Ocean Acidification Effects: Clownfish Senses

Physiological Response to Ocean Acidification

Clownfish use olfactory and auditory senses to evade predators and locate suitable habitats. Juvenile clownfish may use detection of chemicals in the water to determine where adults of their species can be found (Gattuso 2009). Additionally, studies have shown that clownfish use olfactory senses to distinguish between predators and non-predators (Dixson 2010). 

Response to Environment

In a study testing larval clownfishes ability to distinguish between olfactory cues, groups of clownfish were reared in average seawater pH, while others were reared at estimated future pH due to ocean acidification. Larvae reared at normal pH were attracted to vegetation within the water that would be present near suitable habitats, while those reared at lower pH were attracted to unsuitable vegetation (Munday 2009).

In addition, it is favorable for clownfish larvae to be able to locate other populations of clownfish when searching for suitable habitats. That being said, it is preferable for the larvae to locate non-parental clownfish over closely related individuals to avoid inbreeding. In another study done by Munday, it was found that larval clownfish reared in more acidic environments could not distinguish between related and unrelated clownfish, while those raised at higher pH preferred environments with less related individuals. This points to the possibility of more inbreeding with decreased pH and lower clownfish fitness.

Response to Predators

Ocean acidification may also negatively affect the fish's ability to avoid predators. A study of clownfish olfactory systems showed that juveniles raised in low pH environments may actually become fatally attracted to the scent of predators (Dixson 2010). 

In a different study testing auditory instead of olfactory responses, juvenile clownfish raised at normal pH avoided noise from a recording of a predator rich coral reef. Those raised at a much lower pH exhibited no avoidance behavior (Simpson). 

According to numerous studies, if ocean acidification continues at the current rate, clownfish could experience significant sensory impairment. Since clownfish rely on their auditory and olfactory capabilities to evade predators and locate appropriate habitats, there is much indication that ocean acidification will negatively affect their population numbers.  

"Original Figure: individual pictures cited in references"