Abstract

While there is mounting evidence that larval coral reef fishes develop strong behavioral capabilities through ontogeny (e.g. swimming) and at settlement (e.g orientation to sound), the influence of these capabilities on dispersal patterns depends on their ability to orient in the open ocean. A new apparatus was designed to detect, quantify, and understand orientation behavior of larval fish while embedded in oceanic water masses, were they have no apparent frame of reference. The OWNFOR system produces a video clip of pelagic larva(e) swimming within a semi enclosed, drifting chamber. We demonstrate that the in situ system provides unbiased orientation data that are analyzed via the use of Open Source Softwares (OSS) tuned to our specific needs. We show that (1) orientation vs non-orientation behavior can be detected, (2) two kinds of orientation behaviors can be distinguished using two approaches of Rayleigh’s statistics, and (3) the choice of the shape of the drifting chamber and appropriate statistical treatment diminishes the impact of the enclosure of the larva on orientation results. This innovative observational technique is a logical and critical phase to break into emerging questions in the field of larval ecology, providing major biological inputs to larval transport models and potentially to a large array of marine organisms that have a pelagic phase

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