Effects of Cyclone 'Joy' on nearshore coral communities of the Great Barrier Reef

The rain associated with tropical Cyclone 'Joy', in late 1990 and early 1991, led to the third largest recorded flood in central Queensland, Australia. This study examined the effects of floodwaters on nearshore coral communities, in 3 regions of the Great Barrier Reef. The Keppel Island reefs (23" 10' S) were affected by extreme floodwaters which damaged corals to an average depth of 1.3 m below low water datum. Mortality was highest for shallow Acropora spp. and pocilloporids; faviids were most tolerant. The most widespread effect on deeper colonies of Acropora spp. was gross swelling and lysis of the epidermal cells and loss of zooxanthellae from the gastrodermis (bleaching). Shallow waters around Middle Reef (19" 09' S) experienced moderate floodwaters and significant mortality occurred to colon~es of Acropora spp.; other corals were not damaged. The Whitsunday lsland reefs (20' 20' S) were subjected to minor floodwaters and shallow corals suffered little damage, however deep-water pocilloporids died, possibly because of low incident light during the tropical depression.