THE STATE OF
THE GREAT BARRIER REEF
WORLD HERITAGE AREA REPORT
Steve Hillman
long-term monitoring of benthos, fish, climate change, sediments and water quality;
the present status of seagrasses, mangroves, fringing reefs, algae, fish and reef benthos;
crown-of-thorns starfish;
the status of endangered species such as turtle, dugong, crocodiles and some seabirds;
the status of both commercial and recreational fisheries;
management arrangements for fisheries;
the quality of reef tourism and the impacts of these uses of the World Heritage Area;
reef tourism usage, values and experiences;
catchment management;
day-to-day management; and
legislation and planning.
Some of the most diverse reefs with the highest coral cover in the Great Barrier Reef World Heritage Area are found in the relatively turbid waters that are found inshore and concern has been expressed on many occasions that fringing reefs have deteriorated badly due to increased sediment and nutrient run-off into the Great Barrier Reef lagoon.
Information was presented about the reef-flats by Dr David Wachenfeld that showed their condition at present compared with that as seen in historical photographs taken as much as one hundred years ago (see Reef Research Vol. 5, No. 3). Although, of the reef-flats studies, some appeared to have deteriorated badly (four sites), some are indeterminate (four sites), and seven show little or no evidence of change. Quantitative work on fringing reef slopes has been undertaken by Dr Ayling throughout the Great Barrier Reef World Heritage Area over the past 15 years and this shows there has been no degradation in terms of either hard coral cover or species composition over that period.
The crown-of-thorns starfish has been responsible for some of the greatest impacts on the Great Barrier Reef. It is still not known if outbreaks are natural events and, if they are, then the infestations should not be viewed as an adverse ecological event. As regular readers of the COTS COMMS section of this newsletter will be aware, another cycle of the coralliverous starfish, Acanthaster planci, is presently beginning. It appears to be following a similar pattern to the previous two cycles, although the beginnings of these occurrences were never documented since the outbreaks were only discovered after they were in full swing. It is still unclear whether human influences (such as water quality changes or predator removal) are exacerbating outbreaks and targeted research into possible causes of outbreaks is still required to better understand the phenomenon.
Of concern, is the status of dugong populations in the region. While populations in the northern part of the Great Barrier Reef World Heritage Area appear to be relatively stable, numbers south of Dunk Island have declined by about 50% over the past eight years. This decline is likely to be attributable to habitat loss, hunting and mortality in gill nets and varies from area to area. This suggests that dugong and the seagrass habitats require special protection. Seagrass habitats have been mapped for all the shallow areas of the Great Barrier Reef World Heritage Area and surveys in deeper water have recently commenced. About 4000 square kilometres of shallow water seagrass has been mapped and there is an estimated 2000 square kilometres in deeper water. Seagrasses are known to be important areas of primary production and, as well as providing food for dugong and turtles, are nursery areas for many species of fish and crustacea. Although it is thought that impacts are low to moderate, seagrass beds are ephemeral and it is important to increase our understanding of the scale and consequences of natural and anthropogenic impacts.
Also of concern is the status of the various turtle populations that have the Great Barrier Reef World Heritage Area as part of their habitat. All stocks are considered to be endangered or vulnerable and, although many of the threats to these wide-ranging animals are from regions outside the Great Barrier Reef World Heritage Area, harvesting by indigenous people, incidental kills by the commercial fishing industry, boat strikes and effects of lines and ropes are significant impacts that occur within the World Heritage Area. A lack of data for most species impedes management but, given the status of all turtles, it is necessary that they be protected to a greater degree than is presently the case.
Fisheries, both recreational and commercial, are one of the major uses of the region and have the potential to greatly affect the ecological stability of the area. Continued removal of top predators from reefs is bound, to a greater or lesser extent, to alter community dynamics and the large areas of benthos that are swept in the prawn fishery give cause for concern. While it appears that the present level of reef fishing may be sustainable, the effects of trawling in inter-reefal areas are largely unknown. The high level of by-catch from trawling and the disturbance or removal of the thousands of species of benthic organisms are cause for concern for large areas of the Great Barrier Reef World Heritage Area.
All of the above suggests that although the overall Great Barrier Reef World Heritage Area is still relatively pristine, there are a number of described threats and many more potential threats. The knowledge that we have and, just as importantly, the lack of knowledge in many spheres requires that management agencies take into account the precautionary approach when considering usage of the area. With luck, there will be an article on the state of the Great Barrier Reef World Heritage Area with regard to usage and management next issue.
Great Barrier Reef Marine Park Authority
PO Box 1379 TOWNSVILLE QLD 4810. Phone: (077) 500 700, Fax: (077) 726 093
E-mail: registry@gbrmpa.gov.au