Population connectivity among Dry Tortugas, Florida, and Caribbean populations of mutton snapper (Lutjanus analis), inferred from multiple microsatellite loci

Determining patterns of population connectivity is critical to the evaluation of marine reserves as recruitment sources for harvested populations. Mutton snapper (Lutjanus analis) is a good test case because the last known major spawning aggregation in U.S. waters was granted no-take status in the Tortugas South Ecological Reserve (TSER) in 2001. To evaluate the TSER population as a recruitment source, we genotyped mutton snapper from the Dry Tortugas, southeast Florida, and from three locations across the Caribbean at eight microsatellite loci. Both Fstatistics and individual-based Bayesian analyses indicated that genetic substructure was absent across the five populations. Genetic homogeneity of mutton snapper populations is consistent with its pelagic larval duration of 27 to 37 days and adult behavior of annual migrations to large spawning aggregations. Statistical power of future genetic assessments of mutton snapper population connectivity may benefit from more comprehensive geographic sampling, and perhaps from the development of less polymorphic DNA microsatellite loci. Research where alternative methods are used, such as the transgenerational marking of embryonic otoliths with barium stable isotopes, is also needed on this and other species with diverse life history characteristics to further evaluate the TSER as a recruitment source and to define corridors of population connectivity across the Caribbean and Florida

A genetic assessment of population connectivity in mutton snapper, Lutjanus analis

Elucidating patterns of marine population connectivity is a central concern among biologists. Genetic markers are commonly utilized to quantify patterns of connectivity since they can reveal information about the exchange of genes, and thus migration events. The development of microsatellites as polymorphic, high resolution markers has significantly contributed to our understanding of population genetic structure in marine organisms. In this study, microsatellite loci were isolated from an enriched genomic library for the mutton snapper, Lutjanus analis, a commercially and recreationally valuable fish. This species is of particular interest to both conservationists and fishery managers, as the last known mutton snapper spawning aggregation in United States’ waters was recently targeted for the establishment of the Dry Tortugas Ecological Reserve (DTER). In order to evaluate the potential utility of the reserve as a source population for fisheries of the southeastern United States, mutton snapper from five locations around the Caribbean were genotyped at eight loci to estimate interpopulation gene flow. Analyses ranging from population-based F-statistics to individual-based assignment indicated that population genetic substructure was largely absent from the five sample locations. The only evidence for structure identified the population from the west coast of Puerto Rico as most distinct, suggesting that future work on populations in the eastern Caribbean is warranted. The genetic similarity of mutton snapper populations implies free gene flow between populations; however, because the genetic composition of each sample was so similar, it is impossible to discern between the relative contributions of potential source populations. Thus we cannot rule out the possibility that the DTER serves as a significant source of recruits to the southeastern United States. Yet based on the results of this study we cannot confirm that is doe Further research will be required to properly evaluate the utility of the DTER and to clarify corridors of connectivity across both the eastern and western portions of the Caribbean

Population Connectivity in a Dynamic Coastal System: Effects of Mesoscale Eddies on Distribution, Growth, Survival, and Transport of Larval Reef Fishes

Population connectivity (i.e., the exchange of individuals among geographically distinct subpopulations) is an issue of particular relevance in the marine environment, as the majority of benthic marine organisms have complex life cycles and dispersal events occurring in the early life stages are nearly impossible to track. As the magnitude and direction of larval dispersal are shaped ultimately by larval distributions, growth, mortality, and transport to adult habitat, this dissertation examined these processes for larval reef fishes in the Straits of Florida (SOF) to contribute to the understanding of patterns of population connectivity along a continental coastline. An analysis of spatially and temporally extensive ichthyoplankton collections and associated environmental data demonstrated that environmental variation through the vertical water column was most important in structuring larval assemblages in the SOF and that horizontal patterns in larval assemblages were only weakly related to oceanographic features (i.e., mesoscale eddies, ME, and the Florida Current). However, otolith analysis revealed that residence in MEs enhanced larval growth for four out of the five reef fish species examined, and this increased growth was consistent across three sampling periods and two years. These results indicate that MEs provide enhanced feeding environments for larval reef fishes. Additional otolith analysis of cohorts of two reef fishes tracked from the pelagic environment to the reef (i.e., settlement-stage), demonstrated that for one species (Cryptotomus roseus) slow-growing larvae were selectively removed from the population just prior to settlement. In this same species, slow-growing larvae from offshore waters did not contribute to the surviving population of settlement-stage larvae, suggesting that for at least some species and settlement events, upstream Caribbean fish populations are not well-connected to populations in the SOF. Finally, several lines of evidence, including temporal changes in larval assemblages and patterns of larval abundance and age across water masses, are consistent with the existence of nearshore retention of locally-spawned larvae in the SOF and, thus, the potential for self-recruitment in reef fish populations of the Florida Keys

