Dispersal of Grouper Larvae Drives Local Resource Sharing in a Coral Reef Fishery

A rapid increase in tropical species of grouper (Perciformes: Serranidae) in the temperate waters, the Goto Islands, Japan

Global warming has resulted in rapid poleward shifts in the geographical distributions of many tropical fish species. This study conducted daily market surveys from 2008 to 2013 to investigate catch trends of seven commercially important grouper species in the temperate Goto Islands, Japan. Our results revealed that the catch numbers of tropical grouper species increased rapidly by an average of 5.9-fold (12.3-fold at maximum) within six years, whereas the temperate and subtropical species did not exhibit substantial changes. Based on the findings of several previous studies, the rapid increase in the number of tropical groupers in temperate waters was most likely caused by the successful settlement of larvae transported from tropical waters. Large-scale ocean currents may facilitate larval transport from tropical waters because the Goto Islands face the Tsushima Warm Current, which branches from the Kuroshio Current. Meanwhile, the transition processes of size distribution in tropical groupers suggest a possible hypothesis that adults migrating from tropical waters first settle in temperate waters and then enhance their populations by reproduction. Further studies are required to determine how tropical grouper species settle and how their populations increase in temperate waters.

Protected fish spawning aggregations as self-replenishing reservoirs for regional recovery

Dispersal of eggs and larvae from spawning sites is critical to the population dynamics and conservation of marine fishes. For overfished species like critically endangered Nassau grouper (Epinephelus striatus), recovery depends on the fate of eggs spawned at the few remaining aggregation sites. Biophysical models can predict larval dispersal, yet these rely on assumed values of key parameters, such as diffusion and mortality rates, which have historically been difficult or impossible to estimate. We used in situ imaging to record three-dimensional positions of individual eggs and larvae in proximity to oceanographic drifters released into egg plumes from the largest known Nassau grouper spawning aggregation. We then estimated a diffusion-mortality model and applied it to previous years' drifter tracks to evaluate the possibility of retention versus export to nearby sites within 5 days of spawning. Results indicate that larvae were retained locally in 2011 and 2017, with 2011 recruitment being a substantial driver of population recovery on Little Cayman. Export to a nearby island with a depleted population occurred in 2016. After two decades of protection, the population appears to be self-replenishing but also capable of seeding recruitment in the region, supporting calls to incorporate spawning aggregation protections into fisheries management.

Genomic assessment of larval odyssey: self-recruitment and biased settlement in the Hawaiian surgeonfish Acanthurus triostegus sandvicensis

The gap between spawning and settlement location of marine fishes, where the larvae occupy an oceanic phase, is a great mystery in both natural history and conservation. Recent genomic approaches provide some resolution, especially in linking parent to offspring with assays of nucleotide polymorphisms. Here, the authors applied this method to the endemic Hawaiian convict tang (Acanthurus triostegus sandvicensis), a surgeonfish with a long pelagic larval stage of c. 54-77 days. They collected 606 adults and 607 juveniles from 23 locations around the island of O'ahu, Hawai'i. Based on 399 single nucleotide polymorphisms, the authors assigned 68 of these juveniles back to a parent (11.2% assignment rate). Each side of the island showed significant population differentiation, with higher levels in the west and north. The west and north sides of the island also had little evidence of recruitment, which may be due to westerly currents in the region or an artefact of uneven sampling. In contrast, the majority of juveniles (94%) sampled along the eastern shore originated on that side of the island, primarily within semi-enclosed Kāne'ohe Bay. Nearly half of the juveniles assigned to parents were found in the southern part of Kāne'ohe Bay, with local settlement likely facilitated by extended water residence time. Several instances of self-recruitment, when juveniles return to their natal location, were observed along the eastern and southern shores. Cumulatively, these findings indicate that most dispersal is between adjacent regions on the eastern and southern shores. Regional management efforts for Acanthurus triostegus and possibly other reef fishes will be effective only with collaboration among adjacent coastal communities, consistent with the traditional moku system of native Hawaiian resource management.

Isolation-by-distance and isolation-by-oceanography in Maroon Anemonefish (Amphiprion biaculeatus)

Obtaining dispersal estimates for a species is key to understanding local adaptation and population dynamics and to implementing conservation actions. Genetic isolation-by-distance (IBD) patterns can be used for estimating dispersal, and these patterns are especially useful for marine species in which few other methods are available. In this study, we genotyped coral reef fish (Amphiprion biaculeatus) at 16 microsatellite loci across eight sites across 210 km in the central Philippines to generate fine-scale estimates of dispersal. All sites except for one followed IBD patterns. Using IBD theory, we estimated a larval dispersal kernel spread of 8.9 km (95% confidence interval of 2.3-18.4 km). Genetic distance to the remaining site correlated strongly with the inverse probability of larval dispersal from an oceanographic model. Ocean currents were a better explanation for genetic distance at large spatial extents (sites greater than 150 km apart), while geographic distance remained the best explanation for spatial extents less than 150 km. Our study demonstrates the utility of combining IBD patterns with oceanographic simulations to understand connectivity in marine environments and to guide marine conservation strategies.

