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A Survey Of Selected Coral And Fish Assemblages Near The Waianae Ocean Outfall, O'Ahu, Hawai'I, 2004
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2005
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Series: Project Report PR-2005-05
[PDF-1.41 MB]
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Description:In 2004, coral growth and fish abundance were monitored at stations located at and in the vicinity of the Waianae Ocean Outfall. Fish abundance at diffuser station W-3 was 135 individuals representing 23 species. Station W-2, which was a control station in the past, was replaced by Station Z in 2003. This new station (Z), which is located inside the area of fish haven obstructions (artificial reef) controlled by the Hawai'i Department of Land and Natural Resources (DLNR), is approximately 1.0 km southeast of the diffuser at a depth of 16 m. Station W-2 was replaced because of the dangerous deterioration of the sunken ship Mahi at this station. A total of 307 individuals were seen at Station Z, along both transects combined, with 24 species (195 individuals) at Transect 1 and 17 species (112 individuals) at Transect 2. This was an increase from 2003 values. At Station WW, an inshore station located 0.8 km from shore, fish abundance was high, with a total of 1,231 individuals representing 38 species on both transects combined. On the pipeline armor rocks at Station WW, fish aggregated in large numbers, probably due to the artificial relief provided by the rocks. There were large numbers of Lutjanus kasmira (ta'ape) and Abudefduf abdominalis, which are intense competitors for food resources. At this station very large numbers of the damselfish Chromis ovalis were also seen; they accounted for 37% of the total abundance and the large increase in abundance seen in 2004 vs. 2003. The fish species seen inshore are comparable to those seen in similar (boulder) natural biotopes around Hawai'i. Permanent coral quadrats were set up at Station Z and photographed for coral cover. Coral cover at five selected quadrats ranged from 8% to 58%. At the diffuser, 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 (0.07 m3/s), no corals were seen at this location. At inshore station WW, corals were sparsely distributed off the pipeline but were numerous and thriving on the armor rock over the pipeline. In 2003, the inshore transect (Alpha), off the armor rock, was covered (approximately 20%) with the alga Dictyopteris plagiogramma. In 2004, no algal cover was seen. The water was clear at all stations surveyed (12 to 15 m horizontal visibility), and the surrounding sediments were clean and white. The high abundance and diversity of fish indicate that no serious effects are caused by the outfall operation and discharge on the biological community at the stations surveyed. There continues to be no evidence that the Wai'anae outfall is adversely affecting the abundance or diversity of fishes and corals at the selected survey stations in the vicinity of the effluent discharge.
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Sea Grant Document Number:HAWAU-S-05-001
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Rights Information:Public Domain
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