New study into how predators are affected by ocean acidity

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Larval reef fish are not going to be the only victims of increasing ocean acidification, according to a study published in a recent issue of the online journal PLoS ONE.

Although the effect of increasingly acid oceans on the ability of larval reef fish to settle and to detect predators has been established, the impact on the predators themselves is unclear.

Ingrid Cripps, Philip Munday and Mark McCormick demonstrated in their study that elevating the carbon dioxide and reducing the pH levels in sweater caused a common coral reef meso-predator, the brown dottyback (Pseudochromis fuscus), altered both its behaviour and ability to smell prey.

Conducting their study on the Lizard Island Research Station in the northern section of the Great Barrier Reef, the authors introduced Brown dottybacks into tanks that had been divided into two, with one half containing damaged-skin-extracts from juvenile Lemon damselfish (Pomacentrus moluccensis) – a known prey species of the dottyback – and the other containing a seawater control. The time spent in each chamber was recorded. The trials were conducted with varying levels of seawater pH altered by carbon dioxide enrichment.

In a second experiment, the authors recorded the activity level of the fishes, by placing the fish in a shelter, and then introducing food to the tank. The trials were again conducted with varying levels of seawater pH altered by carbon dioxide enrichment.

The authors found that the dottybacks displayed a slight avoidance to olfactory cues of injured prey following exposure to elevated levels of dissolved carbon dioxide in the water. This is in contrast to the natural preference for these cues they display under normal conditions.  

They also found the dottybacks to be more active when exposed to elevated carbon dioxide levels. Coupled with an apparent decline in olfactory abilities, this increased activity could have resulted in the fish relying more on vision than olfaction to detect food.

Previous studies have shown that the larvae of prey fish become attracted to predator odour under acidified conditions. This attraction, compared to the relatively small avoidance of prey cues by predators detected in this study suggest that it is unlikely that negative effects on predators will fully compensate for the increase in mortality rates of larval fish returning to the reef in an acidified ocean.

For more information, see the paper: Cripps IL, PL Munday and MI McCormick (2011) Ocean acidification affects prey detection by a predatory reef fish. PLoS ONE 6, e22736. doi:10.1371/journal.pone.0022736

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