Studies by AIMS scientists are now identifying the potential impacts of climate change on reef fishes. Long term monitoring has shown that the sizes of widely separated populations of fish may rise and fall in synchrony due to fluctuations in climate.

This is the first evidence that variability in coral reef fish populations is strongly linked to the El Niño Southern Oscillation (ENSO), a global climatic phenomenon affecting the ocean and atmosphere that causes a body of unusually warm water to build up in the Eastern Pacific Ocean. El Niño events trigger changes in water temperatures, wind speeds and patterns of water circulation on the east coast of Australia.

Any changes in the nature of ENSO regimes due to global climate change will affect coral reef fishes. According to some climate models, ENSO-like conditions will become increasingly common. The finding that distant populations change in synchrony means that while conditions are favourable, fish will do well across large parts of the GBR, but when conditions are unfavourable, fish populations across large numbers of reefs will be affected simultaneously. In such circumstances, localised extinctions will be more likely, particularly for small populations of short lived species.

Another study by AIMS and the Australian Research Council Centre of Excellence for Coral Reef Studies has investigated the effects of high seawater temperatures on the health and future prospects of baby Ambon damselfish. It has been demonstrated that environmental differences experienced early in life not only have immediate consequences for survival, but also profoundly influence the chances of success later in life.

Survival of the developing embryos was dramatically reduced at 31°C, which is not an uncommon summer temperature in recent years and will become increasingly common as the global oceans warm. The hatching cohort of fish was then tracked through to the juvenile stage, which showed that the environment encountered during their early life has long-lasting consequences on which individuals survive to replenish the next generation.

Future climate change can be expected to exert strong evolutionary pressure upon these populations by selecting for more heat tolerant forms. Whether such adaptation is possible given the unprecedented rate of warming forecast by most climate models is an open question of considerable interest to fish biologists and natural resource managers. In species that cannot accommodate the rate of temperature rises, the most likely response is altered patterns of distribution and abundance.

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