Response of coastal fishes to the Gulf of Mexico oil disaster

The ecosystem-level impacts of the Deepwater Horizon disaster have been largely unpredictable due to the unique setting and magnitude of this spill. We used a five-year (2006-2010) data set within the oil-affected region to explore acute consequences for early-stage survival of fish species inhabiting seagrass nursery habitat. Although many of these species spawned during spring-summer, and produced larvae vulnerable to oil-polluted water, overall and species-by-species catch rates were high in 2010 after the spill (1,989±220 fishes km-towed(-1) [μ ± 1SE]) relative to the previous four years (1,080±43 fishes km-towed(-1)). Also, several exploited species were characterized by notably higher juvenile catch rates during 2010 following large-scale fisheries closures in the northern Gulf, although overall statistical results for the effects of fishery closures on assemblage-wide CPUE data were ambiguous. We conclude that immediate, catastrophic losses of 2010 cohorts were largely avoided, and that no shifts in species composition occurred following the spill. The potential long-term impacts facing fishes as a result of chronic exposure and delayed, indirect effects now require attention.     

Climate-related, decadal-scale assemblage changes of seagrass-associated fishes in the northern Gulf of Mexico

Global temperatures are rising, and are expected to produce a poleward shift in the distribution of many organisms. We quantified changes in fish assemblages within seagrass meadows of the northern Gulf of Mexico (GOM) between the 1970s and 2006–2007, and observed changes consistent with this forecast. During 2006–2007 we sampled seagrass meadows using the same gears and methods previously employed by R. J. Livingston in coastal waters of northwest Florida throughout the 1970s. Comparisons between datasets revealed numerous additions to the fish fauna during 2006–2007 that were completely absent in the 1970s, including: Lutjanus synagris (lane snapper), Epinephelus morio (red grouper), Chaetodon ocellatus (spotfin butterflyfish), Mycteroperca sp (grouper, non gag), Centropristis philadelphica (rock sea bass), Fistularia tabacaria (bluespotted cornetfish), Ocyurus chrysurus (yellowtail snapper), Thalassoma bifasciatum (bluehead wrasse), Abudefduf saxatilis (sergeant major), Acanthuridae spp. (surgeonfishes) and Sparisoma viride (stoplight parrotfish). Several other species showed large increases in abundance during the interval between 1979 and 2006, including Mycteroperca microlepis (gag grouper, up ∼200 ×), Lutjanus griseus (gray snapper, up ∼105 ×), and Nicholsina usta (emerald parrotfish, up ∼22 ×). All of these are tropical or subtropical species that now make up a greater percentage of seagrass-associated fish assemblages in the northern GOM than in the past. Additionally, we observed regional increases in air and sea surface temperatures (> 3 °C) during the ∼30 years that separate Livingston's samples and ours that correlate with northern shifts in the distribution of warm-water fishes. Documenting these range shifts is a critical first step in investigating the consequences of global warming for endemic marine communities and fishery production in the northern GOM.     

The fishes of northern and central Veracruz,Mexico

The hydrographic structure of Abra Harbour, a tidal embayment located at the seaward end of the highly polluted estuary of Bilbao, is influenced by the inflow of a polluted estuarine plume, the asymmetry of the harbour basin, and the tidal circulation pattern. Multivariate analysis of the spatial variability of the zooplankton between May 1981 and May 1982 showed that significant differences in zooplankton abundance and species composition occurred from the inner-eastern to the outer-western side, related to the horizontal structure of the system. The annual temperature cycle, however, was the major source of temporal variability, and the seasonal stratification in the water column was responsible for the predominance of vertical differences in zooplankton composition during the spring-summer period. Wind-induced turbulence and tides were other sources of variation. With increasing turbulence (rough sea), the spatial gradients in zooplankton composition were not as clear, and with decreasing tidal height the compositional differences in the horizontal dimension tended to be more evident. Spionid larvae accounted for strong local differences within the Harbour. They were usually segregated from other taxa, and mainly associated to the deeper waters characterized by a greater hydrological instability.     

