Comparing macroalgal food and habitat choice in sympatric, tube-building amphipods, Ampithoe lacertosa and Peramphithoe humeralis |
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Authors: | P Sean McDonald Brian L Bingham |
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Institution: | (1) School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195-5020, USA;(2) Department of Environmental Sciences, Western Washington University, Bellingham, WA 98225-9160, USA |
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Abstract: | For small tube-building amphipods that live on the algae they consume, food and habitat are tightly linked. This study compared
two closely related amphipods to determine whether the species’ algal preferences are based on the food value of the algae
or on some other aspect of their algal habitat. Ampithoe lacertosa and Peramphithoe humeralis are both abundant on Shannon Point beach (Anacortes, Washington, USA; 48°30.542′ N, 122°41.070′ W) but specialize on different
algae. In observations and laboratory experiments conducted July–September 1997, 2007, and 2008, the two species exhibited
markedly different choices of food and habitat when offered six common macroalgae. Ampithoe
lacertosa ate all algae offered, but preferentially built tubes on the green alga Ulva
lactuca. Survival was relatively low among juveniles maintained on single species diets, except when they were fed Mazzaella splendens. Conversely, P.
humeralis consumed primarily the brown kelp Saccharina latissima, Alaria
marginata, and Desmarestia
ligulata and preferred those species for tube building. Juvenile P.
humeralis could not survive on a diet of U.
lactuca or M. splendens. While A.
lacertosa builds simple, temporary tubes and relocates frequently, P.
humeralis is a highly thigmotactic species that builds long-term, complex tubes on the alga it prefers to eat. Feeding and habitat
preferences of the two species were not clearly linked to nitrogen content of the algae, C:N ratio, or toughness of the algal
tissue. Instead, preferences of the species may be related to their mobility and the permanence of the tubes they build. Ampithoe
lacertosa and P.
humeralis also use different feeding strategies; the former appears to mix algae to produce a high-quality diet, while the latter is
more selective and has a capacity for compensatory feeding. The species are abundant on the same protected rocky shores, but
specialize on different algae for habitat and food. Results suggest that the nutritional requirements of these sympatric mesograzers
differ considerably and even closely related species can exhibit divergent behavioral strategies. |
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