Linking small-scale fisheries co-management to U.N. Sustainable Development Goals

Small-scale fisheries account for 90% of global fishers and 40% of the global catch. Effectively managing small-scale fisheries is, therefore, crucial to progressing the United Nations Sustainable Development Goals (SDGs). Co-management and community-based fisheries management are widely considered the most appropriate forms of governance for many small-scale fisheries. We outlined relationships between small-scale fisheries co-management and attainment of the SDGs, including evidence for impacts and gaps in dominant logic. We identified 11 targets across five SDGs to which small-scale fisheries co-management (including community-based fisheries management) can contribute; the theory of change by which these contributions could be achieved; and the strength of evidence for progress toward SDG targets related to various co-management strategies. Our theory of change links the 11 SDG targets by qualifying that progress toward some targets is contingent on others being achieved first. We then reviewed 58 case studies of co-management impacts from the Pacific Islands--a region rich in local marine governance--to evaluate evidence of where, to what degree, and with how much certainty different co-management strategies conferred positive impacts to each SDG target. These strategies included access restrictions, permanent area closures, periodic closures, and gear and species restrictions. Although many studies provide evidence linking multiple co-management strategies to improvements in resource status (SDG 14.4), there was limited evidence of follow-on effects, such as improvements in catch (SDG 2.3, 2.4), livelihoods (SDG 1.2), consumption (SDG 2.1), and nutrition (SDG 2.2). Our findings suggest that leaps of logic and assumptions are prevalent in co-management planning and evaluation. Hence, when evaluating co-management impacts against the SDGs, consideration of ultimate goals is required, otherwise, there is a risk of shortfalls between aspirations and impact.

Minimum size limits and the reproductive value of numerous, young, mature female fish

Fisheries management relies on various catch and effort controls to preserve spawning stock biomass and maximize sustainable yields while limiting fishery impacts on marine ecosystems. These include species-specific minimum or maximum size limits to protect either small non-reproductive subadults, a portion of reproductively mature adults, or large highly fecund individuals. Protecting size classes of mature fish is expected to yield a viable source of larvae for replenishing populations and reduce the risk of recruitment overfishing, yet size-specific recruitment contributions have rarely been assessed empirically. Here, we apply genetic parentage analysis to measure the reproductive success of a size-structured population of a commercially important species of coral grouper (Plectropomus maculatus-Serranidae) in no-take marine reserves (NTMRs) in the Great Barrier Reef Marine Park, Australia. Although the per capita reproductive success of individual fish increases rapidly with body length, the numerous young mature female fish, below the minimum size limit (MSL) (38 cm total length), were responsible for generating disproportionately large contributions (36%) towards larval replenishment of both fished and reserve reefs. Our findings indicate that MSLs are an effective harvest control measure to safeguard a portion of the spawning stock biomass for coral grouper and supplement recruitment subsidies assured from NTMRs.

Genetic relatedness in social groups of the emerald coral goby Paragobiodon xanthosoma creates potential for weak kin selection

Animals forming social groups that include breeders and nonbreeders present evolutionary paradoxes; why do breeders tolerate nonbreeders? And why do nonbreeders tolerate their situation? Both paradoxes are often explained with kin selection. Kin selection is, however, assumed to play little or no role in social group formation of marine organisms with dispersive larval phases. Yet, in some marine organisms, recent evidence suggests small-scale patterns of relatedness, meaning that this assumption must always be tested. Here, we investigated the genetic relatedness of social groups of the emerald coral goby, Paragobiodon xanthosoma. We genotyped 73 individuals from 16 groups in Kimbe Bay, Papua New Guinea, at 20 microsatellite loci and estimated pairwise relatedness among all individuals. We found that estimated pairwise relatedness among individuals within groups was significantly higher than the pairwise relatedness among individuals from the same reef, and pairwise relatedness among individuals from the same reef was significantly higher than the pairwise relatedness among individuals from different reefs. This spatial signature suggests that there may be very limited dispersal in this species. The slightly positive relatedness within groups creates the potential for weak kin selection, which may help to resolve the paradox of why breeders tolerate subordinates in P. xanthosoma. The other paradox, why nonbreeders tolerate their situation, is better explained by alternative hypotheses such as territory inheritance, and ecological and social constraints. We show that even in marine animals with dispersive larval phases, kin selection needs to be considered to explain the evolution of complex social groups.

Travel with your kin ship! Insights from genetic sibship among settlers of a coral damselfish

Coral reef fish larvae are tiny, exceedingly numerous, and hard to track. They are also highly capable, equipped with swimming and sensory abilities that may influence their dispersal trajectories. Despite the importance of larval input to the dynamics of a population, we remain reliant on indirect insights to the processes influencing larval behavior and transport. Here, we used genetic data (300 independent single nucleotide polymorphisms) derived from a light trap sample of a single recruitment event of Dascyllus abudafur in the Red Sea (N = 168 settlers). We analyzed the genetic composition of the larvae and assessed whether kinship among these was significantly different from random as evidence for cohesive dispersal during the larval phase. We used Monte Carlo simulations of similar-sized recruitment cohorts to compare the expected kinship composition relative to our empirical data. The high number of siblings within the empirical cohort strongly suggests cohesive dispersal among larvae. This work highlights the utility of kinship analysis as a means of inferring dynamics during the pelagic larval phase.

