Abstract
Anthropogenically induced climate change is a driving force to warming oceans. Fish being ectothermic rely on ambient temperatures to regulate physiological processes in order to actively swim, forage, reproduce or escape predators. It is important to understand the effect on tropical ectotherms, as experiencing stable temperatures year-round has caused their operative temperatures to be more refined than those of ectotherms found in temperate environments. Whilst the knowledge of the effect of temperature on fish is well understood, there is little research examining its effects on the escape response of three closely related species. Furthermore, there are minimal studies examining its effects on anti-predator behaviour in coral reef fish. To investigate these, we visited the Lizard Island Research Station, North Great Barrier Reef (14°40'S; 145°28'E) to expose Ambon damsel (Pomacentrus amboinensis), white-tail damsel ( Pomacentrus chrysurus), and Ward’s damsel (Pomacentrus wardi) to projected thermal regimes in accordance with IPCC to quantify any changes in escape behaviours important for recruit success. Following a five-day exposure period, escape performance was quantified using a standardised test that measures key locomotory/non-locomotory variables associated with the fast start response. These included: escape distance, velocity, maximum velocity, latency and directionality. It was determined that when P. chrysurus was exposed to projected thermal regimes, the locomotory variables associated with the fast-start escape response declined in comparison to the other species, suggesting species-specific responses due to a refined thermal niche, indicating a higher vulnerability to predation. Additionally, we examined if elevated temperatures could impact important behaviours such as routine swimming, thigmotaxis and lateralisation in P. amboinensis. Post-five-day exposure, videos of routine swimming & thigmotaxis in a circular arena were analysed, with a detour test used to test lateralisation. Interestingly, it was found that only thigmotaxis was affected, with individuals in the elevated treatment experiencing greater boldness. These findings suggest that elevated temperatures alone may differentially affect closely related phylogenetic species. Increased boldness and unaffected routine swimming and lateralisation, paired with the ability to exhibit successful escape responses, may enable P. amboinensis to thrive under future warming, whilst reduced locomotor performance in P. chrysurus may inherently increase risk of predation. Overall, this thesis highlights the importance of species-specific responses to warming, with emphasis on how acute thermal stress can cause alterations to predator-prey dynamics and the threat it poses for future coral reef community composition.