Survey report - Report on reef surveys in the Innisfail, Townsville and Cairns sectors of the Great Barrier Reef

Dates: 28thApril - 17thMay 2009

Vessel:MV Phoenix

Survey leaders:

Kate Osborne

Innisfail Sector reefs

Townsville Sector reefs

Cairns Sector reefs

Summary

As part of ongoing surveys by the AIMS long term monitoring team, six reefs in the Innisfail sector and five reefs in the Townsville sector of the Great Barrier Reef were surveyed using manta tows. The same five Townsville sector reefs plus four others were also surveyed using SCUBA to provide more detailed information on benthic organisms, reef fishes and agents of coral mortality. One reef in the Cairns sector (Hastings) was surveyed after being missed earlier in the year due to bad weather. Preliminary results of the manta tow surveys and SCUBA searches for causes of coral mortality are presented in this report.

No crown-of-thorns starfish (COTS) were recorded during manta tow surveys in the Townsville or Innisfail sectors. Median reef-wide live hard coral cover (henceforth coral cover) in the Innisfail sector was low (5-10%) on three reefs and moderate (10-30%) on three reefs. Coral cover had increased on all but one reef since the last survey. Small tabulate Acropora spp. hard corals were common. Recovery from low coral cover recorded in previous years now appears to be underway.

Coral cover on one outer reef in the Townsville sector had increased slightly. Two mid-shelf reefs (Rib and Davies) had slightly increased coral cover, while coral cover at John Brewer Reef remained very low. Havannah Reef was the only inner shelf reef to be surveyed. It had low coral cover that was little changed from previous surveys.

SCUBA searches on reefs in the Townsville sector found no COTS. Signs of coral disease were rare on all reefs except Hastings Reef (Cairns sector) where the number of diseased colonies was low. Numbers of Drupella spp. (coral feeding snails) were within the range of previous levels recorded at each reef surveyed. Low levels of bleaching were observed on the inner reefs. Bleaching was likely related to fresh water inundation during the 2008/09 wet season. Incidental observations at Middle Reef suggest there has been substantial mortality of coral on the reef flat. Low levels of physical damage were also noted on four reefs in the Townsville sector (Pandora, Middle, Davies and Rib).

A summary of the results is presented in Tables 1, 2 and 3. A full list of survey reefs appears in the Long-term Monitoring Status Report Number 8. Details of the monitoring program design, the sampling methods and a full explanation of the COTS outbreak terminology used in this report can be found on the AIMS reef monitoring website.

Innisfail Sector reefs

Six reefs were surveyed using manta tows (Table 1). No COTS were recorded on any of the survey reefs during manta tows, but two COTS were seen at Noggin Reef in the lagoon near the anchorage outside surveys. Coral cover was low (5-10%) on three reefs and moderate (10-30%) on three reefs. There had been a small increase in coral cover (>5%) on five of the reefs since the last survey. Scott Reef showed a significant increase and now has the highest coral cover recorded since first surveyed in 1986. The generality of this increase along with obvious increases numbers of tabulate Acropora spp. colonies suggests that these reefs are showing strong signs of recovery from COTS outbreaks in recent years and, in some cases, also from storm damage from Cyclone Larry, a category 5 system that passed through the region early in 2006.

Image 1. Scott Reef in the Innisfail sector is in the process of recovering from a crown-of-thorns starfish outbreak that ended in 1998. It now has the highest reef-wide live coral cover recorded since it was first surveyed by manta tow in 1986.

Photo: AIMS LTMP

Image 2. Beaver Reef (Innisfail sector) is also showing strong signs of recovery from a crown-of-thorns starfish outbreak that ended in 2000 and the effects of Cyclone Larry that impacted reefs in the region in early 2006. Though coral cover remains low it has increased from when last surveyed in 2007.

Photo: AIMS LTMP

Table 1. Summary of manta tow survey results for six reefs in the Innisfail sector.

Manta tow surveys were completed on five reefs in the Townsville sector (Table 2). Two outer shelf reefs, Dip and Myrmidon could not be surveyed due to bad weather. Coral cover on one outer reef, Chicken Reef, has increased (>5%) but does not yet show a consistent recovery trend from a COTS outbreak that ended in 2005. Coral cover on two mid-shelf reefs, Rib and Davies, had increased slightly (>5%) while coral cover on John Brewer was very low (1-5%) and little changed from the last survey. All three reefs are in the early stages of recovering from COTS outbreaks at the start of the decade. Havannah Reef was the only inner shelf reef surveyed. It had low coral cover as in previous surveys. Havannah Reef is showing few signs of recovery from a devastating loss of coral cover due to the 1998 bleaching event.

SCUBA searches on reefs in the Townsville sector found no COTS (Table 3). One COT was seen near the monitoring sites at Rib Reef, which was outside the survey area. Signs of coral disease were rare on all reefs. Numbers of Drupella spp. (coral feeding snails) were within the range previously recorded at each reef. Low levels of bleaching were observed on the inner reefs. Bleaching was likely due to fresh water inundation during the 2008/09 wet season. Incidental observations at Middle Reef suggest there had been substantial mortality of coral on the reef flat. Low levels of physical damage were also noted on four reefs (Pandora, Middle, Davies and Rib). Damage appeared to be related to storm action, with broken branching Acropora spp., overturned tabulate Acropora spp. and Pocillopora spp. being most common. Some large blocks had been overturned at Pandora Reef. The damage at Pandora Reef was almost certainly due to the effects of Cyclone Ellie, a Category 1 system that passed to the north of the reef in early February 2009. Large overturned blocks were also observed at Middle Reef.

Image 3.John Brewer Reef in the Townsville sector suffered a spectacular and intense crown-of-thorns starfish outbreak between 2001 and 2004. The relatively short time elapsed since this outbreak means reef-wide coral cover remains very low. Despite the low coral cover some signs of recovery (such as this small tabulate coral growing on the remains of an old dead one) are now evident.Photo:AIMS LTMP

Image 4.Further south Davies Reef, while supporting large numbers of crown-of-thorns starfish between 2002 and 2005, did not suffer to the same extent as John Brewer Reef hence reef-wide live coral cover is higher. Here a large massivePoritessp. hard coral makes a spectacular backdrop for reef surveys. Photo:AIMS LTMP

Table 2. Summary of manta tow survey results for reefs in the Townsville sector.

Table 3. Summary of results of SCUBA searches on reefs in the Townsville sector.

WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease. Figures are the number of starfish (COTS), number of scars (WS, BBD, BrB, SEB) or snails ( Drupella ) recorded at each reef.

SCUBA searches on Hastings reef in the Cairns sector found no COTS and low levels of coral disease. White Syndrome was the most common but Brown Band and SEB were also recorded. Numbers of Drupella sp. were similar to past years (Table 4).

Table 4. Summary of results of SCUBA searches on reefs in the Cairns sector.

WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease. Figures are the number of starfish (COTS), scars (WS, BBD, BrB, SEB) or snails ( Drupella spp.) recorded at each reef

References

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

 

This project is partially supported by the Marine and Tropical Sciences Research Facility

Dr. Hugh Sweatman , AIMS

Telephone: +61 7 4753 4470

Fax: +61 7 4753 4288

Email: h.sweatman@aims.gov.au