Genetic connectivity in scleractinian corals across the Northern Gulf of Mexico: oil/gas platforms, and relationship to the Flower Garden Banks

The 3,000 oil/gas structures currently deployed in the northern Gulf of Mexico (GOM) provide hard substratum for marine organisms in a region where such has been rare since the Holocene. The major exception to this are the Flower Garden Banks (FGB). Corals are known to have colonized oil/gas platforms around the FGB, facilitating biogeographic expansion. We ask the question, what are the patterns of genetic affinity in these coral populations. We sampled coral tissue from populations of two species occurring on oil and gas platforms: Madracis decactis (hermatype) and Tubastraea coccinea (invasive ahermatype). We sampled 28 platforms along four transects from 20 km offshore to the continental shelf edge off 1) Matagorda Island, TX; 2) Lake Sabine, TX; 3) Terrebonne Bay, LA; and 4) Mobile, AL. The entire population of M. decactis was sampled between depths of 5 m and 37 m. T. coccinea populations were sub-sampled. Genetic variation was assessed using the PCR-based Amplified Fragment Length Polymorphisms (AFLPs). Data were analyzed via AFLPOP and STRUCTURE. Genetic connectivity among M. decactis platform populations was highest near the FGB and decreased to the east. Connectivity increased again in the eastern sector, indicating isolation between the populations from different sides of the Mississippi River (Transects 3 and 4). A point-drop in genetic affinity (relatedness) at the shelf edge south of Terrebonne Bay, LA indicated a population differing from all others in the northern GOM. Genetic affinities among T. coccinea were highest in the west and decreased to the east. Very low genetic affinities off Mobile, AL indicated a dramatic difference between those populations and those west of the Mississippi River, apparently a formidable barrier to larval dispersal.     

Phylogenetic diversity, host-specificity and community profiling of sponge-associated bacteria in the northern Gulf of Mexico

Background

Marine sponges can associate with abundant and diverse consortia of microbial symbionts. However, associated bacteria remain unexamined for the majority of host sponges and few studies use phylogenetic metrics to quantify symbiont community diversity. DNA fingerprinting techniques, such as terminal restriction fragment length polymorphisms (T-RFLP), might provide rapid profiling of these communities, but have not been explicitly compared to traditional methods.

Methodology/Principal Findings

We investigated the bacterial communities associated with the marine sponges Hymeniacidon heliophila and Haliclona tubifera, a sympatric tunicate, Didemnum sp., and ambient seawater from the northern Gulf of Mexico by combining replicated clone libraries with T-RFLP analyses of 16S rRNA gene sequences. Clone libraries revealed that bacterial communities associated with the two sponges exhibited lower species richness and lower species diversity than seawater and tunicate assemblages, with differences in species composition among all four source groups. T-RFLP profiles clustered microbial communities by source; individual T-RFs were matched to the majority (80.6%) of clone library sequences, indicating that T-RFLP analysis can be used to rapidly profile these communities. Phylogenetic metrics of community diversity indicated that the two sponge-associated bacterial communities include dominant and host-specific bacterial lineages that are distinct from bacteria recovered from seawater, tunicates, and unrelated sponge hosts. In addition, a large proportion of the symbionts associated with H. heliophila were shared with distant, conspecific host populations in the southwestern Atlantic (Brazil).

Conclusions/Significance

The low diversity and species-specific nature of bacterial communities associated with H. heliophila and H. tubifera represent a distinctly different pattern from other, reportedly universal, sponge-associated bacterial communities. Our replicated sampling strategy, which included samples that reflect the ambient environment, allowed us to differentiate resident symbionts from potentially transient or prey bacteria. Pairing replicated clone library construction with rapid community profiling via T-RFLP analyses will greatly facilitate future studies of sponge-microbe symbioses.     

Characterization of microbial community structure in Gulf of Mexico gas hydrates: comparative analysis of DNA- and RNA-derived clone libraries

The characterization of microbial assemblages within solid gas hydrate, especially those that may be physiologically active under in situ hydrate conditions, is essential to gain a better understanding of the effects and contributions of microbial activities in Gulf of Mexico (GoM) hydrate ecosystems. In this study, the composition of the Bacteria and Archaea communities was determined by 16S rRNA phylogenetic analyses of clone libraries derived from RNA and DNA extracted from sediment-entrained hydrate (SEH) and interior hydrate (IH). The hydrate was recovered from an exposed mound located in the northern GoM continental slope with a hydrate chipper designed for use on the manned-submersible Johnson Sea Link (water depth, 550 m). Previous geochemical analyses indicated that there was increased metabolic activity in the SEH compared to the IH layer (B. N. Orcutt, A. Boetius, S. K. Lugo, I. R. Macdonald, V. A. Samarkin, and S. Joye, Chem. Geol. 205:239-251). Phylogenetic analysis of RNA- and DNA-derived clones indicated that there was greater diversity in the SEH libraries than in the IH libraries. A majority of the clones obtained from the metabolically active fraction of the microbial community were most closely related to putative sulfate-reducing bacteria and anaerobic methane-oxidizing archaea. Several novel bacterial and archaeal phylotypes for which there were no previously identified closely related cultured isolates were detected in the RNA- and DNA-derived clone libraries. This study was the first phylogenetic analysis of the metabolically active fraction of the microbial community extant in the distinct SEH and IH layers of GoM gas hydrate.     

