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Long-term effects of beach nourishment on intertidal invertebrates


Although beach nourishment is an increasingly popular means to remediate coastal erosion, no consensus exists regarding how long nourishment affects sandy beach intertidal invertebrates, key components of sandy beach ecosystems. We monitored the intertidal invertebrate community for fifteen months following a nourishment project at eight beaches across San Diego County. Each beach was split into nourished and control sections. Nearly all taxa showed major declines in abundance immediately following nourishment. Populations of Talitrid amphipods and the bean clam Donax gouldii recovered within one year, sooner than in previous studies. Populations of the mole crab Emerita analoga bloomed at four months after nourishment, and were more numerous on nourished portions of beaches at that time. Mole crab populations subsequently declined and no longer differed by treatment. The polychaete community, composed of Scolelepis spp. and several other numerically important taxa, showed a strong nourishment-induced reduction in abundance that persisted through the end of the study. The large negative effect of nourishment on polychaetes, coupled with their overall importance to the invertebrate community, resulted in a more than twofold reduction in overall invertebrate abundance on nourished beaches at 15 months. Such reductions may have far reaching consequences for sandy beach ecosystems, as community declines can reduce prey availability for shorebirds and fish. As this and other recent studies have revealed longer times for the recovery of intertidal invertebrates than previously observed, more cautious estimates regarding the magnitude and duration of impacts of beach nourishment should be applied to management practices

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