The shift in the ocean's carbonate system towards a lower pH equilibrium, termed as
ocean acidification, due to anthropogenic emissions of CO2 has potential influence on the
formation of calcium carbonate structures in marine organisms. This is because the
precipitation of the calcified structures is dependent on seawater chemistry, with higher
pH and aragonite saturation state favoring calcification. A number of studies reported
different patterns of impact on calcification ranging from reduction to hypercalcification
with some species showing no effects, which means that compensatory mechanisms are
available to counteract the effects of reduced pH and elevated pCO2. In marine fishes,
the structures for mechanoreception known as otoliths are composed of aragonitic
calcium carbonate and function for detection of motion and acceleration, maintaining
balance, and sound localization. The morphology of the otoliths is species-specific and
linked to the functional requirements for specific habitats and swimming behavior. In
this thesis, the response of the otolith calcification in larval Atlantic cod (Gadus morhua
L.) and Atlantic herring (Clupea harengus L.) to elevated pCO2 and the possible
consequences to the behavior of the larvae were investigated. The main results of the
investigation were derived from an ocean acidification experiment conducted in the landbased
mesocosm facility in the University of Bergen's Espegrend Marine Station from
March to May 2010. Based on the results, the thesis concluded that otolith calcification
in both Atlantic cod and herring larvae was significantly affected by increase in seawater
pCO2 concentrations. However, the direction of the effects was different between the two
species with increase in otolith growth in cod larvae but a decrease in herring larvae. On
the other hand, the changes observed in the otolith growth had no impact on the
swimming behavior of both species. The swimming behavior was resilient to elevated
pCO2 despite the changes in the growth of the otoliths. Ocean acidification is not the
only stressor associated with the increase in anthropogenic CO2 emission. In marine fish
larvae, the relationship between otolith morphology and swimming behavior must
therefore be further investigated by considering additional stressors such as ocean
warming, hypoxia, and fluctuations in food availability
