Trophic ontogeny of a generalist predator is conserved across space.

Consumers can influence ecological patterns and processes through their trophic roles and contributions to the flow of energy through ecosystems. However, the diet and associated trophic roles of consumers commonly change during ontogeny. Despite the prevalence of ontogenetic variation in trophic roles of most animals, we lack an understanding of whether they change consistently across local populations and broad geographic gradients. We examined how the diet and trophic position of a generalist marine predator varied with ontogeny across seven broadly separated locations (~ 750 km). We observed a high degree of heterogeneity in prey consumed without evidence of spatial structuring in this variability. However, compound-specific isotope analysis of amino acids revealed remarkably consistent patterns of increasing trophic position through ontogeny across local populations, suggesting that the roles of this generalist predator scaled with its body size across space. Given the high degree of diet heterogeneity we observed, this finding suggests that even though the dietary patterns differed, the underlying food web architecture transcended variation in prey species across locations for this generalist consumer. Our research addresses a gap in empirical field work regarding the interplay between stage-structured populations and food webs, and suggests ontogenetic changes in trophic position can be consistent in generalist consumers.

Integrating larval connectivity with local demography reveals regional dynamics of a marine metapopulation.

Many ocean species exist within what are called marine metapopulations: networks of otherwise isolated local populations connected by the exchange of larval offspring. In order to manage these species as effectively as possible (e.g., by designing and implementing effective networks of marine protected areas), we must know how many offspring are produced within each local population (i.e., local demography), and where those offspring disperse (i.e., larval connectivity). Although there is much interest in estimating connectivity in the relatively simple sense of identifying the locations of spawning parents and their settling offspring, true measures of demographic connectivity that account for among-site variation in offspring production have been lacking. We combined detailed studies of local reproductive output and larval dispersal of a coral reef fish to quantify demographic connectivity within a regional metapopulation that included four widely spaced islands in the Bahamas. We present a new method for estimating demographic connectivity when the levels of dispersal among populations are inferred by the collection of genetically "tagged" offspring. We estimated that 13.3% of recruits returned to natal islands, on average (95% CI = 1.1-50.3%), that local retention was high on one of the islands (41%, 95% CI = 6.0-97.0%), and that larval connectivity was appreciable, even between islands 129 km apart (mean = 1.6%, 95% CI = 0.20-8.8%). Our results emphasize the importance of properly integrating measurements of production with measurements of connectivity. Had we not accounted for among-site variation in offspring production, our estimates of connectivity would have been inaccurate by a factor as much as 6.5. At a generational timescale, lifetime offspring production varied substantially (a fivefold difference among islands) and the importance of each island to long-term metapopulation growth was dictated by both larval production and connectivity. At the scale of our study (local populations inhabiting 5-ha reefs), the regional metapopulation could not grow without external input. However, an exploratory analysis simulating a network of four marine protected areas suggested that reserves of >65 ha each would ensure persistence of this network. Thus, integrating studies of larval connectivity and local demography hold promise for both managing and conserving marine metapopulations effectively.

Spatial and temporal patterns of larval dispersal in a coral-reef fish metapopulation: evidence of variable reproductive success.

Many marine organisms can be transported hundreds of kilometres during their pelagic larval stage, yet little is known about spatial and temporal patterns of larval dispersal. Although traditional population-genetic tools can be applied to infer movement of larvae on an evolutionary timescale, large effective population sizes and high rates of gene flow present serious challenges to documenting dispersal patterns over shorter, ecologically relevant, timescales. Here, we address these challenges by combining direct parentage analysis and indirect genetic analyses over a 4-year period to document spatial and temporal patterns of larval dispersal in a common coral-reef fish: the bicolour damselfish (Stegastes partitus). At four island locations surrounding Exuma Sound, Bahamas, including a long-established marine reserve, we collected 3278 individuals and genotyped them at 10 microsatellite loci. Using Bayesian parentage analysis, we identified eight parent-offspring pairs, thereby directly documenting dispersal distances ranging from 0 km (i.e., self-recruitment) to 129 km (i.e., larval connectivity). Despite documenting substantial dispersal and gene flow between islands, we observed more self-recruitment events than expected if the larvae were drawn from a common, well-mixed pool (i.e., a completely open population). Additionally, we detected both spatial and temporal variation in signatures of sweepstakes and Wahlund effects. The high variance in reproductive success (i.e., 'sweepstakes') we observed may be influenced by seasonal mesoscale gyres present in the Exuma Sound, which play a prominent role in shaping local oceanographic patterns. This study documents the complex nature of larval dispersal in a coral-reef fish, and highlights the importance of sampling multiple cohorts and coupling both direct and indirect genetic methods in order disentangle patterns of dispersal, gene flow and variable reproductive success.