Influence of hurricanes on coastal ecosystems along the northern Gulf of Mexico

Available literature indicates that hurricanes do not generally produce long-term detrimental impacts to unmodified coastal systems and that they often provide net benefits along the U.S. Gulf Coast. While there is normally initial erosion from hurricanes, they also often result in a large influx of inorganic sediments, creating new wetlands and contributing to the maintenance of existing wetlands. The formation of washover deposits is disastrous where cultural development has occurred, but in natural areas these deposits are part of the natural cycle of shoreline development and contribute to habitat diversity and productivity. Abundant rainfall typically associated with hurricanes often results in large increases of sediment and nutrient inputs into coastal estuaries, leading to both short-term and long-term increases in productivity. Rainfall during tropical disturbances accounts for a significant part of total precipitation along the northern gulf. The immediate impact of hurricanes may be to reduce populations of some species but these populations generally recover rapidly. Overall, productivity in natural systems seems to be increased by periodic hurricanes. Hurricane impacts are often severe and long lasting in wetlands that have been modified by human impacts such as semi- or complete impoundments.     

Microarray-based characterization of microbial community functional structure and heterogeneity in marine sediments from the Gulf of Mexico

Marine sediments of coastal margins are important sites of carbon sequestration and nitrogen cycling. To determine the metabolic potential and structure of marine sediment microbial communities, two cores were collected each from the two stations (GMT at a depth of 200 m and GMS at 800 m) in the Gulf of Mexico, and six subsamples representing different depths were analyzed from each of these two cores using functional gene arrays containing approximately 2,000 probes targeting genes involved in carbon fixation; organic carbon degradation; contaminant degradation; metal resistance; and nitrogen, sulfur, and phosphorous cycling. The geochemistry was highly variable for the sediments based on both site and depth. A total of 930 (47.1%) probes belonging to various functional gene categories showed significant hybridization with at least 1 of the 12 samples. The overall functional gene diversity of the samples from shallow depths was in general lower than those from deep depths at both stations. Also high microbial heterogeneity existed in these marine sediments. In general, the microbial community structure was more similar when the samples were spatially closer. The number of unique genes at GMT increased with depth, from 1.7% at 0.75 cm to 18.9% at 25 cm. The same trend occurred at GMS, from 1.2% at 0.25 cm to 15.2% at 16 cm. In addition, a broad diversity of geochemically important metabolic functional genes related to carbon degradation, nitrification, denitrification, nitrogen fixation, sulfur reduction, phosphorus utilization, contaminant degradation, and metal resistance were observed, implying that marine sediments could play important roles in biogeochemical cycling of carbon, nitrogen, phosphorus, sulfate, and various metals. Finally, the Mantel test revealed significant positive correlations between various specific functional genes and functional processes, and canonical correspondence analysis suggested that sediment depth, PO(4)(3-), NH(4)(+), Mn(II), porosity, and Si(OH)(4) might play major roles in shaping the microbial community structure in the marine sediments.     

