Award: EF-1220480

If a larval fish cannot avoid predators and cannot orient itself in three-dimensional space, the consequences to the individual and the population are dramatic. This research focused on a system critcal to the survival of larval fish - the ear (otoconia). Specificall we studied the impact of ocean acidification on otoliths (ear stones). Otoliths (2 pairs, 3 on each side) are formed by precipitation of calcium carbonate from a bicarbonate-rich and alkaline pH fluid. They are critical to fish movement and orientation. Prior to this research the impact of ocean acidification on fish was thought to be minimal since fish can compensate for carbon dioxide levels in the surrounding waters. We tested that supposition and discovered that the opposite is in fact the case, at least in larvae. Focusing on pre-settlement age larval reef fish (think infant Nemo) we explored how ocean acidification impacts all 6 of the otoliths with tested impacts ranging from simple changes in circularity and length to changes in crystal shape and mineral composition. We found that for the largest otolith, the sagittal otolith, in 3 species of reef fish (2 from the same genus of clownfish) the mineral habit (shape) was larger in fish reared at lower pH with significant differences in the core of these otoliths. We also found that the shape of the lapilli, the otoliths critical to movement and balance, with the circularity of these otoliths increased with decreasing pH. The shape of the otolith directly impacts its interaction with the hair cells of the otoconia with circular otoliths having less surface area available for interactions. This likely negatively impacts the function of these otoliths and so may translate to loss of avoidance and swimming capabilities. In the grunts we found even more extrreme impacts with the lapilli also showing increased ciruclarity with decreased pH. In some otoliths from fish reared at low pH the changes in crystal habitat were profound with significant twinning leading to protuberances, sometimes rendering the otolith non-functional. In the sagittae of grunts we also found, as we did in clownfish, that changes in crystal habit was accompanied by changes in mineral polymorph with otoliths from low pH treatements containing amorphous calcium carbonate, vaterite, and hexagonal aragonite. These forms of calcium carbonate are less stable than the preferred pristmatic aragonite and less dense as well. Density of the otolith is critical to maintaining contact with the macular hair cells. Lower density also translates to loss of function. Our results demonstrate that the impacts of ocean acidification on the earliest life stages of fish are significant and could have profound consequences for survival. Last Modified: 11/15/2015 Submitted by: Robyn E Hannigan