Effects of a bleaching event in 1998 on soft corals (octocorallia) of the Great Barrier Reef

During the the bleaching event on 1998 on April 6-13, video transects and collection of tissue samples from bleached and unbleached alcyonacean colonies (17 genera) were conducted on 9 reefs in the central section of the GBR. Inshore (Phillips, Pandora, Fantome, and Great Palm Island) and offshore (Lodestone, John Brewer, Bramble, Faraday, Myrmidon) reefs were represented.On each reef, 3-4 transects (0.6 x 50 m) were video-recorded at 2 m and 5-6 m depth. Under 5 fixed points on 40 stops of the video (200 points per transect), alcyonacean and scleractinian corals were identified to genus level where possible. Morphologically similar genera that were indistinguishable on video (e.g. Efflatounaria and Cespitularia) were pooled. Categories of bleaching extent for colonies were: not bleached, partially bleached (either parts of the colony bleached, or the whole colony clearly paler than typical for that genus), and totally bleached.Video surveys were complemented by visual surveys of the extent of bleaching in each genus along each of the transects.Genetic identities of intracellular dinoflagellates (Symbiodinium, spp.) in samples were analyzed using PCR denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis of the internal transcribed spacer regions 1 and 2 which yielded 12 genetically distinctive Symbiodinium types consisting of 2clade B types (B1n, B36), 9 clade C (C1:1, C1c, C1:1a, C1:3a, C1:2, C1q, C15, C64, C84a), and one clade D (D3). To assess the relative sensitivities of zooxanthellate octocorals to thermal stress during a bleaching event.To determine whether differences in bleaching susceptibility between species, among individuals of a species, and within colonies could be attributed to different endosymbiotic dinoflagellates. Soft coral species: Anthelia sp.; Asterospicularia laurae; Briareum sp.1; Briareum sp.2; Cespitularia sp.; Clavularia koellikeri; Efflatounaria sp.; Heteroxenia sp.; Lemnalia sp.; Lobophytum compactum; Nephthea sp.; Paralemnalia digitiformis; Paralemnalia thyrsoides; Pinnigorgia flava; Rhytisma sp.; Sarcophyton sp.; Sinularia cf polydactyla; Sinularia flexibilis; Stereonephthya sp.; Xenia sp.