Recovery when you are on your own: Slow population responses in an isolated marine reserve

Geographic isolation is an important yet underappreciated factor affecting marine reserve performance. Isolation, in combination with other factors, may preclude recruit subsidies, thus slowing recovery when base populations are small and causing a mismatch between performance and stakeholder expectations. Mona Island is a small, oceanic island located within a partial biogeographic barrier—44 km from the Puerto Rico shelf. We investigated if Mona Island’s no-take zone (MNTZ), the largest in the U.S. Caribbean, was successful in increasing mean size and density of a suite of snapper and grouper species 14 years after designation. The La Parguera Natural Reserve (LPNR) was chosen for evaluation of temporal trends at a fished location. Despite indications of fishing within the no-take area, a reserve effect at Mona Island was evidenced from increasing mean sizes and densities of some taxa and mean total density 36% greater relative to 2005. However, the largest predatory species remained rare at Mona, preventing meaningful analysis of population trends. In the LPNR, most commercial species (e.g., Lutjanus synagris, Lutjanus apodus, Lutjanus mahogoni) did not change significantly in biomass or abundance, but some (Ocyurus chrysurus, Lachnolaimus maximus), increased in abundance owing to strong recent recruitment. This study documents slow recovery in the MNTZ that is limited to smaller sized species, highlighting both the need for better compliance and the substantial recovery time required by commercially valuable, coral reef fishes in isolated marine reserves.

Successful validation of a larval dispersal model using genetic parentage data

Larval dispersal is a critically important yet enigmatic process in marine ecology, evolution, and conservation. Determining the distance and direction that tiny larvae travel in the open ocean continues to be a challenge. Our current understanding of larval dispersal patterns at management-relevant scales is principally and separately informed by genetic parentage data and biological-oceanographic (biophysical) models. Parentage datasets provide clear evidence of individual larval dispersal events, but their findings are spatially and temporally limited. Biophysical models offer a more complete picture of dispersal patterns at regional scales but are of uncertain accuracy. Here, we develop statistical techniques that integrate these two important sources of information on larval dispersal. We then apply these methods to an extensive genetic parentage dataset to successfully validate a high-resolution biophysical model for the economically important reef fish species Plectropomus maculatus in the southern Great Barrier Reef. Our results demonstrate that biophysical models can provide accurate descriptions of larval dispersal at spatial and temporal scales that are relevant to management. They also show that genetic parentage datasets provide enough statistical power to exclude poor biophysical models. Biophysical models that included species-specific larval behaviour provided markedly better fits to the parentage data than assuming passive behaviour, but incorrect behavioural assumptions led to worse predictions than ignoring behaviour altogether. Our approach capitalises on the complementary strengths of genetic parentage datasets and high-resolution biophysical models to produce an accurate picture of larval dispersal patterns at regional scales. The results provide essential empirical support for the use of accurately parameterised biophysical larval dispersal models in marine spatial planning and management.

Our understanding of marine fish larva dispersal is currently limited by sparse data and unvalidated models; combining DNA parentage matches with an oceanographic model of fish larvae on Australia’s Great Barrier Reef allows the authors to ground-truth a vital tool for sustainably managing coral reef fisheries.

Contrasting population genetic structure in three aggregating groupers (Percoidei: Epinephelidae) in the Indo-West Pacific: the importance of reproductive mode

Background

Understanding the factors shaping population genetic structure is important for evolutionary considerations as well as for management and conservation. While studies have revealed the importance of palaeogeographic changes in shaping phylogeographic patterns in multiple marine fauna, the role of reproductive behaviour is rarely considered in reef fishes. We investigated the population genetics of three commercially important aggregating grouper species in the Indo-West Pacific, namely the camouflage grouper Epinephelus polyphekadion, the squaretail coral grouper Plectropomus areolatus, and the common coral trout P. leopardus, with similar life histories but distinct spatio-temporal characteristics in their patterns of forming spawning aggregations.

Results

By examining their mitochondrial control region and 9–11 microsatellite markers, we found an overarching influence of palaeogeographic events in the population structure of all species, with genetic breaks largely coinciding with major biogeographic barriers. The divergence time of major lineages in these species coincide with the Pleistocene glaciations. Higher connectivity is evident in E. polyphekadion and P. areolatus that assemble in larger numbers at fewer spawning aggregations and in distinctive offshore locations than in P. leopardus which has multiple small, shelf platform aggregations.

Conclusions

While palaeogeographic events played an important role in shaping the population structure of the target species, the disparity in population connectivity detected may be partly attributable to differences in their reproductive behaviour, highlighting the need for more investigations on this characteristic and the need to consider reproductive mode in studies of connectivity and population genetics.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1284-0) contains supplementary material, which is available to authorized users.

