Temporal changes in the polychaete infaunal community surrounding a Hawaiian mariculture operation

Abstract

Benthic monitoring efforts in the vicinity of a Pacific threadfin Polydactylis sexfilis mar- iculture venture have allowed us to examine eutrophic effects on the infaunal community. Polychaete infaunal communities from 2 sites near the point source were compared to 2 control stations beyond the range of fish feed and wastes. Regression analysis indicated significant decreases in Shannon- Weiner diversity over time and near the effluent source. Non-metric multidimensional scaling (nMDS) showed a progression of species succession and turnover at impacted sites but relatively unchanging polychaete communities at control sites. An analysis of similarity (ANOSIM) indicated significant differences between community structures at impacted and control sites but less obvious differences over time. An abundant and regionally widespread polychaete Pionosyllis heterocirrata had disappeared from impacted sites. Increasing abundances of 2 opportunistic polychaetes, Capitella capitata (complex) and Ophryotrocha adherens, resulted in decreasing Shannon-Weiner diversity values (H ') at impacted stations. Expanding populations of C. capitata and O. adherens seem to be preceded by high densities of Myriochele oculata. These 3 species may represent an order of succession due to attrition by anoxia in Hawaiian waters. Deviation of the infaunal polychaete community at impacted sites resulting from the appearance of polychaete pollution indicators, low species richness resulting from the disappearance of ambient polychaete species and depressed com- munity abundance reflect the effects of fish mariculture on the benthic community. Such effects may be diluted by the open-ocean location on the south shore of O'ahu, Hawai'i.