Vertical migrations of reef fish larvae in the Straits of Florida and effects on larval transport

Abstract

The goals of this study were to measure vertical distributions of pelagic coral reef fish larvae, identify significant vertical migrations, and estimate the effects of vertical migrations between depths with different ambient currents on larval transport in the Straits of Florida. Spring, summer, and fall time‐series of plankton net tows were conducted at the edge of the Florida Current offshore of Miami. In each time‐series the upper 100 m of the water column at a fixed station was sampled repeatedly at 3‐h intervals for two diel cycles, with different nets sampling at five discrete depth ranges. Simultaneously, currents‐at‐depth were recorded by shipboard current profilers. Mean and standard deviation of larval depth and statistically significant vertical migrations were determined by nonparametric resampling and tree regression techniques. In 10 taxa, larvae showed ontogenic vertical migrations, gradually moving deeper with growth and development. Vertical distributions of six taxa varied between day and night, revealing diel vertical migrations. Larval transport was estimated by generating progressive vector diagrams from current measurements and larval vertical distributions. The dominant alongshore component of the Florida Current resulted in rapid larval transport through the Straits of Florida, while cross‐shore current was an order of magnitude weaker and highly variable. Larvae at depths > 70 m experienced a 15–75% reduction in transport; thus, deep vertical distributions and downward vertical migrations potentially favor retention and settlement in the Straits of Florida.