The production of toxic compounds by phytoplankton and their subsequent transfer through marine food webs can have fatal consequences for both human consumers and marine predators. This dissertation examines the potential accumulation of toxins produced by dinoflagellates within the genus Alexandrium in marine food webs using both field collected samples and laboratory experiments. In particular, chapter one documents a dramatic change in the taxonomic structure of the phytoplankton community that occurred during the summer of 2004 in Monterey Bay, California—a change that resulted in a shift in the dominant toxin-producing species and the phycotoxins present in the food web. After the shift from a typically diatom-dominated system to a more red-tide, dinoflagellate-dominated system, Alexandrium catenella became more prevalent and the toxins produced by this species, paralytic shellfish toxins (PSTs), were detected in sentinel shellfish more frequently. Chapter two presents results from two laboratory feeding trials designed to investigate the uptake of PSTs and spirolides, two independent groups of toxins derived from A. catenella and A. ostenfeldii, in paddle crabs (Ovalipes catharus) using Greenshell mussels as a vector. Both PSTs and spirolides were detected in the hepatopancreas of paddle crabs, but not in the gills or the mussel tissue. These experiments demonstrated that paddle crabs can acquire these toxins rapidly, reaching dangerous PST concentrations after only 5 days of feeding on toxic mussels, and that uptake of PSTs and/or spirolides could occur in nature when toxic shellfish are present. Chapter three gives the results of a 3-year field study that examines 11 species of commercially harvested finfish and 2 species of rock crab in Monterey Bay for the presence of PSTs and compares the toxin levels in them to the density of A. catenella and concentration of PSTs in the water column. When A. catenella was present, PSTs were detected in 6 species not previously known to acquire PSTs in the region, but most frequently in sardines (Sardinops sagax), anchovies (Engraulis mordax), brown rock crabs ( Cancer antennarius) and red rock crabs (C. productus). Lastly, Appendix A presents toxin and sequence data derived from clones of A. catenella isolated from different regions of the California coast. No distinctive regional pattern was observed between isolates based on either cellular toxin measurements or large subunit ribosomal DNA sequences.
|Advisor:||Silver, Mary W.|
|School:||University of California, Santa Cruz|
|School Location:||United States -- California|
|Source:||DAI-B 69/05, Dissertation Abstracts International|
|Subjects:||Microbiology, Biological oceanography|
|Keywords:||Alexandrium catanella, California, Harmful algal bloom, Marine toxins, Monterey Bay, Paralytic shellfish poisoning, Red tide|
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