Review of impacts of contaminated sediment on microfaunal communities in the Southern California Bight

Abstract

A comparison of foraminiferal faunal trends in pristine and impacted regions on the continental shelf and slope of the Southern California Bight, as well as variations in the temporal foraminiferal distribution patterns from 1955 to 1998, suggest that the benthic microfaunal communities have been greatly affected by the presence of contaminated sediment near the major outfall sites. Six species were most impacted: Trochammina pacifica, Bulimina denudata, Eggerella advena, Buliminella elegantissima, Nonionella stella, and Nonionella basispinata. The silver contaminant-tolerant and organic-waste indicating species Trochammina pacifica and Bulimina denudata dominated the outfall regions in the mid-century but declined in abundance in the 1990s after sewage treatment and sludge disposal activities improved. Over the same time period, the abundance of Eggerella advena, a pioneer colonizer of formerly impacted waste-discharge sites tolerant of most trace-metal and organic contaminants, increased dramatically on the shelf, whereas Buliminella elegantissima, a nitrogen-favoring taxon, dominated the nearshore regions except at the pristine site. In contrast, the contaminant-sensitive species Nonionella stella and Nonionella basi-spinata dominated the shelf assemblages in pristine to low-impacted areas in the late 1950s and early 1960s but were rare to absent near the outfalls, even after remediation efforts were put into effect. Although most other species patterns, as well as the amphipod survival and sea urchin fertilization tests, show that the enhanced sewage treatment programs improved sediment conditions, the inability of Nonionella stella and Nonionella basispinata to reinhabit formerly colonized areas suggests that not all faunal trends have returned to pre- or early-outfall levels even with remediation. The sensitivity of foraminifers to the presence of contaminated sediments suggests that they are a useful tool in evaluating the impact of anthropogenic contamination on microfaunal communities.