Pelagic conditions affect larval behavior, survival, and settlement patterns in the Caribbean coral Montastraea faveolata

The lack of detailed studies on the earliest life stages in corals currently limits the understanding of coral population dynamics. Although pre- and postsettlement processes both play a role in structuring coral populations, their relative importance and interaction are not well understood. By lowering seawater salinity (range: 28 to 36 psu), we created an artificial environmental gradient and followed the responses of Montastraea faveolata (Ellis & Solander, 1786) planulae during their pre- and postsettlement phases. Decreased salinity increased pre- and postsettlement mortality and altered larval behavior and substrate choice upon settlement. The effect of lowered salinity on the survival of M faveolata planulae was mainly expressed during the pelagic life-phase. Reduced salinity levels increased the mobility of planulae, and reduced the duration of the planktonic period and their selectivity among available habitats for settlement. Regardless of salinity, planula behavior changed over time. During the early planktonic phase (0 to 52 h) the proportion of moving and positively geotactic planulae within a population increased towards lower salinity and under dark conditions. Thereafter (> 67 h), most planulae (> 60%) became positively geotactic, regardless of salinity. Settlement started after 144 h and salinity had no effect on settlement rate, i.e. the number of planulae settling per unit of time. As variable pelagic histories influence planular survival and habitat choice upon settlement, the number and distribution of coral settlers was related to their earlier pelagic experiences. This finding experimentally shows that the distribution and subsequent performance of corals early after settlement depends at least partly on their presettlement history and highlights the potential importance of presettlement processes in structuring coral populations.