THE BRITTLESTAR AMPHIODIA-URTICA - A CANDIDATE BIOINDICATOR

The ophiuroid Amphiodia urtica LYMAN is presently under study as a pot ential wastewater discharge indicator species from ocean outfalls in t he Southern California Eight. On the San Pedro Shelf, the maximum abun dance of A. urtica was found at depths from 30 to 100 m, and in sedime nt with a median grain size of 0.085 mm, 60-80% sand, 15-30% silt, 0-3 7% clay, and 0.2-0.5% TOC. The mean abundance of A. urtica fluctuated annually with a slight increase from 1977 through 1993. The hypothesis was posed that the distribution and abundance of A. urtica is not inf luenced by an ocean outfall and its operation on the San Pedro Shelf B ased on long-term (1977-1994) and intensive (2860 samples) sampling, t he hypothesis was rejected. However, the effect of the outfall is not clear because sediment bioassays from test stations and controls produ ced no significant differences in survivorship and growth of juveniles . Amphiodia presently occupies areas within the Zone of Initial Diluti on (ZID) where it was not found during the mid-1970s and early 1980s. While recognizing that A. urtica abundance responds to proximity to th e outfall, the mechanism for this response is still unclear. The appli cation of a single species as a bioindicator is not recommended, and m ost certainly not without fully assessing its role in community struct ure and function.