Geographic isolation and larval dispersal shape seascape genetic patterns differently according to spatial scale

Genetic variation, as a basis of evolutionary change, allows species to adapt and persist in different climates and environments. Yet, a comprehensive assessment of the drivers of genetic variation at different spatial scales is still missing in marine ecosystems. Here, we investigated the influence of environment, geographic isolation, and larval dispersal on the variation in allele frequencies, using an extensive spatial sampling (47 locations) of the striped red mullet (Mullus surmuletus) in the Mediterranean Sea. Univariate multiple regressions were used to test the influence of environment (salinity and temperature), geographic isolation, and larval dispersal on single nucleotide polymorphism (SNP) allele frequencies. We used Moran's eigenvector maps (db-MEMs) and asymmetric eigenvector maps (AEMs) to decompose geographic and dispersal distances in predictors representing different spatial scales. We found that salinity and temperature had only a weak effect on the variation in allele frequencies. Our results revealed the predominance of geographic isolation to explain variation in allele frequencies at large spatial scale (>1,000 km), while larval dispersal was the major predictor at smaller spatial scale (<1,000 km). Our findings stress the importance of including spatial scales to understand the drivers of spatial genetic variation. We suggest that larval dispersal allows to maintain gene flows at small to intermediate scale, while at broad scale, genetic variation may be mostly shaped by adult mobility, demographic history, or multigenerational stepping-stone dispersal. These findings bring out important spatial scale considerations to account for in the design of a protected area network that would efficiently enhance protection and persistence capacity of marine species.

Effect of marine protected areas on distinct fish life-history stages

The role of Marine Protected Areas on distinct life stages of Mediterranean reef fish species (classified on the basis of their economic value and mobility categories) was assessed in a network of marine reserves in SE Spain. Only abundance and biomass of adult of both commercial and demersal species were positively affected by protection. Gradients across reserve boundaries (as a clue to the occurrence of spillover) were observed for fish abundance but not for biomass, indicating a protected fish assemblage with a predominance of small-sized individuals. Also, post-larvae of commercial species were negatively related to protected zones. Active selection of settlement preferred habitats, larval accumulation favoured by the geomorphological configuration of the coast or mixed effects has been proposed as possible explanations. Juveniles showed high spatial variability resulting in a lack of response to fishing protection measures. We highlight the need of including early life stages and overall suitable habitats for them when designing MPA networks due to the crucial importance of these stages to successful fulfillment of MPA objectives.

Temperate marine protected area provides recruitment subsidies to local fisheries

The utility of marine protected areas (MPAs) as a means of protecting exploited species and conserving biodiversity within MPA boundaries is supported by strong empirical evidence. However, the potential contribution of MPAs to fished populations beyond their boundaries is still highly controversial; empirical measures are scarce and modelling studies have produced a range of predictions, including both positive and negative effects. Using a combination of genetic parentage and relatedness analysis, we measured larval subsidies to local fisheries replenishment for Australasian snapper (Chrysophrys auratus: Sparidae) from a small (5.2 km²), well-established, temperate, coastal MPA in northern New Zealand. Adult snapper within the MPA contributed an estimated 10.6% (95% CI: 5.5-18.1%) of newly settled juveniles to surrounding areas (approx. 400 km²), with no decreasing trend in contributions up to 40 km away. Biophysical modelling of larval dispersal matched experimental data, showing larvae produced inside the MPA dispersed over a comparable distance. These results demonstrate that temperate MPAs have the potential to provide recruitment subsidies at magnitudes and spatial scales relevant to fisheries management. The validated biophysical model provides a cost-efficient opportunity to generalize these findings to other locations and climate conditions, and potentially informs the design of MPA networks for enhancing fisheries management.

Widespread hybridization and bidirectional introgression in sympatric species of coral reef fish

Coral reefs are highly diverse ecosystems, where numerous closely related species often coexist. How new species arise and are maintained in these high geneflow environments have been long-standing conundrums. Hybridization and patterns of introgression between sympatric species provide a unique insight into the mechanisms of speciation and the maintenance of species boundaries. In this study, we investigate the extent of hybridization between two closely related species of coral reef fish: the common coral trout (Plectropomus leopardus) and the bar-cheek coral trout (Plectropomus maculatus). Using a complementary set of 25 microsatellite loci, we distinguish pure genotype classes from first- and later-generation hybrids, identifying 124 interspecific hybrids from a collection of 2,991 coral trout sampled in inshore and mid-shelf reefs of the southern Great Barrier Reef. Hybrids were ubiquitous among reefs, fertile and spanned multiple generations suggesting both ecological and evolutionary processes are acting to maintain species barriers. We elaborate on these finding to investigate the extent of genomic introgression and admixture from 2,271 SNP loci recovered from a ddRAD library of pure and hybrid individuals. An analysis of genomic clines on recovered loci indicates that 261 SNP loci deviate from a model of neutral introgression, of which 132 indicate a pattern of introgression consistent with selection favouring both hybrid and parental genotypes. Our findings indicate genome-wide, bidirectional introgression between two sympatric species of coral reef fishes and provide further support to a growing body of evidence for the role of hybridization in the evolution of coral reef fishes.

Exploring the larval fish community of the central Red Sea with an integrated morphological and molecular approach

An important aspect of population dynamics for coral reef fishes is the input of new individuals from the pelagic larval pool. However, the high biodiversity and the difficulty of identifying larvae of closely related species represent obstacles to more fully understanding these populations. In this study, we combined morphology and genetic barcoding (Cytochrome Oxidase I gene) to characterize the seasonal patterns of the larval fish community at two sites in close proximity to coral reefs in the central-north Red Sea: one shallower inshore location (50 m depth) and a nearby site located in deeper and more offshore waters (~ 500 m depth). Fish larvae were collected using oblique tows of a 60 cm-bongo net (500 μm mesh size) every month for one year (2013). During the warmer period of the year (June-November), the larval fish stock was comparable between sampling sites. However, during the colder months, abundances were higher in the inshore than in the offshore waters. Taxonomic composition and temporal variation of community structure differed notably between sites, potentially reflecting habitat differences, reproductive patterns of adults, and/or advective processes in the area. Eleven out of a total of 62 recorded families comprised 69–94% of the fish larval community, depending on sampling site and month. Richness of taxa was notably higher in the inshore station compared to the offshore, particularly during the colder period of the year and especially for the gobiids and apogonids. Two mesopelagic taxa (Vinciguerria sp. and Benthosema spp.) comprised an important component of the larval community at the deeper site with only a small and sporadic occurrence in the shallower inshore waters. Our data provide an important baseline reference for the larval fish communities of the central Red Sea, representing the first such study from Saudi Arabian waters.

