Summary
Eight reefs were surveyed in this sector.
- Sector-wide hard coral cover was high (30-50%).
- Five reefs were previously surveyed in 2018; hard coral cover had increased on three reefs and had declined marginally on two.
- Two reefs were previously surveyed in 2019 and hard coral cover had declined marginally on both.
- Low levels of crown-of-thorns starfish (COTS) were recorded at one reef.
- Low levels of coral bleaching were observed on fixed site surveys.
Hard Coral Cover 0-10% 10-30% 30-50% 50-75% 75-100%
Figure 1: Map showing location of reefs in the Capricorn-Bunker sector. Click the points for more information.
Table 1: Overview of results obtained from manta tow surveys of reefs in the Capricorn-Bunker sector
| Capricorn Bunkers Sector | Summary | Trend since last survey |
|---|---|---|
| Average Coral Cover (%) | 44.5 | Decreased |
| COTS status: | No Outbreaks | Decreased |
| 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 eight reefs in the Capricorn-Bunker 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 high (30-50%) (Table 1) (Fig 2) and had declined marginally since the previous surveys in January 2019 (Fig 2).
Hard coral cover was high (30 to 50%) on seven reefs and very high (50 to 75%) on the remaining one (Table 2). Five reefs were previously surveyed in October 2017 and hard coral cover had increased on three reefs and had declined marginally on two. Masthead Reef was last surveyed in 2014 and currently has high hard coral cover (30 to 50%).
Two COTS were recorded at a single reef during manta tow surveys (Table 2) and sector-wide numbers of COTS were low and had decreased since previous surveys (Table 1, Fig 2). No COTS outbreaks were recorded.
More detailed fixed site surveys on scuba recorded low levels of coral bleaching on most reefs, restricted to scattered individual colonies. Cases of coral disease were low on all reefs and within the range reported in previous years, as were numbers of the corallivorous snail, Drupella spp. Very low numbers of COTS were recorded during fixed site surveys on two reefs Boult Reef and Fairfax Reef.
More detailed results on fish and benthic assemblages from fixed site surveys will be available soon.
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.
Table 2: Summary of manta tow surveys of reefs in the Capricorn-Bunker 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 |
|---|---|---|---|---|---|---|---|---|---|
| BOULT REEF | Outer | 44 | 2018 | 2 | 0.05 ▲ | NO | 49 ▲ | 4 ▼ | 2020 |
| ERSKINE REEF | Outer | 19 | 2018 | 0 | 0 | NO | 42 ▲ | 3.5 ▲ | 2020 |
| FAIRFAX ISLANDS REEF | Outer | 40 | 2018 | 0 | 0 ▼ | NO | 39.3 ▲ | 6.7 ▼ | 2020 |
| HOSKYN ISLANDS REEF | Outer | 33 | 2018 | 0 | 0 | NO | 47.8 ▼ | 4.2 ▼ | 2020 |
| MAST HEAD REEF | Outer | 65 | 2014 | 0 | 0 | NO | 38.2 ▲ | 2.4 ▼ | 2020 |
| NORTH REEF (NORTH) | Outer | 37 | 2018 | 0 | 0 | NO | 41.7 ▼ | 8 ▼ | 2020 |
| BROOMFIELD REEF | Outer | 50 | 2019 | 0 | 0 | NO | 51.7 ▼ | 6.8 ▲ | 2020 |
| LADY MUSGRAVE REEF | Outer | 61 | 2019 | 0 | 0 ▼ | NO ▼ | 49.7 ▼ | 4.8 ▲ | 2020 |
Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Capricorn-Bunker sector of the GBR. Orange trend line = Hard coral. Purple bars = Crown-of-thorns (COTS)
Image 1. A diver conducting fixed site surveys at Lady Musgrave Island.
Image 2. High to very high coral cover was a feature of many reefs in this sector. Many sites situated on the exposed reef slopes were dominated by table Acropora colonies.
Image 3. Some reefs had yet to recover fully from previous disturbances which included cyclones and some crown-of-thorns starfish activities.
Image 4. Turtles were abundant during surveys and could often be seen resting on the bottom sheltered under table corals.
