8th June 2017
Summary
- Coral cover was low across the sector due to effects of crown-of-thorns starfish (COTS), Cyclone Ita (2014), Cyclone Nathan (2015) and coral bleaching (2016).
- COTS activity has decreased with no COTS observed.
- Bleaching was observed at low levels.
Figure 1: Map showing location of reefs in the Cooktown/Lizard Island sector. Click on figure to go to AIMS Spatial Maps and then click on symbols for information on individual reefs.
Table 1: Overview of results obtained from manta tow surveys of reefs in the Cooktown-Lizard sector.
| Cooktown / Lizard Island Sector | Summary | Trend since last survey |
|---|---|---|
| Median Coral Cover | Low (0-10%) | Decreased |
| COTS status: | No Outbreaks | Decreased |
| Coral bleaching: | Low | Stable |
As part of the Long Term Monitoring Program (LTMP), manta tow surveys of coral cover and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster planci, were completed on 11 reefs in the Cooktown-Lizard sector of the Great Barrier Reef (GBR - see Figure 1) during two trips in August, 2016 and January, 2017. Median reef-wide live coral cover (coral cover) was already low at three inner-shelf and mid-shelf reefs (0-5%). Coral cover declined on five outer-shelf reefs and two inner shelf reefs. The southern-most survey reef (15034S) was the only reef where coral cover remained moderate (Table 2). No A. planci were observed during manta tow surveys on these reefs in 2017 (Table 1). Qualitative assessments of bleaching from manta tow surveys in 2017 found low levels of bleaching with the maximum level recorded at any reef being 0-5%. Declines in coral cover may be attributed to a number of factors including coral bleaching in early 2016, mechanical damage resulting from Cyclone Nathan in 2015 and to ongoing COTS feeding activity (Figure 2).
Table 2: Summary of manta tow surveys for reefs in the Cairns sector.Arrows indicate the trend in live coral cover and A. planci since last survey; ▲ = increase, ▼ = decrease, “ ” = no change. Reef status refers to COTS impact where NO = No Outbreak, and RE = Recovering from a previous outbreak.
| Reef | Shelf Position | Tows | Previous survey year | A. planci | A. planci per tow | Median Live Coral Cover | Median Soft Coral Cover | Reef Status |
|---|---|---|---|---|---|---|---|---|
| LINNET | Inner | 36 | 2013 | 0 ▼ | 0 | 0-5% ▼ | 0-5% | RE |
| MARTIN | Inner | 54 | 2013 | 0 ▼ | 0 | 0-5% ▼ | 0-5% | RE |
| LIZARD IS | Mid | 88 | 2015 | 0 ▼ | 0 | 0-5% | 0-5% | RE |
| MACGILLIVRAY | Mid | 14 | 2015 | 0 ▼ | 0 | 0-5% | 0-5% | RE |
| NORTH DIRECTION IS | Mid | 16 | 2015 | 0 | 0 | 0-5% | 0-5% | RE |
| 15-034 | Outer | 29 | 2013 | 0 | 0 | 10-20% | 0-5% | NO |
| CARTER | Outer | 87 | 2015 | 0 | 0 | 0-5% ▼ | 0-5% | NO |
| HARRIER | Outer | 16 | 2015 | 0 | 0 | 5-10% ▼ | 0-5% | NO |
| NO NAME | Outer | 58 | 2015 | 0 | 0 | 0-5% ▼ | 0-5% | NO |
| RIBBON NO.6 | Outer | 55 | 2015 | 0 | 0 | 5-10% ▼ | 0-5% | NO |
| YONGE | Outer | 78 | 2015 | 0 | 0 | 0-5% ▼ | 0-5% | NO |
Dates: 28th August 2016 – 13th January 2017
Vessel: RV Cape Ferguson
Survey leader: Ian Miller and Kate Osborne
Details of the manta tow method and results can be found here.
Click here for further details of the monitoring program design, sampling methods and a full explanation of the A. planci outbreak terminology.
For enquiries, please contact monitoring@aims.gov.au
Figure 2: Sector wide changes in coral cover and the numbers of COTS (A.planci) through time for all survey reefs in the Cooktown-Lizard sector of the GBR.
Image 1: Photograph taken on the reef crest at Carter Reef, an offshore reef in the Cooktown-Lizard sector. Coral bleaching in 2016 extended the zone of low coral cover into the shallows. Much of the reef slope already had low coral cover following cyclones in 2014 and 2015.
Image 2: Some corals have managed to survive three years of repeated disturbance. Small massive corals were the dominant coral lifeform on the reef slope at MacGillivray Reef in 2017.