Consistency in the supply of larval fishes among coral reefs in French Polynesia

For marine fishes with a bipartite life cycle, pelagic larval dispersal can shape the distribution, connectivity, composition and resilience of adult populations. Numerous studies of larval dispersal, and associated settlement and recruitment processes, have examined the relationship between population connectivity and oceanographic features. However, relatively little is known about spatial and temporal variation in the abundance of larvae settling among different reefs and the extent to which the species assemblage of larvae settling at one location is reflective of the assemblage in neighbouring areas. Here, using crest nets, which provide a non-selective measure of the total abundance and assemblage of larvae settling to a reef (i.e. larval supply), we collected larval coral reef fishes at five locations surrounding two spatially disparate French Polynesian islands: Moorea and Nengo-Nengo. Overall, larval settlement patterns were correlated with the lunar cycle, with larval abundance peaking during the new moon. Although there were some spatial differences in larval supply among the five monitored sites, settlement patterns were largely consistent, even at the species level, irrespective of factors such as coastline orientation or distance between sites. This study provides further insights into the mechanisms driving patterns of dispersal and settlement of larval fishes over large spatial scales.

Spatial variation in coral reef fish and benthic communities in the central Saudi Arabian Red Sea

Local-scale ecological information is critical as a sound basis for spatial management and conservation and as support for ongoing research in relatively unstudied areas. We conducted visual surveys of fish and benthic communities on nine reefs (3–24 km from shore) in the Thuwal area of the central Saudi Arabian Red Sea. Fish biomass increased with increasing distance from shore, but was generally low compared to reefs experiencing minimal human influence around the world. All reefs had a herbivore-dominated trophic structure and few top predators, such as sharks, jacks, or large groupers. Coral cover was considerably lower on inshore reefs, likely due to a 2010 bleaching event. Community analyses showed inshore reefs to be characterized by turf algae, slower-growing corals, lower herbivore diversity, and highly abundant turf-farming damselfishes. Offshore reefs had more planktivorous fishes, a more diverse herbivore assemblage, and faster-growing corals. All reefs appear to be impacted by overfishing, and inshore reefs seem more vulnerable to thermal bleaching. The study provides a description of the spatial variation in biomass and community structure in the central Saudi Arabian Red Sea and provides a basis for spatial prioritization and subsequent marine protected area design in Thuwal.

Impact of life history traits on gene flow: A multispecies systematic review across oceanographic barriers in the Mediterranean Sea

BACKGROUND

Marine species can demonstrate strong genetic differentiation and population structure despite the hypothesis of open seas and high connectivity. Some suggested drivers causing the genetic breaks are oceanographic barriers and the species' biology. We assessed the relevance of seven major oceanographic fronts on species connectivity while considering their dispersal capacity and life strategy.

METHODS

We systematically reviewed the scientific articles reporting population genetic differentiation along the Mediterranean Sea and across the Atlantic-Mediterranean transition. We retained those considering at least one sampling locality at each side of an oceanographic front, and at least two localities with no-front between them to correctly assess the effect of the front. To estimate the impact of life history characteristics affecting connectivity we considered the planktonic larval duration (PLD) and adult life strategy.

RESULTS

Oceanographic barriers in the Mediterranean Sea seem to reduce gene flow globally; however, this effect is not homogeneous considering the life history traits of the species. The effect of the oceanographic fronts reduces gene flow in highly mobile species with PLD larger than 2-4 weeks. Benthic sessile species and/or with short PLD (< 2 weeks) have more significant genetic breaks between localities than species with higher motility; however, genetic differentiation occurs independently of the presence of a front.

CONCLUSION

Genetic connectivity is important for populations to recover from anthropogenic or natural impacts. We show that species with low mobility, mostly habitat-formers, have high genetic differentiation but low gene flow reduction mediated by the front, therefore, considering the importance of these species, we emphasize the vulnerability of the Mediterranean ecosystems and the necessity of protection strategies based on the whole ecosystem.

