Status of Coral Reefs of the World 2000

Status of Coral Reefs of the World: 2000
CASE STUDY 3: BLEACHING AND RECOVERY OF WESTERN AUSTRALIAN
CORAL REEFS POST 1998
A complex pattern of bleaching and mortality occurred on remote and nearshore coral
reefs off the coast of Western Australia during the first half of 1998. These reefs
receive very minor land runoff and minimal anthropogenic damage, but the patterns
were very different on adjacent reefs:
• Ashmore Reef (S 12 o 16’ E 123 o 00’) only minor bleaching seen in the lagoon
of these atoll-like reefs.
• Seringapatam Reef (S 13 o 39’ E 122 o 02’); extensive bleaching with
reductions in hard coral cover from 45% to 5%, and soft coral cover from
10% to 2% on the outer slopes. There was almost 100% mortality of mostly
Acropora corals in the relatively shallow lagoon, small patch reefs have
suffered 90 to 100% mortality and a very old single colony of Pavona
minuta over 100 m diameter and 6m high was almost entirely killed with
0.5m2 still alive. Many species have become locally extinct.
• Scott Reef (S 14 o 11’ E 121 o 48’; 50 x 35km) was the most seriously
bleached of these isolated reefs, with extensive coral mortality at all depths
in April 1998. There was almost 100% mortality of large Acropora beds with
no survivors on most lagoon patch reefs. Corals on the reef crests were
devastated, with few survivors. Data along 9m depth transects showed all
animals with symbiotic algae were wholly or partially bleached, with variable
recovery. The majority of branching Acropora were 80 to 100% killed, and
100% of Millepora were dead at all sites except one. Porites cover was
reduced by 50%, with many colonies having only small patches of live tissue
a year later. The once common Pocilloporids and Acropora bruggemanni are
either extremely rare or locally extinct. Soft corals suffered at all sites with
between 50% and 80% of soft corals dying, depending on the site. Even at
30m depth, 80% of the corals were bleached. The coral community has
changed dramatically. Recruitment studies between 1995 and 1999 reveal
that recruitment in 1998 and 1999 was less than 1% of the pre-1998 levels.
• Rowley Shoals (including Mermaid, Clerke and Imperiuse Reefs Reef between
(S 17 o 04’ and 17 o 33’; E 114 o 38’ and 119 o 23’) showed only minor
bleaching in 1998, with a few Pocilloporids and branching Porites cyclindrica
bleached. Mortality was minor with no changes in coral cover since the first
surveys in 1994.
• Dampier Archipelago (S 20 o 38’ E 116 o 39’) showed severe bleaching in
March-April, 1998 on the fringing reefs of the inner islands, but the impacts
were patchy. Most hard corals were partially bleached, while soft corals,
anemones and zoanthids also suffered varying degrees of bleaching.
Recovery was highly variable, with most Pocilloporids and Fungids dying,
while many massive corals (Turbinia, Mussids, Pectinids) recovered. Bleaching
on the outer island areas was almost non-existent.
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