Structural and chemical defenses of echinoderms from the northern Gulf of Mexico

The feeding deterrent effects of echinoderm body-wall tissues and ethanolic extracts containing mid-polarity compounds were evaluated utilizing generalist fish and crabs as model predators. The body-wall tissues of the echinoderms examined ranged 10-fold from 0.9–9.4 mm in thickness, and four and a half-fold in level of mineralization (17.8–82.7% ash content). Holothuroids had the thickest body-wall tissues and contained the lowest levels of mineralization in their body-walls. Crinoids and ophiuroids had high levels of mineralization in their arms. Asteroid body-wall tissues varied the most in thickness and ash content (0.9–3.9 mm in thickness and 29.2–55.5% in ash content). Body-wall tissues of 19 species of echinoderms were tested for their feeding deterrent properties against the marine fishes Lagodon rhomboides (Linnaeus) and Cyprinodon variegatus (Lacepede), as well as the decapod crustacean Libinia emarginata (Leach). Equivalent sized pieces of fresh body-wall tissue of 16 species of echinoderms caused observable feeding deterrence responses in at least two of the three model predators. There was no significant correlation between body-wall thickness or percent ash and its palatability to any of the three model predators. Agar pellets containing ethanolic body-wall extracts of 12 of 18 echinoderm species caused observable feeding deterrence responses in the fish L. rhomboides. In similar experiments with the arrow crab Stenorhyncus seticornis (Herbst), using carrageenan fish-meal blocks as food models, no differences in consumption of control fish-meal and experimental body-wall extract blocks were detected. Our findings indicate that invertebrate and vertebrate predators may respond quite differently to echinoderm body-wall extracts.     

Spatial and bathymetric trends in Harpacticoida (Copepoda) community structure in the Northern Gulf of Mexico deep-sea

Harpacticoid copepod community structure was analyzed at 43 stations in the northern Gulf of Mexico deep-sea to test regional and bathymetric patterns of diversity in relation to environmental variables and topographic complexity of the continental slope. Depth, longitude, and proximity to the Florida Escarpment significantly affect average phylogenetic diversity, but basins and canyons do not. Multivariate analysis reveals a significant inverse relationship between diversity and POM flux, which is confirmed by significant region-scale depth and longitude differences. Although species richness declines linearly with increasing depth, the expected number of species (rarefraction) is maximized at approximately 1200 m, and average taxonomic and phylogenetic diversity continue to increase with depth, suggesting greater morphological or functional harpacticoid diversity with increasing depth. Most stations have unique species compositions, suggesting high regional (2200 species) and global (10⁵-10⁶ species) diversity by extrapolation. Therefore, processes maintaining harpacticoid diversity in the northern Gulf of Mexico deep-sea seem to rely on both small-scale dispersal and large-scale food supply mechanisms.     

Decline in condition of gorgonian octocorals on mesophotic reefs in the northern Gulf of Mexico: before and after the Deepwater Horizon oil spill

Hard-bottom ‘mesophotic’ reefs along the ‘40-fathom’ (73 m) shelf edge in the northern Gulf of Mexico were investigated for potential effects of the Deepwater Horizon (DWH) oil spill from the Macondo well in April 2010. Alabama Alps Reef, Roughtongue Reef, and Yellowtail Reef were near the well, situated 60–88 m below floating oil discharged during the DWH spill for several weeks and subject to dispersant applications. In contrast, Coral Trees Reef and Madison Swanson South Reef were far from the DWH spill site and below the slick for less than a week or not at all, respectively. The reefs were surveyed by ROV in 2010, 2011, and 2014 and compared to similar surveys conducted one and two decades earlier. Large gorgonian octocorals were present at all sites in moderate abundance including Swiftia exserta, Hypnogorgia pendula, Thesea spp., and Placogorgia spp. The gorgonians were assessed for health and condition in a before-after-control-impact (BACI) research design using still images captured from ROV video transects. Injury was modeled as a categorical response to proximity and time using logistic regression. Condition of gorgonians at sites near Macondo well declined significantly post-spill. Before the spill, injury was observed for 4–9 % of large gorgonians. After the spill, injury was observed in 38–50 % of large gorgonians. Odds of injury for sites near Macondo were 10.8 times higher post-spill, but unchanged at far sites. The majority of marked injured colonies in 2011 declined further in condition by 2014. Marked healthy colonies generally remained healthy. Background stresses to corals, including fishing activity, fishing debris, and coral predation, were noted during surveys, but do not appear to account for the decline in condition at study sites near Macondo well.     

