Report on surveys of the Swain and Pompey sectors of the Great Barrier Reef

Dates: 22^nd November to 13^th December 2013

Vessel: MV Capricorn Star

Survey leader: Alistair Cheal

Manta tow surveys for the 2014 survey year were completed on ten reefs in the Swain sector, and six reefs in the Pompey sector of the Great Barrier Reef (GBR). Detailed surveys for benthic organisms, visual census of fishes and surveys for agents of coral mortality (scuba search) were made on the ten reefs in the Swain sector plus one more that had been manta towed previously. Detailed surveys were also made on four of the six reefs that were manta towed in the Pompey sector. Preliminary results of the manta tow and scuba search surveys are presented in this report.

Median reef-wide live coral cover in the Swain sector had increased or remained similar to that recorded during previous surveys with either moderate (10-30%) or high (30-40%) cover in 2014. Only two crown-of-thorns starfish (COTS) were recorded on one reef in the Swain sector during manta tows and none were observed during scuba surveys. A remarkable increase in coral cover on some reefs in the Swain sector highlights a general recovery in coral cover on reefs in the sector following widespread destruction by Severe Tropical Cyclone Hamish in March 2009.

In contrast, reefs in the Pompey sector showed few signs of recovery from Cyclone Hamish. Coral cover at five of six reefs that were manta towed in the Pompey sector had either remained low (0-10%) or had decreased to low levels in 2014. Active Outbreaks of COTS were recorded on three reefs in the Pompey sector. COTS in a range of sizes were also recorded during intensive scuba searches on two reefs. These outbreaks had been building since COTS were first recorded on those reefs in 2008 or 2010 suggesting that COTS numbers are increasing in the Pompey region. Overall, Cyclone Hamish followed by intensifying COTS outbreaks have combined to cause major coral declines in the Pompey sector since the mid-late 2000's when cover ranged between moderate and high (20 -50%) on all six reefs. Only one reef (Pompey No.1) showed signs of recovery in coral cover in 2014.

Signs of coral disease and counts of Drupella spp. on reefs surveyed using scuba were generally similar to previous surveys. Exceptions were Small Lagoon Reef and the adjacent Jenkins Reef in the Swain sector, where incidences of white syndrome and brown band disease were relatively high, and Reef 20-348 in the Pompey sector where skeletal eroding band disease was high compared to previous years.

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]. For a full explanation of COTS outbreak terminology refer to the following web-page: Crown-of-thorns on the Great Barrier Reef.

* Survey year reflects financial year of survey, for instance the 2012 survey year represents reefs surveyed between July 2011 and June 2012. Surveys for this current financial

Perimeters of ten reefs were surveyed using manta tow (Table 1). Three sites on each of these reefs were also surveyed in detail using scuba (Table 2). Only two COTS were recorded during manta tows, both on Reef 21-245. No COTS were observed using scuba search. The majority of reefs in this sector were heavily impacted by Cyclone Hamish in March 2009. Surveys in 2014 found evidence of recovery in coral cover on the majority of reefs. Reef 21-139, 21-187, 21-245, 21-296 and Small Lagoon have shown an increase in coral cover from a low level (0-10%) recorded post Cyclone Hamish to moderate levels (10-30%) in 2014. Coral cover at Jenkins Reef and Reef 21-558 has increased even more rapidly from low levels post Cyclone Hamish to high levels (30-50%) in 2014.

Table 1. Summary of manta tow surveys for reefs in the Swain sector.

Scuba searches on the intensive survey sites (Table 2) found that incidences of disease were generally low or isolated with no consistent patterns among reefs. Incidences of white syndrome and brown band disease were relatively high on Small Lagoon Reef and the adjacent Jenkins Reef but the significance of this is not clear. Counts of Drupella spp. were variable among reefs but were particularly elevated at Small Lagoon Reef and Wade Reef compared to previous years. However, these values were within the ranges of previous counts on all eleven reefs in the Swain sector.

Table 2. Summary of SCUBA search survey results for the Swain sector.

I=inner, M=mid, O=outer, WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease.

For more information on coral disease refer to the AIMS web site at: AIMS Long Term Monitoring - Coral Diseases on the Great Barrier Reef - Introduction

Perimeters of six reefs were surveyed using manta tow (Table 3). Sites on four of these reefs were also surveyed in detail using scuba (Table 4). COTS were recorded during manta tow surveys at four reefs. One of these reefs was designated No Outbreak as only one COTS was seen, but numbers of COTS on the other three reefs were large enough to constitute Active Outbreaks. Reef 21-062 was designated Active Outbreak when last surveyed in 2008. COTS numbers have continued to increase on both Reef 21-060 and Reef 21-064 since they had Incipient Outbreak densities of starfish in 2010, (both reefs were reclassified as Active Outbreaks in 2012). Two of these reefs (21-062 and 21-064) were also surveyed using scuba and adult COTS of a range of sizes were found on each.

Median reef-wide live coral cover on survey reefs had either remained relatively stable or had decreased since last surveyed. Decreases in coral cover were almost certainly caused by a combination of damage from Cyclone Hamish in 2009 and subsequent COTS activity. COTS were active on Reef 21-060, Reef 21-062 and Reef 21-064 and coral communities had been decimated with coral cover at low (5-10%) to very low (0-5%) levels. While the relative impact of COTS versus cyclone activity is unclear, high densities of COTS (up to 2.96 COTS/tow, Table 3) would have caused significant mortality to corals that survived Cyclone Hamish. For example, at Reef 21-064 there is little doubt that loss of over half the coral cover (20-30% to 5-10%) since 2012 is largely due to COTS. This followed previous declines (40-50% to 20-30%) due to Cyclone Hamish. Overall, the impacts of Cyclone Hamish, backed up by intensifying COTS outbreaks, have caused cover of coral in the Pompey sector to decline considerably over an extended period. In the mid-late 2000's coral was abundant on all six reefs with cover ranging from moderate to high (20 -50%). By 2014 five of these reefs had low to very low cover (0-10%) and only Pompey Reef (No.1) had recovered to a moderate cover (20-30%) post Cyclone Hamish.

The ongoing outbreaks reflect a pattern of elevated COTS activity recorded over the last decade on reefs in the Pompey sector. These outbreaks may represent the current position of the wave of COTS outbreaks that was first detected in the Lizard Is region in 1994 and has progressed southwards in the intervening period. The remoteness of these reefs makes it unlikely that terrestrial runoff has a direct role in the occurrence of the outbreaks. The results of manta tow surveys in the Pompey sector show how COTS activity can severely curtail any recovery on reefs that have suffered other disturbances such as cyclones. They stand in stark contrast to the remarkable recovery in coral cover seen on reefs in the Swains sector in the absence of COTS.

Table 3. Summary of manta tow survey results for the Pompey sector.

Scuba searches on four reefs in this sector found very low incidences of coral disease, except for skeletal eroding band disease on Reef 20-348 (Table 4). The reason for this increase is unknown. Drupella spp. were observed on all three reefs but in numbers that would not be considered exceptional.

Table 4. Summary of SCUBA search survey results for the Pompey sector.

M=mid, WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease.