Whitsunday Pompey and Swain sectors 2015

Dates: 10^th January to 29^th January 2015

Vessel: RV Cape Ferguson

Survey leader: Ian Miller

As part of the Long Term Monitoring Program (LTMP), reef-wide live hard coral cover (henceforth coral cover) and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster planci, were completed on six reefs in the Whitsunday sector, four reefs in the Pompey sector and three reefs in the Swain sector of the Great Barrier Reef (GBR) using manta tow surveys. Intensive scuba surveys for benthic organisms and fishes as well as scuba searches for agents of coral mortality were also completed on nine reefs in the Whitsunday sector and two reefs in the Swain sector. Preliminary results of manta tow and scuba searches are presented in this report.

Coral cover on reefs surveyed by manta tow in the Whitsunday sector was moderate (10-30%) on mid-shelf reefs and low (0-10%) on outer-shelf reefs. No COTS were recorded during manta tows. All survey reefs in the Whitsunday sector were in the early stages of recovery from the effects of Severe Tropical Cyclone (STC) Hamish (category 5) that passed through the region in March 2009. Inner and mid-shelf reefs were less damaged by Cyclone Hamish than the outer-shelf reefs, which were effectively stripped of coral cover. Whitsunday reefs were also affected by Cyclone Ului, a category 2 storm that passed through this sector in March 2010. Low levels of coral bleaching that affected small numbers of individual scattered coral colonies were observed on all reefs manta towed in this sector except for one (Rebe Reef).

Coral cover on the four mid-shelf reefs surveyed by manta tow in the Pompey sector was moderate to high (30-50%) and had increased or remained similar to that recorded during previous surveys. No COTS were recorded during manta tow surveys. Reefs in this sector were also in the early stages of recovery following widespread destruction by STC Hamish. Low levels of coral bleaching were observed on all reefs manta towed in this sector.

Three reefs, one mid-shelf and two outer-shelf reefs in the Swain sector were surveyed by manta tows. Coral cover had increased on two reefs and decreased slightly on the third. Overall, reefs conform to the general trend of increasing coral cover seen recently on other reefs in this sector as they recover from the effects of COTS outbreaks and STC Hamish. Small numbers of COTS were observed on one outer-shelf reef and low levels of coral bleaching were observed on the one mid-shelf reef surveyed.

Occurrence of coral diseases on survey reefs in the Whitsunday sector was generally at or below background levels. Numbers of Drupella spp. (coral feeding snails) were also low, although large individuals of Drupella spp. were causing noticeable mortality on two reefs. Bleached corals were fairly obvious on three Whitsunday reefs. Agents of coral mortality recorded during scuba searches of two Swain reefs were around background levels at Chinaman Reef. The incidence of white-syndrome and brown band disease had increased on Horseshoe reef, probably related to a marked increase in coral cover in recent years. Levels of coral bleaching and numbers of Drupella spp. recorded in scuba searches on both reefs in the Swain sector were unexceptional when compared to previous surveys.

A summary of the results is presented in Tables 1 to 5. A full list of survey reefs appears in the Long-term Monitoring Status Report Number 8. Details of the monitoring program design, sampling methods and a full explanation of the COTS outbreak terminology used in this report can be found on the AIMS website.

Six reefs were surveyed using manta tow (Table 1) and intensive scuba searches were made on nine reefs (Table 2). All outer shelf reefs had low coral cover due to past mechanical damage from STC Hamish, a severe category 5 tropical rotating storm that passed within 40km of these reefs in March 2009. Outer-shelf reefs suffered the brunt of ocean swells generated by this intense weather system. As a result, hard and soft corals were stripped from much of the reef perimeters, leaving behind bare reef framework. Subsequent recovery was then hampered by the effects of Cyclone Ului, a category 2 system that passed through the region in March 2010. While Rebe Reef is yet to show any clear signs of recovery both Hyde and Slate Reef are showing the early stages of recovery with slightly increased coral cover since they were last surveyed in 2013. No COTS were observed on outer-shelf reefs in this sector in 2015.

