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Author for correspondence: Edson A. Vieira, Email: [email protected] *
Current Address: Departamento de Oceanografia e Limnologia, Universidade Federal do Rio Grande do Norte, Av Via Costeira Senador Dinarte Medeiros Mariz, 59014-002, Natal, RN, Brazil.
Introduction
Organisms living in the intertidal zone are under constant variation of abiotic and biotic factors (Raffaelli & Hawkins, 1996). Combined with desiccation (Somero, 2002), wave impact is one of the most important physical factors controlling the survival and morphology of intertidal organisms (Denny et al., 1985). Hydrodynamic forces can negatively affect growth of benthic invertebrates by reducing the foraging windows, resulting in less energy intake (Brown & Quinn, 1988). Other consequences of intense wave exposure on organisms inhabiting the rocky intertidal include damage and dislodgement (Dayton, 1971; Paine & Levin, 1981).
To avoid wave dislodgement, several adaptations have been selected in organisms living in the intertidal zone, including plastic responses of behavioural and morphological traits (Denny, 2006). Mobile invertebrates frequently exhibit behavioural strategies to minimize the impact of waves. Crabs can modulate their postures according to water flow, minimizing the risk of dislodgement (Martinez, 2001) while hermit crabs can actively choose shells of distinct morphology according to the wave action conditions (Argüelles et al., 2009). Sessile animals are exposed to wave impact during their whole lifetime and morphological attributes are selected to minimize the stress caused by the impact of waves on them, allowing their survival under variable regimes of wave exposure. For example, the feeding legs of barnacles are longer in calm waters for enhancing filtration rates, but shorten with wave exposure, being smaller in turbulent areas to remain erect and ensure filtration (Arsenault et al., 2001). Mussel shells are smaller and narrower in exposed sites, reducing the impact of hydrodynamic forces (Steffani & Branch, 2003). More sedentary animals may show morphological adaptations rather than specialized behaviours to cope with the abiotic pressure from harsh coastal environments. Sea stars, for example, can alter their body form in response to water flow resulting in reduced lift and drag, developing narrower arms and lighter bodies when transplanted from sheltered to exposed areas (Hayne & Palmer, 2013). Intertidal periwinkles have developed larger feet in higher hydrodynamic conditions in both laboratory flume experiments and field translocation experiments, indicating that phenotypic...