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AIMS
long-term monitoring of the Great Barrier Reef
Report
of April - May 1998 survey observations -
Townsville, Cape Upstart and Whitsunday sectors
Manta tow surveys
were conducted on nine reefs in the Townsville
sector, six reefs in the Cape Upstart sector, and
three reefs in the Whitsunday sector of the Great
Barrier Reef between 20 April and 8 May 1998. No
active crown-of-thorns starfish outbreaks were
recorded in these sectors. Coral cover has
decreased significantly on two of the reefs
surveyed, while an increase in live coral cover
was recorded on two reefs. One reef has been
reclassified as 'non-outbreaking' in the Cape
Upstart sector. Fish and benthic surveys were
conducted on eight reefs in the Townsville
sector, completing our annual survey of reefs for
the 1997/98 year.
A list of reefs
surveyed in the Townsville and Cape Upstart
sectors are detailed in
Long-Term Monitoring Status report
number 2 summary,
Sweatman 1997.
Three other reefs
were surveyed in the Whitsunday sector. Pandora
Reef was surveyed in February, so results are not
included in this report.
Click on
this map for a high resolution image.
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Broadscale surveys were
undertaken on nine reefs in this sector.
A total of six crown-of-thorns starfish
were seen on the nine reefs. Coral cover
remains stable on most reefs. Median live
coral cover on Havannah Island has
dropped from 40-50 per cent when surveyed
in 1996/97 to a current level of 10-20
per cent. Two reefs, John Brewer and
Wheeler have both shown an increase in
median live coral cover from 10-20 per
cent when they were last surveyed (in
96/97 and 94/95 respectively) to a
current level of 40-50 per cent. Coral bleaching
was observed to some extent on all reefs
surveyed.
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The highest levels of bleaching
were seen on the inshore reefs where
bleaching affected up to 75 per cent of
coral cover on some reefs. Less bleaching
was apparent on midshelf reefs and little
bleaching occurred on outer shelf reefs.
On those reefs where bleaching was common
there appeared to be a hierarchy of
corals affected depending on the extent
of the bleaching and the species present.
Havannah Island and Middle Reef
had extensive bleaching over the entire
reef area, particularly in the shallower
areas. Havannah Island has large areas of
dead standing coral that are now covered
in a film of turf algae. A median dead
coral cover of 10-20 per cent was
recorded for Havannah Island. Dead coral
cover of this magnitude has not been
observed on reefs by the long-term
monitoring program since the last series
of crown-of-thorns starfish outbreaks.
The corals appear to have died only in
the past few weeks to months.
Bleaching on Middle Reef is also
extensive although die-off is not as high
as at Havannah Island. There is no effect
of depth on the bleaching as Middle Reef
is mostly in shallow water (3-5 metres).
The bleaching on this reef has affected
both soft and hard corals. This reef is
not surveyed by manta towing due to poor
visibility; observations are based on
three permanent sites on the northern
edge of the reef. However at low tide it
was easy to see from the surface that the
bleaching has affected the entire reef.
Most of the soft corals are bleached, and
about 60-80 per cent of the hard corals
are affected.
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Click on
this map for a high resolution image.
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Six reefs in this sector were
surveyed by manta tows. Three
crown-of-thorns starfish were seen on two
of these reefs. Most reefs in this sector
had poor coral cover, and remain
relatively unchanged since they were last
surveyed. The exception was Reef 19098,
which has shown a drop in live coral
cover from 40-50 per cent (when last
surveyed in 1994/95) to a current median
live coral cover of 10-20 per cent. This
is possibly as a result of Cyclone Justin
which was considered responsible for loss
of coral cover on many reefs in this
sector during the 1996/97 survey year. Faith Reef has
been reclassified from 'recovering' to
'non-outbreaking' having reached a
sustained level of coral cover equivalent
to that recorded before the last
crown-of-thorns outbreak on this reef.
Bleaching
was also common on these reefs although
not usually more than 1-5 per cent per
two-minute manta tow.
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Click on
this map for a high resolution image.
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Three reefs were
surveyed using manta tow in this sector.
Unfortunately, although the weather was
calm and fine, the visibility on these
reefs was very poor. In some cases, for
example Langford and Bird Island,
visibility proved to be too low to carry
out valid manta tow surveys.
No crown-of-thorns starfish,
changes in the coral cover, or changes in
the status of these reefs were observed,
based on recent surveys.
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For further information contact:
Ian Miller, AIMS
Telephone: +61 7 47534471
e-Mail: i.miller@aims.gov.au
 AIMS home page
web@aims.gov.au
Last updated - 23 July 98
Copyright ©1996-1998 Australian Institute of
Marine Science
URL
http://www.aims.gov.au
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