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Marine Ecology Progress Series

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MEPS 553:49-66 (2016)  -  DOI:

Quantifying the top-down effects of grazers on a rocky shore: selective grazing and the potential for competition

Diana E. LaScala-Gruenewald1,*, Luke P. Miller1,4, Matthew E. S. Bracken2, Bengt J. Allen3, Mark W. Denny1

1Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA
2Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, CA 92697, USA
3Department of Biological Sciences, California State University Long Beach, Long Beach, CA 90840, USA
4Present address: Department of Biological Sciences, San Jose State University, San Jose, CA 95192, USA
*Corresponding author:

ABSTRACT: The effect of grazers on the diversity, distribution, and composition of their principal food source has rarely been described for the high intertidal zone of rocky shores, a model system for studying the potential effects of climate change. Along rocky, wave-swept shores in central California, the microphytobenthos (MPB) supports diverse assemblages of limpets and littorine snails, which, at current benign temperatures, could potentially partition food resources in a complementary fashion, thereby enhancing secondary productivity. Two limpet species in particular, Lottia scabra and L. austrodigitalis, may partition components of the MPB, and are likely to affect the composition of the MPB on which they graze. In this study, we describe the composition, nutritional value (C:N ratio), and fluorescence (an index of chlorophyll density) of ungrazed, L. scabra-grazed and L. austrodigitalis-grazed MPB, each as a function of temperature. Fluorescence decreased with increased average daily maximum temperature for ungrazed MPB, but temperature had no discernible effects on either fluorescence or the composition of the MPB of grazed assemblages. L. austrodigitalis and L. scabra did not partition the MPB, and did not exhibit complementarity. Both species exhibited an ordered grazing scheme, in which limpets grazed down certain components of the MPB before others, and grazing increased the C:N ratio of the MPB, decreasing its nutritional value. Taken together, these results suggest that L. austrodigitalis and L. scabra may experience increased competition as warming temperatures reduce the available MPB.

KEY WORDS: Selective grazing · Intertidal zone · Biofilm · Microalgae · Microphytobenthos · Lottia · Limpets

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Cite this article as: LaScala-Gruenewald DE, Miller LP, Bracken MES, Allen BJ, Denny MW (2016) Quantifying the top-down effects of grazers on a rocky shore: selective grazing and the potential for competition. Mar Ecol Prog Ser 553:49-66.

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