Project Report PR-95-09
Benthic Faunal Sampling Adjacent to Sand Island Ocean Outfall, Oahu, Hawaii, August 1994
Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay
Benthic infauna in the vicinity of the Sand Island Ocean Outfall were sampled at seven stations along the diffuser isobath in August 1994. Stations were located both within and on the boundary of the zone of initial dilution (ZID) and at distances of 1.2 to 2.0 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. Sediment oil and grease values were highest at reference station B2. Station B2 had significantly more nonmollusk individuals than all the other stations, and Station Z had significantly more individuals than Stations B6 and B1. No other differences among stations were significant. Station B2 had significantly more nonmollusk species than Stations B1, B3, and B6; Stations Z and B5 had significantly more species than Stations B1 and B3; and Station B4 had significantly more species than Station B1. No other differences among stations were significant. Therefore, there was no relationship between nearness to the diffuser and mean nonmollusk species richness. Most stations differed significantly from each other in mollusk abundance. Mollusk species richness was significantly greater at near-ZID station B5 and ZID station Z than at all other stations. This pattern is the reverse of that expected as a result of an impact related to the discharge of effluent from an outfall diffuser. Cluster analysis of nonmollusk species composition and abundance in 1994 produced a substantially different pattern from the analysis in 1993. In 1993, stations in closest geographic proximity to each other tended to be clustered together, as was the case in previous sampling years. In 1994, reference stations B1 and B6, which are most distant from each other, were grouped together; and 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 species richness of the crustacean component and not for other faunal components as in past years. The response patterns of benthic infauna near the Sand Island Ocean Outfall showed little indication of a strong influence by the diffuser effluent.