Reef Fish and Climate Change: A Case Study

The synchronizing effects of climate on population dynamics have been observed for a range of land animals and marine species such as the Californian sardine but such patterns had not previously been documented in coral reef systems because of a lack of long-term and broad scale data. We now have the first evidence that variability in coral reef fish populations is strongly linked to a global climatic phenomenon, the El Niño - Southern Oscillation (ENSO), which refers to changes in the ocean and atmosphere that result in a body of unusually warm water building up in the Eastern Pacific Ocean. El Niño events cause changes in water temperatures, wind speeds and patterns of water circulation on the east coast of Australia. All of these parameters can affect the breeding success of reef fishes and survival of their larvae. Conditions during ENSO events in 1995 and 1998, for example, were good for small reef fishes. Many other reef organisms with similar life cycles probably benefited as well. One year after El Niño events, the researchers at the Australian Institute of Marine Science (AIMS) documented an increase in damselfish populations on many reefs of the Great Barrier Reef (GBR).

According to some climate models, ENSO-like conditions will become increasingly common. It now appears that reef fish populations are affected by climate. Then we may expect that

• any changes in the nature of ENSO regimes due to global climate change will affect coral reef fishes
• distant populations change in synchrony
• 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
• localized extinctions will be more likely, particularly for small populations of short lived species