Acute, static, and fluctuating ocean acidification effects on the olfactory system of the yellow shore crab, <i>Hemigrapsus oregonensis</i>

Increases in atmospheric carbon dioxide accelerate ocean acidification (OA), which has been shown to alter olfactory behaviours in marine organisms. Coastal regions currently experience partial pressure of carbon dioxide ( pCO 2 ) greater than end-of-century open ocean predictions with daily and seasonal fluctuations. Therefore, we hypothesized that marine organisms inhabiting the coastal regions are tolerant to the effects of OA. The acute, static, and fluctuating effects of acidification on the olfactory system were investigated in the coastal yellow shore crab ( Hemigrapsus oregonensis (Dana, 1851)). After exposures, the olfactory behaviour to a food cue, putrescine, was measured, and changes in olfactory sensory receptors and neurons (OSNs) were determined using immunohistochemistry. Crabs took three times longer to locate the odorant and preferred it less after acute (minutes) and long-term (14 days) static exposures to OA. This impairment was correlated with a 16%–30% decrease in olfactory receptor protein (ionotropic receptor 25a (IR25a)) immunoreactivity and a 20% decrease in OSN volume. Crabs exposed to daily fluctuating pCO 2 (7 days) displayed behavioural responses intermediate to crabs in control or static acidification conditions, and showed no changes in IR25a. These results indicate that despite their variable natural environment, yellow shore crabs are affected by acidification, being particularly vulnerable during sustained upwelling events (long-term static high pCO 2 ).