Project Report PR-95-01
Benthic Faunal Sampling Adjacent to Barbers Point Ocean Outfall, Oahu, Hawaii, January – February 1994
Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay
Benthic infauna in the vicinity of the Barbers Point Ocean Outfall were sampled at seven stations on 31 January and 12 and 13 February 1994 with a modified Van Veen grab sampler. The stations were located along the diffuser isobath (61 m) as follows: Station HZ within the zone of initial dilution (ZID), Stations HB2, HB3, and HB4 on the ZID boundary, Station HB6 at 0.5 km from the ZID, and Stations HB1 and HB7 at 3.5 km from the ZID. For the four stations for which sediments grain sizes were analyzed, sediments were predominantly (>91%) fine to coarse sands. Station HB7 had relatively coarser sediments than the other stations. Values for total organic carbon in the sediments at all stations were lower in 1994 than in 1993. The difference is believed to be due to problems experienced with the analytical techniques in 1993. Values for total organics were not elevated at stations in or near the ZID. Values of oxidation-reduction potential showed no indication of significant organic buildup in sediments at any station. A total of 6,246 nonmollusk individuals representing 159 taxa were collected. Polychaetes comprised 43%, nematodes 17.6%, oligochaetes 11.6%, and crustaceans 17.9% of total nonmollusk abundance. Nonmollusk densities ranged from 140.8 individuals per sample (31,032/m2) at Station HB7 to 211.8 individuals per sample (46,680/m2) at Station HB4. Mean crustacean abundances ranged from 13.2 (2,909/m2) at Station HZ to 53.6 (11,813/m2) at Station HB7. Mollusks were analyzed separately because they represented time-averaged collections of live and dead shells. Mollusk densities ranged from 129.8 per 10 cm3 of substratum sampled at Station HB2 to 277.2 per 10 cm3 at Station HB1. From comparisons of abundance among stations, no pattern of significant differences that could be related to proximity to the diffuser pipe was determined for any faunal component. There were no significant differences among stations in number of nonmollusk species, nor were there any significant differences for the crustacean component of the nonmollusks. No clear pattern of differences among stations with regard to mollusk species richness was seen. Both diversity and evenness values were generally similar among all stations for both nonmollusks and mollusks. Cluster analysis of nonmollusk Data confirmed that all stations were relatively similar to one another in terms of species composition and relative abundance.