Metamorphosis of a coral reef fish (Acanthurus triostegus, Linnaeus 1758) and its importance in larval recruitment facing climate change

Supervisors: David Leccini (CRIOBE-Moorea) & Eric Parmentier (Univ. Liege)
Coral reef fish metamorphosis, the larva to juvenile transition, is a key step of coral reef fish life cycle, since its good development directly impacts on larval recruitment success and subsequent stock replenishment. Surprisingly there is a lack of data available on metamorphosis physiology and the potential impact of global warming on this crucial shift. In this study, we conducted in situ sampling of Acanthurus triostegus (surgeonfish) larvae at Moorea Island, French Polynesia, and deciphered the importance of thyroid hormones (THs) on coral reef fish metamorphosis, as well as the impact of increasing water temperature on this process. THs appeared to trigger metamorphosis, under currently unknown environmental conditions. Hormonal treatments affecting the TH pathway confirmed that THs are also responsible for the development of the lateral line and the acquisition of visual recognition of conspecifics and predators. A 3°C rise in water temperature led to defects in fish visual recognition, and also caused lower levels of THs in fish. This work is one of the first studies to tackle the role of THs in metamorphosis of coral reef fish, and the first one conducted with in situ sampled specimens. We provide here relevant insights into some physiological mechanisms of metamorphosis, with a particular emphasis on how global warming might negatively impact this transition by affecting fish endocrinology.