Influence of ocean acidification on otolith calcification and behavior in fish larvae

The shift in the ocean's carbonate system towards a lower pH equilibrium, termed asocean acidification, due to anthropogenic emissions of CO2 has potential influence on theformation of calcium carbonate structures in marine organisms. This is because theprecipitation of the calcified structures is dependent on seawater chemistry, with higherpH and aragonite saturation state favoring calcification. A number of studies reporteddifferent patterns of impact on calcification ranging from reduction to hypercalcificationwith some species showing no effects, which means that compensatory mechanisms areavailable to counteract the effects of reduced pH and elevated pCO2. In marine fishes,the structures for mechanoreception known as otoliths are composed of aragoniticcalcium carbonate and function for detection of motion and acceleration, maintainingbalance, and sound localization. The morphology of the otoliths is species-specific andlinked to the functional requirements for specific habitats and swimming behavior. Inthis thesis, the response of the otolith calcification in larval Atlantic cod (Gadus morhuaL.) and Atlantic herring (Clupea harengus L.) to elevated pCO2 and the possibleconsequences to the behavior of the larvae were investigated. The main results of theinvestigation were derived from an ocean acidification experiment conducted in the landbasedmesocosm facility in the University of Bergen's Espegrend Marine Station fromMarch to May 2010. Based on the results, the thesis concluded that otolith calcificationin both Atlantic cod and herring larvae was significantly affected by increase in seawaterpCO2 concentrations. However, the direction of the effects was different between the twospecies with increase in otolith growth in cod larvae but a decrease in herring larvae. Onthe other hand, the changes observed in the otolith growth had no impact on theswimming behavior of both species. The swimming behavior was resilient to elevatedpCO2 despite the changes in the growth of the otoliths. Ocean acidification is not theonly stressor associated with the increase in anthropogenic CO2 emission. In marine fishlarvae, the relationship between otolith morphology and swimming behavior musttherefore be further investigated by considering additional stressors such as oceanwarming, hypoxia, and fluctuations in food availability.