[Coral-List] Status of near-shore reefs of the Great Barrier Reef

[Hugh Sweatman]

Colleagues

A report on a the first large-scale survey of the status of nearshore reefs of the Great Barrier Reef is now available on line; you will be pleasantly surprised to find the news is not all bad.

See http://www.rrrc.org.au/publications/report_2.html

Here are some selections from the summary:

Near-shore reefs of the Great Barrier Reef (GBR) cover only a small part of the World Heritage Area, but they have disproportionate significance as signals of the condition of the ecosystem. These reefs are the most accessible to coastal communities and they are the most at risk from runoff. While there have been many studies of near-shore reefs, there has not been a large-scale, systematic assessment of their status. This study had dual aims: (1) to assess the current status of a large sample of near-shore reefs along the GBR coast; and (2) to assemble a list of past studies and incorporate their findings as appropriate. 

In 2004, we surveyed the benthic communities at 33 reefs in six regions between Cape Tribulation (16°S) and Keppel Is (23°S). 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. 

Principal findings were as follows: 

* The near-shore reef communities were very variable in 2004. 

* Coral cover was extremely high in some locations in some cases more than 80% cover of living hard coral. Nearly a quarter of the locations had more than 50% cover of hard corals. Coral cover was less than 10% at ten locations. Over all, the average cover of living hard coral was 33%. This is slightly higher than the average cover of 30% from 36 reefs in middle and outer regions of the GBR lagoon that were surveyed by the Australian Institute of Marine Science (AIMS) in 2004/2005. 

* The number of species of hard corals ranged widely. There was an average of 22 spp. per location on the shallow slopes of some reefs in the Keppel region whereas there were more than 100 spp. in some locations in the Whitsunday region. The overall average number of species was 69. 

* Densities of small colonies (<10 cm maximum dimension, density corrected for the area of suitable substrate) ranged from a mean of less than 1 per m2 on  some sites in the Mackay region to more than 40 per m2 in at sites in Innisfail region (Wet Tropics). The overall mean density was 15.6 small colonies per m2. 

* Three broad community types were recognised: Acropora dominated communities, Porites dominated communities and mixed communities. Communities dominated by Acropora were common in the Keppel region while Porites communities were most common in the Innisfail region. Variation in community structure was correlated with the grainsize of sediment at the locations (an indicator of the resuspension/ deposition regime). There was only a weak relationship with an estimate of risk of exposure to runoff. The divergent communities in the Keppel and Innisfail regions contributed substantially to both these relationships. 


Hugh Sweatman


Long-term Monitoring Program
Australian Institute of Marine Science
PMB3 Townsville MC
Qld 4810, Australia
 
www.aims.gov.au/reef-monitoring



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