Hidden functional groups may play critical roles in recovery processes in post-disturbed coral reefs

With climate change mortalities become increasingly frequent in tropical systems, coral reef system dynamics is increasingly driven by the strength of its recovery trajectories. The ability of fish functional groups to... [ view full abstract ]

With climate change mortalities become increasingly frequent in tropical systems, coral reef system dynamics is increasingly driven by the strength of its recovery trajectories. The ability of fish functional groups to maintain algal-free substrates after coral mass mortalities is a critical first step in ensuring successful settlement and growth of coral recruits. There has been a growing acknowledgement of the essential role that herbivore fish play, with several studies identifying them as cornerstones of resilience in recovering reefs. We examined the direct and indirect role of other trophic groups in contributing to the maintenance of algal-free substrates on post-disturbed reefs. We quantified the capacity of fish assemblages to control algal growth and to examine the species responsible for this control. We developed an underwater video assay that involved observing bite rates taken off bits of dead coral colonised by turf algae, collected from territorial damselfish gardens. The bits were recorded for two hours. Our results indicate that while a range of species within the assemblage contribute to algal offtake, a few species like the herbivore Ctenochaetus striatus is disproportionately important. More interestingly, several other microinvertivore species of fish played vital roles, both directly and indirectly in algal offtake. These species were often the initiators of algal offtake, incidentally removing large amounts of algal turf from the substrate while foraging for microinvertebrates. These could represent hidden functional groups that contribute significantly to the resilience of reefs by providing a function that goes beyond their trophic roles.