Report on surveys of the Cooktown-Lizard sector of the Great Barrier Reef

Summary

• 26 reefs were surveyed in the Cooktown-Lizard Island sector.
• Sector-wide hard coral cover was moderate (10-30%) and has shown strong recovery from cumulative disturbances between 2013 and 2017.
• Hard coral cover had increased on twenty reefs and had declined on six reefs.
• Low levels of crown-of-thorns starfish (COTS) were recorded at two reefs.
• Low levels of hard coral bleaching were observed on one reef.

Hard Coral Cover   0-10%  10-30%  30-50%  50-75%  75-100%

Figure 1: Map showing location of reefs in the Cooktown-Lizard sector. Click the points for more information.

Table 1: Overview of results obtained from manta tow surveys of reefs in the Cooktown-Lizard sector

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 26 reefs in the Cooktown-Lizard Island 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 2019 (Fig 2).

Hard coral cover was very high (50 to 75%) on one reef, high (30 to 50%) on four reefs, moderate (10-30%) on eighteen reefs and low (0 to 10%) on three reefs (Table 2). Since the previous surveys hard coral cover had increased on twenty reefs and declined on six reefs (Table 2).

One COTS were recorded each at Lizard Island and Fly 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 one reef, restricted to scattered individual colonies.

Table 2: Summary of manta tow surveys of reefs in the Cooktown-Lizard 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.

Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Cooktown-Lizard sector of the GBR. Orange trend line = Hard coral. Purple bars = Crown-of-thorns (COTS)

Image 1. High coral cover on Linnet Reef indicating strong recovery from cumulative disturbances since 2013 which have included crown-of-thorns starfish outbreaks, mass coral bleaching and two severe tropical cyclones.

Image 2. The front reef slope at Carter Reef with moderate coral cover. While there has been some recovery on these outer reefs, the dominant corals have changed from table Acropora to sub-massive Pocillopora colonies.

Image 3. An AIMS diver conducting surveys of agents of coral mortality at Yonge Reef.

Image 4. A school of snub-nosed darts (Trachinotus blochii) patrol the front reef of Reef 14-075.

Trends in benthic community compostion from fixed site surveys