by Jennifer Fields
Ocean acidification is known to have significant impacts on marine invertebrates in terms of calcification and reproduction; however, the effects of increased CO2 on marine invertebrate behavior are largely unknown. Watson et al. (2014) predicted marine conch snail predator-escape behavior to its predator cone shell would be impaired with near-future CO2 levels. The authors found that the decision-making of the conch snail was in fact impaired by ocean acidification, leaving the snails more vulnerable to predation. The change in behavior was fully restored by treatment with gabazine, suggesting that changes in acid-base regulation caused by increased CO2 in the ocean interfere with the invertebrate’s neurotransmitter receptor function. These alterations in behavior in marine invertebrates could have wide-ranging implications for the whole entire marine ecosystem.
Ocean acidification decreases concentrations of calcium carbonate and can result in changes in organismal calcification, due to decrease in calcium carbonate, reproduction, and more recently, changes in marine organism behavior due to changes in the acid-base regulation in the nervous system. Some of these behavioral aspects that are altered by elevated CO2 in the water column include exercise ability, escape response, metabolism, unwariness of risks, and decision-making. This study authors measured the predator-escape behavior of a jumping conch snail, which has a modified foot that it uses to jump away from a predatory cone shell under current (405 ppm CO2; pH of 8.17) and end of century (961 ppm CO2; pH of 7.85) ocean acidification conditions through the several behavioral assays. The jumping snails were housed in separate groups in both the control and elevated-CO2 conditions in an aquarium facility for five days and were then tested. The behavioral assays were a self-righting experiment to determine whether or not elevated-CO2 affected the ability for the snail to jump. To measure the full escape response of the conch snail, the snail was placed within an arena with a predator cone shell. The escape response, including angle of escape and number of jumps was recorded. The oxygen consumption of the snail was also measured during jumping and stationary states to see if the metabolism was affected by the increase of CO2, which could have influence on the snail’s ability to escape. Finally, the snail’s ability to respond to its cone shell predator chemical cue was tested. To examine this, snails were placed in individual tanks with the addition of predator cue water, and the jumping response of the snail was recorded. The addition of gabazine, a GABA neurotransmitter antagonist, was used in some of the trials to test the involvement of ocean acidification on the nervous system, as previously tested with marine fish (Nilsson et al. 2012). The GABA neurotransmitter maintains the function of the decision-making and most behavior aspects of marine fish and invertebrates. Elevated-CO2 interferes with neurotransmitter interfered with and its function is impaired. Gabazine allows for that acid-base regulation to return to normal and prevent the GABA neurotransmitter from being blocked.
As previously predicted by the authors, elevated CO2 concentrations as predicted at the end of this century will have significant impacts on marine invertebrate behavior. Higher CO2 concentrations lead to a change of escape behavior in the marine jumping snail. These concentrations impaired its instinctual predator-escape response by affecting its decision-making. However, the snail’s physical ability to jump as tested in the self-righting and metabolism experiments was not affected, therefore, the capacity to escape was retained. Elevated CO2 caused a reduction in the jumping response of the snail as well as an increase in latency of jumping, thus increasing the exposure time to predation, and escape trajectory by the snails escaping at closer angle and distance to the predator. The anti-predator response of the jumping snail was fully restored in the elevated-CO2 group with the addition of gabazine, which suggests that GABA-like receptors are responsible for the changes in behavior in these invertebrates, similar to marine fish.
This change in decision-making can lead to decrease in predator avoidance, wariness, and/or escape behavior, which could cause an increase in mortality from predation. With the near-future ocean acidification scenario, it is possible that changes in predator-prey interactions will have wide-ranging negative impacts on the marine food web and the fisheries that depend on the stability of that delicate dynamic.
Watson, S.A., Lefevre, S., McCormick, M.I., Domenici, P., Nilsson, G.E., Munday, P.L. 2014. Marine Mollusc Predator-escape Behaviour Altered by Near-future Carbon Dioxide Levels. Proc. R. Soc. B published ahead of print November 13, 2013,http://dx.doi.org/10.1098/rspb.2013.2377. http://royalsocietypublishing.org/content/281/1774/20132377.full