Rapid changes in shelf waters and pelagic communities on the southern Northwest Shelf, Australia, following a tropical cyclone

A pronounced shift in water column characteristics and in the composition of plankton communities was observed following the passage of Tropical Cyclone Tiffany along the margin of the southern Northwest Shelf, Australia in January 1998. Satellite-derived images of sea surface temperature, meteorological and hydrographic data indicate a southward movement of shelf waters into the study area near North West Cape (21°46′S). Changes in water mass temperature and salinity characteristics also occurred as a result of local heating and evaporation. Local in situ growth was likely to have caused increases in micro-phytoplankton abundance, biomass and primary production on the shelf. A diverse, copepod-dominated shelf mesozooplankton community changed to a less diverse assemblage dominated by copepods usually found in shallow nearshore habitats. Post-cyclone larval fish catches included families absent or rare in pre-cyclone samples. In the case of copepods and larval fish, southward transport of water masses along the shelf was most likely to have caused the observed changes. Long-shore water transport forced by cyclonic winds may be a recurrent, but episodic mechanism of planktonic dispersal on the North West Shelf.