Bleaching and the GBR [slight return]

[Hugh Sweatman]

Harking back to the correspondence about a month ago concerning the
Reuter's/PlanetArk posting on coral bleaching and the Great Barrier Reef,
the first results of the AIMS Long Term Monitoring Program's assessment of
the broadscale effects of the 1998 bleaching can now be seen at:

http://www.aims.gov.au/pages/research/coral-bleaching/Broadscale-bleaching/b
eb-01.html

(or look up bleaching in the Topics Index)

The AIMS program surveys 47 reefs once a year at about the same time each
year.  For a valid comparison estimates of hard coral cover from 1997
surveys [well before bleaching] were compared with those from 1999 surveys
[well after bleaching].  The figure shows total living coral cover for the
survey sites on reefs, arranged by latitude and position across the GBR
lagoon [inshore to offshore].  Study areas on most survey reefs showed an
increase in hard coral cover over the period.  These estimates are from
video transects (methods are described elsewhere on the AIMS webpage); the
important point in this context is that the study sites are generally at
6-9 m depth [not on reef crests].

Reefs that showed a net loss of hard coral are mid-shelf reefs in the
Cooktown/ Lizard Is sector, inner reefs in the Cairns and Townsville
sectors and some reefs in the Swains sector.  The Cooktown / Lizard Is
reefs and the Swains reefs are known to have populations of the
crown-of-thorns starfish which eats corals.  The implication is that, of
the reefs that are surveyed, only inner reefs in the Cairns and Townsville
sectors were badly affected by the bleaching.  

While the program's coverage of nearshore reefs is not very extensive and
inshore reefs in other sectors may have been affected, the important point
is that less shallow areas of much of the GBR were NOT devastated.

Total cover of live coral is a very simple measure: corals clearly differ
in their susceptibility to bleaching, so the composition of assemblages may
have changed even though the total cover has not decreased.  Graphical
checks do not show gross patterns with the taxonomic resolution that is
possible with U/W video, but we have not applied heavy-duty statistical
procedures yet.

Finally, to reiterate the point made by Terry Done in this forum, this is a
measure of what HAS happened on the GBR; Ove Hoegh-Gulberg's recent paper
concerns what MIGHT happen - the Australian media often fail to make that
distinction.  However, most predictions are dire and constant vigilance is
required to follow developments - the AIMS program is part of that.


Hugh Sweatman
Long Term Monitoring Program,
Australian Institute of Marine Science,
PMB3 Townsville MC, Qld 4810
Australia
ph: (07) 4753 4470 / +61 7 4753 4470 [GMT +10] 
faxes: (07) 4753 4288 / 4772 5852
h.sweatman at aims.gov.au   web: http//www.aims.gov.au/
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