Atlantic Cod Avoid Both CO2 and Predator Odor After Long-term Exposure to Elevated CO2

by Jennifer Fields

Many recent studies have suggested that the behavior of teleost coral reef fish will be highly affected by ocean acidification. While elevated CO2 reduces predator avoidance in coral reef fish, it is still unknown if elevated CO2 has the same effects on teleosts in other parts of the world. Teleosts have unique receptors that detect ambient CO2 concentrations, and therefore they might be able to avoid areas of high CO2. Jutfelt and Hedgärde (2013) investigated how long-term exposure to end of century CO2 concentrations affects CO2 avoidance and predator avoidance in juvenile teleost Atlantic cod. After six weeks of exposure to elevated CO2, fish were put in a flume and given a choice between conditions of control seawater and no predator cue versus elevated-CO2 water with predator cue. Despite the long-term exposure to elevated CO2, the cod avoided the smell of the predator, suggesting that cod may be tolerant to elevated CO2. Both treatment groups had a strong avoidance to water with high CO2, suggesting that fish similar to Atlantic cod may alter their movements and migrations in search of water with lower CO2 levels.

Increased CO2 concentrations in the water can cause alterations in sensory and physiological responses in fish. Recent studies have suggested that there is decreased predator avoidance when coral reef fish are exposed to elevated CO2 concentrations. However, it is unknown whether teleost fish in other areas will have the same response. It is also unknown if long-term exposure and acclimation to elevated CO2 levels will influence behavioral choices. Jutfelt and Hedgärde (2013) examined how long-term exposure to CO2 affected Atlantic cod’s ability to discriminate between control and CO2-enriched water and to avoid predator chemical cues. To investigate this, the authors exposed the cod for six weeks to the proposed end of this century CO2 concentrations. For both the predator cue and CO2 avoidance tests, a two-choice flume channel was used. The flume channel has two water masses that the fish can freely choose between. For the predator cue test, one side of the flume contained a predator cue and one side contained no predator cue. For the CO2 avoidance test, one side of the flume contained elevated CO2 concentrations while the other side contained current day CO2 water. During each experiment, the preferred side for each fish was determined as the side where the fish spent more than 50% of the time.

The authors found quite different predator avoidance results from those of coral reef fish species. Both control and elevated CO2 fish actively avoided both CO2-enriched and predator cued water. There was no difference between the control and elevated-CO2 fish in the strength of avoidance behavior to CO2 or to the predator cue.

The results demonstrate that even with long-term CO2 exposure, juvenile Atlantic cod avoided CO2-enriched water in favor of control water. Fish spent 90% of their time in the control water, suggesting that elevated CO2 is undesirable to cod. There was the same level of avoidance to CO2-enriched water between the control and CO2-exposed fish. This suggests that habituation to the high CO2 levels may be a very slow or even nonexistent process in these fish. CO2 avoidance behavior in fish can affect their distribution, migration patterns and, therefore, the structure of the marine ecosystem. Ocean acidification could cause a shift in the daily migration patterns of cod and may even lead to an avoidance range of the fish to avoid areas of high CO2. Previous research that suggested that there would be reversal in predator avoidance, the authors found this to be inaccurate with cod. Long-term exposure to CO2 did not deter the cod’s ability to avoid predators, demonstrating that the reversal of predator avoidance that is present in coral reef fish is not universal; and that Atlantic cod may not demonstrate behavioral changes to future ocean acidification other than attempting to avoid it.

Jutfelt, F. and Hedgärde, M. 2013. Atlantic cod actively avoid CO2 and predator odour, even after long-term CO2 exposure. Frontiers in Zoology 10, 1–8.

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