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Simeone S.,Fondazione IMC Centro Marino Internazionale ONLUS | Simeone S.,CNR Institute for Coastal Marine Environment | Palombo L.,Fondazione IMC Centro Marino Internazionale ONLUS | De Falco G.,CNR Institute for Coastal Marine Environment
Journal of Coastal Research | Year: 2013

This study evaluates the reliability of the Short morphodynamic model by using experimental data on the wave climate, sediment budget, and topographic beach profiles of an embayed beach located in western Sardinia, Mediterranean Sea. Wave parameters, measured by an offshore buoy located to the NW of Sardinia were downloaded daily, from the Rete Ondamentrica Nazionale Web site. Beach elevation data were collected in 2005 and 2010, using a Differential Global Positioning System, to determine the volume of beach sediments. Three beach profiles were measured in the northern, central, and southern areas of the beach from September 2010 to May 2011 to investigate morphological variability. Grain-size and composition of beach sediments were determined. From 2005 to 2010, the sediment volume did not show any significant changes (14,200 m 3 and 13,800 m3, respectively). Sediments were sandy to gravelly, whereas the composition was siliciclastic. Morphological variability occurred in the swash zone, where the northern and southern profiles showed an opposite trend, in terms of changes in elevation. This was related to the longshore redistribution of sediments and occurred mainly during the autumn-winter season. The Short model revealed that, for 98% of the available data, Is Arutas assumed a "normal" or "transitional" morphodynamic state. The sediment remained constrained between the headlands, in accordance with the results of the Short model, which showed the assumed morphodynamic states did not implicate the transport of sediment outside the system. Experimental data confirmed that the Short morphodynamic model can be applied to studies on sediment exchange on embayed Mediterranean beaches. © 2013, the Coastal Education & Research Foundation (CERF).

Farina S.,CSIC - Center for Advanced Studies of Blanes | Farina S.,Fondazione IMC Centro Marino Internazionale Onlus | Arthur R.,Nature Conservation Foundation | Pages J.F.,CSIC - Center for Advanced Studies of Blanes | And 9 more authors.
Oikos | Year: 2014

Structural complexity strongly influences the outcome of predator-prey interactions in benthic marine communities affecting both prey concealment and predator hunting efficacy. How habitat structure interacts with species-specific differences in predatory style and antipredatory strategies may therefore be critical in determining higher trophic functions. We examined the role of structural complexity in mediating predator-prey interactions across several macrophyte habitats along a gradient of structural complexity in three different bioregions: western Mediterranean Sea (WMS), eastern Indian Ocean (EIO) and northern Gulf of Mexico (NGM). Using sea urchins as model prey, we measured survival rates of small (juveniles) and medium (young adults) size classes in different habitat zones: within the macrophyte habitat, along the edge and in bare sandy spaces. At each site we also measured structural variables and predator abundance. Generalised linear models identified biomass and predatory fish abundance as the main determinants of predation intensity but the efficiency of predation was also influenced by urchin size class. Interestingly though, the direction of structure-mediated effects on predation risk was markedly different between habitats and bioregions. In WMS and NGM, where predation by roving fish was relatively high, structure served as a critical prey refuge, particularly for juvenile urchins. In contrast, in EIO, where roving fish predation was low, predation was generally higher inside structurally complex environments where sea stars were responsible for much of the predation. Larger prey were generally less affected by predation in all habitats, probably due to the absence of large predators. Overall, our results indicate that, while the structural complexity of habitats is critical in mediating predator-prey interactions, the direction of this mediation is strongly influenced by differences in predator composition. Whether the regional pool of predators is dominated by visual roving species or chemotactic benthic predators may determine if structure dampens or enhances the influence of top-down control in marine macrophyte communities. © 2014 The Authors.

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