Settlement plates were deployed at Helix Reef immediately prior to the 1983 coral spawning period, to obtain numerical data on patterns of coral recruitment, including species composition, abundance and mortality rates. Twenty-four moorings were deployed around Helix Reef at 0, 0.3, 0.6, 1.2, 2.5 and 5.0 km from the reef perimeter along four arms forming counterclockwise spiral paths. Racks of five settlement plates (600 cm² discs of coral skeleton), were mounted on each mooring at two depths: shallow (15-18 m below the surface) and deep (4 m above the bottom). The racks were free turning with vanes which enabled the plates to be oriented into the current.
After 7 months the settlement plates were retrieved, wrapped in plastic and frozen at -18°C. Once thawed, non-coral epibiota were removed and the plates were cleaned with a water jet and then oven dried at 55°C. Coral spat were identified using a dissecting microscope, with taxonomic resolution varying between suborder and species.
Spat were assessed for condition (alive or dead), discernable through infestation by endolithic green algae or overgrowth by other epibiota. Coral recruits were also assessed for condition and post settlement mortality. Condition was recorded as one of the following: skeleton intact and remnants of tissue evident; coral overgrown by another sessile organism; skeleton physically damaged; both overgrown and damaged; complete colony mortality.
Water movements were recorded concurrently using current meters and tide gauges.