Coral cover on mid-shelf reefs was moderate in 2015 (Table 1) and similar to the value recorded in the last survey in 2013. Coral cover had increased at two reefs (20-104 and 19-138) and remained stable at Reef 19-131. In the absence of COTS, increasing coral cover on reefs in this sector reflect the early stages of recovery after the effects of Cyclones Hamish and Ului.

Table 1. Summary results of manta tow surveys of reefs in the Whitsunday sector.

Reef	Shelf Position	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
19-131	Mid	55	0	0	10 to 20	0 to 5	0 to 5	NO
19-138	Mid	32	0	0	20 to 30	0 to 5	0 to 5	RE
20-104	Mid	25	0	0	20 to 30	0 to 5	0 to 5	RE
SLATE REEF	Outer	34	0	0	5 to 10	0 to 0	0 to 5	NO
HYDE	Outer	56	0	0	5 to 10	0 to 0	0 to 5	NO
REBE	Outer	32	0	0	0 to 5	0 to 0	5 to 10	NO
Overall GBR average for last survey – 2013	All			0.22	10 to 20	0 to 5	0 to 5	-
Long-term average value	Inner			0.01	10 to 20	0 to 5	10 to 20	-
Long-term average value	Mid			0.05	10 to 20	0 to 5	0 to 5	-
Long-term average value	Outer			0	20 to 30	0 to 5	10 to 20	-
Average last survey - 2013	Inner			0.03	5 to 10	0	10 to 20	-
Average last survey - 2013	Mid			0.02	10 to 20	0 to 5	0 to 5	-
Average last survey - 2013	Outer			0	0 to 5	0	0 to 5	-

Scuba searches on the nine intensive survey reefs (Table 2) found coral diseases including white syndrome (a disease-like necrosis found particularly on tabulate Acropora spp.), brown band disease and skeletal eroding band were at or below background levels. Virtually no diseases were seen on outer-shelf reefs, but coral cover on these reefs was low. Disease was rare elsewhere except at two reefs: 19-131 and 19-138, where there were above average levels of white syndrome. Numbers of Drupella spp. (coral feeding snails) were generally similar to those recorded when these reefs were last surveyed in 2013. The exceptions were Hayman Island Reef, Border Island Reef and Reef 20-104, where the density of snails was higher than the long term average. One COTS was recorded during scuba searches of the marked survey sites on Slate Reef. Above average levels of bleaching were recorded from three reefs (Slate, 19-138, 20-104) but was not widespread and only affected relatively small numbers of individual scattered coral colonies (mainly Seriatopora spp.).

Table 2. Summary results of scuba searches of reefs in the Whitsunday sector.

Reef	Shelf Position	COTS (<5cm)	COTS (>5cm)	COTS (>15cm)	COTS (>25cm)	WS	BBD	BrB	SEB	Drupella
HAYMAN IS	I	0	0	0	0	2	1	3	4	10
LANGFORD AND BIRD IS'S	I	0	0	0	0	9	0	3	0	0
BORDER IS (A)	I	0	0	0	0	0	0	0	0	18
19-131	M	0	0	0	0	14	1	2	1	3
19-138	M	0	0	0	0	12	0	2	0	3
20-104	M	0	0	0	0	8	0	1	5	15
SLATE REEF	O	0	0	1	0	2	0	0	0	5
HYDE	O	0	0	0	0	0	0	0	0	0
REBE	O	0	0	0	0	0	0	0	0	1
Overall GBR Average for last survey – 2013	All	0.15	1.1	2.2	1.2	5.4	0.085	2.7	2.4	11
Long term average	I	0	0	0	0	5.4	0.36	3.4	0.93	4.6
Long term average	M	0	0.14	0.16	0.13	9.3	0.056	5.3	2.2	8.7
Long term average	O	0.02	0.02	0.06	0	2.6	0.056	0.14	0.25	5.3
Average for last survey – 2013	I	0	0	0	0	4.3	0	7.3	0.33	13
Average for last survey – 2013	M	0	0	0.33	0	11	0	6.7	3.3	9.3
Average for last survey – 2013	O	0	0	0	0	0.33	0	0	0	3.3

