Bleaching of coral communities on nearshore reefs of the central Great Barrier Reef after Cyclone Sadie (1994)

Brief description

The nearshore reefs, Brook Islands Reef (2 sites), Iris Point Reef at Orpheus Island (1 site) and Pandora Reef (4 sites) were surveyed using swim survey and video techniques in February 1994. The Pandora Reef sites were resurveyed in April 1994. Meandering SCUBA and/or snorkel swims were used to record an inventory of the coral species at each site and to estimate the severity of coral bleaching. Swims of approximately 100 m were conducted at depths of between 0 to 3 m, 4 to 7 m and 8 to 12 m below approximate mean low water (mlw) level. For each species, the relative abundances of unaffected, partially bleached and totally bleached colonies were estimated to the nearest 20%. At Iris Point Reef and Pandora Reef, the coral communities were also filmed using a Sony Hi-8 Video camera from about 50 cm above the substrate during the swims, producing video profiles covering about 30-50 cm width of reef substrate. The videos were inspected for additional species not previously recorded during the swims. The perimeter of bleached tissue was filmed on four partially-bleached massive corals and marked with stainless steel nails. At Pandora Reef, video belt-transects of 50 m length were filmed at three depths (1 to 3 m, 4 to 6 m and 9 to 11 m below approximate mlw level) at four sites around the reef perimeter. The sites were selected haphazardly within areas known to support the range of major coral community types present. Transects were marked with a glass fibre metric tape measure laid along the depth contours. The starting point of each transect was marked with a buoy. The transects were filmed from approximately 50 cm above the substratum, providing a video band-width of 30 to 50 cm. Each transect took about 4 minutes to film. The transects in the second survey (April 1994) were located near the buoyed positions, in the same depth ranges and community types, but did not follow the precise path of the original transects. The nearshore reefs (Brook Islands Reef, Iris Point Reef at Orpheus Island and Pandora Reef), were surveyed to determine the extent and severity of bleaching due to the influence of a coalesced flood plume associated with Cyclone Sadie. Pandora Reef was resurveyed eight weeks after exposure to the plume to assess whether recovery from the bleaching event had occurred. Tropical cyclone Sadie degenerated into an intense rain depression over the North Queensland coast on the 31st January 1994. A flood plume from the Herbert River and adjacent streams extended approximately 20 km offshore on the 2nd February 1994. Several nearshore reefs were covered by the plume, including Pandora Reef, and reefs fringing the Brook and Palm Island groups. Further heavy rain occurred some two weeks following the cyclone, particularly in the Ingham area causing a second flood of smaller magnitude than that associated with cyclone Sadie.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Locations of the study sites were recorded with a portable GPS unit, using the WGS 84 map datum. The methods used to film benthic communities and video transects are described in:Carleton JH and Done TJ (1995) Quantitative video sampling of coral reef benthos: large scale application. Coral Reefs 14:35-46.Christie CA, Bass DK, Neale SJ, Osborne K and Oxley WG (1996) Surveys of sessile benthic communities using the video technique. Long term monitoring of the Great Barrier Reef. Standard operational procedure No. 2. SOP-2. Australian Institute of Marine Science. 41 p.Video analysis (transects):Transects were subsampled at regularly spaced intervals to provide 70 stops of the video tape along a 50m transect (Christie and Mapstone 1994). At each stop of the tape, the identity of the benthic organisms under five fixed, 'face-centred' points was recorded into a spreadsheet. Identifications were made to the following levels: hard corals - species or genus and growth-form; soft corals - genus; most macro-algae - genus; sponges, zoanthids and other benthos - order.The 'extent' of bleaching was categorised as 'none', 'partial' or 'total'. The 'severity' of bleaching of the tissue located under each of the 5 points on the video monitor was recorded as 'bleached' (white - no pigment visible in tissues), 'blanched' (some colour visible but not normal pigmentation), or 'normal' (normal pigmentation). Injured or recently-dead colony areas, indicated by the recent growth of algae on bleached surfaces, were also recorded. The percent cover of each taxon was determined as a proportion of the total number of points sampled (n/ 350 x 100). The relative percentage of each category of bleaching among the sample points was calculated.Christie C and Mapstone B (1994) Use of high resolution video for estimation of percent cover of sessile reef benthos. Joint Scientific Conference on Science, Management and Sustainability of Marine Habitats in the 21st Century, Townsville, Abstracts Booklet, p11.

Notes

Credit
DeVantier, Lyndon M, Dr (Principal Investigator)