Marine Reserve Targets to Sustain and Rebuild Unregulated Fisheries

Overfishing threatens the sustainability of coastal marine biodiversity, especially in tropical developing countries. To counter this problem, about 200 governments worldwide have committed to protecting 10%–20% of national coastal marine areas. However, associated impacts on fisheries productivity are unclear and could weaken the food security of hundreds of millions of people who depend on diverse and largely unregulated fishing activities. Here, we present a systematic theoretic analysis of the ability of reserves to rebuild fisheries under such complex conditions, and we identify maximum reserve coverages for biodiversity conservation that do not impair long-term fisheries productivity. Our analysis assumes that fishers have no viable alternative to fishing, such that total fishing effort remains constant (at best). We find that realistic reserve networks, which protect 10%–30% of fished habitats in 1–20 km wide reserves, should benefit the long-term productivity of almost any complex fishery. We discover a “rule of thumb” to safeguard against the long-term catch depletion of particular species: individual reserves should export 30% or more of locally produced larvae to adjacent fishing grounds. Specifically on coral reefs, where fishers tend to overexploit species whose dispersal distances as larvae exceed the home ranges of adults, decisions on the size of reserves needed to meet the 30% larval export rule are unlikely to compromise the protection of resident adults. Even achieving the modest Aichi Target 11 of 10% “effective protection” can then help rebuild depleted catch. However, strictly protecting 20%–30% of fished habitats is unlikely to diminish catch even if overfishing is not yet a problem while providing greater potential for biodiversity conservation and fishery rebuilding if overfishing is substantial. These findings are important because they suggest that doubling or tripling the only globally enforced marine reserve target will benefit biodiversity conservation and higher fisheries productivity where both are most urgently needed.

Marine reserves are an important tool to conserve biodiversity but increasingly are relied upon also to benefit fisheries, specifically in diverse, unassessed, and otherwise unregulated systems. Whether the globally adopted Aichi Target 11 (10% “effective” protection of national coastal marine areas) can help sustain or rebuild fisheries under such complex conditions is unclear. Based on a systematic theoretic analysis that incorporates previously unavailable data on fish movements, we show that 20%–30% strict protection of fished habitats is unlikely to harm complex and otherwise unregulated fisheries even if most fish populations are still healthy while providing greater potential to rebuild depleted fisheries and protect biodiversity than the 10% Aichi target. This finding is important because it suggests that doubling or tripling the only internationally enforced marine reserve target will support biodiversity conservation and higher fisheries productivity where both are most urgently needed.

Marine Dispersal Scales Are Congruent over Evolutionary and Ecological Time

The degree to which offspring remain near their parents or disperse widely is critical for understanding population dynamics, evolution, and biogeography, and for designing conservation actions. In the ocean, most estimates suggesting short-distance dispersal are based on direct ecological observations of dispersing individuals, while indirect evolutionary estimates often suggest substantially greater homogeneity among populations. Reconciling these two approaches and their seemingly competing perspectives on dispersal has been a major challenge. Here we show for the first time that evolutionary and ecological measures of larval dispersal can closely agree by using both to estimate the distribution of dispersal distances. In orange clownfish (Amphiprion percula) populations in Kimbe Bay, Papua New Guinea, we found that evolutionary dispersal kernels were 17 km (95% confidence interval: 12-24 km) wide, while an exhaustive set of direct larval dispersal observations suggested kernel widths of 27 km (19-36 km) or 19 km (15-27 km) across two years. The similarity between these two approaches suggests that ecological and evolutionary dispersal kernels can be equivalent, and that the apparent disagreement between direct and indirect measurements can be overcome. Our results suggest that carefully applied evolutionary methods, which are often less expensive, can be broadly relevant for understanding ecological dispersal across the tree of life.

Returns from matching management resolution to ecological variation in a coral reef fishery

When managing heterogeneous socioecological systems, decision-makers must choose a spatial resolution at which to define management policies. Complex spatial policies allow managers to better reflect underlying ecological and economic heterogeneity, but incur higher compliance and enforcement costs. To choose the most appropriate management resolution, we need to characterize the relationship between management resolution and performance. We parameterize a model of the commercial coral trout fishery in the Great Barrier Reef, Australia, which is currently managed by a single, spatially homogeneous management policy. We use this model to estimate how the spatial resolution of management policies affect the amount of revenue generated, and assess whether a more spatially complex policy can be justified. Our results suggest that economic variation is likely to be a more important source of heterogeneity than ecological differences, and that the majority of this variation can be captured by a relatively simple spatial management policy. Moreover, while an increase in policy resolution can improve performance, the location of policy changes also needs to align with ecological and socioeconomic variation. Interestingly, the highly complex process of larval dispersal, which plays a critical ecological role in coral reef ecosystem dynamics, may not demand equally complex management policies.

Patterns of Fish Connectivity between a Marine Protected Area and Surrounding Fished Areas

Patterns of connectivity and self-recruitment are recognized as key factors shaping the dynamics of marine populations. Connectivity is also essential for maintaining and restoring natural ecological processes with genetic diversity contributing to the adaptation and persistence of any species in the face of global disturbances. Estimates of connectivity are crucial to inform the design of both marine protected areas (MPAs) and MPA networks. Among several approaches, genetic structure is frequently used as a proxy for patterns of connectivity. Using 8 microsatellite loci, we investigated genetic structure of the two-banded sea bream Diplodus vulgaris, a coastal fish that is both commercially and ecologically important. Adults were sampled in 7 locations (stretches of coastline approximately 8 km long) and juveniles in 14 sites (~100 to 200 m of coastline) along 200 km of the Apulian Adriatic coast (SW Adriatic Sea), within and outside an MPA (Torre Guaceto MPA, Italy). Our study found similar genetic diversity indices for both the MPA and the surrounding fished areas. An overall lack of genetic structure among samples suggests high gene flow (i.e. connectivity) across a scale of at least 200 km. However, some local genetic divergences found in two locations demonstrate some heterogeneity in processes renewing the population along the Apulian Adriatic coast. Furthermore, two sites appeared genetically divergent, reinforcing our observations within the genetic makeup of adults and confirming heterogeneity in early stage genetics that can come from either different supply populations or from chaotic genetic patchiness occurring under temporal variation in recruitment and in the reproductive success. While the specific role of the MPA is not entirely known in this case, these results confirm the presence of regional processes and the key role of connectivity in maintaining the local population supply.

