SITE DESCRIPTION Wheeler Reef is an outer reef located east of Townsville and is sheltered on one side. It is a green zone in the GBRMP and would be considered one of the most pristine sites in the area due to its high percentage of live coral cover. It is visited by up to 3 liveaboard operations and one day boat 4 times a week and anthropogenic impact is considered low. Dive tourism and anchoring could be considered the main impact. There is one public mooring and anchoring does occur at the site. The reef flat leads to a wall and a number of bommies, canyons and patches of reef surrounded by sand, reaching depths of 40m and above. There is a large lagoonal area and sand cay. The site exhibits a huge coral coverage and diversity. The shallow transect on the north side of the reef had a larger proportion of sand as the reef was mainly bommies and a wall, whereas the deeper site on the west side of the reef was more consistent reef community. A comparison was not made with data collected in 2003 due to insufficient data.
SUBSTRATE SURVEY Site 1 Shallow: Wheelr Reef has an extremely high level of hard coral cover with 57.5% noted in the 5m site. 37.5% of this amount is branching Acropora sp. There is 17.5% of Rock with equal levels of turf algae and coralline algae. There is just over 6% soft coral cover and 16% of sand on the transect (figures 1 and 2).
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Percent Cover of Substrate for Wheeler Reef (Site 1 5m depth) 25-04-04
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Figure 1: 57.5% of the substrate is hard coral in the 5m site. Percent Cover of Substrate for Wheeler Reef (Site 1 5m depth) 25-04-04 70
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Figure 2: Branching hard coral dominates the substrate in the 5m site.
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Site 2 Deep: Just over 70% of the substrate in the 8m site is hard coral, of which 56% is branching hard coral, namely Acropora sp. There was 14.4% of Rock, the majority of this being turf algae. There is only 5.6% of sand on the transect (figures 3 and 4).
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Percent Cover of Substrate for Wheeler Reef (site 2 8m depth) 24-04-04 80 70 60 50 40 30 20 10 0 HC
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Figure 3: The hard coral cover is even higher at the 8m site Percent Cover of Substrate for Wheeler Reef ( site 2 8m depth) 24-04-04 80
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Figure 4: Similar to the shallow site, the majority of the substrate is branching hard coral.
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INVERTEBRATES SURVEY Site 1 Shallow: Giant clams are the dominant invertebrate found at the shallow site with a mean abundance of 4.75 per 100m2. There is a mean abundance of Drupella of 3.25 and occurrences of Diadema, four sea cucumber species and Crown of Thorns (figure 5). The majority of giant clam sizes are 20-30cm (figure 6). Mean Abundance of Invertebrates at Wheeler Reef (Site 1 5m depth) 25-04-04
7
Mean Abundance +-SE
6 5 4 3 2 1
Figure 5: The dominant key invertebrate in the shallow site is the Giant Clam. Distribution of Giant Clams by Size at Wheeler Reef (Site 1 5m depth) 25-04-04
2.5 100 m2
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Figure 6: The majority of the Giant Clams found at the 5m site were 2030cm in length.
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Site 2 Deep: There is a mean abundance of 9.5 Drupella per 100m2 at the 8m site and a larger number of Crown of Thorns (mean abundance 3 per 100m2) than at the 5m site. There were fewer giant clams (mean abundance 3 per 100m2).See figure 7. Mean Abundance of Invertebrates at Wheeler Reef (site 2 8m depth) 24-04-04 20 18
Mean Abundance +-SE
16 14 12 10 8 6 4 2
Figure 7: The dominant key invertebrate at the 8m site is the coral eating snail Drupella.
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IMPACTS SURVEY Site 1 Shallow: There is a mean of 4.5 Drupella scars per 100m2 counted at the site and other damage and other scars at approximately 5 counted per 100m2 (figure 9). Mean Abundance of Impacts at Wheeler Reef Mean Abundance per 100 m2
(Site 1 5m depth) 25-04-04
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Figure 9: Drupella snails proved to be the largest impact in the shallow site. Site 2 Deep: Crown of Thorns Scars, indicating the presence of Crown of Thorns, are the largest impacts with a mean abundance of 5.75 per 100m2 followed by Drupella at 5.5 per 100m2. Other scars and other damage had mean abundances of 2.75 and 3.25 per 100m2 respectively (Figure 10)
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(site 2 8m depth) 25-04-04
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Mean Abundance per 100 m2
Mean Abundance of Impacts at Wheeler Reef
Figure 10: Crown of Thorns and Drupella were the largest impacts in the 8m site.
BLEACHING Site 1 Shallow: Only 3% of the coral population in the 5m site was found to be bleached and out of this an average of 30% of the coral surface was affected by bleaching, namely the upper surfaces of branching Acropora sp.(figure 11) There was a greater abundance of bleached corals with less than 25% of their surface bleached (figure 12) Estimated Percentage of Coral Population
Estimated Mean Percentage of Coral
Affected by Bleaching
Surface affected by Bleaching
Wheeler Reef Site 1 25-04-04
Wheeler Reef Site 1 25-04-04
3%
Bleached Corals (%) Non-bleached Corals (%)
Colony surface bleached (%)
30%
Colony surface non-bleached (%)
70%
97%
Figure 11: Estimated percentages of the total coral population affected by bleaching and the surface area affected. Bleached Coral Distribution at Wheeler Reef (Site 1 5m depth) 25-04-04 7 6