Project Report PR-96-07
Benthic Faunal Sampling Adjacent to Sand Island Ocean Outfall, Oahu, Hawaii, August 1995
Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay
March 1996
ABSTRACT
Benthic fauna in the vicinity of the Sand Island Ocean Outfall was sampled at seven stations along the diffuser isobath in August 1995. Stations were located both within and on the boundary of the zone of initial dilution (ZID) and at distances of 1.2 to 2 km from the ZID boundary. Values for total organic carbon, total Kjeldahl nitrogen, and oxidation-reduction potential showed no indication of significant organic buildup in sediments at any station. Correlations between sediment oil and grease from Sand Island samples and both crustacean abundance and species richness were not significant. Mean nonmollusk abundance and crustacean abundance did not differ significantly among stations. Mean nonmollusk species richness was not significantly different among stations. Mean crustacean species richness was significantly lower at Station B3 as compared only to reference station B1. Therefore, there was no general relationship between nearness to the diffuser and mean nonmollusk or crustacean species richness. Mean mollusk abundance was significantly greater at Station B4, located on the ZID boundary, than at reference station B1 or Station B5, located near the ZID. Mean mollusk species richness was highest at Stations B5 and Z, located either on the ZID boundary or within the ZID, as compared to most other stations. These patterns are the reverse of those expected as a result of an impact related to the diffuser effluent. Cluster analysis of nonmollusk species composition and abundance showed two groupings of stations; the three reference stations formed one group and the four stations near the diffuser formed a second group. In 1994, reference station B2 was grouped with the ZID and near-ZID stations. There was no pattern of lower diversity or evenness for either nonmollusk or mollusk groups at ZID or near-ZID stations relative to the other stations. The long-term pattern of lower species richness at Station B3, as compared to the other stations, was observed only for crustacean species richness and not for other faunal components. The response patterns of benthic fauna near the Sand Island Ocean Outfall showed little indication of a strong influence by the diffuser effluent.