Abstract: Early life history stages of marine organisms can be difficult to study in the field, in part due to their inherently small size. Understanding to what extent early post-settlement processes shape fluctuations in the size and structure of adult populations is, however, essential to effectively manage fished stocks or to protect threatened species. Population irruptions of the crown-of-thorns starfish (CoTS) are one of the foremost contributors to the global degradation of coral reefs, but causes of irruptions have been debated for decades. Research into the early post-settlement life history of CoTS has been greatly hindered by difficulties related to detecting algal-feeding juveniles in the field. This has generated much controversy and greatly hampered our understanding of CoTS population dynamics. Today, I will introduce you to the habitat of early stage juvenile CoTS, with a strong focus on the elusive algal feeding stage. I will talk about their growth and their vulnerability to predation based on the incidence of sub-lethal injuries. Importantly, I will show, based on extensive field sampling of early stage juvenile starfish (n=3,532), that marked variation in body size among juveniles is linked to an ontogenetic diet shift from coralline algae to coral. This transition in diet leads to exponential growth in juveniles and is essential to reach maturity. Because smaller individuals experience higher mortality and growth is stunted on an algal diet, the ontogenetic shift to corallivory enhances individual fitness and replenishment success. Our findings suggest that the availability of coral prey facilitates early ontogenetic diet shifts and may be fundamental in initiating population irruptions.

Biography: Jennifer completed her degree in Biological Sciences at the Free University of Brussels (Belgium). She attended the BIOMAR marine biology laboratory for six months, where she wrote her final year thesis on the biodiversity of Antarctic starfish. She continued to display her passion for the marine environment through various roles: as marine research officer in Madagascar, marine environmental consultant in the United Kingdom and crown-of-thorns starfish (CoTS) diver in Australia. From 2014 to 2016, she spent more than 450 days at sea working with the CoTS control program on the Great Barrier Reef. This position provided her with ample opportunities to observe and study crown-of-thorns starfish in their natural environment and set in motion her PhD on early stage juvenile CoTS.