prev. No subject= coral bleaching in Fiji
JKoven at aol.com
JKoven at aol.com
Wed Aug 30 14:26:00 EDT 2000
regret not to have titled report on Astrolabe Reefs' bleaching this year.
You may have deleted it, as I would have, because it had no subject.
The corals on Fijis Astrolabe Reefs appear to have fared somewhat better
than those reported on by Dick Murphy, Ed Lovell and Bruce Carlson. Half of
all specimens counted remained alive and unbleached a month after the SSTs
had lowered. I suggest that this is due to fewer anthropogenic influences
(inhabitants of the islands within the lagoon are counted in hundreds, not
thousands) and their location amid ocean currents unmitigated by any large
land mass. Except for the area around Kadavu, the only high island, there is
not a lot of fresh water run-off into the lagoon and there are virtually no
It does not explain why often 1 of 2 or more specimens of the same species
occurring side by side was bleached and the other not.
In late May and early June I assessed the extent of coral bleaching on the
Great and North Astrolabe Reefs in Fiji. The northern most parts of these
reefs are located 30 -35 NM south of Suva, below the Beqa reefs but still
well within the range of the higher SSTs that occurred from Feb-April.
The survey included sites inside the lagoon and relatively close to the
inhabited Dravuni Island as well as those outside the reefs and at a remote
windward corner of the North Reef which is rarely visited/fished.
As reported by others, most of the bleaching was within the first 25 M
although there were some very large completely bleached specimens of
Montastrea and Montipora near the first bench at 27 M, on the leeward side.
Some very large (3-4 M high and wide) Porites colonies in alleys behind the
outer reef pinnacles were bleached. Bleaching was rare between 27 and 40 M
and almost non-existant below that.
34% of the corals in the lagoon of the Great Astrolabe Reef were bleached -
17% had died recently and were already covered by blue-green algae.
26% of corals on the leeward side of the GAR and windward on the North Reef
were currently bleached with another 20% recently dead.
Among the Acropora 16% of those in the lagoon were bleached but 33% had died
recently and were over-grown by blue-greens. As Bruce Carlson reported, the
smaller specimens (>10 cm) were unaffected. Some of the large Acropora
robusta and formosa specimens in the lagoon exhibited the shade effect
mentioned by Bruce with the underside of branches appearing normal, the
upperside bleached. Only 9% of Acroporids outside the lagoon were bleached
but 28% had died recently.
The Seriatopora were almost entirely wiped out - in 60 dives I saw only one
live specimen. On the survey sites all of them had bleached, died and been
covered by blue-greens. Stylenocoellia and Symphyllia., both with a small
number of representatives, were either bleached or dead at these sites,
but.were seen live elsewhere.
Whereas in the past I had seen Millepora move in after the death of other
corals, with bleaching their representation has been cut by nearly 65%.
43% of the Halimetra pileus specimens at a deep lagoon site were a brilliant
fluorescent yellow with another 31% bleached or partially bleached.
The normally hardy Diploastrea was never seen completely bleached but often
bore a mottled appearance. In one case the outer 10 cm rim of a large colony
was completely white. Lobophyllia colonies were also often mottled with
individual corallites being bleached, completely unbleached or somewhere in
Sinularia and Sarcophyton were almost all bleached, as were many anemone.
Least affected were Achrelia, Anacropora, Euphyllia, Goniastrea,
Goniopora/Alveopora, Pectinia, Turbinaria, Tubastrea.
There was an outbreak of Acanthaster plancii on the crest of the North
Astrolabe Reef with 35 specimens in one 300 square meter area along the crest
- I have never seen that many in all of 12 years on these reefs. Although
they were not that numerous in other areas of the reef this yar, there were
more than ever seen before.
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