pH Challenges in the Life of Pagurus bernhardus: Chemotaxis, Feeding, and Energy Allocation

It is established that decreasing ocean pH is adversely impacting marine organisms’ behaviour and physiology. In this thesis, I tested the hypothesis that challenges in the life of ocean acidification are not an isolated mechanism but an interplay between chemical communication, physiological shifts, and energy dynamics. Chemotactic traits were explored utilising pH-dependent signalling molecules at current and future predicted pH conditions to identify if chemoreceptive disruption is at the detection level or potentially physiological. The chemotactic traits in speed, acceleration, distance moved, and the average distance from chemicals were measured in individuals across pH treatments (7.7 and 8.2). The results show that ocean acidification negatively impacted chemotactic traits under the pH-sensitive chemical, which protonates more under reduced pH than the control, suggesting chemotaxis is altered by infodisruption and not energy conservation. During the chemotactic experiment, food ingestion rates of P.bernhardus were analysed at the same time at pH 8.2 and pH 7.7. Reduced pH increased the rate of food consumption immediately; these effects were exacerbated with pH exposure time. The scope for growth, or P.bernhardus was conducted in current pH (8.2), future pre-dicted pH (7.7), and extreme predicted intertidal pH (7.4) to identify the energy budget reserves of organisms.A reduced pH of 7.7 limits scope for growth potential, while a pH of 7.4 causes metabolic depression and increases SFG. Enzymatic and surface morphology analysis showed that reduced pH treatments can inflict energetic costs and potentially damage to the surface of the exoskeleton and sites of chemoreceptive organ anchorage (setae).The results obtained from this doctoral thesis provide substantiating evidence for the proposition that diminished pH constitutes a multifaceted stressor, capable of instigating both behavioural and physiological repercussions. The intricate interplay between these factors may give rise to extensive ramifications for intertidal populations in climate change scenarios.