The rapid uptake of carbon dioxide (CO₂) by the world’s oceans since the Industrial Revolution is causing a rapid decline in ocean pH and a rise in temperatures. This change in ocean chemistry has affected major ecophysiological mechanisms in fishes, including the development of otoliths. Changes in otolith morphology have previously been linked to decreased hearing sensitivity in fishes. To investigate the potential of CO₂-induced hearing loss we assayed Hi-hat (Pareques acuminatus), a tropical soniferous sciaenid species. Sound production and reception are critical to the ecology of sciaenids, which are known model organisms for teleost bioacoustics. In this study, we compared the effects of three pH levels and two temperatures reflecting future ocean scenarios and their natural ambient conditions for two different exposure durations (19 wk and 5 wk). The sagittal otoliths were then extracted, imaged, measured, and analyzed in ImageJ. Three standardized ratios were calculated from the measurements: otolith thickness:fish length, otolith length:fish length, and otolith mass:fish mass. The 19-week otoliths from fish exposed to pH 7 had significantly higher otolith mass:fish mass ratio (ANOVA; p < 0.001), otolith length:fish length ratio (ANOVA; p < 0.01), and otolith thickness:fish length ratio (ANOVA; p < 0.01). Fish exposed to pH 7 for 19 weeks were significantly smaller than those from the control group (ANOVA; p < 0.05), however their otoliths had similar thickness:length ratio (p>0.05) to the larger higher pH fish. The relative increase in the mass, thickness, and length of Hi-hat otoliths following exposure to high levels of CO₂ may affect how the otolith function. Ultimately, changes can otolith form and function may affect acoustic performance and reproductive success of soniferous species.

Primary Presenter: Jonathan Nash, Hampton University (jonathan.nash1234@gmail.com)

Authors:

Jonathan Nash, Hampton University  (jonathan.nash1234@gmail.com)

Cara Schweitzer, NOAA  (cara.schweitzer@noaa.gov)

Andrij Horodysky, NOAA  (andrij.horodysky@noaa.gov)