The effect of UV radiation on habitat use of two species of intertidal fishes that inhabit the same pools but exhibit different activity levels and diets was measured: the highly active omnivorous Girella laevifrons and the cryptic carnivorous Graus nigra. Individuals of each species were acclimated to a tank divided in three sections with different illumination; no light (NL), ultraviolet light (UV) and white light (WL), and the time spent and number of visits to each section were recorded. Although both species preferred the NL section, G. laevifrons spent more time in UV and less time in WL compared with G. nigra; G. laevifrons also displayed higher number of visits to UV, suggesting a different tendency in space use in response to UV exposure in intertidal fishes.

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Summary:Predator impacts on intertidal community structure have been studied for rocky platforms, but intertidal boulder fields, a habitat with a greater extension and heterogeneity, have not yet been considered. Keeping in mind that disturbances are considered an important force in determining intertidal habitat diversity, the aims of this work were to describe and quantify boulder field community structure and to assess boulder field community dynamics by proposing possible food webs, taking into consideration predatory and anthropogenic impacts. These aims were achieved by installing predator-exclusion cages outfitted with rocks that were monitored monthly over one year in two study zones, a Management and Exploitation Area for Benthic Resources (MEABR, Playa Chica) and open-access area (OAA, Playa Grande). For both study zones, juveniles were the dominant observed ontogenetic state and invertebrate richness and density were higher inside exclusion cages. Furthermore, the MEABR had a differentiated impact on community structure and dynamics in comparison with the OAA. In conclusion, the roles played by boulder fields in intertidal diversity, especially in recruitment and as a nursery zone, are important to consider in management plans.Keywords: Management and Exploitation Areas for Benthic Resources; intertidal zone; boulder beaches; community structure; food web. Depredación e impacto antropogénico sobre la estructura comunitaria de playas de bolonesResumen: El impacto depredador sobre la estructura comunitaria intermareal ha sido estudiado para plataformas rocosas, pero no ha sido abordado en campos de bolones intermareales, un hábitat de mayor extensión y heterogeneidad. Considerando que las perturbaciones son una fuerza importante en determinar la diversidad del hábitat intermareal, los objetivos de este trabajo fueron describir y cuantificar la estructura comunitaria de campos de bolones, y evaluar la dinámica comunitaria de este hábitat proponiendo posibles tramas tróficas; considerando el impacto de depredadores y antropogénico. Estos objetivos se lograron mediante la instalación de jaulas de exclusión de depredadores equipadas con rocas, que fueron monitoreadas mensualmente durante un año en dos zonas de estudio, un Área de Manejo y Exclusión de Recursos Bentónicos (AMERB, Playa Chica) y un área de acceso abierto (AAA, Playa Grande). Para ambas zonas de estudio, los juveniles fueron el estado ontogenético dominante, y la riqueza y densidad de invertebrados fueron mayores dentro de las jaulas de exclusión. Además, el AMERB tuvo un impacto diferenciado sobre la estructura y dinámica comunitaria comparado al AAA. En conclusión, el rol que cumplen los campos de bolones en la diversidad intermareal, especialmente en el reclutamiento y área de crianza, son importantes y debiesen ser considerados en los planes de manejo.Palabras clave: Área de Manejo y Exclusión de Recursos Bentónicos; zona intermareal; playas de bolones; estructura comunitaria; trama trófica. Editor: E. Cebrián.