Changes in epifaunal assemblages in response to marina operations and boating activities

A number of features of epifaunal assemblages suggest that they have the potential to provide an excellent integrated field-based measure of marine environmental quality. In this study we have used epifaunal assemblages to investigate the ecological effects of potential gradients of environmental stress arising from marina operations and boating activities. Replicate slate panels, initially colonized by solitary ascidian-dominated assemblages at a site remote from marina operations, were placed at five sites in or near each of two boat mooring areas, Okahu Bay boat harbour and Pine Harbour marina, in the Waitemata Harbour, New Zealand. In addition, panels were immersed at Station Bay, a site remote from marina operations and boating activities. Sites were positioned along putative gradients of contaminant levels (e.g. copper and zinc), as well as hydrodynamic and sedimentation regimes. The changes in assemblage structure on panels immersed at sites along these gradients were compared. After 3–6 months, significant differences were evident among the epifaunal assemblages along the gradients of environmental stress. The most conspicuous effect was the loss of cover by the abundant and spatially dominant solitary ascidians at sites inside the marinas. Concomitant with this loss, was a marked increase in space availability, and a small increase in the cover of sponges, hydroids, erect and encrusting bryozoans, and colonial ascidians. There were also significant differences in assemblage structure between Pine Harbour and Okahu Bay, as well as between the marinas and Station Bay.