LINKS BETWEEN RAIN, SALINITY, AND PREDATION IN A ROCKY SUBTIDAL COMMUNITY

Abstract

Physical control of predation appeared likely in subtidal habitats of fjords in southwestern New Zealand because they intersect a shallow low-salinity layer (LSL) where marine predators might be excluded by low-salinity stress. We investigated links between predator distributions, predation intensity, rainfall, the depth of the LSL, and sessile invertebrate community structure at two sites in Doubtful Sound, New Zealand. Sessile invertebrate communities living on the rock walls of the fjord showed striking patterns of vertical zonation corresponding to the depth of the LSL. Barnacles and mussels, Mytilus edulis galloprovincialis, were most abundant at the 1–3 m depth range commonly bathed by the LSL, while sponges, bryozoans, and ascidians dominated space below it (6–18 m depth). Mussel abundance declined sharply with depth at both sites, from maxima of 52–80% cover in the LSL (3 m) to <2% cover just below the LSL (6 m). To test the hypothesis that the LSL influences the lower limit of the mussel zone by ...