Summary
- 17 reefs were surveyed in the Cairns sector.
- Sector-wide hard coral cover was moderate (10-30%) and has shown strong recovery from cumulative disturbances between 2016 and 2019 including mass coral bleaching and outbreaks of crown-of-thorns starfish (COTS).
- Hard coral cover had increased on all 17 reefs.
- One COTS was recorded at one reef.
- Low levels of hard coral bleaching were observed on several reefs.
Hard Coral Cover 0-10% 10-30% 30-50% 50-75% 75-100%
Figure 1: Map showing location of reefs in the Cairns sector. Click the points for more information.
Table 1: Overview of results obtained from manta tow surveys of reefs in the Cairns sector
| Cairns Sector | Summary | Trend since last survey |
|---|---|---|
| Average Coral Cover (%) | 21.9 | Increased |
| COTS status: | No Outbreaks | Stable |
| Coral bleaching: | Low | Stable |
As part of the Long-Term Monitoring Program (LTMP), manta tow surveys of hard coral cover and the abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris were completed on 17 reefs in the Cairns sector of the Great Barrier Reef (GBR) (Fig 1).
Preliminary results of the manta tow surveys are presented in Tables 1 and 2. The overall median hard coral cover for the sector was moderate (10-30%) (Table 1) (Fig 2) and had increased since previous surveys in 2020 (Fig 2).
Hard coral cover was very high (50 to 75%) on one reef, high (30 to 50%) on three reefs, and moderate (10-30%) on thirteen reefs (Table 2). Since the previous surveys hard coral cover had increased on all 17 reefs (Table 2).
One COTS was recorded at Evening Reef during manta tow surveys (Table 2). Sector-wide numbers of COTS were low and stable since previous surveys (Table 1, Fig 2).
Low levels of coral bleaching were recorded at a number of reefs, restricted to scattered individual colonies.
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 Long-Term Monitoring Program can be found on the AIMS website.
Table 2: Summary of manta tow surveys of reefs in the Cairns sector. Arrows indicate the trend in live coral cover and A. solaris since last survey; ▲ = increase, ▼ = decrease, " " = no change. Outbreak Status: NO no outbreak, PO potential outbreak >0.1 COTS per tow, IO incipient outbreak >.22 COTS per tow, RE recovering, AO = Active Outbreak>1 COTS per tow.
| Reef | Shelf Position | Tows | Previous survey year | Total A. solaris per reef | A. solaris per tow | A. Solaris Outbreak Status | Live Hard Coral Cover % | Soft Coral Cover % | Survey Year |
|---|---|---|---|---|---|---|---|---|---|
| FITZROY ISLAND REEF | Inner | 36 | 2017 | 0 | 0 | NO | 28.6 ▲ | 16 ▼ | 2021 |
| GREEN ISLAND REEF | Inner | 39 | 2019 | 0 | 0 | RE | 11.6 ▲ | 9.4 ▲ | 2021 |
| LOW ISLANDS REEF | Inner | 32 | 2020 | 0 | 0 | NO | 25 ▲ | 10.3 ▲ | 2021 |
| 16013A | Mid | 10 | 2020 | 0 | 0 | NO | 23.9 ▲ | 13.8 ▲ | 2021 |
| 16013B | Mid | 8 | 2020 | 0 | 0 | NO | 65.2 ▲ | 3 ▼ | 2021 |
| 16013C | Mid | 4 | 2020 | 0 | 0 | NO | 23.2 ▲ | 4 ▲ | 2021 |
| EVENING REEF | Mid | 50 | 2020 | 1 | 0.02 ▲ | RE | 25.6 ▲ | 4.3 ▲ | 2021 |
| MICHAELMAS REEF | Mid | 105 | 2019 | 0 | 0 | NO | 10.7 ▲ | 13.4 ▲ | 2021 |
| PICKERSGILL REEF | Mid | 81 | 2020 | 0 | 0 | NO | 33.7 ▲ | 7.3 ▲ | 2021 |
| NORMAN REEF | Outer | 35 | 2020 | 0 | 0 | NO | 19.2 ▲ | 6.9 ▲ | 2021 |
| OPAL (2) | Outer | 78 | 2019 | 0 | 0 | NO | 11.6 ▲ | 10.1 ▲ | 2021 |
| RACHEL CARSON REEF | Outer | 42 | 2020 | 0 | 0 | NO | 30.7 ▲ | 3.5 | 2021 |
| HASTINGS REEF | Mid | 65 | 2020 | 0 | 0 | NO | 15.9 ▲ | 13.1 ▲ | 2021 |
| MACKAY REEF | Mid | 23 | 2019 | 0 | 0 | RE | 32.8 ▲ | 7.7 ▲ | 2021 |
| THETFORD REEF | Mid | 39 | 2020 | 0 | 0 | NO | 15.5 ▲ | 13.4 ▲ | 2021 |
| AGINCOURT REEFS (NO 1) | Outer | 34 | 2020 | 0 | 0 | NO | 31.7 ▲ | 7.3 ▲ | 2021 |
| ST CRISPIN REEF | Outer | 82 | 2020 | 0 | 0 | NO | 19.9 ▲ | 9.2 ▲ | 2021 |
Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Cairns sector of the GBR. Orange trend line = Hard coral. Purple bars = Crown-of-thorns (COTS)
Image 1. A healthy coral assemblage on St. Crispin Reef indicating strong recovery from recurrent mass coral bleaching events in 2016, 2017 and 2020.
Image 2. Only one single COTS was recorded during manta tow surveys across seventeen reefs in the Cairns sector. This indicates that the current fourth wave has progressed south of this sector and in the absence of further disturbances, reefs offshore from Cairns should continue to recover back to pre-disturbance levels.
Image 3. The RV Solander is AIMS’ largest vessel and is an excellent platform from which to conduct research cruises for extended periods at sea.
Image 4. A promising sign for the future. Juvenile corals abound on the dead skeletons of their predecessors. This was a common sight during this cruise and indicates recovery has begun following COTS outbreaks and recurrent mass coral bleaching events.
