The bipartite life history of most marine organisms leads to complex patterns of replenishment in benthic populations. High variation in adult spawning, dynamic oceanographic currents, and often unknown larval behaviors create challenges in accurately predicting spatial and temporal patterns in the supply and settlement of pelagic larvae to nearshore juvenile habitats. Yet, understanding and predicting larval exchange underlies population dynamics, ecological interactions, and conservation practices. We compared observed patterns of larval settlement of the bicolor damselfish Stegastes partitus (Pomacentridae) along the Florida Keys, USA, to those obtained through model simulations using a high-resolution biophysical model parameterized with species-specific early life-history information. Light traps intercepted settlement-stage larvae, and divers censused new recruits at 2 replicate reefs in each of the upper (eastern) (UK) and lower (western) Keys (LK) during 6 peak settlement periods. Damselfish settlement and recruitment to the LK consistently exceeded that to the UK. Remarkably, model simulations successfully explained 70% of temporal variation in settlement within each region. However, the model did not capture the relative magnitude of observed settlement between the regions: settlement was either overestimated in the UK or underestimated in the LK. Potential causes include weak larval settlement cues or larval ability to navigate and swim to settlement habitat in the UK, higher larval condition and survival in the more productive waters of the LK, or substantial spatial variation in reproductive output. Connectivity matrices indicate that a majority of S. partitus settlement to the Florida Keys is sourced from Keys populations.

Oceanographic features, such as eddies and fronts, enhance and concentrate productivity, generating high-quality patches that dispersive marine larvae may encounter in the plankton. Although broad-scale movement of larvae associated with these features can be captured in biophysical models, direct evidence of processes influencing survival within them, and subsequent effects on population replenishment, are unknown. We sequentially sampled cohorts of coral reef fishes in the plankton and nearshore juvenile habitats in the Straits of Florida and used otolith microstructure analysis to compare growth and size-at-age of larvae collected inside and outside of mesoscale eddies to those that survived to settlement. Larval habitat altered patterns of growth and selective mortality: Thalassoma bifasciatum and Cryptotomus roseus that encountered eddies in the plankton grew faster than larvae outside of eddies and likely experienced higher survival to settlement. During warm periods, T. bifasciatum residing outside of eddies in the oligotrophic Florida Current experienced high mortality and only the slowest growers survived early larval life. Such slow growth is advantageous in nutrient poor habitats when warm temperatures increase metabolic demands but is insufficient for survival beyond the larval stage because only fast-growing larvae successfully settled to reefs. Because larvae arriving to the Straits of Florida from distant sources must spend long periods of time outside of eddies, our results indicate that they have a survival disadvantage. High productivity features such as eddies not only enhance the survival of pelagic larvae, but also potentially increase the contribution of locally spawned larvae to reef populations. population connectivity | selective mortality | otolith microstructure | mesoscale eddies | reef fish settlement

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.

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Benthic marine populations are often replenished by a combination of larvae from local and distant sources. To promote retention of locally spawned larvae in strong, unidirectional boundary current systems, benthic marine organisms must utilize biophysical mechanisms to minimize advective loss. We examined patterns in larval fish abundance, age distribution, and assemblage in relation to environmental variables in the Straits of Florida to better understand the factors underlying larval transport and retention in a boundary current system. Depth was the primary structuring element; larval assemblages were more distinct across vertical distances of tens of metres than they were over horizontal distances of tens to hundreds of kilometres. However, depth distributions were species-specific, and larval assemblages inside and outside of mesoscale eddies were distinct. Age distributions were consistent with the hypothesis that mesoscale eddies provide opportunities for retention. Our data indicate that the effect of eddies on larval retention is likely taxon-specific and temporally variable, as synchronization of reproductive output, larval distribution, and timing of eddy passage are prerequisite to entrainment and subsequent retention of locally spawned larvae.