Angry damsels: do species interactions after overfishing enhance or inhibit coral reef recovery?

Coral reef species are undergoing widespread mortality under increasingly frequent mass coral bleaching events, which will continue until global efforts reduce CO2 emissions. In the meantime, it is critical to enhance reef resilience and recovery processes. Overharvesting of herbivorous fishes threatens these processes and can encourage phase-shifts towards algal-dominated reefs.

Less obvious is that overfishing also alters the relative abundance of other fishes within the community, disrupting complex species interactions. Whether these more subtle impacts enhance or inhibit the function of herbivores is unclear. Resolving how species interactions mediate responses to ecological disturbance in hyper-diverse communities is necessary to provide realistic predictions on future impacts of global environmental change.

Damselfishes live amongst the branches of coral colonies and aggressively defend their coral hosts against intruders. In areas of high fishing intensity, damselfish are largely ignored whereas their predators are targeted. This differential targeting can lead to a surge in damselfish abundance, increasing the proportion of reef that is aggressively defended. The extent to which this "Wild West" scenario prevents herbivores from grazing, and consequently its impact on resilience and recovery of reefs, is unknown yet potentially significant.

This project aims to reveal the impact of heightened aggression between species on coral reef resilience and recovery. The student will take advantage of new methods pioneered by CASE Partner Operation Wallacea using stereo-video to generate 3D-heatmaps of space use and interactions between damselfishes and other herbivores across a gradient of fishing pressure. Additionally, field experiments will assess the influence of damselfish abundance on aggressive interactions. Data will be used to parameterise an ecosystem-based model to explore the effect of this cross-species interference at larger spatial scales and explore scenarios of its impact on future reef resilience and recovery. Model outputs will inform management strategies to maintain optimum relative fish abundance for recovery.