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

Four mid-shelf reefs were surveyed using manta tow in the Pompey sector (Table 3). Coral cover was moderate on Credlin and Southampton Reefs. Coral cover on Credlin reef had increased from a very low level (0-5%) recorded in 2011 following a COTS outbreak in 2008 and the effects of STC Hamish that passed some 40km to the east of Credlin Reef in March 2009. Similarly coral cover at Southampton Reefs had increased from a very low level recorded in 2009 due to STC Hamish and prior COTS activity. Over the same time frame, coral cover on Reef 21-074 had increased from a moderate level in 2009 to a high level in 2015. No change in coral cover was recorded from Reef 21-140. No COTS were observed during manta tow surveys of reefs in this sector.

Table 3. Summary results of manta tow surveys of reefs in the Pompey sector

Reef	Shelf Position	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
CREDLIN	Mid	51	0	0	10 to 20	0 to 0	0 to 5	RE
SOUTHAMPTON (BRIGGS)	Mid	9	0	0	20 to 30	0 to 5	0 to 5	NO
21-074	Mid	37	0	0	30 to 40	0 to 5	0 to 5	NO
21-140	Mid	49	0	0	30 to 40	0 to 5	0 to 5	NO
Overall GBR average for last survey - 2013	All			0.22	10 to 20	0 to 5	0 to 5	-
Long-term average value	Inner			0	0 to 5	0	0 to 5	-
Long-term average value	Mid			0.27	30 to 40	0 to 5	0 to 5	-
Long-term average value	Outer			0	30 to 40	0 to 5	5 to 10	-
Average last survey - 2013	Mid			0.1	5 to 10	0	0 to 5	-
Average last survey - 2013	Outer			0	0 to 5	0	0 to 5	-

Three reefs, Chinaman, Horseshoe and East Cay were surveyed by manta tow in this sector (Table 3). Coral cover on Chinaman Reef had continued to increase and was very high (50-62%). Coral cover on Horseshoe Reef had increased from low to moderate. Both Horseshoe Reef and Chinaman Reef were recovering from the effects of STC Hamish and prior COTS outbreaks. Coral cover on East Cay had declined slightly but remained moderate. COTS were observed on East Cay but in numbers considered too low to impact on coral cover, so COTS are unlikely to have been responsible for the small decline on this reef compared to when it was last surveyed in 2014.

Table 4. Summary results of manta tow surveys of reefs in the Swain sector.

Reef	Shelf Position	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
CHINAMAN	Mid	29	0	0	50 to 63	0 to 5	0 to 5	NO
HORSESHOE	Mid	80	0	0	20 to 30	0 to 5	0 to 5	RE
EAST CAY	Outer	63	2	0.03	10 to 20	0 to 5	0 to 5	NO
Overall GBR average for last survey – 2013	All			0.22	10 to 20	0 to 5	0 to 5	-
Long-term average value	Inner			0	30 to 40	0 to 5	0	-
Long-term average value	Mid			1.24	10 to 20	0 to 5	0 to 5	-
Long-term average value	Outer			1.02	20 to 30	0 to 5	0 to 5	-
Average last survey – 2013	Mid			0.03	5 to 10	0	0 to 5	-
Average last survey – 2013	Outer			0.02	10 to 20	0 to 5	0 to 5	-

Two reefs were surveyed in detailed using scuba searches on fixed sites. Coral diseases including white-syndrome brown-band disease and skeletal eroding band were below historical background levels at Chinaman Reef, as were counts of Drupella spp. In contrast scuba searches at Horseshoe Reef found elevated levels of coral disease, particularly white-syndrome and brown band disease. Incidence of disease is strongly related to coral cover and in this case is likely a reflection on the good recovery in coral cover on this part of the reef (first flank) from a very low level in 2005 to the high level recorded in 2015.