Assessing the impact of water flow, including velocity and dynamics, on the survival and growth of coral recruits during the initial weeks after settlement.

The health of recently settled coral recruits in reefs and aquaculture settings may be influenced by various factors. An often neglected parameter is fluid velocity, despite its potential to influence the morphology, growth, and survival of coral recruits. This study investigates the effects of flow velocity on the morphology and growth rate of up to 7-week-old Acropora abrolhosensis recruits. A flume setup was designed to achieve linear flow, and the effects of flow velocity were investigated by photographically determining morphological changes (e.g. bending and retracting tentacles) during a short-term assay. Furthermore, coral growth and survival were monitored in a 7-week experiment under a linear flow gradient from 5 to 20 cm s-1. The results indicate that A. abrolhosensis recruits respond to both acute and long-term differences in water velocity, with complete polyp retraction observed for acute exposures above 55 cm s-1, and a relative growth increase of 151% during rearing at 20 cm s-1compared to at 5 cm s-1. These observations suggest that flow velocities can significantly affect the outcomes of coral aquaculture and that further investigations are needed to fully understand the growth responses of early coral life stages under a wider range of velocities across coral taxa.