Project Report PR-95-12
Benthic Faunal Sampling Adjacent to Barbers Point Ocean Outfall, Oahu, Hawaii, January 1995
Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay
May 1995
ABSTRACT
Benthic infauna in the vicinity of the Barbers Point Ocean Outfall was sampled at seven stations on 8 and 9 January 1995 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. 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 similar to values measured in 1994. Values for total organics were not elevated at stations in or near the ZID. Values for oxidation-reduction potential and sediment oil and grease showed no indication of significant organic buildup in sediments at any station. A total of 5,980 nonmollusk individuals from 151 taxa were collected. Polychaetes represented 42%, nematodes 21.5%, oligochaetes 14.5%, and crustaceans 11.9% of total nonmollusk abundance. Mean total nonmollusk abundance ranged from 96.2 individuals per sample (17,669/m2) at Station HB7 to 229.4 individuals per sample (42,133/m2) at Station HB4. Mean crustacean abundances ranged from 9.0 (1,984/m2) at Station HZ to 33.6 (7,405/m2) at Station HB1. Mollusks were analyzed separately because they represented time-averaged collections of live and dead shells. Mollusk densities ranged from 129.8 at Station HB2 to 238.0 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. Although there were significant differences among stations in number of species both for the crustacean component of the nonmollusks and for the mollusks, no clear pattern of differences related to proximity to the diffuser was seen among stations. 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. The response patterns of the benthic fauna and the sediment chemical analyses show no indications of the types of changes in bottom communities which are predicted by a hypothesis of organic enrichment resulting from the discharge of effluent from an outfall diffuser.