Fishes in the pomacentrid subfamily Amphiprioninae, most of which are in the genus Amphiprion, are known as clownfishes or anemonefishes. As a result of their close associations with anemones clownfishes are indirectly threatened by any factors that cause populations of their anemone associates to decline. Clownfishes often occur with anemones living on coral reefs. Because coral reefs have been seriously and negatively impacted by global climate change, populations of reef dwellers such as clownfishes are expected to suffer as well (IUCN 2009). Globally, coral reefs are seriously declining as a result of mass bleaching, ocean acidification, and other environmental impacts. In 1998, one of the most severe global coral bleaching events in recorded history led to the complete disappearance of several anemone species used by clownfishes in the corals reefs around Sesoko Island, Japan, causing local clownfish population declines (Arvedlund and Takemura 2005 and references therein).
The acidification of the oceans as they absorb more carbon dioxide due to increasing atmospheric carbon dioxide levels poses an interesting and potentially serious threat to clownfishes. Recent studies have indicated that lowering the pH of seawater (i.e., making it more acidic) may disrupt the ability of larval clownfish to detect the chemical signals necessary for recognizing and locating appropriate reef sites and anemone hosts (Munday et al. 2009).
Increasing water temperatures pose additional direct threats to clownfishes. Juvenile clownfish have been shown to develop faster as water temperatures increase (assuming sufficient food is available). This may yield immediate benefits to individuals, such as earlier reproduction, but more rapid growth would likely also mean that individuals would disperse shorter distances from their parents’ anemone before their developmental stage triggers the instinct to find their own anemone. The resulting decrease in dispersal distance could mean greater competition for local dwelling places, greater likelihood of predation, and increased inbreeding. A further threat to clownfishes associated with warming ocean temperatures is that they are known to reproduce only within a very narrow temperature range and an increase in temperature could therefore disrupt breeding. High temperatures have also been shown to reduce egg survival (IUCN 2009).
It is possible that clownfishes might be able to adapt physiologically and/or behaviorally to cope with the new conditions produced by global climate change. For example, one species of clownfish has recently been shown to use soft corals as an alternative habitat, something previously observed only in captivity (Arvedlund and Takemura 2005). It remains unknown, however, to what degree clownfishes can adapt to their changing environment and, in particular, whether they will be able to adapt sufficiently quickly to match the rapidly changing environmental conditions that lie ahead.
Both clownfishes and their sea-anemone hosts face other threats, unrelated to climate change, as well. Both are highly sought after for the aquarium trade and have become increasingly popular targets for collection. However, reef destruction and degradation due to human activities, including global climate modification, remain the greatest threat at present (IUCN 2009).