Effects of the crown-of-thorns starfish, Acanthaster planci, on soft coral abundance on the central Great Barrier Reef

The distribution and abundance of soft coral genera on 14 reefs of the central Great Barrier Reef was investigated in relation to reef position, recent history of disturbance, wave exposure, substratum slope and depth. Eighty-five 25 m long transects were surveyed at 10 m depth on the windward sides of these mid- and outer-shelf reefs. At Davies Reef a further 75 transects in different zones were censused along contours at 5 m depth increments: windward side 5-30 m; leeward 5-25 m; north and south flanks 5-20 m; lagoon 5-15 m (deepest depths were at the base of the reef at each site). Transects were standardised by subtracting the proportion of sand and unconsolidated coral rubble.Percentage cover (of total consolidated reef substratum); abundance (number per linear meter); size frequency distribution of 11 benthos categories (massive, encrusting and branching forms of scleractinian corals; soft corals; turf and coralline algae; sponges; zoanthids; tunicates; macroalgae; Halimeda and 'other'); and 'space' were estimated. (Space was defined as the proportion of consolidated hard substrata covered by filamentous or coralline algae but not occupied by macro-invertebrates or macro-algae). Identity and size of 12,603 soft coral colonies growing in a 0.5 m wide strip along the transects was also recorded. Chord length (indicating colony or patch diameter) of turf algae (TA), coralline algae (CA), massive corals (CM), encrusting corals (CE), branching corals (CB), and soft corals (SC) was measured.Soft corals were identified to genus, and the longest and shortest diameters of each colony recorded. The two genera Nephthea/Stereonephthya, and Xenia/Heteroxenia, were each treated as one category, as not all colonies could be distinguished with certainty.Whether high densities of the crown-of-thorns starfish, Acanthaster planci, had been active (8 reefs) on each reef 5-10 years prior to the study, or not (6 reefs), was also recorded.
 To determine if there were differences in area cover and abundance of specific soft coral taxa between reefs that were and were not recently affected by Acanthaster planci.Differences in cover, abundance and colony sizes of the relatively fast-growing branching stony corals and the slower-growing massive and encrusting stony coral taxa, and in cover and abundance of several other common macro-benthos groups (sponges, zoanthidae, tunicates, macroalgae, and Halimeda) were also assessed.To assess the potential effect of some abiotic parameters (current and wave exposure, substratum angle, and water depth), as well as of space competition with hard corals, on cover and abundance of common soft coral taxa.
 Soft coral species: Alcyoniidae (Alcyonium, Cladiella, Lobophytum, Parerythropodium, Sarcophyton, Sinularia); Xeniidae (Anthelia, Cespitularia, Efflatounaria, Heteroxenia, Sympodium, Xenia); Nephtheidae (Capnella, Dendronephthya, Lemnalia, Nephthea, Paralemnalia, Stereonephthya); Asterospiculariidae (Asterospicularia); Briareidae (Briareum); Isididae (Isis); Gorgoniidae (Rumphella, Pinnigorgia flava); Clavulariidae (Clavularia); Other genera.Reefs were: Outer-shelf (18-025, Bowl, Chicken, Coil, Dip, Fork, Needle); Mid-shelf (Brewer, Centipede, Davies, Faraday, Grub, Rib, Yankee); affected by Acanthaster planci (18-025, Brewer, Dip, Fork, Grub, Needle, Rib, Yankee).

Organization: Australian Ocean Data Network