Replenishment of fish populations is threatened by ocean acidification

Abstract

There is increasing concern that ocean acidification, caused by the uptake of additional CO(2) at the ocean surface, could affect the functioning of marine ecosystems; however, the mechanisms by which population declines will occur have not been identified, especially for noncalcifying species such as fishes. Here, we use a combination of laboratory and field-based experiments to show that levels of dissolved CO(2) predicted to occur in the ocean this century alter the behavior of larval fish and dramatically decrease their survival during recruitment to adult populations. Altered behavior of larvae was detected at 700 ppm CO(2), with many individuals becoming attracted to the smell of predators. At 850 ppm CO(2), the ability to sense predators was completely impaired. Larvae exposed to elevated CO(2) were more active and exhibited riskier behavior in natural coral-reef habitat. As a result, they had 5-9 times higher mortality from predation than current-day controls, with mortality increasing with CO(2) concentration. Our results show that additional CO(2) absorbed into the ocean will reduce recruitment success and have far-reaching consequences for the sustainability of fish populations.

Fig. 1.

Effects of elevated CO₂ concentrations on olfactory ability of clownfish larvae. Clownfish were exposed to 390 (control), 550, 700, or 850 ppm CO₂ from hatching, and their behavioral responses were assessed at regular ontogenetic stages using a flume chamber where they could freely move between a stream of water containing the predator cue and a stream of water without the cue. Shown is mean time (±SD) that clownfish larvae spent in the stream of water containing the predator odor. The untreated category shows the time larvae spent on one side of the chamber when neither water stream contained the predator cue.

Fig. 2.

Duration of exposure to elevated CO₂ required to cause olfactory impairment in (A) laboratory-reared settlement-stage clownfish and (B) wild-caught settlement-stage damselfish. Settlement-stage clownfish and damselfish were transferred from untreated water to water treated with 390 (control), 550, 700, or 850 ppm CO₂, and their behavioral responses to predator odor were assessed at 24-h intervals. Shown is mean time (±SD) that fish spent in the stream of water containing the chemical cues from a common predator when presented in a two-channel flume chamber.

Fig. 3.

Percent mortality of settlement-stage damselfish on patch reefs in nature after exposure to 390 (control), 700, or 850 ppm CO₂. N shown above bars.