Status of near shore reefs of the Great Barrier Reef 2004 (CRC Reef Research Centre: Project C1.14)

Brief description

The benthic communities at 33 near shore reefs between Cape Tribulation (16°S) and Keppel Is (23°S) were surveyed in 2004. Prospective near-shore coral reef sampling locations were initially selected from six broad geographic regions of the GBR: Cairns, Innisfail, Townsville, Whitsunday, Mackay, and Keppel. Each of these regions has a unique combination of climatic regime, coastal and shelf topography and the characteristics of adjacent catchments. Where topography allowed, two depths were surveyed at replicate sites at each reef giving a total of 63 locations. Surveys measured benthic cover, community composition, diversity of coral species and size-structures of coral communities. Environmental factors recorded included sediment composition, transect depth, adjacent depth, exposure to runoff, exposure, fetch and distance to land.Voucher specimens of some coral species of uncertain identity were collected and lodged with the Museum of Tropical Queensland for identification and future reference. The objectives of this study were twofold:1. to describe near-shore reefs of the Great Barrier Reef province and assess their status; and2. to collate information on the past condition of near-shore reefs, particularly from the grey literature, for comparison with the current status. The status of near-shore reefs is of concern largely because they are the portion of the GBR that is most at risk from runoff. The most deleterious effects of runoff on corals appear to be caused by sediment. Coral reproduction and the early survival of juveniles are the population processes that are most likely to be affected. For these reasons, the descriptions of the study reefs include not only measures of coral cover, but also estimates of species diversity and measures of size-frequency of colonies - attributes that indicate the stage that a reef community has reached in its development.A subset of the data has been provided to the Ocean Biogeographic Information System (OBIS, http://www.iobis.org/OBISWEB/DisplayMetaData.jsp?content=meta/137.html).

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Survey Methods:Two replicate sites were surveyed at each survey location. Ideally each site consisted of five 20m transects, separated by about 5m, laid along depth contours on the reef slope at each of two depths: 2 and 5 metres below Lowest Astronomical Tide (LAT). At several locations there were no coral communities at or deeper than 5m below LAT and therefore only the 2m depth stratum was sampled. At Pandora Reef an additional depth of 8m was sampled.Four types of data were gathered on these transects:1. Benthic cover: Cover of benthic organisms was estimated from five 20m video point intercept transects. Points were identified to highest possible taxonomic resolution governed by image quality (see Abdo et al. 2003). The video footage was taken along the upslope side of the transect line such that the tape marking the line was not included in the field of view.Abdo D, Burgess S, Coleman G, Osborne K (2003) Surveys of benthic reef communities using underwater video: Long-term Monitoring of the Great Barrier Reef. Australian Institute of Marine Science, Townsville.2. Community demographics: Hard and soft coral colonies falling wholly or partially within a 0.34m (slate width) wide belt were recorded in the first 10m of each of the five 20m long transects. These five sections were summed for analysis, ensuring that sampling was spread across the site. Each colony was assigned to one of the following size categories: 3. Species lists: An observer spent about 50 minutes searching in the vicinity of the transects, listing all hard coral species. When an observer could not identify a particular coral to species in the field, the colony was photographed for comparison with coral identification texts and the image was saved in a database. If identification was still questionable, corals were only identified to genus. In such cases, the number of unidentified species within a genus was noted.4. Agents of coral mortality: The perceived cause of all new scars (patches of bare white skeleton) were recorded in a belt 2m wide, 20m long and centred on the five 20m transects. Potential agents of mortality included Drupella spp., crown-of-thorns starfish and several groups of coral disease. Cases where the agent responsible could not be identified were recorded as "unknown". The proportion of colonies affected by coral bleaching or scarring were scored as follows: 0 = no colonies; 0+ = a few colonies; 1 = 1-10% of colonies; 2 =10-30% of colonies; 3 = 30-50% of colonies; 4 = 50-75% of colonies and 5 = >75% of colonies.Environmental Factors:1. Sediment composition: Sediment samples were collected from 23 near-shore reefs as part of a separate investigation during 2005. Thirteen of these samples were from locations that were surveyed for this project. At each location, four 10mm deep by 28mm diameter plugs of surface sediment were collected from patches of sediment haphazardly spread over 100m along the 5m contour. The composition of the samples from the 13 reefs surveyed during 2004 were categorised visually as follows:1 - fine mud/silt2 - mud with some fine sand3 - sand with some mud4 - coarse sandFor the remaining locations, sediment composition was estimated from notes and by interpolation from the 23 locations where sediment was collected.2. Adjacent depth: Maximum depth of seabed within 3 nautical miles of the reef as read from marine charts3. Exposure to runoff: Continuous with values calculated from formulae and river pollution indices published by Devlin et al. (2003).Devlin M, Brodie J, Waterhouse J, Mitchell A, Audas D, Haynes D (2003) Exposure of Great Barrier Reef inner-shelf reefs to river-borne contaminants. Proceedings of the 2nd National Conference on Aquatic Environments: Sustaining Our Aquatic Environments - Implementing Solutions, Townsville, 20-23 November 2001. Queensland Department of Natural Resources and Mines, Brisbane.4. Exposure: Hierarchical1 - aspect between 250 and 20 degrees or fetch 2 - aspect between 20 and 50 or 220 and 250 degrees or fetch 5-15 km3 - aspect between 50 and 90 or 220 and 180 degrees or fetch 15-30 km4 - aspect 90-180 degrees and fetch >30 kmFetch: Hierarchical 1 - 2 - 10-20 km3 - 20-30 km4 - >30 km5. Distance to land: Distance in km of the reef from the nearest point of mainlandVoucher Specimens:Colonies were photographed in situ prior to collection. These photographs are archived in a database and included on a searchable DVD housed along with the collection at the Museum of Tropical Queensland.

Notes

Credit
Sweatman, Hugh PA, Dr (Custodian)