Contrasting behavioural responses to ocean acidification and warming have the potential to disrupt herbivory

Global change has the potential to affect organisms and re-structure ecosystems where key species interactions, such as herbivory, are disrupted. The fastest ways individual herbivores – and therefore ecosystems – can respond to climate change is through shifts in behaviour. In marine habitats, environmental changes of particular concern in the future are ocean acidification and warming. Consequently, we reviewed the existing literature in this area of research, to identify if there were any over-arching trends or emerging patterns in behavioural responses of marine herbivores to ocean acidification and warming. We identified that while the body of research is growing, focus remains primarily on few locations (temperate areas), phyla (Mollusca, especially gastropods; Crustacea; Echinodermata), and behaviours (grazing rate, movement). Although representing a relatively narrow view of future herbivory, this review indicates that in many cases, the key behaviours of feeding and movement could be maintained under ocean acidification and warming. However, where change is observed, it is more likely grazing will be enhanced and movement impaired. If such patterns were to manifest under future climates, it would mean that the herbivores present would consume more yet there may be less of them as impaired movement and escape behaviours would have made them more vulnerable to predation. The exact responses will, however, likely be context-dependant. Therefore, we recommend future studies address the research gaps our review identified (i.e., a lack of understanding in tropical and polar regions, economically and ecologically important Crustacean and Echinoderm species, early life history stages, and more behavioural responses in addition to feeding and movement). Understanding the diversity of responses expected under varied contexts will be important to uncover trends in how marine invertebrates will behave under global change.