Project Report PR-98-12
Community Structure of Fish and Macrobenthos at Selected Shallow-Water Sites in Relation to the Barbers Point Ocean Outfall, 1998
Richard E. Brock
This report provides the results of the seventh year of an annual quantitative monitoring of shallow marine communities inshore of the Barbers Point Ocean Outfall located in 61 m of water offshore of Ewa Beach, Oahu, Hawaii. The monitoring effort focuses on benthic and fish community structure and is designed to detect changes in these communities. Field sampling was first carried out in August 1991 when three study stations were established: Station BP-1, a control station 2.2 km inshore and east of the outfall terminus; Station BP-2, an experimental station about 1.5 km inshore of the terminus; and Station BP-3, an experimental station about 2.9 km west and inshore of the terminus. The second field effort, completed in May and September 1993, resurveyed the above stations as well as established a fourth station (BP-4) on and adjacent to the basalt armor caprock protecting the discharge pipe in 13 m of water and directly inshore of the outfall terminus. The third field survey was completed in March and April 1994, the fourth in June 1995, the fifth in May 1996, the sixth in February and April 1997, and the seventh in January – March 1998; each sampled all four stations. These stations are sited to capitalize on presumed gradients of impact that may be created by the discharge and movement of treated sewage effluent toward the shore and the coral reef communities. Data from the first survey suggested that marine communities offshore of Ewa Beach receive disturbance from a number of possible sources, with the largest perturbation probably coming from natural disturbance caused by occasional wave impact. This was most evident at the station directly inshore of the outfall. Data from Station BP-4 showed that benthic communities situated on armor rock which rises above the flat limestone substratum are not subjected to the same sand scour as those situated on the limestone; thus the coral communities on the elevated caprock are better developed on this substrate.A comparison of the Data from the seven annual surveys indicated that no statistically significant change has occurred in the measured biological parameters at these permanent stations, despite the imposition of a major hurricane on these marine communities in September 1992. Thus the Data to date support the contention that the operation of the Barbers Point deep-ocean outfall is not having a quantifiable impact on the coral reef resources situated inshore of the outfall terminus.