Hopkins Marine Station Student Paper

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Title: Field observations of Nucella emarginata: effects of temperature on feeding behavior
Student Author(s): Burrow, Tom
Faculty Advisor(s): Watanabe, Jim
Pages: 26
Location: Final papers Biology 175H
Date: June 2003
Abstract: I studied the effects of temperature stress associated with sun-exposure on feeding behavior in the carnivorous intertidal whelk, Nucella emarginata. Seventy individual whelks were marked and observed at each day-time low tide over a 3 week period at 2 wave protected sites at Hopkins Marine Station. Temperatures ranged from <15º C on cold, overcast days to >30º C on calm, sunny days. Temperatures of sun-exposed regions of each site averaged 7.5º C warmer than sun-protected regions, with the greatest differences on the warmest days. Most larger prey of N. emarginata (Balanus glandula and Mytilus californianus) were more abundant is sun-exposed regions while smaller prey species (Chthamalus spp.) were more abundant is sun-protected areas. Proportions of marked whelks that were feeding varied widely between 5 and 68% on days when exposed temperature was below 28º C. Above 28º C, however, percent feeding never exceeded 10% and declined as temperatures rose higher. Whelks that remained feeding in sun exposed areas at the higher temperatures fed predominately on larger, more valuable prey that can take several days to drill and consume, thus experiencing greater potential thermal stress. Whelks transplanted to a nearby site traveled farther than control whelks and sought appropriate shelter before the next low tide (avg. temp = 31.2º C). They remained more sedentary than controls for the week following transplant, after which they resumed foraging similar to the controls. These results suggest that N. emarginata is conservative in its response to high temperatures during low tide. The response does, however, limit the time available for feeding on larger prey. Consistently warmer temperatures could serve to shift the preferred prey species.