Project Report PR-97-06
Benthic Faunal Sampling Adjacent to Sand Island Ocean Outfall, Oahu, Hawaii, September 1996
Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay
Benthic fauna in the vicinity of the Sand Island Ocean Outfall was sampled at seven stations along the diffuser isobath in September 1996. 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 showed no evidence of a negative relationship. Mean nonmollusk abundance was significantly greater at Station B2 than at Stations B1 and B6, and mean nonmollusk taxa richness was significantly greater at Station B5 than at Station B1. Station B2 had significantly greater mean crustacean abundance than Stations B3, B1, and Z and greater mean number of crustacean taxa than all other stations. No other pairwise differences in stations for the nonmollusk or crustacean component of the benthic fauna were significant. 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 all other stations, and at reference station B2 than at reference station B1 and ZID station Z. Mean mollusk species richness was significantly greater at Stations B5 and Z, respectively located on the ZID boundary and within the ZID, as compared to all other stations, and significantly greater at ZID-boundary station B4 as compared to reference station B1. These patterns show no evidence of a negative effect of the diffuser effluent on mollusks. Cluster analysis of nonmollusk species composition and abundance showed two groupings of stations; one group consisted of two reference stations (B2 and B6), and the second group consisted of the four stations located near the diffuser outfall (B3, B4, B5, and Z). Station B1 was most different from all other stations in 1996. 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 the crustacean component 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.