Project Report PR-96-01
A Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii, 1995
Anthony R. Russo
August 1995
ABSTRACT
In 1995, 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 1995, 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 outfall diffuser. However, from 1986 to 1995 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 and speciose on the armor rock covering the pipeline. The fish species seen in 1994 were present in 1995, along with the 13 new species recorded at this station. These species 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 1994 to 1995 at Station W-2. However, there was a significant increase (5.2%) in total mean coral cover at selected quadrats from 1991 to 1995. 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 corals were numerous and thriving. The inshore transect (Alpha), off the armor rock, was heavily covered (60% to 70%) with the alga Dictyopteris plagiogramma. This alga was sparse when seen at this location in 1994. The water was clear (10- to 15-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.