First genealogy for a wild marine fish population reveals multigenerational philopatry

Natal philopatry, the return of individuals to their natal area for reproduction, has advantages and disadvantages for animal populations. Natal philopatry may generate local genetic adaptation, but it may also increase the probability of inbreeding that can compromise persistence. Although natal philopatry is well documented in anadromous fishes, marine fish may also return to their birth site to spawn. How philopatry shapes wild fish populations is, however, unclear because it requires constructing multigenerational pedigrees that are currently lacking for marine fishes. Here we present the first multigenerational pedigree for a marine fish population by repeatedly genotyping all individuals in a population of the orange clownfish (Amphiprion percula) at Kimbe Island (Papua New Guinea) during a 10-y period. Based on 2927 individuals, our pedigree analysis revealed that longitudinal philopatry was recurrent over five generations. Progeny tended to settle close to their parents, with related individuals often sharing the same colony. However, successful inbreeding was rare, and genetic diversity remained high, suggesting occasional inbreeding does not impair local population persistence. Local reproductive success was dependent on the habitat larvae settled into, rather than the habitat they came from. Our study suggests that longitudinal philopatry can influence both population replenishment and local adaptation of marine fishes. Resolving multigenerational pedigrees during a relatively short period, as we present here, provides a framework for assessing the ability of marine populations to persist and adapt to accelerating climate change.

Planning Marine Reserve Networks for Both Feature Representation and Demographic Persistence Using Connectivity Patterns

Marine reserve networks must ensure the representation of important conservation features, and also guarantee the persistence of key populations. For many species, designing reserve networks is complicated by the absence or limited availability of spatial and life-history data. This is particularly true for data on larval dispersal, which has only recently become available. However, systematic conservation planning methods currently incorporate demographic processes through unsatisfactory surrogates. There are therefore two key challenges to designing marine reserve networks that achieve feature representation and demographic persistence constraints. First, constructing a method that efficiently incorporates persistence as well as complementary feature representation. Second, incorporating persistence using a mechanistic description of population viability, rather than a proxy such as size or distance. Here we construct a novel systematic conservation planning method that addresses both challenges, and parameterise it to design a hypothetical marine reserve network for fringing coral reefs in the Keppel Islands, Great Barrier Reef, Australia. For this application, we describe how demographic persistence goals can be constructed for an important reef fish species in the region, the bar-cheeked trout (Plectropomus maculatus). We compare reserve networks that are optimally designed for either feature representation or demographic persistence, with a reserve network that achieves both goals simultaneously. As well as being practically applicable, our analyses also provide general insights into marine reserve planning for both representation and demographic persistence. First, persistence constraints for dispersive organisms are likely to be much harder to achieve than representation targets, due to their greater complexity. Second, persistence and representation constraints pull the reserve network design process in divergent directions, making it difficult to efficiently achieve both constraints. Although our method can be readily applied to the data-rich Keppel Islands case study, we finally consider the factors that limit the method's utility in information-poor contexts common in marine conservation.

Fishery consequences of marine reserves: short-term pain for longer-term gain

Marine reserves are often established in areas that support fisheries. Larval export from reserves is argued to help compensate for the loss of fishable habitat; however, previous modeling studies have focused on long-term equilibrium outcomes. We examined the transient consequences of reserve establishment for fished metapopulations, considering both a well-mixed larval pool and a spatially explicit model based on a coral trout (Plectropomus spp.) metapopulation. When fishing pressure was reallocated relative to the area protected, yields decreased initially, then recovered, and ultimately exceeded pre-reserve levels. However, recovery time was on the order of several years to decades. If fishing pressure intensified to maintain pre-reserve yields, reserves were sometimes unable to support the increased mortality and the metapopulation collapsed. This was more likely when reserves were small, or located peripherally within the metapopulation. Overall, reserves can achieve positive conservation and fishery benefits, but fisheries management complementary to reserve implementation is essential.

Restricted grouper reproductive migrations support community-based management

Conservation commonly requires trade-offs between social and ecological goals. For tropical small-scale fisheries, spatial scales of socially appropriate management are generally small-the median no-take locally managed marine area (LMMA) area throughout the Pacific is less than 1 km(2). This is of particular concern for large coral reef fishes, such as many species of grouper, which migrate to aggregations to spawn. Current data suggest that the catchment areas (i.e. total area from which individuals are drawn) of such aggregations are at spatial scales that preclude effective community-based management with no-take LMMAs. We used acoustic telemetry and tag-returns to examine reproductive migrations and catchment areas of the grouper Epinephelus fuscoguttatus at a spawning aggregation in Papua New Guinea. Protection of the resultant catchment area of approximately 16 km(2) using a no-take LMMA is socially untenable here and throughout much of the Pacific region. However, we found that spawning migrations were skewed towards shorter distances. Consequently, expanding the current 0.2 km(2) no-take LMMA to 1-2 km(2) would protect approximately 30-50% of the spawning population throughout the non-spawning season. Contrasting with current knowledge, our results demonstrate that species with moderate reproductive migrations can be managed at scales congruous with spatially restricted management tools.

