Introduction

Benthic Faunal Sampling Adjacent to Barbers Point Ocean Outfall, Oahu, Hawaii, January 1996

Benthic Faunal Sampling Adjacent to Barbers Point Ocean Outfall, Oahu, Hawaii, January 1996

Project Report PR-96-08
Benthic Faunal Sampling Adjacent to Barbers Point Ocean Outfall, Oahu, Hawaii, January 1996

Walter G. Nelson, Julie H. Bailey – Brock, William J. Cooke, and E. Alison Kay

May 1996

ABSTRACT

Benthic infauna in the vicinity of the Barbers Point Ocean Outfall was sampled at seven stations on 11 and 12 January 1996 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 (>90%) fine to coarse sands. Station HB7 had relatively coarser sediments and Station HB2 had a higher percentage of silt and clay than the other stations. Total organic carbon in the sediments at all stations was below the detection limit of the analytical method used. 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 8,727 nonmollusk individuals from 147 taxa were collected. Polychaetes represented 44.0%, nematodes 28.6%, oligochaetes 13.2%, and crustaceans 7.5% of total nonmollusk abundance. Mean total nonmollusk abundance ranged from 121.2 individuals per sample (22,371/m2) at Station HB7 to 347.0 individuals per sample (64,246/m2) at Station HZ. Mean crustacean abundances ranged from 13.8 (3,041/m2) at Station HZ to 25.0 (5,510/m2) at Station HB1. Mollusks were analyzed separately because they represent time-averaged collections of live and dead shells. Mean mollusk densities ranged from 173.6 at Station HB2 to 279.6 at Station HB4. From comparisons of nonmollusk abundance among stations, ZID-boundary station HB4 and ZID station HZ had significantly greater mean abundances than reference station HB7. There has been a significant trend of increased abundance of nonmollusks within the entire study area since 1990, although there has been no trend either for the crustacean component of the nonmollusks or for the mollusks. Significantly elevated abundances of nonmollusks over the entire study period have occurred at two stations near the diffuser relative not only to two of the reference stations but also to a third near-diffuser station. There were no significant differences among stations in number of nonmollusk or crustacean species. Although there were significant differences among stations in number of species 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. There is no indication of any marked alteration of the benthic community composition related to station proximity to the diffuser.