Summary
- One reef (Bowden Reef) was surveyed in this sector.
- Coral cover was higher than sector-wide cover recorded during previous surveys.
- Small numbers of COTS were observed.
Figure 1: Map showing location of reefs in the Cape Upstart sector. Click on figure to go to AIMS Spatial Maps for information on individual reefs.
Table 1: Overview of the results of manta tow surveys of one reef in the Cape Upstart sector.
| Cape Upstart Sector | Summary | Trend since last survey |
|---|---|---|
| Median Coral Cover | Moderate (10-30%) | Increased |
| COTS status: | No Outbreaks | Stable |
| Coral bleaching: | None | Decreased |
As part of the Long Term Monitoring Program (LTMP), Bowden Reef in the Cape Upstart sector of the Great Barrier Reef (GBR) was surveyed for coral cover and the abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris* by manta tow. Preliminary results are presented in Tables 1 and 2. These show that median reef-wide live coral cover (coral cover) on Bowden Reef declined slightly since last surveyed in 2015 but remained moderate (20-30%). This was possibly due to effects of coral bleaching in 2017. Small numbers of COTS were also recorded but at levels below those expected to cause significant coral mortality. The presence of COTS on this reef fits with the hypothesis that waves of COTS outbreaks move southward through the northern and central GBR as COTS larvae are transported on prevailing currents. COTS numbers can be expected to increase on reefs in the sector in coming years as has happened in the past. In 2018 coral cover on Bowden Reef was higher than the average coral cover on reefs in this sector in 2015.
Details of the manta tow method can be found in the Standard Operational Procedure No. 9 [AIMS Research - Crown-of-thorns Starfish and Coral Surveys - Standard Operational Procedure 9]. Further details of the monitoring program design, sampling methods and a full explanation of the A. solaris outbreak terminology can be found on the AIMS website.
*Note: genetic studies show that there are at least four species of COTS. These are the North and South Indian Ocean species (A. planci and A. mauritiensis), a Red Sea species (not yet named) and a Pacific species. The range of the Pacific includes the Great Barrier Reef and it has been provisionally named Acanthaster solaris (Haszprunar et. al. 2017).
Table 2: Summary of manta tow surveys of reefs in the Cape Upstart sector. Arrows indicate the trend in live coral cover and A. cf. solaris since last survey; ▲ = increase, ▼ = decrease, “ ” = no change.
| Reef | Shelf Position | Tows | Previous survey year | A. solaris | A. solaris per tow | Median Live Coral Cover | Median Soft Coral Cover | Reef Status |
|---|---|---|---|---|---|---|---|---|
| BOWDEN | Mid | 80 | 2015 | 3 ▲ | 0.04 | 10-30% ▼ | 0-5% | RE |
Figure 2: Sector-wide changes in coral cover and the numbers of A. cf. solaris on survey reefs in the Cape Upstart sector of the GBR.
Image 1: Coral cover was very high on parts of the front reef and included a variety of different colours and life forms.
Image 2: Large areas of sand on the back reef were characterized by callianassid shrimp mounds. These crustaceans burrow into the bottom and play an important role turning over sediments.
Image 3: The presence of COTS on Bowden Reef was unsurprising given that there have been outbreaks on several reefs just to the north in recent years.
