by Jennifer Fields
Anthropogenic CO2 emissions are causing an increase in dissolution of CO2 into the oceans resulting in ocean acidification. Teleost fish have been thought to have a high tolerance to ocean acidification because their specialized gills allow them to regulate the pH of their blood. However, recent studies have reported strong behavioral effects of ocean acidification in tropical coral reef species. The studies found that there was a diminishment of risk-assessment, learning, lateralization, and prey detection with increased dissolved CO2. But, little is known about the behavioral changes of temperate fish under the same conditions. Jutfelt et al. (2013) observed behavioral disturbances in boldness, exploratory behavior, lateralization, and learning in temperate fish under end of century ocean acidification conditions. The findings suggest that behavioral changes from increased CO2 are not limited to sensitive tropical species and could affect fish on a global scale by the end of the century.
Ocean acidification is predicted to affect marine fish species in variable ways. Tropical fish have been thought to be most susceptible to changes in their chemical environment, and therefore, changes in pH caused by increased CO2 have been expected to have greater effects on their behavior. The authors utilized a species of temperate fish that they deemed more tolerant to chemical changes than tropical species and exposed it to both present-day anticipated 2100 surface CO2 concentrations for 20 and 40 days of exposure. The behavior assays included lateralization, novel object, and escape chamber tests. For the lateralization test, a fish was placed into a double T-chamber and encouraged by a plastic rod to move forward until a left or right turning choice was made. The lateralization test was used to measure the individual’s side preference in turning. The novel object test involved placing a fish in a tank with a novel object; the number of times and duration of the fish’s investigation of the object were recorded during seven-minute trials. The novel object test was meant to measure the fear of novelty, and therefore can be used to determine the boldness of the individual. Lastly, for the escape chamber test, a fish was placed backwards in a circular chamber with an exit hole, as the time spent inside the chamber recorded. The test was designed to assess the exploratory behavior of the individual.
The authors found behavioral disturbances in all of the behavioral assays. For lateralization, the control group exhibited widespread turning preferences, while CO2-exposed fish had a reduced distribution of lateralization. Control fish turned to their preferred side 70% of the time, whereas CO2-exposed fish turned to each side 50% of the time. This difference between groups also increased between day 20 and day 40 of CO2 exposure. A side preference is beneficial for multi-tasking, orientation, and escape from predators therefore a disturbance in this lateralization could result in reduced fitness. In the novel object test, control fish explored the object five times more than the CO2-exposed fish, which could suggest decreased boldness of the fish; however, the fitness implications of this change in behavior are unknown. The escape chamber yielded no difference between groups at day 20, but at day 40, control fish were six times faster at escaping the chamber than at day 20; there was no change in CO2-exposed fish. This suggests that the learning ability of the fish could have been altered by CO2. Learning is necessary for fish to identify their predators and limit harm or injury to themselves through risk assessment. When this learning ability is impaired, it will affect fish survival through decreased predator avoidance.
Because of the difference in severity of behavioral effects of short-term versus long-term CO2, the authors conclude that fish may not be able to acclimate to rapid changes in pH of their environment without evolutionary selection. They suggest that the reason for lack of ability to acclimate to changes in CO2 could be result of the adaption of the GABAA receptor to a narrow range of CO2 levels. This GABAA receptor is known to affect many aspects of behavior in vertebrates. Overall, the results indicate that temperate species will have similar behavioral disturbances as tropical species with increased CO2 exposure. These behavior changes will possibly result in a level of decreased fitness in the individual, and as a possible result, reduced fitness of the species as a whole. Ocean acidification could potentially affect most marine teleost species on a global scale. If the evolution of the resistance to increased CO2 in species is slower than the rate of the CO2 uptake of the oceans, the ecological impact of ocean acidification could be severe enough to affect the entire marine food web and threaten the stability of marine fisheries.
Jutfelt, F., Bresolin de Souza, K. Vuylsteke, A., Sturve, J. 2013. Behavioural Disturbances in a Temperate Fish Exposed to Sustained High-CO2 Levels. PLoS ONE published ahead of print June 4, 2013,doi:10.1371/journal.pone.0065825. http://dx.plos.org/10.1371/journal.pone.0065825.g006