PH22 Large-Scale Investigations of Contaminated Sediments
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(PH247) Benthic invertebrate condition in coastal southern California.

Ranasinghe, J1, Montagne, D2, Smith, R3, Mikel, T4, Weisberg, S1, Cadien, D2, Velarde, R5, Dalkey, A6, 1 Southern California Coastal Water Research Project, Westminster, CA, USA2 County Sanitation Districts of Los Angeles County, Whittier, CA, USA3 PO Box 1537, Ojai, CA, USA4 Aquatic Bioassay and Consulting Laboratories, Ventura, CA, USA5 City of San Diego EMTS Laboratory, San Diego, CA, USA6 City of Los Angeles, Environmental Monitoring Division, Playa del Rey, CA, USA

ABSTRACT- Large spatial scale investigations of benthic invertebrate condition depend on (1) sampling schemes representative of the entire area and sub-populations of interest, and (2) the availability of measures to assess benthos in all habitats on the same scale. Southern California benthic condition was assessed in 1998 by random tessellation stratified sampling and evaluating benthic invertebrate condition using the Benthic Response Index (BRI) approach. The BRI is the abundance-weighted pollution tolerance score of species present in a sample; it has thresholds associated with five levels of condition ranging from reference to defaunation. We sampled the mainland and island shelves and coastal bays of the Southern California Bight (SCB). Our results indicated that benthic invertebrates in 98.05% of the SCB were in reference condition or deviated only marginally from reference; disturbed communities occupied only 107 km2. The island shelf was in best condition (0% disturbed area), the bays in worst condition (17.09% disturbed area), and the mainland shelf in intermediate condition (2.27% disturbed area). The severity of disturbance was also higher in bays than in other habitats. Bays occupied only 4.3% of the area of the SCB but contributed 37.4% of the area with disturbed benthos. Within the bays, the extent of disturbed benthic communities was greater at marinas and ports than areas subject to other uses.

Key words: benthic response index, benthic invertebrate condition, southern california bight, bay port marina continental shelf

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