Wayward youth: how maturity, reproduction and seaweed drive snapper (Lutjanus spp.) habitat shifts.

Despite snappers' (family Lutjanidae) commercial and ecological significance, knowledge gaps remain regarding life history, ontogeny and ecology across their range in the Caribbean and south Atlantic. There is also a need to explore the efficacy of marine protected areas (MPAs) as a tool for enhancing nursery and spawning habitat conservation for multiple snapper species. Additionally, even as hurricanes and sargassum inundation have become rising issues for coastal communities, there is a scarcity of data on how commercially important species respond to these environmental disturbances. To address these data gaps, we investigated the spatial and temporal movements of 32 snappers of multiple species in mangrove estuary, reef and shelf edge habitats in St Croix, US Virgin Islands for up to a year using surgically implanted acoustic transmitters and hydrophone arrays. We documented ontogenetic habitat shifts as individuals moved incrementally from juvenile mangrove habitat to adult reef habitat, and several were tracked migrating >30 km to a potential spawning site. Results demonstrated the connectivity of a series of MPAs and their management potential across lutjanid life stages. Size and growth estimates during these movements highlighted the regional variability in lutjanid ontogeny and the need for population-specific life-history studies. Snapper displayed no change in behaviour during a direct hurricane impact, but a significant number of fish made temporary or permanent habitat shifts coinciding with a severe sargassum event inside a bay, providing one of the first descriptions of fishes' behavioural responses to coastal sargassum inundation.