A survey of selected coral and fish assemblages near the Waianae Ocean Outfall, Oahu, Hawaii, 1994

In 1994, coral growth and fish abundance were monitored at stations located at and in the vicinity of the Waianae Ocean Outfall. This report summarizes the results of that survey and comparatively analyzes the data with data collected in previous sampling years. From 1986 to 1994, no significant differences were seen in the species composition or relative abundances of fish populations at Station W-2 (the sunken ship Mahi), which is located 1.2 km south of the diffuser. However, from 1986 to 1994 fish abundance and species richness increased at Station W-3, which is located at the diffuser. At Station WW, which is located 1 km from shore, fish were abundant near and on the armor rock covering the pipeline. Fish species at all stations were essentially the same as those seen in similar natural biotopes around Hawaii. As for coral growth, no significant differences were seen in total mean coral cover at selected quadrats from 1993 to 1994 or for previous years at Station W-2. At Station W-3, corals were seen growing on the diffuser pipe and on the riser discharge ports. In 1986, when the diffuser began operation at a discharge rate of 1.5 mgd, no corals were seen at this location. At inshore station WW corals seen off the pipeline were sparsely distributed, but on the armor rock over the pipeline both corals and fishes were numerous and thriving. Station WW, a new station set up in 1994, replaces Station W-4, which was located near the diffuser in the artificial fish haven. Station W-4 was not surveyed because in 1992 Hurricane Iniki covered the bottom with coarse sand. The water was clear (10- to 16-m horizontal visibility) at all stations surveyed, and the surrounding sediments were clean and white. No significant deleterious effects resulting from outfall operation and discharge were seen on the biological community at the stations surveyed.