No abstract

Abstract. Aerial photographic surveys were used to study the distribution and abundance of the nearsurface shoaling juvenile phase of the galatheid crab Munida gregaria in southeastern N.Z. continental shelf waters. On numerous occasions shoals were concentrated into aggregations many metres to a few kilometres long at river plume and headland fronts, and in mid-shelf internal waves. Laboratory experiments established that M. gregaria juveniles showed strong positive phototaxis and that they could sustain swimming speeds of = 16 cm s _ '. Field experiments showed that when M. gregaria were displaced to deeper waters, their response was to swim back towards the surface. These results suggest that juveniles swept into convergent zones would resist downward displacement. Since convergent zones occur at coastal front and internal wave sites this mechanism could explain the aggregations of shoals observed and photographed from the air. This mechanism is discussed in relation to literature on physical processes at such sites and to studies of plankton distribution and behaviour.

No abstract

Intertidal communities of Doubtful Sound, New Zealand, were surveyed in 1995 to establish the extent of changes since they were first surveyed 30 years earlier, before the Manapouri power scheme was completed in 1969. This scheme resulted in more than a 3-fold increase of freshwater inflow to Doubtful Sound, through a tailrace to Deep Cove. Thickness of the low salinity surface layer exceeded the tidal range and was greater at high than low contemporary volumes of tailrace inflow. Intertidal habitats were mostly steep shores of solid rock, little more than 2 m in vertical extent. Freshwater run-off, groundwater seepage, and aspect to sun were all major factors affecting the intertidal communities. Algae and lichens dominated shore communities. Normally common invertebrates were scarce, especially molluscan grazers. Major changes since the early 1960s included almost total disappearance of Hormosira banksii and exclusion of many other species notably Apophloea lyallii and Elminius modestus to outer reaches of the Sound.

No abstract