Wave exposure and prey size selection in an intertidal predator

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Effects of wave action on feeding rates and prey size selection of the intertidal snail Stramonita (= Thais) haemastoma (L.) common along the Louisiana shoreline of the Gulf of Mexico were studied. In laboratory wave simulators, numbers of oysters eaten and tissue mass consumed were reduced in comparison to controls, but size of prey selected was not affected. Handling times for and profits (g dry tissue/handling time) did not differ between oysters in wave simulators and control aquaria. Over both treatments, smaller oysters had shorter handling times but similar profits as large oysters. In field cage experiments at two exposed and two protected sites, wave exposure actually increased the number of oysters eaten, but not total tissue consumption. Electivity indices suggested this was because snails at exposed sites chose smaller prey. Thus, under laboratory conditions with continuous wave disturbance, feeding rates were reduced, but under variable field conditions snails maintained similar tissue consumption and possibly lowered risk of dislodgement by switching to smaller prey with shorter handling times. Although oyster and barnacle prey were more abundant at an exposed site, snails were significantly smaller than those at a protected site. Along with field results, these data suggest that neither decreased energy intake nor fewer available prey account for smaller predator size at the exposed site. Changes in intertidal predator foraging behavior caused by wave action and the role of prey size vs. profit may affect average predator size and the impact on prey populations. © 1990.

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Journal of Experimental Marine Biology and Ecology

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