Report on surveys of reefs in the Cooktown-Lizard Island sector.


Dates:  15th October  - 4th November 2010
Vessel: MV Floreat
Survey leader:
Mike Emslie 

 

Image 1. Crown-of-thorns starfish numbers continue to increase in this sector. Incipient Outbreak levels of COTS were recorded on Startle East Reef during surveys. The last series of COTS outbreaks on the central and northern GBR (1994- 2008) were first seen on reefs in this sector.
Photo: AIMS LTMP.

Image 2. Hard coral cover was moderate (10-30%) on most reefs in the Cooktown – Lizard Island sector and has remained generally stable since 2008. The majority of the reefs where hard coral increased were recovering from earlier COTS outbreaks in the late 1990's.
Photo: AIMS LTMP.

 

Summary

Fifteen reefs in the Cooktown – Lizard Island sector were surveyed for crown-of-thorns starfish and coral disease outbreaks using manta tow. Intensive SCUBA surveys for benthic organisms, reef fishes and agents of coral mortality (SCUBA searches) were also completed on sites on eight of these reefs. Preliminary results of the manta tow surveys and SCUBA searches are presented in this report.

No active outbreaks of crown-of-thorns starfish (COTS) were found but one Incipient Outbreak was recorded at Startle Reef. COTS were recorded in low numbers on seven reefs during manta tow surveys with localized Incipient Outbreak levels of COTS observed on five. COTS were also observed on five reefs during SCUBA searches. COTS feeding scars were recorded on many of the survey reefs and a number of spot checks revealed a few individuals hiding in amongst the reef matrix. Above normal levels of coral mortality were also observed on parts of the Startle Reef (Incipient Outbreak). The directors of the Lizard Island Research Station also reported that COTS have been seen regularly around Lizard Island in increasing numbers in recent years. This correlates well with LTMP data that have regularly recorded low numbers of COTS on reefs in this sector since the last active outbreak ended in 1999. No Active Outbreaks have been recorded from this sector since 1999 however COTS activity has shown a steady increase in this sector since 2006. The last series of COTS outbreaks on the central and northern GBR (1994- 2008) were first seen on reefs in this sector. In 2010, three reefs were still designated as Recovering from outbreaks in the 1990s.

Hard coral cover was moderate (10-30%) on most reefs in the Cooktown – Lizard Island sector and has remained generally stable since 2008. However, hard coral cover had increased (>5%) on two reefs and declined (>5%) on two reefs, with the remaining eleven reefs unchanged since 2008. The majority of the reefs where hard coral increased were recovering from earlier COTS outbreaks.

SCUBA searches found moderate incidences of "white syndrome" (a disease-like necrosis found particularly on tabulate Acropora spp.) and "skeletal eroding band" coral disease on all reefs. The incidence of white syndrome has been stable or has increased slightly on all the inshore and midshelf reefs. On the three outer reefs (Carter, No Name and Yonge) numbers of diseased colonies were similar to previous surveys. Numbers of Drupella spp. (coral feeding snails) were variable with no consistent patterns among reefs based on previous surveys in 2008.

A summary of the results is presented in Tables 1 and 2. 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.

Cooktown – Lizard Island Sector

Eight core reefs were surveyed intensively using SCUBA (Table 2) and all of these plus an additional seven reefs were also surveyed by manta tow (Table 1). COTS were recorded on seven of the reefs during manta tows. COTS were only recorded in low numbers on the majority of reefs, so none of the reefs were classified as having outbreaks except Startle, which was classified as an Incipient Outbreak. However, COTS feeding scars were commonly observed during manta tow surveys, and adult COTS were also recorded during SCUBA searches on five of the eight reefs (Table 2). In recent years COTS activity has continued to increase in this sector (Graph 1). Of the seven reefs where COTS were recorded on manta tow five of these, Linnet, Helsdon, Lizard Island, North Direction Island and Startle East had localized populations of COTS that exceeded Incipient Outbreak levels. Research suggests that Active Outbreaks on the northern and central GBR are likely to occur as a result of a series of recruitment events over a number of years on reefs in this sector. Under this scenario, numbers of COTS can gradually build up over time in this sector until they reach high enough densities to produce very large numbers of larvae that colonize reefs downstream in the prevailing currents in large numbers and give rise to outbreaks. If this pattern is repeated the numbers of COTS in this sector may be expected rise in the future with important implications for coral cover on those reefs to the south.

Graph 1. Average crown-of-thorns starfish densities on survey reefs in the Cooktown – Lizard Island sector for Inner (I), Mid (M) and Outer (O) shelf reefs. The threshold for Incipient Outbreak status is a mean 0.22 starfish per tow on a reef.
 