Benthic foraminifera in Gulf of Mexico show temporal and spatial dynamics of microplastics.

Microplastics have accumulated in the environment since plastic production began, with present-day observations that range from marine trenches to mountains. However, research on microplastics has only recently begun so it is unclear how they have changed over time in many oceanic regions. Our study addressed this gap by quantifying the temporal and spatial dynamics of microplastics in two deep-water regions of the Gulf of Mexico (GOM). We isolated agglutinated foraminifera from sediment cores and assessed microplastics that were incorporated into their tests. Our results indicated that microplastics were incorporated by agglutinated foraminifera after plastic production began. Microplastics were higher at deep-water sites and closer to the Mississippi River. This study confirms the presence of microplastic incorporation into agglutinated foraminifera tests and investigates microplastics in deep-water sediments in the GOM. Additional work is needed to fully identify the distribution of microplastics across the GOM and other oceanic basins.

Evaluation of DNA metabarcoding for identifying fish eggs: a case study on the West Florida Shelf.

A critical factor in fisheries management is the protection of spawning sites for ecologically and economically important fish species. DNA barcoding (i.e., amplification and sequencing of the mitochondrial cytochrome c oxidase I (COI) gene) of fish eggs has emerged as a powerful technique for identifying spawning sites. However, DNA barcoding of individual fish eggs is time-consuming and expensive. In an attempt to reduce costs and effort for long-term fisheries monitoring programs, here we used DNA metabarcoding, in which DNA is extracted and amplified from a composited sample containing all the fish eggs collected at a given site, to identify fish eggs from 49 stations on the West Florida Shelf. A total of 37 taxa were recovered from 4,719 fish eggs. Egg distributions on the West Florida Shelf corresponded with the known habitat types occupied by these taxa, which included burrower, coastal pelagic, epipelagic, mesopelagic, demersal, deep demersal, commensal, and reef-associated taxa. Metabarcoding of fish eggs was faster and far less expensive than barcoding individual eggs; however, this method cannot provide absolute taxon proportions due to variable copy numbers of mitochondrial DNA in different taxa, different numbers of cells within eggs depending on developmental stage, and PCR amplification biases. In addition, some samples yielded sequences from more taxa than the number of eggs present, demonstrating the presence of contaminating DNA and requiring the application of a threshold proportion of sequences required for counting a taxon as present. Finally, we review the advantages and disadvantages of using metabarcoding vs. individual fish egg barcoding for long-term monitoring programs.

Microplastics do not affect bleaching of Acropora cervicornis at ambient or elevated temperatures.

Microplastic pollution can harm organisms and ecosystems such as coral reefs. Corals are important habitat-forming organisms that are sensitive to environmental conditions and have been declining due to stressors associated with climate change. Despite their ecological importance, it is unclear how corals may be affected by microplastics or if there are synergistic effects with rising ocean temperatures. To address this research gap, we experimentally examined the combined effects of environmentally relevant microplastic concentrations (i.e., the global average) and elevated temperatures on bleaching of the threatened Caribbean coral, Acropora cervicornis. In a controlled laboratory setting, we exposed coral fragments to orthogonally crossed treatment levels of low-density polyethylene microplastic beads (0 and 11.8 particles L-1) and water temperatures (ambient at 28 °C and elevated at 32 °C). Zooxanthellae densities were quantified after the 17-day experiment to measure the bleaching response. Regardless of microplastic treatment level, corals in the elevated temperature treatment were visibly bleached and necrotic (i.e., significant negative effect on zooxanthellae density) while those exposed to ambient temperature remained healthy. Thus, our study successfully elicited the expected bleaching response to a high-water temperature. However, we did not observe significant effects of microplastics at either individual (ambient temperature) or combined levels (elevated temperature). Although elevated temperatures remain a larger threat to corals, responses to microplastics are complex and may vary based on focal organisms or on plastic conditions (e.g., concentration, size, shape). Our findings add to a small but growing body of research on the effects of microplastics on corals, but further work is warranted in this emerging field to fully understand how sensitive ecosystems are affected by this pollutant.

