Radiotracer studies on the feeding of two marine bivalves on the toxic and nontoxic dinoflagellate Alexandrium tamarense

Harmful algae are found to have significant impact on the feeding activity of bivalve mollusks. Previous studies on the particle selectivity of bivalves only focused on particles with contrasting sizes, fluorescence, or chlorophyll a contents. If bivalves are capable of selectively ingesting particles based on their paralytic shellfish (PSP) toxin content is still poorly known, probably due to the lack of a reliable monitoring technique. In this study, we employed a radiotracer technique to determine the selective feeding behavior of the mussel Perna viridis and the clam Ruditapes philippinarum on an algal mixture containing both toxic and nontoxic Alexandrium tamarense (same algal species, but different clones). The toxic and nontoxic algal cells were radiolabeled with ¹⁰⁹Cd and ⁷⁵Se, respectively, and then presented to the bivalves in a mixture. The radioactivity remaining in the algal cells was used to calculate the clearance and ingestion rates (IRs) of the bivalves. Both bivalves had comparable clearance rates (CRs) and ingestion rates of both toxic and nontoxic A. tamarense. Selective ingestion of toxic and/or nontoxic alga in the algal mixture was not observed, indicating that the two bivalves were unable to distinguish the particles with different PSP toxin contents. Our study demonstrates that the dual radiotracer technique can be applied to study particle selection by marine bivalves based on the PSP toxin content of algal particles. © 2001 Elsevier Science B.V. All rights reserved.