EFFECTS OF CYCLONE JOY ON NEARSHORE CORAL COMMUNITIES OF THE GREAT-BARRIER-REEF

The rain associated with tropical Cyclone 'Joy', in late 1990 and earl y 1991, led to the third largest recorded flood in central Queensland, Australia. This study examined the effects of floodwaters on nearshor e coral communities, in 3 regions of the Great Barrier Reef. The Keppe l Island reefs (23 degrees 10' S) were affected by extreme floodwaters which damaged corals to an average depth of 1.3 m below low water dat um. Mortality was highest for shallow Acropora spp. and pocilloporids; faviids were most tolerant. The most widespread effect on deeper colo nies of Acropora spp. was gross swelling and lysis of the epidermal ce lls and loss of zooxanthellae from the gastrodermis (bleaching). Shall ow waters around Middle Reef (19 degrees 09' S) experienced moderate f loodwaters and significant mortality occurred to colonies of Acropora spp.; other corals were not damaged. The Whitsunday Island reefs (20 d egrees 20' S) were subjected to minor floodwaters and shallow corals s uffered little damage; however deep-water pocilloporids died, possibly because of low incident light during the tropical depression.