Self-recruitment and sweepstakes reproduction amid extensive gene flow in a coral-reef fish.

Identifying patterns of larval dispersal within marine metapopulations is vital for effective fisheries management, appropriate marine reserve design, and conservation efforts. We employed genetic markers (microsatellites) to determine dispersal patterns in bicolour damselfish (Pomacentridae: Stegastes partitus). Tissue samples of 751 fish were collected in 2004 and 2005 from 11 sites encompassing the Exuma Sound, Bahamas. Bayesian parentage analysis identified two parent-offspring pairs, which is remarkable given the large population sizes and 28 day pelagic larval duration of bicolour damselfish. The two parent-offspring pairs directly documented self-recruitment at the two northern-most sites, one of which is a long-established marine reserve. Principal coordinates analyses of pair-wise relatedness values further indicated that self-recruitment was common in all sampled populations. Nevertheless, measures of genetic differentiation (F(ST)) and results from assignment methods suggested high levels of gene flow among populations. Comparisons of heterozygosity and relatedness among samples of adults and recruits indicated spatially and temporally independent sweepstakes events, whereby only a subset of adults successfully contribute to subsequent generations. These results indicate that self-recruitment and sweepstakes reproduction are the predominant, ecologically-relevant processes that shape patterns of larval dispersal in this system.

Population dynamics of Pinfish in the eastern Gulf of Mexico (1998-2016).

Forage fishes play an important role in marine ecosystems by transferring energy and nutrients through the food web. The population dynamics of forage species can therefore have cascading effects across multiple trophic levels. Here, we analyzed a 19-year dataset on Pinfish (Lagodon rhomboides) across four eastern Gulf of Mexico estuaries to investigate population dynamics, inter- and intra-annual synchrony, metapopulation portfolio effects, growth, and habitat effects. Young-of-year growth rates did not differ among estuaries. The population dynamics of these four systems were stable in the long-term, but highly dynamic inter-annually. Intra-annual dynamics were stable and predictable despite variation in long-term means. Some estuaries exhibited positive inter-annual synchrony, and all four estuaries were synchronous intra-annually. There was evidence for stronger portfolio effects for the entire four-estuary metapopulation, as well as for the two northern estuaries while the southern estuaries appeared to act as a single population. Submerged aquatic vegetation was by far the most important predictor for both presence and abundance of Pinfish. It is important to understand the factors driving forage fish population fluctuations to better predict ecosystem effects, including those to species of economic and ecological importance. These predictors can be useful for the implementation of ecosystem-based management decisions.

Indirect effects of an exploited predator on recruitment of coral-reef fishes.

The more ecologists examine the role of trait-mediated indirect interactions (TMIIs), especially in regulating predator-prey interactions, the more we recognize their fundamental role in structuring food webs. However, most empirical evidence for TMIIs comes from studies that are either conducted in laboratory or mesocosm venues or are restricted to simple food webs involving lower trophic-level animals. Here, I quantified the direct and indirect effects of interactions between high-level vertebrate predators on their vertebrate prey using a field experiment. Specifically, I tested how varying densities of a large-bodied, top predator (Nassau grouper; Epinephelus striatus) affected persistence, growth, and behavior of two smaller-bodied, intermediate predators (coney and graysby groupers; Cephalopholis fulva and C. cruentata) on 20 isolated patch reefs in the Bahamas. Large-bodied groupers are capable of consuming their smaller-bodied counterparts, and previous observational studies have indicated that local abundances of these groupers are negatively correlated. I measured the effects of interactions among groupers on lower trophic-level prey by quantifying recruitment of coral-reef fishes to the reefs. The field experiment demonstrated a strong trophic cascade that was entirely mediated by modified behavior of the intermediate predators. These results indicate that indirect, nonlethal interactions in natural systems can have strong cascading effects even at high trophic levels and in high-diversity food webs. Incorporating the complexity of such indirect effects into fisheries management may improve the sustainability of fished populations and strengthen marine conservation efforts; however these results also indicate that the effects of fishing are complex and difficult to predict.

