Reef monitoring

Survey report

Dates:  15^th August - 5^th September 2007
Vessel: RV Lady Basten
Survey leaders: Alistair Cheal and Kate Osborne

Cooktown / Lizard Island sector
Cairns sector
Innisfail sector
 

Eight reefs in the Cooktown-Lizard sector of the Great Barrier Reef (GBR) were surveyed by manta tow. Detailed benthic surveys, counts of fishes and surveys for agents of coral mortality (SCUBA searches) were made on three pairs of reefs that have been selected as part of a program to assess the effects of rezoning the GBRMP in 2004 on reefs in the Cairns and Innisfail sectors. The overall program involves monitoring six pairs of reefs in each of 5 regions. The reefs in each pair were similar in size, morphology and distance from shore etc. One reef in each pair was open to fishing prior to 2004 and remained open to fishing; the other reef was also open to fishing prior to 2004 but was then rezoned as a no-take area. A further 3 reefs in the Cairns sector and 3 reefs in the Innisfail sector were surveyed by manta tow. Poor weather prevented surveys on 3 further pairs of rezoning assessment reefs that would complete the planned sampling for the Cairns area. These reefs will be surveyed later in the year. Pairs of reefs that were surveyed were Peart and Feather, McCulloch and Hedley, and Thetford and Moore. Preliminary results of the manta tow surveys and SCUBA search surveys are presented in this report.

There were no Active Outbreaks of crown-of-thorns starfish (COTS) on any of the surveyed reefs in the Cooktown Lizard, Cairns or Innisfail sectors. Several COTS were seen on Lizard Island Reef. Although COTS densities were below outbreak levels, this combined with the evidence of COTS activity on nearby reefs mean that starfish numbers on reefs in this region need to be followed closely. Increases in starfish numbers on reefs around or near Lizard Island in the early 1990s heralded the start of the current wave of outbreaks, so the low level COTS activity recorded over the last two years could signal the beginnings of a new series of outbreaks. Median reef-wide live coral cover on reefs in the Cooktown-Lizard and Cairns sectors was moderate (10-30%) and similar to those at the last survey. Median reef-wide live coral cover on reefs in the Innisfail sector was low (0-10%).

Six COTS was observed during manta surveys at Lizard Island compared with four COTS seen last year. Feeding scars were seen at North Direction Island and MacGillivray Reef during the manta tows and snorkellers found cryptic COTS nearby in each instance. Last year COTS were also recorded on North Direction Reef and Linnet Reef as well as at other reefs (Mackay, Stapleton and Reef 15-047) that were not surveyed this year. COTS numbers in the region declined from a peak of 0.53 COTS/tow in 1997 to zero in 2005, but small numbers of COTS have been recorded again in the last two annual surveys. The continued low level COTS activity on reefs on and around Lizard Island in the last two survey years may be significant. The first indication of the most recent series of outbreaks to affect reefs on the northern and central GBR (1992 – present) was a build up of COTS numbers on reefs in this area in the early 1990s. Importantly it appeared that these outbreaks were initiated from small increases in COTS abundance on a number of reefs over a number of years rather than one "primary outbreak" on a specific reef in a specific year. Reefs in this region will be watched closely in case this is the beginning of a new series of outbreaks for the northern and central GBR.

Click here for a larger view  Image 1: Large massive hard coral colonies (Diploastrea heliopora) stand out amongst the many smaller coral colonies that are indicative of recovery of coral cover on Lizard Island. This species of massive coral is usually avoided by crown-of-thorns starfish even when they are in outbreak densities. Photo: AIMS LTM

Image 2: Outer reef slope on Carter Reef showing dead tabulate corals in the immediate foreground, a live colony in the mid-ground and a colony with active white syndrome in the background (top right). There were many dead colonies such as this indicating disease has been recently active on this reef. Photo: AIMS LTM Click here for a larger view

Table 1. Summary of results of manta tow surveys of reefs in the Cooktown-Lizard sector of the Great Barrier Reef Marine Park 2007.

Reef	Shelf Position	Tows	Cots	Cots per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
LINNET	Inner	35	0	0	10 to 20	0 to 5	0 to 5	NO
MARTIN	Inner	51	0	0	10 to 20	0 to 5	0 to 5	NO
LIZARD IS	Mid	88	6	0.07	10 to 20	0 to 5	0 to 5	RE
MACGILLIVRAY	Mid	14	0	0	20 to 30	0 to 5	0 to 5	RE
NORTH DIRECTION IS	Mid	15	0	0	20 to 30	0 to 5	0 to 5	NO
CARTER	Outer	94	0	0	10 to 20	0 to 5	0 to 5	NO
NO NAME	Outer	51	0	0	10 to 20	0 to 5	0 to 5	NO
YONGE	Outer	75	0	0	10 to 20	0 to 5	0 to 5	NO

 

Cairns Sector

Click here for a larger view  Image 3: View of the reef slope on Low Isles showing a healthy cover Montipora spp. hard corals. These types of coral are common on inshore reefs and can increase coral cover rapidly once established. Photo: AIMS LTM

Click here for a larger view  Image 4: A view of reef slope taken on the first flank of Thetford Reef. This area of the reef now supports many small tabulate, digitate and sub massive corals following a COTS outbreak in 2000. Photo: AIMS LTM

Table 2. Summary of results of manta tow surveys of reefs in the Cairns sector of the Great Barrier Reef Marine Park 2007.

Reef	Shelf Position	Tows	Cots	Cots per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
FITZROY IS	Inner	35	0	0	20 to 30	0 to 5	0 to 5	NO
LOW ISLETS	Inner	32	0	0	20 to 30	0 to 5	20 to 30	NO
MACKAY	Mid	23	0	0	20 to 30	0 to 5	0 to 5	RE
PICKERSGILL	Mid	79	0	0	10 to 20	0 to 5	0 to 5	RE
THETFORD	Mid	41	0	0	10 to 20	0 to 5	5 to 10	RE

 

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References

English, S., Wilkinson, C. and Baker, V. (1997) Survey Manual for Tropical Marine Resources (2^nd Edition). Australian Institute of Marine Science. Townsville.

For further information contact
Dr. Hugh Sweatman, AIMS
Telephone: +61 7 4753 4470
Fax: +61 7 4753 4288
Email: h.sweatman@aims.gov.au  

October 10, 2007