Hypercapnia-induced disruption of long-distance mate-detection and reduction of energy expenditure in a coastal keystone crustacean.

Ocean acidification (OA) has been shown to disrupt behavioural responses either by affecting metabolic processes, or by effectively impairing an organisms' ability to gather and assess information and make decisions. Given the lack of information regarding the effects of high CO2 on olfactory-mediated mating behaviours in crustaceans, the possible chemosensory disruption in male mate-tracking in the keystone amphipod (Gammarus locusta) was assessed (after a two-generation acclimation to high CO2 conditions). In a series of behavioural trials, the response time, first direction of movement and the proportion of time spent in the presence of female scent cues were quantified. The possibility of high CO2 -induced metabolic changes was assessed through routine metabolic rate (RMR) quantification. We found that hypercapnia was responsible for inducing a delay in response time latency and effectively disrupted accurate female cue-tracking. Moreover, RMR were significantly reduced under high CO2 in both genders. Such finding supports the hypothesis of hypercapnia-induced metabolic depression, which potentially underpins the increased latency in response time verified. Overall, the present study hints the potential disruption of chemosensory-dependent sexual behaviours, through some degree of chemosensory and metabolic disruption. These results emphasize the need for further behavioural tests regarding chemosensory communication in amphipods and energy metabolism, and suggest cascading consequences for the species' reproductive success and overall fitness in a future less alkaline ocean.