Report on surveys of the Capricorn-Bunker, Swain and Pompey sectors of the Great Barrier Reef

Dates: 22^nd August to 11^th September 2012

Vessel: RV Cape Ferguson

Survey leader: Alistair Cheal

Summary

Manta tow surveys and scuba surveys for benthic organisms, fishes and agents of coral mortality were completed on four reefs in the Capricorn-Bunker sector and seven reefs in the Swain sector of the Great Barrier Reef (GBR). A further six reefs in the Pompey sector were manta towed. Preliminary results of the manta tow and scuba searches for agents of coral mortality are presented in this report.

Median reef-wide live coral cover was variable but most often low (<10%) in all three sectors predominantly, due to the devastating and widespread effects of severe cyclone Hamish in 2009. Coral cover at each reef was generally similar to that last reported in 2010 or 2011.

Crown-of-thorns starfish (COTS) were recorded during manta tow surveys at one reef in the Capricorn-Bunker sector, two reefs in the Swain sector and one reef in the Pompey sector. Numbers of COTS were sufficient at Lady Musgrave Island Reef (Capricorn-Bunker sector) and Creal Reef (Pompey sector) for these reefs to be reclassified as Incipient Outbreaks; the first such outbreaks at either reef since manta tow surveys began in the mid 1980's.

Scuba surveys revealed that incidences of coral disease were low in the Capricorn-Bunker sector but had increased on two reefs in the Swain sector. Incidences of White Syndrome disease and Brown Band disease at Horseshoe Reef and the incidence of White Syndrome disease at East Cay were high. These levels of disease were the highest yet recorded at each reefs and were also substantially higher than the long-term averages for GBR reefs in the same position on the continental shelf. Counts of Drupella spp. from scuba surveys were generally low or within the range of previous surveys in both the Capricorn-Bunker and Swain sectors, with the exception of Gannet Cay. The numbers of Drupella spp. at this preservation zone reef in the Swain sector were the highest yet recorded and were well above the long term GBR average for mid-shelf reefs. The SCUBA search results are summarised in Tables 2 and 4.

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 the COTS outbreak terminology used in this report refer to the following web-page: Crown-of-thorns on the Great Barrier Reef.

Capricorn-Bunker Sector

Perimeters of four reefs were surveyed using manta tow (Table 1). Sites on each these reefs were also surveyed in detail using scuba (Table 2). COTS were recorded during manta tow surveys at Lady Musgrave Island in numbers sufficient to represent an Incipient Outbreak (n = 16). No COTS were recorded during scuba searches at this reef because the starfish were aggregated along the north-west facing reef edge, where coral cover was highest, well away from scuba sites. Five COTS have been recorded at this reef since manta tow surveys began in 1986, but only as single individuals randomly encountered throughout the years. This is the second outbreak to be recorded from this sector in as many years. Last year a larger Active Outbreak was recorded on Fairfax Island just to the north of Lady Musgrave Island. No COTS have been recorded during manta tow surveys over a similar time period on the other three reefs surveyed in the Capricorn-Bunker sector. These are the first two COTS outbreaks to be recorded from reefs in this sector in nearly thirty years of survey.

Median reef-wide live coral cover ranged from 5 to 10% on one reef, 10-20% on two reefs and 20-30% on one reef (Table 1). In general, coral cover had remained relatively stable on reefs in this sector since last surveyed one to two years previous. The variability in coral cover among reefs reflects differences in exposure to the damaging waves from offshore storms in 2008 and from Cyclone Hamish in 2009. Large numbers of coral recruits were observed during scuba searches at all reefs suggesting that recovery in coral cover was well underway. One caveat is the increase in COTS activity that will almost certainly hamper any recovery in coral cover on affected reefs.

Scuba searches on the intensive survey sites showed that incidences of coral disease were low. For more information on coral disease refer to the AIMS web site at:AIMS Research – Coral Disease. Numbers of Drupella spp. were low to average based on GBR wide data (Table 2).

 

Tawny nurse sharks (Nebrius ferrugineus) have a placid disposition and are often seen in sandy lagoon habitats throughout the GBR. Here an inquisitive shark, escorted by three remoras (Echenius naucrates) and seven juvenile golden trevallies (Gnathanodon speciosus), approaches a diver. Remora are fish species that have a unique pad on the top of their heads, allowing them to suck onto the body of larger animals, particularly sharks. This special adaptation allows them to get a free ride and gain protection from predators but also places them in a good position to feed on shark faeces or the food scraps generated when the shark feeds. The distinctive golden trevallies accompany sharks and large fishes for similar reasons and may benefit the host by consuming parasites on their skin. As golden trevallies age and become larger they lose the vivid golden colouration and cease to accompany larger sea creatures.

Table 1. Summary of manta tow survey results for the Capricorn-Bunker sector.

