CYLINDRICAL TUBE TRAPS FOR LARVAL SAMPLING

Recent interest in the relationship between larval input to an area and settlement and recruitment density has generated a need for a larval sampling device that integrates abundance over time. A simple modification of the cylindrical tube trap commonly used in sedimentation studies can provide unbiased samples of larval dynamics. Our design utilizes a high aspect (height-to-width) ratio and an internal Formalin layer to limit the potential resuspension of collected larvae. Tests both in a laboratory flow tank and under field conditions suggest that capture rate scales linearly with both larval concentration and horizontal advection-two components of larval flux. The important role of horizontal advection has additional implications for the use of such traps to measure sedimentation rates, where only vertical particle flux is of interest. In the field, we found a strong correlation between the capture rate of Semibalanus balanoides larvae and daily settlement rates on adjacent shores. These traps, like sediment traps, may exhibit a particle-size bias in collection efficiency. Consequently, this technique is probably most appropriate for examining intraspecific spatial and temporal variation in the dynamics of a given larval stage.