Patterns in the distribution of sediment fauna on the central Great Barrier Reef

Brief description

The sediment environment and fauna from reefs in a broad transect across the Great Barrier Reef were quantitatively surveyed. The study was conducted on six reefs in two transects across the continental shelf in the central region of the Great Barrier Reef. Each transect consisted of one inner shelf reef (Pandora or Phillips) located approximately 18km from the coast, one middle shelf reef (Rib or Lodestone) approximately 70km from the coast and one reef on the outer edge of the continental shelf (Myrmidon or Dip) approximately 110km offshore.Within each reef, three or four sites were sampled representing the different sediment environments. Sites were placed at intervals along the gradient of wave energy from shallow windward reef flat to deep leeward lagoon. On the inner shelf reefs, which have no distinct lagoon, sites were positioned on the windward and leeward sides according to the prevailing south east trade wind.One transect of three reefs (Pandora, Rib and Myrmidon) was sampled on four occasions at approximately three monthly intervals throughout a year. The second transect (Phillips, Lodestone and Dip) was sampled once. This study was undertaken to investigate the spatial variability of reef sediment fauna at three levels:1) among reefs along a cross-shelf transect2) among reefs at similar positions along a cross-shelf transect3) among zones within reefsTemporal variability in community structure was also investigated to determine whether distribution patterns were persistent over time.Sediment analysis was also carried out to determine whether there was a relationship between sediment characteristics and faunal community structure. Sediment samples were taken with a cylindrical PVC corer of 55mm internal diameter, which was pushed manually to a depth of 200-250mm into the sediment. At each site 15 (1st sampling occasion) or 20 (all subsequent occasions) cores were collected for faunal analysis. Sampling was designed to minimise the effects of local patchiness. Four sets (3 on the 1st occasion) of five cores were taken from an area about 1m2 and the sets were spaced about 4m apart. The five cores in each set were bulked to form the basic sample unit (119 cm2).At each site, one additional core was collected for analysis of sediment characteristics on each occasion.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Samples were washed on a 0.5 mm square-meshed sieve, preserved in 10% formalin solution in seawater and stained with Rose Bengal to aid sorting. Animals were separated from the sediment by flotation during repeated washings. The sediment residue was finally checked under a dissecting microscope.Macrofaunal taxa were identified to Family level. Representatives of the meiofaunal groups Turbellaria, Nemertinea, Oligochaeta and Ostracoda were commonly retained in the sieve and were identified to Class.Samples for sediment analysis were stored at -18°C. Grain size was analysed following the methods of Folk (1974). Total organic carbon was analysed using a Beckman Tocamaster Total Carbon Analyser following the methods of Sandstrom et al. (1986). Total carbon and organic nitrogen were measured using a Leco Model 600 CHN analyser. Calcium carbonate content was estimated from the equation (Total C-Organic C) x 8.33 (Sandstrom et al. 1986)Folk RL (1974). Petrology of sedimentary rocks. Hemphills, Austin, Texas.Sandstrom MW, Tirendi F, Nott A (1986). Direct determination of organic carbon in modern reef sediments and calcareous organisms after dissolution of carbonate.

Notes

Credit
Riddle, Martin J, Dr (Principal Investigator)