Using known and inferred life-history information, we estimated the dispersal potential of 501 polychaete species sampled during a 1998 monitoring study in the Southern California Bight. We tested the hypothesis that species having life-history traits that suggest long-distance dispersal will be encountered more frequently throughout the region than will species having life histories that suggest limited dispersal. When all 501 species and all 200 sampling sites were analyzed, occurrence frequency (percentage of sites at which a species was collected) was not significantly related to dispersal potential. When data from 53 shelf sites in the Channel Islands were analyzed separately from collections at 147 mainland-shelf sites, there was a significant positive relationship between dispersal potential and occurrence frequency at the island sites but not at the mainland sites. Of the 501 species, 119 were collected only at island sites, 98 were found only at mainland sites, and 284 were found at both island and mainland sites. The majority of the 'island only' species had life-history traits indicating low dispersal potential. In contrast, only 13 % of the 'mainland only' species were categorized as having low dispersal potential. The 'cosmopolitan' species had a broad range of dispersal potential. Models indicate that efforts to conserve biodiversity by establishing Marine Protected Areas (MPAs) must consider species' dispersal. In the shelf communities of the Southern California Bight, networks of small reserves that are located in existing areas of high diversity should succeed in the Channel Islands, where the majority of polychaete species tend to have limited dispersal potential. On the mainland shelf, however, designing effective MPAs will be more challenging due to the prevalence of species that have a greater potential for long-distance dispersal to or from unprotected sites.
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