Abundance, population structure and claw morphology of the semi-terrestrial crab Pachygrapsus marmoratus (Fabricius, 178
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ORIGINAL PAPER
Abundance, population structure and claw morphology of the semi-terrestrial crab Pachygrapsus marmoratus (Fabricius, 1787) on shores of diVering wave exposure Ana Catarina Ferreira Silva · Sónia Brazão · Steve J. Hawkins · Richard C. Thompson · Diana M. Boaventura
Received: 12 March 2009 / Accepted: 11 August 2009 / Published online: 27 August 2009 © Springer-Verlag 2009
Abstract Wave action is known to inXuence the abundance and distribution of intertidal organisms. Wave action will also determine the duration and suitability of various foraging windows (high-tide and low-tide, day and night) for predation and can also aVect predator behaviour, both directly by impeding prey handling and indirectly by inXuencing prey abundance. It remains uncertain whether semiterrestrial mobile predators such as crabs which can access intertidal prey during emersion when the eVects of wave action are minimal, are inXuenced by exposure. Here, we assessed the eVect of wave action on the abundance and population structure (size and gender) of the semi-terrestrial intertidal crab Pachygrapsus marmoratus on rocky
Communicated by S. D. Connell. A. C. F. Silva (&) · R. C. Thompson Marine Biology & Ecology Research Group, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK e-mail: [email protected] A. C. F. Silva · S. J. Hawkins Marine Biological Association of the United Kingdom, Citadel Hill, Plymouth PL1 2PB, UK S. Brazão · D. M. Boaventura Laboratório Marítimo da Guia, Centro de OceanograWa da Faculdade de Ciências da Universidade de Lisboa, Avenida Nossa Senhora do Cabo, no. 939, 2750-374 Cascais, Portugal S. J. Hawkins School of Ocean Sciences, Bangor University, Menai Bridge, Ynys Mon LL59 5AB, Wales, UK D. M. Boaventura Escola Superior de Educação João de Deus, Av. Álvares Cabral, 69, 1269-094 Lisbon, Portugal
shores in Portugal. The activity of P. marmoratus with the tidal cycle on sheltered and exposed shores was established using baited pots at high-tide to examine whether there was activity during intertidal immersion and by low-tide searches. Because prey abundance varies along a wave exposure gradient on most Portuguese shores and because morphology of crab chelipeds are known to be related to diet composition, we further tested the hypothesis that predator stomach contents reXected diVerences in prey abundance along the horizontal gradient in wave exposure and that this would be correlated with the crab cheliped morphology. Thus, we examined phenotypic variation in P. marmoratus chelipeds across shores of diVering exposure to wave action. P. marmoratus was only active during lowtide. Patterns of abundance and population structure of crabs did not vary with exposure to wave action. Stomach contents, however, varied signiWcantly between shores of diVering exposure with a higher consumption of hardshelled prey (mussels) on exposed locations, where this type of prey is more abundant, and a higher consumption of barnacles on sheltered shores. Multivariate geometric analysis of crab claws showed that claws w
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