Patterns, causes, and consequences of marine larval dispersal

Quantifying the probability of larval exchange among marine populations is key to predicting local population dynamics and optimizing networks of marine protected areas. The pattern of connectivity among populations can be described by the measurement of a dispersal kernel. However, a statistically robust, empirical dispersal kernel has been lacking for any marine species. Here, we use genetic parentage analysis to quantify a dispersal kernel for the reef fish Elacatinus lori, demonstrating that dispersal declines exponentially with distance. The spatial scale of dispersal is an order of magnitude less than previous estimates-the median dispersal distance is just 1.7 km and no dispersal events exceed 16.4 km despite intensive sampling out to 30 km from source. Overlaid on this strong pattern is subtle spatial variation, but neither pelagic larval duration nor direction is associated with the probability of successful dispersal. Given the strong relationship between distance and dispersal, we show that distance-driven logistic models have strong power to predict dispersal probabilities. Moreover, connectivity matrices generated from these models are congruent with empirical estimates of spatial genetic structure, suggesting that the pattern of dispersal we uncovered reflects long-term patterns of gene flow. These results challenge assumptions regarding the spatial scale and presumed predictors of marine population connectivity. We conclude that if marine reserve networks aim to connect whole communities of fishes and conserve biodiversity broadly, then reserves that are close in space (<10 km) will accommodate those members of the community that are short-distance dispersers.

Development of polymorphic microsatellite loci for conservation genetic studies of the coral reef fish Centropyge bicolor

A total of 23 novel polymorphic microsatellite marker loci were developed for the angelfish Centropyge bicolor through 454 sequencing, and further tested on two spatially separated populations (90 individuals each) from Kimbe Bay in Papua New Guinea. The mean ± s.e. number of alleles per locus was 14·65 ± 1·05, and mean ± s.e. observed (HO ) and expected (HE ) heterozygosity frequencies were 0·676 ± 0·021 and 0·749 ± 0·018, respectively. The markers reported here constitute the first specific set for this genus and will be useful for future conservation genetic studies in the Indo-Pacific region.

Using neutral, selected, and hitchhiker loci to assess connectivity of marine populations in the genomic era

Estimating the rate of exchange of individuals among populations is a central concern to evolutionary ecology and its applications to conservation and management. For instance, the efficiency of protected areas in sustaining locally endangered populations and ecosystems depends on reserve network connectivity. The population genetics theory offers a powerful framework for estimating dispersal distances and migration rates from molecular data. In the marine realm, however, decades of molecular studies have met limited success in inferring genetic connectivity, due to the frequent lack of spatial genetic structure in species exhibiting high fecundity and dispersal capabilities. This is especially true within biogeographic regions bounded by well-known hotspots of genetic differentiation. Here, we provide an overview of the current methods for estimating genetic connectivity using molecular markers and propose several directions for improving existing approaches using large population genomic datasets. We highlight several issues that limit the effectiveness of methods based on neutral markers when there is virtually no genetic differentiation among samples. We then focus on alternative methods based on markers influenced by selection. Although some of these methodologies are still underexplored, our aim was to stimulate new research to test how broadly they are applicable to nonmodel marine species. We argue that the increased ability to apply the concepts of cline analyses will improve dispersal inferences across physical and ecological barriers that reduce connectivity locally. We finally present how neutral markers hitchhiking with selected loci can also provide information about connectivity patterns within apparently well-mixed biogeographic regions. We contend that one of the most promising applications of population genomics is the use of outlier loci to delineate relevant conservation units and related eco-geographic features across which connectivity can be measured.

Derelict fishing line provides a useful proxy for estimating levels of non-compliance with no-take marine reserves

No-take marine reserves (NTMRs) are increasingly being established to conserve or restore biodiversity and to enhance the sustainability of fisheries. Although effectively designed and protected NTMR networks can yield conservation and fishery benefits, reserve effects often fail to manifest in systems where there are high levels of non-compliance by fishers (poaching). Obtaining reliable estimates of NTMR non-compliance can be expensive and logistically challenging, particularly in areas with limited or non-existent resources for conducting surveillance and enforcement. Here we assess the utility of density estimates and re-accumulation rates of derelict (lost and abandoned) fishing line as a proxy for fishing effort and NTMR non-compliance on fringing coral reefs in three island groups of the Great Barrier Reef Marine Park (GBRMP), Australia. Densities of derelict fishing line were consistently lower on reefs within old (>20 year) NTMRs than on non-NTMR reefs (significantly in the Palm and Whitsunday Islands), whereas line densities did not differ significantly between reefs in new NTMRs (5 years of protection) and non-NTMR reefs. A manipulative experiment in which derelict fishing lines were removed from a subset of the monitoring sites demonstrated that lines re-accumulated on NTMR reefs at approximately one third (32.4%) of the rate observed on non-NTMR reefs over a thirty-two month period. Although these inshore NTMRs have long been considered some of the best protected within the GBRMP, evidence presented here suggests that the level of non-compliance with NTMR regulations is higher than previously assumed.