-A practical application of reduced-copper antifouling paint in marine biological research.

Biofouling of experimental cages and other field apparatuses can be problematic for scientists and has traditionally been addressed using frequent manual removal (e.g., scraping, scrubbing). Recent environmental restrictions and legislative changes have driven the development of less hazardous antifouling products, making antifouling paint a potential alternative option to manual removal. Consequently, the viability of using these newly developed products as a replacement for the manual cleaning of exclusion cages was experimentally investigated. There were six treatments tested, comprising three with settlement tiles in experimental cages coated with antifouling paint, two with settlement tiles in unpainted experimental cages, and one cage-free suspended tile. The three antifouling treatments comprised two reduced-copper paints (21% Cu2O and 40% Cu2O) and one copper-free, Econea (™)-based paint (labeled "ecofriendly"). Antifouling paints were assessed for performance of preventing fouling of the cages and whether they elicited local effects on settlement tiles contained within them. All three paints performed well to reduce fouling of the cages during the initial six weeks of the experiment, but the efficacy of "ecofriendly" paint began to decrease during an extended deployment that lasted 14 weeks. The macro-community composition, biomass, and percent cover of settled organism on tiles within cages treated with copper-based paints (21% and 40% concentrations) were indistinguishable from tiles within the manually scrubbed cages. In contrast, settlement to tiles from the "ecofriendly" treatment was different in composition of macro-community and lower in biomass, suggesting the presence of local effects and therefore rendering it unsuitable for use in settlement experiments. The results of this study suggest that reduced-copper paints have the potential to serve as an alternative to manual maintenance, which may be useful for deployments in locations that are difficult to access on a frequent schedule.

Quantification of Boat Visitation Rates at Artificial and Natural Reefs in the Eastern Gulf of Mexico Using Acoustic Recorders.

Artificial reefs are commonly used as a management tool, in part to provide ecosystem services, including opportunities for recreational fishing and diving. Quantifying the use of artificial reefs by recreational boaters is essential for determining their value as ecosystem services. In this study, four artificial-natural reef pairs in the eastern Gulf of Mexico (off western Florida) were investigated for boat visitation rates using autonomous acoustic recorders. Digital SpectroGram (DSG) recorders were used to collect sound files from April 2013 to March 2015. An automatic detection algorithm was used to identify boat noise in individual files using the harmonic peaks generated by boat engines, and by comparing the sound amplitude of each file with surrounding files. In all four pairs, visitation rates were significantly higher at the artificial reef than the natural reef. This increase in boat visitation was likely due to actual or perceived increased quality of fishing and diving at the artificial reefs, or to lack of knowledge of the presence or locations of the natural reefs. Inshore reefs (<15 m depth) had high variability in monthly visitation rates, which were generally highest in warmer months. However the seasonal signal was dampened on offshore reefs (>25 m depth). This study appears to be the first to use acoustic data to measure participant use of boating destinations, and highlights the utility of acoustic monitoring for the valuation of this important ecosystem service provided by artificial reefs.

Non-lethal approach identifies variability of δ (15)N values in the fin rays of Atlantic Goliath Grouper, Epinephelus itajara.

