How Sensory Systems Influence Settlement Patterns in Larval Red Drum (Sciaenops ocellatus)

Settlement is arguably the last stage of high mortality in the life cycle of marine fishes, making the number of larvae that successfully settle to a benthic habitat a reasonable determinant of future population size.  Habitat selection during settlement is likely an active process, however, much of what we know comes from studies focused exclusively on coral reef ecosystems.  We conducted experiments to examine how estuarine fish larvae (red drum, Sciaenops ocellatus) might actively choose settlement sites based on information received from their senses.  Larvae reduced their activity in the presence of elevated sound pressure levels (acoustic noise).  Their activity increased in the presence of the chemical cue lignin, whereas tannin did not cause a change in activity.  Larvae spent more time in water masses taken from seagrass beds compared to control saltwater.  Larvae positioned themselves differently in the water column depending on the substrate color, moving closer to a yellow (sand) bottom than a green (seagrass) bottom at pre-settlement sizes.  Additionally, red drum settled at different sizes to sand, oyster shells and seagrass.  We interpret these findings as evidence for active settlement in an estuarine-dependent fish species.