Undergraduate, Peer-Reviewed Science Journal
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Issue 1, June 1999 Alaskan Sea Otters and Toxic Algae Blooms: Researching Marine Predator-Prey Interactions Mary Patyten Earth Systems Science, CSU Monterey Bay patyten@jyi.org
Rikk Kvitek, a zoologist and researcher interested in how high-level predators react to algal toxins sequestered in prey items, has been involved in a long-term quest to answer these and related questions. In 1988, Kvitek conducted research to determine how captive sea otters (Enhydra lutris) would respond to toxic butter clams (Saxidomus giganteus), a favorite prey of otters in the wild. Butter clams can concentrate high levels of PSP toxin in their tissues, especially in the siphon area. Rikk first gave the otters non-toxic clams, followed by toxic clams. Behavioral changes were swift and significant when the otters were presented with the toxic clams. They ate less, often discarding the toxic siphons or the entire cracked clam. Did otters in the wild behave similarly? And more to the point, would the presence of toxic clams affect the distribution of the animals' recovering population? The sea otter was hunted to extinction in southeast Alaska by fur traders in the 18th and 19th centuries. In the mid-1960's, 402 otters from the northern reaches of Alaska were re-introduced to their southern habitat, and by 1987 the population there had grown to about 3,500 animals. Kvitek was one of the first researchers in the late 1980's to record the expanding population. This rapid expansion, and the pervasive presence of toxic butter clams throughout southeast Alaska, provided Kvitek with the perfect opportunity to set up a comprehensive study . Through observation of the animals, collection of discarded sea otter prey, and sampling prey in areas yet uninhabited by otters, Kvitek hoped to determine whether the foraging behavior and distribution of sea otters under natural conditions was mediated by clam toxicity. Did seasonal toxic algal blooms determine when and where sea otters settled and foraged? Kvitek applied for and received a National Science Foundation (NSF) grant (award 9726263) to fund the study. The grant paid for cruise time aboard the R/V Alpha Helix, a 133' research vessel based in Seward and run by the University of Alaska for the NSF. Kvitek and a team of researchers planned two cruises aboard the Helix to observe the animals in their natural setting. The first cruise, conducted during the summer of 1998, focused on likely sea otter habitat in southeast Alaska during the last weeks of July and early August.
In addition to gathering fundamental sea otter ecology data, the project provided an exciting platform for training students in field biology methods. Ten California State University, Monterey Bay undergraduate students and Moss Landing Marine Laboratories graduate students participated in the project, recording sea otter foraging behavior and collecting prey tissue samples. Using spotting scopes and field glasses, the teams observed and recorded the length of time otters spent underwater on each foraging dive, their hunting success rates, and the identity of their prey. After reviewing observations, Rikk and the research team dove with SCUBA gear to collect samples of otter prey items and discarded prey. These samples would provide concrete evidence of what the otters were - or were not - eating. Samples from each site were shipped to the Alaska State Department of Environmental Health Shellfish Program for PSP toxin testing.
One of their most exciting observation days came on their last day in Sea Otter Sound, as related by Earth Systems Science & Policy student Kate Thomas. "As we were about ready to wrap up our final day of observing from shore, a sea otter came in very close, and we observed him very definitely discarding parts. So I radioed the Helix NOT to pick us up ... this is why we came here, to find out if we would see this behavior! He [The otter] would nibble a butter clam, then throw it away. Huge amounts of tissue were being discarded, and its not like an otter to throw away food."The discarding behavior, which Rikk had observed in captive otters, would later be correlated with high levels of toxin in Sea Otter Sound clams.
Preliminary review of sample analysis data shows that otters were found foraging at sites with relatively non-toxic prey, with the exception of Sea Otter Sound. Sea otters were almost completely absent from sites where butter clam toxin levels paralleled or exceeded the toxin level in Sea Otter Sound clams. Rikk said the cruise was both productive and great fun. "Watching the research team coalesce and pull together as they got to know each other, and realize that they could actually work in the harsh environmental conditions of Alaska, was rewarding" he said. This NSF grant also funds a study on the effects of toxic prey on predatory marine shorebirds, such as black oystercatchers and marbled godwits in California. California State University, Monterey Bay students are collecting samples of marine bird prey items such as California mussels and mole crabs, and videotaping and recording feeding behavior. According to Rikk, "We still do not know the extent to which marine mammals and birds react to algal toxins in their natural setting, which is why I got the grant to study it. We now know that [sea] otters may alter their diet, and are able to detect and avoid ingesting lethal levels of PSP toxin. We know very little about other harmful algae bloom-related toxins and marine mammals, although it now looks as though we had quite a few sea lions die in our area this past spring as a result of domoic acid poisoning. This toxin came from blooms of toxic diatoms that were consumed by anchovies and then eaten by the sea lions."Although toxic algae blooms are often predictable seasonal occurances, the extent to which they affect the natural selection patterns or evolution of both predators and prey is not known. Rikk and his fellow researchers, concerned about the evident global increase in toxic algae blooms, are continuing to work towards understanding the relationships between toxic algae, prey and predators. Rikk Kvitek is currently on his second cruise through southeast Alaska studying sea otter feeding behavior while working on myriad other projects and teaching classes in marine science at CSU Monterey Bay.
Journal
of Young Investigators. 1999. Volume Two.
Copyright © 1999 by Mary Patyten and JYI. All rights reserved. |
JYI is supported by: The National Science Foundation, The Burroughs Wellcome Fund, Glaxo Wellcome Inc., Science Magazine, Science's Next Wave, Swarthmore College, Duke University, Georgetown University, and many others.