The Atlantic Goliath Grouper, Epinephelus itajara, is critically endangered throughout its range but has begun to show initial signs of recovery in Florida state waters. As the population continues to rebound, researchers face a pressing need to fill the knowledge gaps about this iconic species. Here, we examined the δ (15)N isotopic records in fin rays collected from Atlantic Goliath Grouper, and related changes of isotopic ratios over time to life history characteristics. Fin-ray analysis was used as a non-lethal technique to sample individuals from two locations at similar latitudes from the west and east coasts of Florida, USA. δ (15)N data were acquired by mechanically separating the annuli of each fin ray and then analyzing the material in an Irradiance Elemental Analyzer Mass Spectrometer. The δ (15)N values were consistent among individuals within populations from each coast of Florida, and mirrored the expected changes over the lives of the fish. Overall, differences were found between δ (15)N values at juvenile life history phases versus adult phases, but the patterns associated with these differences were unique to each coastal group. We demonstrated, for the first time, that δ (15)N values from fin rays can be used to assess the life histories of Atlantic Goliath Grouper. The non-lethal strategies outlined here can be used to acquire information essential to the management of species of concern, such as those that are threatened or endangered.

Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ (13)C and δ (15)N).

Research that uses stable isotope analysis often involves a delay between sample collection in the field and laboratory processing, therefore requiring preservation to prevent or reduce tissue degradation and associated isotopic compositions. Although there is a growing literature describing the effects of various preservation techniques, the results are often contextual, unpredictable and vary among taxa, suggesting the need to treat each species individually. We conducted a controlled experiment to test the effects of four preservation methods of muscle tissue from four species of upper trophic-level reef fish collected from the eastern Gulf of Mexico (Red Grouper Epinephelus morio, Gag Mycteroperca microlepis, Scamp Mycteroperca phenax, and Red Snapper Lutjanus campechanus). We used a paired design to measure the effects on isotopic values for carbon and nitrogen after storage using ice, 95% ethanol, and sodium chloride (table salt), against that in a liquid nitrogen control. Mean offsets for both δ (13)C and δ (15)N values from controls were lowest for samples preserved on ice, intermediate for those preserved with salt, and highest with ethanol. Within species, both salt and ethanol significantly enriched the δ (15)N values in nearly all comparisons. Ethanol also had strong effects on the δ (13)C values in all three groupers. Conversely, for samples preserved on ice, we did not detect a significant offset in either isotopic ratio for any of the focal species. Previous studies have addressed preservation-induced offsets in isotope values using a mass balance correction that accounts for changes in the isotope value to that in the C/N ratio. We tested the application of standard mass balance corrections for isotope values that were significantly affected by the preservation methods and found generally poor agreement between corrected and control values. The poor performance by the correction may have been due to preferential loss of lighter isotopes and corresponding low levels of mass loss with a substantial change in the isotope value of the sample. Regardless of mechanism, it was evident that accounting for offsets caused by different preservation methods was not possible using the standard correction. Caution is warranted when interpreting the results from specimens stored in either ethanol or salt, especially when using those from multiple preservation techniques. We suggest the use of ice as the preferred preservation technique for muscle tissue when conducting stable isotope analysis as it is widely available, inexpensive, easy to transport and did not impart a significant offset in measured isotopic values. Our results provide additional evidence that preservation effects on stable isotope analysis can be highly contextual, thus requiring their effects to be measured and understood for each species and isotopic ratio of interest before addressing research questions.

Fishery-independent data reveal negative effect of human population density on Caribbean predatory fish communities.

BACKGROUND: Understanding the current status of predatory fish communities, and the effects fishing has on them, is vitally important information for management. However, data are often insufficient at region-wide scales to assess the effects of extraction in coral reef ecosystems of developing nations. METHODOLOGY/PRINCIPAL FINDINGS: Here, I overcome this difficulty by using a publicly accessible, fisheries-independent database to provide a broad scale, comprehensive analysis of human impacts on predatory reef fish communities across the greater Caribbean region. Specifically, this study analyzed presence and diversity of predatory reef fishes over a gradient of human population density. Across the region, as human population density increases, presence of large-bodied fishes declines, and fish communities become dominated by a few smaller-bodied species. CONCLUSIONS/SIGNIFICANCE: Complete disappearance of several large-bodied fishes indicates ecological and local extinctions have occurred in some densely populated areas. These findings fill a fundamentally important gap in our knowledge of the ecosystem effects of artisanal fisheries in developing nations, and provide support for multiple approaches to data collection where they are commonly unavailable.