Status of Coral Reefs of the World 2000

Status of Coral Reefs of Australasia
INTERPRETATION OF VALUES FOR CORAL COVER
This report refers frequently to percent coral cover. The average reef-wide cover of
hard coral on GBR reefs was estimated at 23% in 2000, with values ranging from 3-
51%. More precise estimates from underwater video records on a range of NE facing
slopes show relatively higher cover of hard coral with a mean value of 28% and range of
4-68%. These relatively low values reflect fairly frequent disturbances such as cyclones
and crown-of-thorns starfish outbreaks during the last few decades. Much of the
change in coral cover on the GBR is due to growth and destruction of table Acropora
spp. (e.g. A. cytherea and A. hyacinthus). These table corals live in areas of high water
movement and grow rapidly to cover a large area, but they become increasingly
susceptible to storm damage as they grow. On reefs close to the equator, where
cyclones are rare, such corals cover much of the reef and average values for coral cover
will be higher (up to 80% or more in places). Thus different disturbance regimes will
lead to different norms for the extent of coral cover. Therefore, it is essential to know
the environmental regime of an area to interpret coral cover. An estimate of 30% on
the GBR is often an indication that the reefs are in excellent health as storms and COTS
tend to keep coral populations down. Whereas in other areas, cover of 30% would be
viewed with alarm, as reefs in parts of the Red Sea, the Maldives, Indonesia, and parts of
the Caribbean often have levels way over 70%, due to a lack of tropical storms or they
are in protected waterways like the Red Sea.
Lord Howe Island
This high volcanic island (14.6km 2 ) is 603km off the east coast of Australia and one of the
most southern coral fringing reefs in the world (31 o 40’S). The reefs have low species
diversity, but good coral cover on the rocky slopes in passes and lagoons. The island and
surrounding seas were declared a World Heritage Area in 1982, a Marine Park was declared
in June 2000, and a reef-monitoring program is being implemented. Two previous surveys
found significant differences in the composition of coral species between 1978 and 1993,
suggesting some turnover of rare species. There was an increase in crown-of-thorns starfish
numbers in the early 1990s and some coral bleaching in the late 1990s, but impacts have
been minimal and the condition of the reefs is good. Fish, plants and invertebrates have a
mix of tropical and temperate species and a number of endemic species. There is a
management plan to protect the World Heritage values while allowing recreational fishing,
and fishing to supply locals and tourists.
There is coral growth on rocky reefs south of the GBR in southern Queensland: the Gneering
Shoals (26 o S), Flinders Reefs (27 o S) and northern New South Wales (28 o S 30’S) on rocky
reefs with populations of corals up to 50% coral cover.
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