Reef	Shelf Position	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
BROOMFIELD	Outer	55	0	0	20 to 30	0 to 5	0 to 5	NO
WRECK IS	Outer	41	0	0	10 to 20	0 to 0	0 to 5	NO
ONE TREE IS	Outer	64	0	0	10 to 20	0 to 0	0 to 5	NO
LADY MUSGRAVE IS	Outer	61	16	0.26	5 to 10	0 to 0	0 to 5	IO
Overall GBR average for last survey - visit 19	All			0.02	10 to 20	0 to 5	0 to 5	-
Long-term average value	Outer			0.01	20 to 30	0 to 5	0 to 5	-
Average last survey - visit 19	Outer			0	10 to 20	0	0 to 5	-

 

Table 2. Summary of SCUBA search survey results for the Capricorn-Bunker sector.

Reef	Shelf Position	COTS (<5cm)	COTS (>5cm)	COTS (>15cm)	COTS (>25cm)	WS	BBD	BrB	SEB	Drupella
BROOMFIELD	O	0	0	0	0	11	0	1	0	7
WRECK IS	O	0	0	0	0	5	0	7	0	0
ONE TREE IS	O	0	0	0	0	0	0	0	0	5
LADY MUSGRAVE IS	O	0	0	0	0	0	0	0	0	0
Overall GBR Average for last survey - visit 19	All	0	0.021	0.11	0.34	7	0.064	3.6	2.7	11
Long term average	O	0	0.033	0.12	0.085	33	0.12	4.1	1.7	7.8
Average for last survey - visit 19	O	0	0	0	0	1.3	0	1	0	2.5

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

Swain Sector

Perimeters of seven reefs in the Swain sector were surveyed using manta tow (Table 3). Sites on each of these reefs were also surveyed in detail using scuba (Table 4). COTS were recorded in very low numbers during manta tow surveys at Chinaman Reef and East Cay. Such occurrences of COTS are not unusual on those reefs in past surveys. No COTS were observed during manta tows of the other five reefs, nor during scuba searches on any of the reefs.

 

Small hard corals provide important refuges for many reef fishes, particularly on reefs recovering from major storm damage. Here at Gannet Cay in the Swain sector, small black and white damselfishes known as humbugs (Dascyllus aruanus) seek shelter in the branches of a small coral colony growing amidst an expanse of rubble and sand.

 

The steep sided reef slopes on the front of Horseshoe Reef in the Swain sector support a healthy community of corals and fishes.

 

At reef 21-529 in the Swain sector, previously luxuriant fields of branching Acropora spp. corals were turned to rubble by explosive wave action during Cyclone Hamish in 2009. Large areas of rubble still remain on the sea floor and this once glorious seascape is a mere vestige of its former self.

Median reef-wide live coral cover was low (<10%) on four reefs: Reef 21-529, Gannet Cay and Snake Reef, all of which were recovering from major coral mortality caused by either Cyclone Hamish in 2009 or COTS outbreaks prior to 2006 (Horseshoe Reef and Gannet Cay). The other three reefs had moderate coral cover from 10 to 30%. Coral cover on all reefs was similar to that recorded one to two years previously.

Table 3. Summary of manta tow survey results for 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
21-529	Mid	30	0	0	0 to 5	0 to 0	0 to 5	NO
GANNET CAY	Mid	19	0	0	5 to 10	0 to 5	0 to 5	RE
SNAKE	Mid	95	0	0	5 to 10	0 to 0	0 to 5	NO
CHINAMAN	Mid	31	4	0.13	20 to 30	0 to 5	5 to 10	NO
HORSESHOE	Mid	77	0	0	5 to 10	0 to 0	0 to 5	RE
EAST CAY	Outer	63	2	0.03	20 to 30	0 to 5	5 to 10	NO
TURNER CAY	Outer	51	0	0	10 to 20	0 to 5	0 to 5	RE
Overall GBR average for last survey - visit 19	All			0.02	10 to 20	0 to 5	0 to 5	-
Long-term average value	Mid			1.34	10 to 20	0 to 5	0 to 5	-
Long-term average value	Outer			1.11	20 to 30	0 to 5	0 to 5	-
Average last survey - visit 19	Mid			0	0 to 5	0	0 to 5	-
Average last survey - visit 19	Outer			0.01	5 to 10	0	0 to 5	-

 

Scuba searches at the intensive survey sites on reefs in the Swain sector recorded incidences of White Syndrome disease on East Cay and Horseshoe Reef that were the highest recorded on these reefs since scuba surveys began in the mid 1990's. These incidences of White Syndrome disease were also higher than the long term averages for GBR reefs in similar positions on the continental shelf (Table 4). In addition, the incidence of Brown Band disease at Horseshoe Reef (n = 28) was well above the previous highest value (n = 5). Given the generally low cover of hard coral in this sector due to a long history of COTS outbreaks followed by cyclone damage, such increase in two types of coral disease could be significant. Incidence of White Syndrome and Brown Band disease on the other five reefs were within the range of previous values. Other diseases only occurred at low levels. Numbers of Drupella spp. were within the ranges previously recorded at each reef except at Gannet Cay. The numbers of Drupella spp. were the highest yet recorded at this preservation zone reef (n = 66) and well over the long term GBR average for mid-shelf reefs (n = 22). This may be important for a reef struggling to recover from a long sequence of disturbances.

