Close encounters with eddies: oceanographic features increase growth of larval reef fishes during their journey to the reef

Abstract

Like most benthic marine organisms, coral reef fishes produce larvae that traverse open ocean waters before settling and metamorphosing into juveniles. Where larvae are transported and how they survive is a central question in marine and fisheries ecology. While there is increasing success in modelling potential larval trajectories, our knowledge of the physical and biological processes contributing to larval survivorship during dispersal remains relatively poor. Mesoscale eddies (MEs) are ubiquitous throughout the world's oceans and their propagation is often accompanied by upwelling and increased productivity. Enhanced production suggests that eddies may serve as important habitat for the larval stages of marine organisms, yet there is a lack of empirical data on the growth rates of larvae associated with these eddies. During three cruises in the Straits of Florida, we sampled larval fishes inside and outside five cyclonic MEs. Otolith microstructure analysis revealed that four of five species of reef fish examined had consistently faster growth inside these eddies. Because increased larval growth often leads to higher survivorship, larvae that encounter MEs during transit are more likely to contribute to reef populations. Successful dispersal in oligotrophic waters may rely on larval encounter with such oceanographic features.

Keywords: larval dispersal; larval fish growth; mesoscale eddies; otolith microstructure; population replenishment; reef fish.

Figure 1.

Map of study area for each of the three sampling periods, indicating positions of mesoscale eddies (dashed lines) and locations of eddy (ED, black points) and non-eddy (NE, grey points) stations. Eddies are identified numerically in the order in which they propagated through the Straits of Florida.

Figure 2.

Comparisons of recent larval growth between larvae collected inside (ED; black) and outside (NE; grey) mesoscale eddies. Squares, comparisons with all ages included; circles, young age group only; and triangles, old age group only. p_Y, p-value for young age group comparisons; p_O, p-value for old age group comparisons. Sample size indicated to the right of each data point.