Patterns and Drivers of Reef Fish Biodiversity in the Florida Keys National Marine Sanctuary from 1999 - 2016

The biodiversity of reef fish in the Florida Keys National Marine Sanctuary was evaluated in terms of abundance, biomass, evenness, species richness, Shannon diversity, Simpson diversity, and functional diversity, using observations collected from 1999 – 2016 by the Reef Visual Census program. To compare the different diversity indices, species richness, Shannon diversity, Simpson diversity, and functional diversity were converted into effective number of species. We examined the seven indices by level of protection and type of no-take marine zones and by three habitat strata. The study detected abundance, biomass, and diversity were significantly greater (except evenness) inside no-take marine zones compared to areas open to fishing. Smaller reserves had higher abundance, biomass, and richness values than larger reserves and areas open to fishing, but had moderately higher diversity values. This may be attributed to a few species with many individuals that are dominant inside and outside no-take marine zones. Surprisingly, none of the indices were significantly different (except for functional diversity) between the larger Ecological Reserve and areas open for consumption. This may be due to spillover effects. Furthermore, the no-take marine zones only explained a small proportion of total percent deviance in the indices. Habitat type had a greater influence on patterns in composition and diversity where high relief reef habitats had the greatest abundance, biomass, and diversity indices. Based on our results managers should prioritize preserving high relief reefs through a network of small reserves to enhance reef fish composition and biodiversity

Data_Sheet_1_Behavioral mechanisms underlying trait-mediated survival in a coral reef fish.PDF

Fast growth and large size generally increase survivorship in organisms with indeterminate growth. These traits frequently covary, but where they do not, trade-offs often exist in the behavioral choices of organisms. Juvenile bicolor damselfish Stegastes partitus that settle on coral reefs at larger sizes generally experience enhanced survivorship but have slower juvenile growth rates. We hypothesized that differences in behavior may mediate this trade-off. To test whether it is trait-related behaviors or the traits themselves that enhance early survival, we combined individual behavioral observations with otolith (ear stone)-based daily growth measurements for juvenile S. partitus in the Florida Keys. Foraging, sheltering, and chasing behaviors of 256 fish were measured during 5 different months (2008–2009), and patterns of differential survival were similar to those from a 6-year (2003–2008) recruitment time series. We found a trade-off between sheltering and foraging that significantly explained patterns in size-at-settlement: damselfish that settled at larger sizes spent less time sheltered and more time feeding high in the water column. Juvenile growth rates were unrelated to any of the sheltering–foraging behaviors but instead were inversely related to adult conspecific density. Damselfish that settled near higher densities of conspecifics were subjected to increased territorial chasing. Chasing intensity interacted with settlement size such that large juveniles who were chased more frequently exhibited slower growth rates, whereas smaller settlers did not experience this energetic cost. Thus, the dominant survival strategy of S. partitus is to settle at a large size and spend more time foraging high in the water column while dodging conspecifics at an energetic cost to their growth rates. Size-at-settlement is determined during the larval period and after settlement, this trait is key to subsequent behaviors and the strength of trait-mediated survival. Understanding how somatic growth, body size, and survival are intertwined in early life is necessary to help explain population dynamics.</p

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

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

A synthesis of larval bluefin tuna growth dynamics from otolith microstructure in the Gulf of Mexico

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