The status of Brampton Island fringing reefs, Great Barrier Reef

Brief description

Coral communities and environmental parameters were surveyed at 6 sites around Brampton Island in February 1995. Study sites were established at Brampton Roads (Sites 1a, 1b), Turtle Bay (Site 2), Dinghy Bay (Site 3), Western Bay (Site 4), Osprey Point (Site 5) and Pelican Island (Site 6).The overall status of coral communities in the area was assessed using semi-quantitative surveys, consisting of 20-30 minute SCUBA-swims on the shallow reef slopes at each site. A comprehensive list of the sessile benthic taxa, identified in situ to genus and species for hard corals, genus or species for most soft corals and macro-algae, and to higher taxonomic rank for other benthos was compiled. Each taxon was ranked subjectively in terms of its relative abundance and the approximate proportion of coral colonies that were in each of three size classes. The approximate proportion of colonies that had sustained substantial injury to >50% of colony surface area was estimated. In addition, visual estimates of the approximate percent cover of the overall substrate at each site attributed to major biotic and abiotic benthos were made.Quantitative surveys were conducted at three sites to determine the percent cover, size structures and levels of injury of the coral communities as well as the abundance of macro-algae. At Brampton Roads, sites were surveyed in the impacted area, in the vicinity of the Snorkel Adventure Trail (SAT) (Site 1a) and near the opposite end of the patch reef (Site 1b). Site 6, near the south-western corner of Pelican Island was used as a control. Video transects were used to estimate percent cover. At each site, five haphazardly placed, 50 m long video belt-transects were filmed by a diver swimming at a near constant-speed and set-height above the substratum. The resulting video-transect width ranged from about 30-50 cm of reef substrate. Three 32 m x 0.6 m belt-transects were surveyed at each of the three sites (on video transects 1, 3 and 5 at Sites 1a, 1b and 6). The sessile benthos located within each transect were recorded to species or genus and growth-form for hard corals, genus for most soft corals and zoanthids, and order or higher taxonomic rank for other sessile benthos. The maximum diameter of each organism (to the nearest cm for organisms Water and sediment samples were collected for nutrient analysis from all sites except for Brampton Roads Site 1b. At Brampton Roads (Site 1a) and Pelican Island (Site 6) duplicate water, sediment, as well as algal (Sargassum and Padina) samples were collected at three points on three of the five transects established at each reef. At these two sites, one of the replicate sediment samples was used for nutrient analysis and the duplicate used for sediment grain size analysis. At sites 2, 3, 4 and 5 duplicate water and sediment samples were taken at each of 3 points approximately 50 m apart.The spatial distribution of dissolved nutrients between the resort and the Brampton Roads reef was also measured using a series of 5, parallel 50 m transects in the bay between the beach and the reef. This sandy bottom area lies between the potable water dam adjacent to the airstrip, and the sandspit at the north end of the resort. Duplicate water and sediment samples were taken at three randomly located points on each transect and transects were spaced about 50 m apart. At the southeastern end of this area, the small stream of water running from the base of the potable water dam during low tides was sampled for dissolved nutrients at three points along the stream (low tide level, halfway and at the base of the dam) taking duplicate samples on 23 February and a single sample on the following day. The coral reefs around Brampton Island were surveyed in February 1995, as part of a pilot study conducted in response to concern expressed by the Brampton Island Resort that the reef in Brampton Roads (the Channel between Brampton and Carlisle Islands) was deteriorating and being overgrown by Sargassum spp. macro-algae.

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Maintenance and Update Frequency: notPlanned

Statement: Statement: The location of each site was recorded with a portable GPS unit, to enable accurate relocation during any future surveys.Categories used in visual estimates of relative abundance, population structures and injury (semi-quantitative surveys):Relative abundance0 absent1 rare2 uncommon 3 common4 abundant5 dominantSize structure a) 1-10 cmb) 11-50 cmc) >50 cmInjury0.0- 1.0Benthic attributes and cover categories used in visual estimates of the approximate percent cover occupied by the major benthic attributes: Attribute:Biotic:Hard coralDead standing coralRecently-dead coralSoft coralTurf algaeSargassum spp.Other macro-algaeAbiotic:Hard substrateContinuous pavementLarge blocks (diam > 1 m)Small blocks (diam RubbleSandSilt% Cover Category1) 1 - 10%2) 11- 30%3) 31- 50%4) 51- 75%5) 76- 100%Video transects:The video transects were analysed using a SONY Hi-8 video editor and monitor. A time code was displayed on each transect from which the elapsed time was determined. The transects were sampled at regularly-spaced intervals to provide 100 stops of the video tape along the 50 m transect. At each stop of the tape, the identity of the benthic organisms (as a category) under five fixed ''face-centred" points was recorded into a spreadsheet. For each category, the proportion of points in the 500 point-records of each transect provided an estimate of its percent cover.Categories used in analysis of video transects:Hard corals:Acropora spp. branchingAcropora spp. other growth formsMontipora spp.Isopora spp.PocilloporidaeCoral - other spp.Soft corals:Sinularia spp.Sarcophyton and other soft coralsAlgae:Sargassum (plus Cystoseira, Hormophysa spp.)Padina sp.Other macro-algae (MA, plus other algae)Urchins:Diadema sp.Other: All other sessile benthosAbioticSand / rubbleDead standing coral (DSC)Undetermined:UnidentifiedFurther information on the method used for video transect surveys is available in: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.Sample collection and handling:Water samples were taken in mid-water column by a snorkellor using an acid cleaned syringe and filtered through a Sartorius 0.2 µm filter into acid washed tubes. These were placed on ice immediately. Plants and sediments were placed in plastic bags and put on ice immediately. All samples were then frozen as soon as feasible at the Brampton Island resort after each dive trip. Differences in physical conditions occurred at sampling times, since there were dramatic changes in water mixing due to tide and weather. This was unavoidable given the limitations on field time and funds for the pilot study. Samples were transported by plane to AIMS and frozen until analysis by the AIMS analytical services lab.Nutrient analysis:Dissolved nutrients before and after 8 hrs of UV photo oxidation (PO4, NH4, NO2 + NO3, NO2) were analyzed using a Skalar segmented flow autoanalyzer. Plant tissues and sediments for nutrient analysis were dried at 60°C and ground to a uniform powder. Subsamples were then analyzed on a Perkin Elmer CHNS 2400 analyzer for carbon and nitrogen. Phosphorous and iron were determined by Inductively Coupled Plasma Optical Emission Spectrophotometry.Grain size analysis:Sediments were defrosted, and a subsample treated with concentrated hydrogen peroxide to oxidize associated organics. The 4 mm, 2 mm, 1 mm, 710 µm, 500 µm, 355 µm, 200 µm, 180 µm, 125 µm, 90 µm, and 63 µm. Each size fraction was weighed and the percent total computed.

Notes

Credit
Burns, Kathryn A, Dr (Principal Investigator)