April 29 2009

12:00 LSB 2320

Rikk Kvitek
Division of Science and Environmental Policy, Californiat State University, Monterey Bay

Mediation of the foraging behavior, spatial distribution and ecological influence of sea otters and shorebirds by harmful algal bloom


Here I will present evidence from a series of investigations suggesting that partial predation by siphon-nipping fish may have selected for sequestration of paralytic shellfish poisoning toxins (PSPT) in butter clam (Saxidomus spp.) siphons, and that once acquired, this defense mediates predation by other species (sea otters and shorebirds) thereby altering the ecological influence of these high-level predators in regions where blooms of toxic dinoflagellates occur. I will describe in greater detail testing of the general hypothesis that the foraging behavior and distribution of sea otters and shorebirds under natural conditions are mediated by benthic prey toxicity due to harmful algal blooms (HABs). Sea otters in southeast Alaska did change their foraging behavior at sites where Butter Clams (Saxidomus giganteus) were found to contain paralytic shellfish poisoning toxins (PSPT) in high concentrations. At the most toxic sites Sea Otters shifted their diet away from their primary Butter Clam prey to smaller and less abundant non-toxic species. At sites of intermediate prey toxicity some Sea Otters continued to forage on Butter Clams while discarding the most toxic body parts. In California, observed changes in shorebird feeding behavior (mainly Oystercatchers, Willets, Godwits and Whimbrels) was correlated with seasonal changes in PSPT in their primary prey, sea mussels (Mytilus californianus) and mole crabs (Emerita analoga). In rocky habitats where mussel toxicity exceeded 150mgSTX/ 100g, Oystercatchers significantly increased their consumption of limpets as well as their discard rate of mussel tissue. In sandy beach habitats where Emerita toxicity exceeded 150mgSTX/ 100g, shorebird abundance decreased significantly, while their rejection rate of Emerita prey increased significantly. We conclude that these predators reduce their exposure to PSP toxins during HAB events through a variety of behavioral responses including: changing their diet, discarding toxic prey and/or avoiding affected areas. These responses may account for the rarity of sea otter and shorebird mortality due to HABs, and result in HAB toxins providing a refuge from predation for some prey populations.















































































































































































































































































































































































































































































































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