Toxic species of Pseudo-nitzschia are often present in great abundance in Louisiana coastal waters, including areas where there are oyster beds. Elsewhere, the toxin domoic acid has accumulated in bivalves (such as mussels and razor clams) that feed on Pseudo-nitzschia, causing human illness and death from amnesic shellfish poisoning (ASP), and leading to long closures of shellfish harvesting waters. At present, it is not known whether oysters feed on Pseudo-nitzschia or accumulate the toxin. There have been no known outbreaks of ASP in Louisiana, possibly because isolated cases have not been recognized, or levels of the toxin are not yet high enough, or oysters do not become toxic. However, the presence of Pseudo-nitzschia species in Louisiana waters and the likelihood that their abundance will increase as coastal eutrophication increases suggest that it is only a matter of time before an outbreak occurs if oysters can become toxic. In order to assess the possible threat to human health, the researcher will conduct feeding and toxin accumulation studies to determine whether oysters can filter, ingest, digest and accumulate domoic acid from toxic Pseudo-nitzschia species.