Detection and quantification of marine larvae orientation in the pelagic environment

The pelagic larval phase represents a major opportunity for dispersal in benthic organisms, yet behaviors controlling and potentially limiting dispersal are still largely unknown for most larvae. Here, we present a new means of observing the orientation of larvae of all developmental stages in the pelagic environment. A cylindrical frame holding a semi-open arena in which larvae are filmed is set to drift at a controlled depth within the natural environment. Larval trajectories are extracted from video data and used to quantify orientation behavior. Field tests with late-stage coral reef fish larvae show that orientation can be detected from individual larval positions in the arena and can be significantly differentiated from random movement or artifactual behavior.