CORDIO Status Report 1999.pdf

Coral bleaching effects on reef fish
communities and fisheries
MARCUS C. ÖHMAN
Department of Zoology, Stockholm University, Sweden
ABSTRACT
Large proportions of the world’s coral reefs were
affected by the 1997 and 1998 coral bleaching event.
This may have a profound impact on coral reef fauna,
especially when the coral bleaching leads to coral
mortality. Reef fishes are influenced by the structure of
the reef habitat, and as habitat degradation through
coral mortality will affect a large variety of interactions
within the coral reef system, the composition and size of
fish stocks may be altered. This, in turn, could imperil
resources for a large number of people depending on
fish for subsistence purposes or as a source of income.
Due to the variety of factors that regulate reef fish
numbers it is difficult to anticipate how coral reef fish
assemblages are affected by coral mortality, and only a
few studies have considered this issue. The effects of
coral mortality could vary from one reef to another,
depending on the fish community composition and
habitat interactions before the impact, recruitment
dynamics, and habitat structure before and after the
disturbance. When the dominant coral fauna is affected
and there are close interactions between corals and the
existing fish populations, a shift in community composition
can be expected. If large-scale habitat destruction
follows coral mortality (i.e. the corals are broken into
coral rubble), fish abundance and species diversity may
decrease. In addition, coral mortality could decrease fish
catches, which may have profound socio-economic
effects. The impact of coral mortality on reef fisheries is
likely to depend on aspects such as the nature of the fish
community, target species and their habitat requirements,
as well as the fishing techniques used.
INTRODUCTION
In 1997 and 1998, large proportions of coral reefs
around the world were affected by coral bleaching.
Corals are susceptible to variations in temperature
(Drollet et al., 1994; Kobluk & Lysenko, 1994; Fang et
al., 1997; Jones, 1997; Kushmaro et al., 1997; Lesser,
1997; Podesta & Glynn, 1997) and the bleaching event is
believed to be related to increasing water temperatures
due to the 1997–1998 El Niño (Wilkinson et al., 1998;
1999). Temperature stress can cause corals to expel their
symbiotic algae (zooxanthellae). As a consequence, they
appear white and if the stress is prolonged it will lead to
coral death. During 1997–1998, coral bleaching and
subsequent coral mortality was reported from reef areas
in East Africa, the central Indian Ocean, the Middle
East, the Indian sub-continent, South-East Asia, East
Asia, large parts of the Pacific, as well as the Caribbean
and the Atlantic (Baird & Marshall, 1998; Huppert &
Stone, 1998; Winter et al., 1998; Wilkinson et al., 1998;
1999).
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