Long-term changes in the benthic community on the coastal shelf of Palos Verdes,Southern California

Between 1972 and 1982, both wastewater discharge and natural perturbations played important roles in directing marine benthic community structure on the Palos Verdes Shelf in Southern California, USA. Community succession was traced along a gradient of eleven 60 m-depth stations extending from the submarine outfalls. Spatial and temporal biological patterns were identified via direct gradient, clustering and principal-coordinates analyses. Species associations which occupied sites distant from the outfalls in the early 1970s gradually became established closer to the diffusers during the decade. The areal extent of outfall impacts shrank, reflecting both improvements in effluent quality and co-occurring beneficial natural events, specifically the short-term settlement of large numbers of the echiuran Listriolobus pelodes.