Capricorn-Bunker sector of the Great Barrier Reef 2015

Dates: 1^st October to 20^th October 2015

Vessel: RV Cape Ferguson

Survey leader: Ian Miller

Manta tow surveys were completed on seven reefs in the Capricorn-Bunker sector, and one reef in the Pompey sector of the Great Barrier Reef (GBR) Marine Park. Detailed surveys for benthic organisms, visual census of fishes and surveys for agents of coral mortality (scuba search) were made on eight reefs in the Capricorn-Bunker sector. Preliminary results of the manta tow and scuba search surveys are presented in this report.

 

Median reef-wide live coral cover (henceforth coral cover) on Capricorn-Bunker reefs had increased or remained at levels similar to those recorded during previous surveys in 2014* when hard coral cover on the majority of survey reefs was showing the first signs of recovery from declines due to the combined effects of a large storm in 2008 and Severe Cyclone Hamish in March 2009. Severe Tropical Cyclone Marcia crossed the coast some 130km to the north of the Capricorn-Bunker Group in February 2015 but appears to have had little impact. Coral cover on Credlin Reef in the Pompey sector was moderate and still recovering from the impacts of Severe Tropical Cyclone Hamish and a number of prior disturbance events.

 

Crown-of-thorns starfish (COTS) populations on a number of reefs in the Capricorn-Bunker sector in 2014 have declined to below outbreak levels. There is no longer an Active Outbreak on Fairfax Reef or an Incipient Outbreak on Lady Musgrave Island Reef. Low numbers of COTS, below outbreak densities, were observed on Boult Reef. No COTS were observed on Credlin Reef in the Pompey sector. Manta tow survey results are summarised in Tables 1 and 3.

 

No COTS were recorded during scuba search surveys on reefs in the Capricorn-Bunker sector. On all reefs surveyed, signs of coral disease, counts of Drupella spp. and coral bleaching were generally below those seen previously. The SCUBA search results are summarised in Tables 2.

 

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.

 

* Survey year is the same as financial year of survey, for instance the 2014 survey year represents reefs surveyed between July 2013 and June 2014. Surveys for this current financial year are presented as 2016 despite surveys actually taking place in the 2015 calendar year.

Perimeters of seven reefs were surveyed using manta tow (Table 1). Three sites on each of these reefs and one other reef were also surveyed in detail using scuba (Table 2). Small numbers of COTS were observed in manta tows surveys of Boult Reef, Fairfax Reef and Lady Musgrave Island Reef. Coral cover on the back reef area of both Fairfax Reef and Lady Musgrave Island Reef has been severely depleted in recent years from outbreaking COTS populations. While residual COTS are well below outbreak densities, the coral on these areas of reef is yet to recover.

Reefs in this sector were recently characterised by their relatively low coral cover resulting from large storms in 2008 and Severe Tropical Cyclone Hamish, which passed some 100km to the east of the Capricorn-Bunker reef complex in March 2009. There has been a remarkable recovery since surveys in 2012. Coral cover has increased on six of the survey reefs in this sector (Boult, Broomfield, Fairfax, Hoskyn, Lady Musgrave, North) while remaining stable on Erskine (Table 1). This is despite the impact of COTS outbreaks on Lady Musgrave Island Reef and Fairfax Reef in recent years as well as Severe Tropical Cyclone Marcia that tracked inland down the coast some 100km to the east of the sector in February 2015. On some reefs the recovery is remarkable and Broomfield Reef and North Reef showed the highest coral cover recorded since they were first surveyed in 1986 and 1991 respectively. No bleaching of hard corals was recorded during manta tow surveys of reefs in this sector in 2016.

 

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

 

Reef	Shelf	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
NORTH (A)	Outer	34	0	0	40 to 50	0 to 5	0 to 5	NO
BROOMFIELD	Outer	51	0	0	40 to 50	0 to 0	0 to 5	NO
ERSKINE ISLAND	Outer	20	0	0	10 to 20	0 to 5	0 to 5	NO
BOULT	Outer	38	1	0.03	30 to 40	0 to 0	0 to 5	NO
HOSKYN IS'S	Outer	28	0	0	30 to 40	0 to 0	0 to 5	NO
FAIRFAX IS'S	Outer	35	4	0.11	20 to 30	0 to 5	0 to 5	RE
LADY MUSGRAVE IS	Outer	57	3	0.05	30 to 40	0 to 0	0 to 5	NO
GBR average for last survey – 2014	All			0.13	10 to 20	0 to 5	0 to 5	-
Long-term average value	Mid			0	30 to 40	0 to 5	0	-
Long-term average value	Outer			0.02	20 to 30	0 to 5	0 to 5	-
Average last survey - 2014	Outer			0.2	10 to 20	0 to 5	0 to 5	-

 

Scuba searches on the intensive survey sites (Table 2) found signs of white syndrome disease and scars due to unknown causes on all reefs in this sector, but at unexceptional levels compared to those recorded in previous surveys. Similar unexceptional levels of brown band disease were recorded from all reefs except for Hoskyn Island Reef. Signs of black band disease, though recorded in manta tow surveys of two reefs (Broomfield and Boult), were absent from the intensive survey sites. Skeletal Eroding Band disease was rare, being recorded at low levels from two reefs: Erskine Island and Masthead Island. No COTS were observed during scuba searches and counts of Drupella spp. were generally below those recorded in previous years.

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

 

Reef	Shelf	COTS (<5cm)	COTS (>5cm)	COTS (>15cm)	COTS (>25cm)	WS	BBD	BrB	SEB	Drupella
NORTH (A)	O	0	0	0	0	20	0	13	0	5
BROOMFIELD	O	0	0	0	0	11	0	1	0	4
ERSKINE ISLAND	O	0	0	0	0	33	0	5	5	5
MASTHEAD IS	O	0	0	0	0	6	0	11	5	2
BOULT	O	0	0	0	0	17	0	6	0	0
HOSKYN IS'S	O	0	0	0	0	9	0	0	0	18
FAIRFAX IS'S	O	0	0	0	0	19	0	1	0	5
LADY MUSGRAVE IS	O	0	0	0	0	18	0	0	0	0
Overall GBR Average for last survey - visit 2014	All	0	0.04	0.16	0.48	9.7	0.04	5	5.4	11
Long term average	O	0	0.027	0.099	0.059	29	0.095	5.2	1.6	7.3
Average for last survey - visit 2014	O	0	0	0	0	16	0	14	1.8	4.8

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

The perimeter of Credlin Reef was surveyed using manta tow (Table 3). Coral cover on Credlin Reef suffered for over a decade from a number of impacts including Cyclone Justin (1997) COTS (2000 to 2006) coral bleaching (2002) and Severe Tropical Cyclone Hamish (2009). Surveys in 2016 indicate some clear signs of recovery on this reef and coral cover was moderate (10-20%). This was despite Severe Tropical Cyclone Marcia passing 90 km to the east of the reef in February 2015.

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

 

Reef	Shelf	Tows	COTS	COTS per tow	Median % Live Coral Cover	Median % Dead Coral Cover	Median % Soft Coral Cover	Reef Status
CREDLIN	Mid	58	0	0	10 to 20	0 to 0	0 to 5	NO
GBR average for last survey - 2014	All			0.13	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			0.26	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 - 2014	Mid			0.6	5 to 10	0 to 5	0 to 5	-