Herbivory and zonation of Sargassum spp. within fringing reefs of the central Great Barrier Reef

Brief description

A series of transplant and caging experiments, using the macroalgae Sargassum spp., were carried out in Coolgaree (Challenger) Bay, Great Palm Island and Brook Island between December 1992 and January 1994.Seasonal effects were investigated in two experiments conducted on the landward edge of the coral dominated zone in Coolgaree Bay, Great Palm Island. In the first experiment, which commenced in December 1992, mixtures of 'mature phase' adult Sargassum species, predominantly Sargassum oligocystum and Sargassum tenerrimum, attached to coral rubble rocks, were collected in the Sargassum zone in Coolgaree Bay. The plants were counted, sorted into roughly even groups by frond numbers and three replicate groups were assigned randomly to each of four treatments in plots within the coral dominated zone. The treatments were: open (uncaged) transplant; transplant with cage; partial cage control; and a "return transplant" returned to the Sargassum zone. Frond densities were counted before allocation and at 1 and 3 months and categorised as numbers of primary laterals (fronds/plot) in four size classes (0 to 5 cm; 5 to 15 cm; 15 to 50 cm; >50 cm). After 3 months, the plants were retrieved, dried and weighed. In a similar experiment, initiated in July 1993, dormant plants with few fronds longer than 5 cm (none >15 cm) were used. These were retrieved, counted, dried and weighed in January 1994. Qualitative data collected included regular observations of plant condition, and observations of sites and mobile species composition at night and at different tide levels.A Sargassum recruitment experiment commenced on Great Palm Island in December 1992. Each plot in the coral dominated zone was chosen to include a large, flat block of carboniferous substrate (~0.5 m²), with no Sargassum or other fucalean macroalgae, and little or no live coral. Blocks were scraped and wire-brushed at the beginning of the experiment to remove most of the turf algae and sediments covering them. Three replicate plots were randomly assigned to each of three treatments: open (uncaged); caged; and partial cage control. Quantitative descriptions were made of algae on each block every 2 to 3 months until January 1994, when any Sargassum recruits were counted, dried and weighed.A within-reef transplant experiment commenced at Brook Island in mid-November 1992. Coral rocks, with mixtures of Sargassum oligocystum and Sargassum tenerrimum plants attached, were collected and counted. Five replicate groups of plants were randomly assigned to either Sargassum or coral patches. Plants were recounted, collected, dried and weighed after 1 month. Qualitative observations included plant condition and mobile species composition, the latter observed at night and at different tide levels. This research was undertaken to test the importance of herbivory, physiological tolerance limits, and recruitment and dispersal in regulating the distribution and abundance of the genus Sargassum on nearshore fringing reefs of the central Great Barrier Reef.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Experimental setup:Open (uncaged) plots were marked with four pegs (0.3 m long, 10 mm steel rod). Cages were 0.75 m by 0.75 m x 0.75 m, and were made of 12 mm plastic mesh (Nylex, 'Trical' high density polyethylene), anchored with steel-fence stakes and plastic cable ties.In the 'regrowth' experiment, 8 mm steel-rod frames were used to attach the mesh. Partial cages were identical to cages, except that 1 to 2 large holes (40 cm x 40 cm) were cut in each side to allow access for swimming herbivores. Both partial and complete cages were scrubbed every 1 to 2 months, as required, to remove fouling filamentous algae.

Notes

Credit
McCook, Laurence J, Dr (Principal Investigator)