Abstract

Understanding patterns of larval dispersal is key in determining whether no-take marine reserves are self-sustaining, what will be protected inside reserves and where the benefits of reserves will be observed. We followed a multidisciplinary approach that merged detailed descriptions of fishing zones and spawning time at 17 sites distributed in the Midriff Island region of the Gulf of California with a biophysical oceanographic model that simulated larval transport at Pelagic Larval Duration (PLD) 14, 21 and 28 days for the most common and targeted predatory reef fish, (leopard grouper Mycteroperca rosacea). We tested the hypothesis that source–sink larval metapopulation dynamics describing the direction and frequency of larval dispersal according to an oceanographic model can help to explain empirical genetic data. We described modeled metapopulation dynamics using graph theory and employed empirical sequence data from a subset of 11 sites at two mitochondrial genes to verify the model predictions based on patterns of genetic diversity within sites and genetic structure between sites. We employed a population graph describing a network of genetic relationships among sites and contrasted it against modeled networks. While our results failed to explain genetic diversity within sites, they confirmed that ocean models summarized via graph and adjacency distances over modeled networks can explain seemingly chaotic patterns of genetic structure between sites. Empirical and modeled networks showed significant similarities in the clustering coefficients of each site and adjacency matrices between sites. Most of the connectivity patterns observed towards downstream sites (Sonora coast) were strictly asymmetric, while those between upstream sites (Baja and the Midriffs) were symmetric. The best-supported gene flow model and analyses of modularity of the modeled networks confirmed a pulse of larvae from the Baja Peninsula, across the Midriff Island region and towards the Sonoran coastline that acts like a larval sink, in agreement with the cyclonic gyre (anti-clockwise) present at the peak of spawning (May–June). Our approach provided a mechanistic explanation of the location of fishing zones: most of the largest areas where fishing takes place seem to be sustained simultaneously by high levels of local retention, contribution of larvae from upstream sites and oceanographic patterns that concentrate larval density from all over the region. The general asymmetry in marine connectivity observed highlights that benefits from reserves are biased towards particular directions, that no-take areas need to be located upstream of targeted fishing zones, and that some fishing localities might not directly benefit from avoiding fishing within reserves located adjacent to their communities. We discuss the implications of marine connectivity for the current network of marine protected areas and no-take zones, and identify ways of improving it.

Highlights

  • Knowledge of patterns of larval dispersal is essential to implement fully-protected marine reserves, a tool frequently used to enhance the conservation of biodiversity and the recovery of fisheries (Gaines et al 2010)

  • Our study contribute to a growing body of literature (Alberto et al 2011; Crandall et al 2012; Feutry et al 2013; Foster et al 2012; Galindo et al 2010; Petitgas et al 2012; Selkoe et al 2010; Soria et al 2012) highlighting the inherent value of verifying outputs of biophysical oceanographic models with empirical genetic data to inform larval dispersal patterns and marine connectivity

  • Concordance of genetic and biophysical modeling data for M. rosacea elucidate the role of oceanographic processes in driving patterns of larval dispersal, while models helped to explain seemingly chaotic patterns of genetic diversity and structure

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Summary

Introduction

Knowledge of patterns of larval dispersal is essential to implement fully-protected marine reserves (no-take zones), a tool frequently used to enhance the conservation of biodiversity and the recovery of fisheries (Gaines et al 2010). Many commercially exploited species of invertebrates and fishes display meta populations that are connected via larval dispersal (Cowen 2000). This is why relatively few attempts have been done to establish multidisciplinary approaches to understand marine connectivity, and the great challenge is to find a key species that can be a relevant case study, and which can be use to gather this information relative and can be use as an umbrella species to design marine reserves

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