Sediment deposition and resuspension of particulate material are key factors in the functioning of coastal ecosystems. This paper reports the results of a study from February 2001 to June 2002 of a rocky sublittoral sponge community influenced by seasonal sand deposition. The largest impacts on the assemblages were a reduction in diversity, losses and substitution of species, and a shift from a relatively mature and stable community to a more unstable, less diverse community dominated by encrusting species more adapted to the local environmental conditions. These observations are consistent with studies that show that morphological diversity of sponge communities decreases when perturbation increases. Encrusting sponges such as Microciona sp. and Spirastrella decumbens were the most abundant and persistent throughout the study, followed by boring sponges of the genus Cliona. Massive species such as Haliclona caerulea, massive branching species such as Mycalesp., and cushion-shaped species such as Callyspongia californica were present only before deposition events. The general fluctuation in the patterns was consistent with the environmental conditions in this bay; the results suggest that the changes in the sponge assemblages may be due partly to great fluctuations in sediment deposition produced by a change in the direction of the dominant winds (from north to south) during the transition from the drought to the rainy season. This change provoked an increase in sedimentation/resuspension (up to 13 kg·m−2·d−1 in May 2001) and water movement in the zone, which were key factors influencing the structure and composition of sponge assemblages.
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Vol. 13 • No. 1