The purpose of this study was to quantify patterns in octocoral biodiversity and their environmental drivers on the GBR. The data are based on visual surveys of octocoral communities (soft corals and sea fans) on 163 GBR reefs. Octocorals contain taxa with and without endosymbiotic microalgae (zooxanthellae), and these two groups have contrasting distributions and ecological niches (Fabricius and De¿ath 2008). Richness is therefore presented as number of taxa with and without zooxanthellae.
The data set also contains visual estimates of the cover of the main benthos groups such as hard corals, soft corals, macroalgae and crustose coralline algae (unit: percent cover), and estimates of some aspects of the physical environmental conditions at that site such as slope angle, visibility and sedimentation. Data are based on swim surveys by one experienced observer (KF) along ~200 m following the reef contour at each of up to 5 depth zones (between 18 m depth and the reef flat) at each of one to three sites per reef. The Soft_Corals_Reef data are based on reef-averaged data, while the Soft_Corals_Transect data are data from individual transects.
As part of the Reef Atlas project (now the eAtlas) the octocorals observations were interpolated over the whole GBR by Glenn De'ath using Generalized Additive Models with a Quasibinomial fit for Total macroalgae, Sargassum and Non Sargassum layers, and Quasipoisson fit for the other layers. This produced a gridded version of the dataset and is available as a number of KMLs and ASCII grid data files in WGS84 projection.