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Rare Species as Bioindicators in Marine Monitoring





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Soft-bottom invertebrates commonly form the core of marine moni- toring studies. Accordingly, those species which occur frequently and abundantly are favored in analyses, and rare species are normally excluded from consider- ation. Since rare species commonly occur at their geographic limits under sub- optimal conditions, it has been postulated that they would be vulnerable to natural and anthropogenic stresses. We examined the potential of rare species as bioin- dicators in monitoring a major marine outfall on the San Pedro Shelf, California. A rare species was operationally defined as occurring only once per sample (0.1m 2 Van Veen Grab). Based on 780 quantitative benthic samples, distributed over thirteen 60 m (outfall depth) stations, and 12 years, we concluded that the number of rare species generally declined towards outfall stations. We suggested that a more conventional definition of rarity based on actual geographic range might provide an increased degree of sensitivity to identify bioindicators.