Used epifaunal assemblages to investigate the ecological effects of potential gradients of environmental stress arising from marina operations and boating activities in New Zealand. After 3-6 months, significant differences were evident among the epifaunal assemblages. The most conspicuous effect was the loss of cover by the spatially dominant solitary ascidians at sites inside 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.