Median reef-wide live coral cover on the 15 reefs that were surveyed by manta tow varied from low (10-20%) to high (40-50%) (Table 1). COTS were observed on seven of these reefs during the surveys, although numbers were below outbreak levels, except for Startle Reef, which was classified as Incipient Outbreak. Coral cover has risen by at least one median category on three reefs (Linnet, Martin and Carter) since the last survey, declined on two reefs (Helsdon and North Direction) and remained stable on the other seven.
 

Table 1. Summary of manta tow survey results for the Cooktown – Lizard Island sector

Reef

Shelf Position

Tows

COTS

COTS per tow

Median % Live Coral Cover

Median % Dead Coral Cover

Median % Soft Coral Cover

Reef Status

Boulder

Inner

69

0

0

20 to 30

0 to 5

0 to 5

NO

Egret

Inner

57

0

0

10 to 20

0 to 5

0 to 5

NO

Linnet

Inner

31

2

0.06

30 to 40

0 to 5

0 to 5

NO

Martin

Inner

54

1

0.02

30 to 40

0 to 5

0 to 5

NO

Two Isles

Inner

22

0

0

40 to 50

0 to 5

0 to 5

NO

Helsdon

Mid

50

6

0.12

10 to 20

0 to 5

0 to 5

RE

Lizard Is

Mid

93

15

0.16

10 to 20

0 to 5

0 to 5

RE

MacGillivray

Mid

16

0

0

20 to 30

0 to 5

0 to 5

RE

Marx

Mid

29

0

0

20 to 30

0 to 5

0 to 5

NO

North direction Is

Mid

19

3

0.16

20 to 30

0 to 5

0 to 5

NO

Startle (east)

Mid

35

11

0.31

10 to 20

0 to 5

0 to 5

IO

15-047

Mid

43

2

0.05

10 to 20

0 to 5

0 to 5

NO

Carter

Outer

80

0

0

20 to 30

0 to 5

0 to 5

NO

No Name

Outer

59

0

0

10 to 20

0 to 5

0 to 5

NO

Yonge

Outer

87

0

0

10 to 20

0 to 0

0 to 5

NO

Overall GBR average for last survey (2008)

All

   

0.01

10 to 20

0 to 5

0 to 5

-

Long-term average value

Inner

   

0.1

20 to 30

0 to 5

0 to 5

-

Long-term average value

Mid

   

0.11

10 to 20

0 to 5

0 to 5

-

Long-term average value

Outer

   

0

10 to 20

0 to 5

0 to 5

-

Average last survey(2008)

Inner

   

0

10 to 20

0 to 5

0 to 5

-

Average last survey(2008)

Mid

   

0.03

10 to 20

0 to 5

0 to 5

-

Average last survey(2008)

Outer

   

0

10 to 20

0 to 5

0 to 5

-

 

SCUBA searches on the intensive survey sites (Table 2) showed a high incidence of "white syndrome" (a disease-like necrosis found particularly on tabulate Acropora spp.) and low to moderate incidences of "skeletal eroding band" disease (SEB). There were no consistent temporal trends in the incidence of coral diseases: the number of infected colonies increased on some reefs since last survey and declined on others. SEB has only been identified relatively recently and may have been overlooked in the past. It is uncertain what densities of infected colonies lead to significant coral mortality.

Numbers of the corallivorous snail, Drupella spp., were found on every survey reef however, there was no clear spatial pattern in Drupella spp. numbers among reefs in this year's survey nor was there a trend compared to previous surveys in 2008.

 

Table 2. Summary of results of SCUBA searches on reefs in the Cooktown – Lizard Island sector

Reef

Shelf Position

COTS (<5cm)

COTS (>5cm)

COTS (>15cm)

COTS (>25cm)

WS

BBD

BrB

SEB

Drupella

Linnet

I

0

1

3

0

34

0

5

8

26

Martin

I

0

0

1

3

27

0

2

3

2

Lizard Island

M

0

0

1

1

10

0

0

40

10

MacGillivray

M

0

0

0

1

10

0

2

3

9

North Direction

M

0

0

0

3

4

0

2

6

36

Carter

O

0

0

0

0

20

0

2

5

36

No Name

O

0

0

0

0

26

0

3

0

23

Yonge reef

O

0

0

0

0

22

0

8

1

28

Overall GBR Average for last survey (2008)

All

0

0.054

0.34

0.57

10

0.18

3.1

6.9

8.1

Long term average

I

0.073

0.77

1.5

0.5

9

0.26

1.9

9.2

25

Long term average

M

0.067

0.22

2.1

0.89

4.3

0.067

0.8

6.9

48

Long term average

O

0

0.047

0

0

28

0.24

1.8

2

15

Average for last survey (2008)

I

0

0

0

0

0

0

0

20

2.5

Average for last survey (2008)

M

0

0

0

0.67

3.7

0.67

0

4

35

Average for last survey (2008)

O

0

0

0

0

31

1.1

0

1.5

13

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

  

 


References

English, S., Wilkinson, C. and Baker, V. (1997) Survey Manual for Tropical Marine Resources (2nd Edition). 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