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

Reef	Shelf Position	COTS (<5cm)	COTS (>5cm)	COTS (>15cm)	COTS (>25cm)	WS	BBD	BrB	SEB	Drupella
21-529	M	0	0	0	0	0	0	0	3	2
GANNET CAY	M	0	0	0	0	7	0	0	3	66
SNAKE	M	0	0	0	0	10	0	2	4	18
CHINAMAN	M	0	0	0	0	5	0	2	0	17
HORSESHOE	M	0	0	0	0	54	0	28	0	27
EAST CAY	O	0	0	0	0	21	0	0	2	11
TURNER CAY	O	0	0	0	0	7	0	1	1	0
Overall GBR Average for last survey - visit 19	All	0	0.021	0.11	0.34	7	0.064	3.6	2.7	11
Long term average	M	0.017	0.39	2.8	0	11	0.17	2.1	2.7	22
Long term average	O	0	0.1	2.8	0	3.2	0.079	0.36	0.87	4.5
Average for last survey - visit 19	M	0	0	0	0	4	0	1	1	7.8
Average for last survey - visit 19	O	0	0	0	0	1	0	0	1.5	0.5

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

Pompey Sector

Perimeters of six reefs in the Pompey sector were surveyed using manta tow (Table 5). No scuba surveys were conducted in this sector. COTS were only recorded at Creal Reef but in numbers high enough for this reef to be reclassified as having an Incipient Outbreak. Previously, COTS had only been recorded in very low numbers at Creal Reef on three occasions since surveys began in 1986.The COTS were aggregated along one of the few sections of reef where large branching corals had escaped the ravages of Cyclone Hamish in 2009. As such the prognosis for healthy recovery of this section of Creal Reef is poor. Reefs in the Pompey sector continue to be a centre for COTS activity, with outbreaks of COTS recorded at six reefs in this sector since 2008.

 

On a brighter note, at Packer Reef in the Pompey sector large areas of reef alongside a protected channel escaped the ravages of Cyclone Hamish and supported an extremely high cover of hard corals, particularly branching Acropora spp. This type of seascape was common throughout the Pompey sector prior to Cyclone Hamish and resembles what Reef 21-529 (previous image) used to be like. A lone snapper (Lutjanus carponotatus) seemed content in the lush thicket of coral.

Median reef-wide live coral cover was low (<10%) on all but one reef due either to past COTS outbreaks (one reef) or the devastating effects of Cyclone Hamish at the others. Coral cover was higher at Packer Reef even though some sections of this reef had been damaged by Cyclone Hamish. Coral cover was high (30-40%) due largely to the fact that Packer Reef consists of two emergent reefs separated by a narrow deeper channel that lie within a larger reef complex. The protected edges of this channel were spared the wrath of Hamish and retained their coral cover. There was a stark difference between the lush coral growth in the channel where coral cover was close to 100% and the pulverized coral skeletons covered by turf algae in nearby sections of reef that had been exposed to cyclonic waves.

 

Green sea turtles (Chelonia mydas) are particularly common in the southern GBR. This inquisitive juvenile repeatedly approached snorkel divers at the relatively unvisited Edgell Reef in the Pompey sector.

Table 5. Summary of manta tow survey results for 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
CONDER	Mid	69	0	0	0 to 5	0 to 0	0 to 5	NO
EDGELL	Mid	80	0	0	5 to 10	0 to 0	0 to 5	NO
PACKER	Mid	30	0	0	30 to 40	0 to 5	0 to 5	NO
CREDLIN	Mid	51	0	0	5 to 10	0 to 0	0 to 5	RE
CREAL	Mid	21	10	0.48	0 to 5	0 to 5	0 to 5	IO
BEN	Outer	12	0	0	0 to 5	0 to 0	0 to 5	NO
Overall GBR average for last survey - visit 19	All			0.02	10 to 20	0 to 5	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 - visit 19	Mid			0.02	0 to 5	0	0 to 5	-
Average last survey - visit 19	Outer			0	0 to 5	0	0 to 5	-

 

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

For further information contact

Dr. Hugh Sweatman , AIMS

Telephone: +61 7 4753 4470

Fax: +61 7 4753 4288

Email: h.sweatman@aims.gov.au