and persistent harmful algal blooms have raised increasing concerns about the long-term effects on local fisheries, including critical species of bivalve shellfish (Shumway and Cucci, 1987; Shumway, 1990; Landsberg, 1996). The toxic dinoflagellate, Karenia brevis (=Gymnodinium breve) Hansen and Moestrup, causes periodic and extensive red tides along the south-central Gulf coast of Florida (Steidinger et al., 1995) and produces potent neurotoxins (=brevetoxins). These brevetoxins are lethal to fish and cause neurotoxic shellfish poisoning (NSP) in humans from the consumption of contaminated shellfish (Baden, 1988; Steidinger et al., 1998). At the same time, K. brevis blooms pose a potential threat to Florida's shellfish resources and growing bivalve aquaculture industry (Blake et al., 2000; Adams and Sturmer, 2004). Red tides occur more frequently during the summer and fall along the Florida west coast (Steidinger, 1975) at a time when native shellfish species are spawning (Barber and Blake, 1983; Hesselman et al., 1989). Shellfish populations could thus be exposed to K. brevis blooms at a critical stage in their life history, and the relative success or failure of recruitment could depend on whether there are detrimental effects of exposure to K. brevis on the developmental stages of affected shellfish species. We therefore examined the effects of the NSP-producing alga, K. brevis, on survival and development of larvae from three species of bivalve molluscs: the northern quahog (=hard clams) (Mercenaria mercenaria), the bay scallop (Argopecten irradians) and the Eastern oyster (Crassostrea virginica). We also sought to distinguish whether differences in survival were due to the dinoflagellate itself or its constituent toxins.