Community structure of fish and macrobenthos at selected sites fronting Sand Island, Oahu, Hawaii in relation to the Sand Island Deep Ocean Sewage Outfall, 1990 - 1998 (NCEI Accession 0000177)

This report provides the results of nine years of an annual quantitative monitoring of shallow marine communities inshore of the Sand Island Ocean Outfall, Oahu, Hawaii. This monitoring effort focuses on benthic and fish community structure and is designed to detect changes in these communities. Marine communities offshore of Honolulu have received considerable perturbation over the last 100 years. Dumping of raw sewage in shallow water, which occurred from 1955 to 1977, was halted in 1978; however, point and nonpoint sources of pollution from both urban activities and industry continue. All of these disturbances may serve to obscure any impacts that may be caused by treated effluent discharged from the deep-ocean outfall. The marine communities show a considerable range in development that is probably related to historical impacts. Stations have been located to take advantage of these gradients. Analysis of the nine years of data showed that there has been no statistically significant change in any of the biological parameters measured in this study other than for the mean number of invertebrate species and numbers of individual invertebrates encountered per transect. In these cases the data for 1998 showed significantly greater numbers of species and individuals over other years. These changes are probably the result of higher than usual counts of the Christmas tree worm Spirobranchus giganteus corniculatus as well as just more invertebrate species present at most stations. All other measures of the communities in this study (i.e., percent coral cover, number of coral species, number of fish species, total number of fishes counted, and the biomass of fishes present at each station) showed no significant changes through the period of this study. Hurricane Iniki, which occurred in September 1992, impacted marine communities along the south shore of Oahu. Coral communities received considerable damage, especially at the westernmost study station. Recovery in these communities is evident from the six years of data collected since the storm. Thus far, this study has not detected a quantifiable negative impact from the operation of the Sand Island Ocean Outfall.