Otolith size and the vestibulo-ocular reflex of larvae of white seabass Atractoscion nobilis at high pCO2

Abstract

We investigated vestibular function and otolith size (OS) in larvae of white seabass Atractoscion nobilis exposed to high partial pressure of CO 2 (pCO 2 ) The context for our study is the increasing concentration of CO 2 in seawater that is causing ocean acidification (OA). The utricular otoliths are aragonitic structures in the inner ear of fish that act to detect orientation and acceleration. Stimulation of the utricular otoliths during head movement results in a behavioral response called the vestibulo-ocular reflex (VOR). The VOR is a compensatory eye rotation that serves to maintain a stable image during movement. VOR is characterized by gain (ratio of eye amplitude to head amplitude) and phase shift (temporal synchrony). We hypothesized that elevated pCO 2 would increase OS and affect the VOR. We found that the sagittae and lapilli of young larvae reared at 2500 µatm pCO 2 (treatment) were 14 to 20% and 37 to 39% larger in area, respectively, than those of larvae reared at 400 µatm pCO 2 (control). The mean gain of treatment larvae (0.39 ± 0.05, n = 28) was not statistically different from that of control larvae (0.30 ± 0.03, n = 20), although there was a tendency for treatment larvae to have a larger gain. Phase shift was unchanged. Our lack of detection of a significant effect of elevated pCO 2 on the VOR may be a result of the low turbulence conditions of the experiments, large natural variation in otolith size, calibration of the VOR or mechanism of acid−base regulation of white seabass larvae.

Influence of ontogenetic development, temperature, and pCO2 on otolith calcium carbonate polymorph composition in sturgeons

“…Despite p CO 2 reportedly having an influence on the otolith morphology of multiple marine teleosts (e.g., Refs. 29 , 30 , 47 , 48 ), environmental p CO 2 (and therefore pH) had no effect on otolith size or polymorph composition in our study. Acid–base regulation is a critical physiological process as inappropriate maintenance will influence the overall performance of the individual by impacting the functionality of proteins and other essential macromolecules 49 .…”

Ocean acidification alters morphology of all otolith types in Clark’s anemonefish (Amphiprion clarkii)

“…Although there remains no evidence of ocean acidification-induced vaterite replacement in otoliths, including in A. clarkii , there is some evidence for calcite replacement in sagittae and lapilli at elevated pCO 2 (Coll-Lladó et al, 2018); calcite is similarly less dense than aragonite (Nakamura Filho et al, 2014). In terms of kinesthesia, some fish with abnormal and/or asymmetric sagittae/lapilli exhibited kinetoses (Söllner, 2003; Anken, Knie & Hilbig, 2017); however, other studies observed pCO 2 impacts on otolith morphology without observing impacts on behavior (Bignami, Sponaugle & Cowen, 2013; Bignami, Sponaugle & Cowen, 2014; Shen et al, 2016). It is possible the pCO 2 impacts on otolith morphology and asymmetry observed here could impair A. clarkii hearing and kinesthesia, but no sensory or behavioral assays were conducted, so hypotheses remain speculative.…”

Elucidating the acid-base mechanisms underlying otolith overgrowth in fish exposed to ocean acidification

“…Coupled with functional studies (e.g. [11,48]), this information will help predict whether the inner ear vestibular and auditory sensory systems of fish will be affected by OA. Furthermore, understanding the mechanisms responsible for otolith biomineralization and overgrowth during OA exposure can help improve the accuracy of otolith-reliant aging techniques in the future ocean.…”

“…Originally, it was predicted that CO2-induced ocean acidification (OA) would impair otolith biomineralization because the associated decreases in seawater pH and [CO3 2-] hamper CaCO3 precipitation [9]. However, subsequent studies reported that fish exposed to OA developed enlarged otoliths [10][11][12][13][14][15][16]. These findings led to a broader awareness otolith biomineralization is strongly linked to endolymph and blood chemistries, and to the hypothesis that biological regulation of endolymph pH could lead to increased [CO3 2-] resulting in otolith overgrowth [10].…”