Behaviour in flow: perspectives on the distribution and dispersion of meroplanktonic larvae in the water column

For marine benthic invertebrates with meroplanktonic larvae, the relative i mportance of hydrodynamics and swimming behaviour in determining larval dis persal in the water column, particularly at small spatial scales, has not b een determined. In the field, larval aggregations recorded at physical and biological discontinuities in the water column were attributed to hydrodyna mics. Similar aggregations obtained in the absence of flow in the laborator y indicate a potentially significant role of behaviour. At large spatial sc ales, larval distribution in the plankton is mainly regulated by horizontal advection. However, the ability of larvae to behaviourally regulate their position at scales of micrometres to metres when exposed to turbulent fluid motion in the water column, as evidenced in the benthic boundary layer, is unknown. Evaluation of swimming in turbulent flows in the water column is an intriguing area of research, which involves several constraints. In the field, quantification of behaviour is limited by low success in tracking la rvae and lack of appropriate observational tools. In the laboratory, the ge neration and quantification of flow regimes that are representative of thos e in the field remains a challenge. An approach that integrates biological and physical measurements within realistic ranges is necessary to advance o ur understanding of larval dispersal.