How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

The Transgenerational Acclimation of Juvenile Anemone Fish to Ocean Acidification
Allan, B.J.M., Miller, G.M., McCormick, M.I., Domenici, P. and Munday, P.L. 2014. Parental effects improve escape performance of juvenile reef fish in a high-CO2 world. Proceedings of the Royal Society B 281: 20132179.

According to Allan et al. (2014), although many scientists have studied the potential impacts of rising temperatures and declining seawater pH on marine organisms, "the potential for adaptation or acclimation over climate change relevant timescales remains largely unresolved (Kelly and Hofmann, 2013)." Yet they note that "the environmental conditions experienced by parents may affect their [offspring's] physiological condition and provide the opportunity for non-genetic effects to be transferred to their offspring (Marshall and Morgan, 2011; Bonduriansky et al., 2012)." In exploring this possibility for what they describe as transgenerational acclimation, Allan et al. studied the ability of juvenile cinnamon anemone fish (Amphiprion melanopus) to adjust their escape responses from predators across generations of exposure to elevated CO2.

What was done
To accomplish their design, the researchers examined "the acute (within-generation) effects of increased CO2 on juvenile escape performance," testing "whether such effects were mediated by exposure of parents to increased CO2." Seven variables were utilized to assess the escape response, which was initiated by a simulated predatory disturbance that included the sudden release of an object into the tank. Four of the variables examined related to motion-response distance (total distance traveled in response to the simulated disturbance), mean response speed (as measured by the average duration of the first two flips of a fish's tail), maximum speed (recorded at any time during the response), and response duration (total elapsed time from the start of the simulated disturbance until the fish came to rest). The other three variables assessed fish responsiveness (the percent of fish that responded to the simulated disturbance with a sudden acceleration of movement), directionality (whether the escape response was directed toward or away from the simulated disturbance), and response latency (the time elapsed between the initial disturbance and initial fish movement).

All testing was conducted in an environmentally-controlled aquarium facility at James Cook University, Townsville, Australia. Three treatment groups were used to study the difference between acute exposure to CO2 and parental (transgenerational) effects of CO2 on juvenile reef fish - (i) juveniles from parents reared in control CO2 (400 µatm) hatched into control CO2 levels (400 µatm), (ii) juveniles from parents acclimated to high CO2 (1087 µatm) hatched into high CO2 (1087 µatm), and (iii) juveniles from parents reared in control CO2 (400 µatm) hatched into high CO2 (1087 µatm) - where juvenile fish escape performance was analyzed at the end of the pelagic larval phase (10-11 days posthatching).

What was learned
Acute exposure to high CO2 levels of juveniles from parents reared in control CO2 had a statistically significant negative effect on each of the four variables pertaining to motion (response distance, mean response speed, maximum speed, response duration). However, the response of juveniles whose parents had been acclimated to high CO2 was not statistically different from the response of juveniles reared under control conditions, indicating that the parental effects of transgenerational acclimation reduced the negative effects of elevated CO2 exposure.

A similar situation was observed with respect to fish responsiveness and directionality. Juveniles that descended from parents reared under control CO2 conditions responded negatively under acute exposure to high CO2, while juveniles that descended from parents who were previously acclimated to high CO2 exhibited escape responses that were not statistically different from control conditions. Response latency remained unaffected by CO2 treatment.

What it means
In the words of the authors, the results of this study are important because they indicate that "transgenerational acclimation can help to overcome behavioral impairment observed in fishes exposed to high CO2," adding that "as CO2 levels rise over coming decades, both parental and offspring generations will experience similar elevated CO2 levels; thus our results indicate that this parental exposure will help to reduce some of the negative effects of high CO2 on behavior." Unfortunately, only a few studies have incorporated the concept of transgenerational acclimation when studying the response of marine life to rising temperatures and CO2. Given the findings of Allan et al., more researchers would be wise to incorporate it into their experimental design; for in so doing, they will likely come closer to the true response of marine life to future climate and seawater pH conditions.

Bonduriansky, R., Crean, A.J. and Day, T. 2012. The implications of nongenetic inheritance for evolution in changing environments. Evolutionary Applications 5: 192-201, doi:10.1111/j.1752-4571.2011.00213.x.

Kelly, M.W. and Hofmann, G.E. 2013. Adaptation and the physiology of ocean acidification. Functional Ecology 27: 980-990, doi:10.1111/j.1365-2435.2012.02061.x.

Marshall, D.J. and Morgan, S.G. 2011. Ecological and evolutionary consequences of linked life-history stages in the sea. Current Biology 21: R718-R725, doi:10.1016/j.cub.2011.08.022.

Reviewed 13 August 2014