Effects of crown-of-thorns starfish (Acanthaster planci) outbreaks on coral community structure at John Brewer Reef and Rib Reef, Great Barrier Reef

Permanent transects, which were established in 1974 by RG Pearson (Queensland Fisheries Service) at two sites on John Brewer Reef after a crown-of-thorns starfish outbreak, were resurveyed using stereophotography (from a range of 1.8 to 1.9 m) on four occasions from 1980 to 1983. The 10 x 1m transects were located at 6 and 12 metres depth at Site A (on the southeast forereef slope) and at 3 metres depth at Site B (on the northern back reef slope). Coral identifications were made in the field.

Colonies too small to be censused using photography and those hidden in the substratum were censused visually. Their positions were plotted throughout the 10 m² area of each fore-reef transect at 6 monthly intervals on three occasions commencing in November 1983, soon after a new starfish outbreak. The identity, maximum diameter and grid position of each coral located was recorded using a 1m² quadrat divided into a 5 x 5 grid of 20 cm squares, which was systematically searched, one square at a time, until all 10 square metres of the transect had been searched.

A further 135, 0.25 m² quadrats were searched at other reef slope locations on John Brewer Reef and adjacent Rib Reef. Each quadrat was placed at random on hard substrate in areas where coral mortality was estimated to be in excess of 95% over hundreds of square metres. In these searches, genus and the abundance of each genus of surviving coral remnants was recorded along with depth and location.

Massive corals >= 10cm in diameter were surveyed in 1984 and the diameter of each coral and proportion of living tissue recorded. The categories used to describe the proportion of living tissue were: 0 living tissue. For colonies up to 60 cm diameter, the survey was made using a total of 1.8 km of line transects, in 50 m units at depths of 3, 6 and 9 m at 12 locations around John Brewer Reef. For colonies over 60 cm diameter, the survey consisted of 2.4 km of standard swims in 200 m units at the same 12 locations. In these swims, the reef slope was searched in a slow, meandering swim, down current, on scuba. The depth range searched was from 2 to 12 m. The line transect was assumed to sample a strip 0.3 m wide and the standard swim a strip 20 m wide. The results were standardized to number of individuals per 1000 m².