Geochemical environments of continental shelf-upper slope sediments in the northern Gulf of Mexico

Geochemical environments were characterized for 14 sites along the northern Gulf of Mexico continental shelf and upper slope, in an effort to examine the relationship between sediment geochemistry and carbonate shell taphonomy in a long-term study—Shelf and Slope Experimental Taphonomy Initiative (SSETI). Three groups of environments of preservation (seep, near-seep, and shelf-and-slope) were identified based on their geochemical characteristics (i.e., oxygen uptake rate and penetration depth, pore-water saturation states, and carbonate dissolution fluxes). Diffusive oxygen uptake rate increased in the order of shelf-and-slope, near-seep, and seep, although carbonate dissolution flux did not show significant correlation with O₂ flux, presumably due to non-diffusive behavior at some sites. Using pore-water saturation indices with respect to aragonite and calcite and sedimentation rates, we defined a semi-quantitative parameter, carbonate dissolution index (CDI), to predict carbonate preservation potential during the taphonomic processes. Our limited database suggests that both the seep and the shelf-and-slope sediments may have higher carbonate preservation potential than the near-seep sediments.     

Carbon sequestration in wetland soils of the northern Gulf of Mexico coastal region

Coastal wetlands play an important but complex role in the global carbon cycle, contributing to the ecosystem service of greenhouse gas regulation through carbon sequestration. Although coastal wetlands occupy a small percent of the total US land area, their potential for carbon storage, especially in soils, often exceeds that of other terrestrial ecosystems. More than half of the coastal wetlands in the US are located in the northern Gulf of Mexico, yet these wetlands continue to be degraded at an alarming rate, resulting in a significant loss of stored carbon and reduction in capacity for carbon sequestration. We provide estimates of surface soil carbon densities for wetlands in the northern Gulf of Mexico coastal region, calculated from field measurements of bulk density and soil carbon content in the upper 10–15 cm of soil. We combined these estimates with soil accretion rates derived from the literature and wetland area estimates to calculate surface soil carbon pools and accumulation rates. Wetlands in the northern Gulf of Mexico coastal region potentially store 34–47 Mg C ha^?1 and could potentially accumulate 11,517 Gg C year^?1. These estimates provide important information that can be used to incorporate the value of wetlands in the northern Gulf of Mexico coastal region in future wetland management decisions related to global climate change. Estimates of carbon sequestration potential should be considered along with estimates of other ecosystem services provided by wetlands in the northern Gulf of Mexico coastal region to strengthen and enhance the conservation, sustainable management, and restoration of these important natural resources.     

Lipid content and energy density of forage fishes from the northern Gulf of Alaska

Piscivorous predators can experience multi-fold differences in energy intake rates based solely on the types of fishes consumed. We estimated energy density of 1151 fish from 39 species by proximate analysis of lipid, water, ash-free lean dry matter, and ash contents and evaluated factors contributing to variation in composition. Lipid content was the primary determinant of energy density, ranging from 2 to 61% dry mass and resulting in a five-fold difference in energy density of individuals (2.0-10.8 kJg(-1) wet mass). Energy density varied widely within and between species. Schooling pelagic fishes had relatively high or low values, whereas nearshore demersal fishes were intermediate. Pelagic species maturing at a smaller size had higher and more variable energy density than pelagic or nearshore species maturing larger. High-lipid fishes had less water and more protein than low-lipid fishes. In some forage fishes, size, month, reproductive status, or location contributed significantly to intraspecific variation in energy density. Differences in quality are sufficient to potentially affect diet selection of breeding seabirds, especially when transporting food for their young to the nest site.     

Variation in ecosystem carbon dynamics of saltwater marshes in the northern Gulf of Mexico

Wetlands are highly productive ecosystems that can sequester large quantities of carbon. However, variation in physiological potential can alter their capacity to sequester carbon. To examine variation in ecosystem physiological capacity, we established three coastal marsh sites in Mississippi and Alabama spanning a productivity gradient. Over 1 year, we measured ecophysiological activity and spectral indices in two vegetation zones within each marsh to develop a better understanding of variation in ecosystem responses and health. Gross ecosystem exchange of carbon and ecosystem respiration rates (R_eco) differed significantly among sites, with the highest activity at Grand Bay, Mississippi and Point Aux Pines, Alabama and lower ecophysiological activity at Dauphin Island, Alabama. Net ecosystem exchange was similar for all three study areas because greater carbon assimilation was negated by higher levels of respiration. Spectral indices and leaf area were significantly different by marsh vegetation zone, suggesting that alterations in species composition and plant productivity can have important implications for carbon sequestration. While limited to 1 year, this study establishes a foundation by which to evaluate future research conducted over greater temporal and spatial scales, thereby enhancing our understanding of marsh physiological activity.     

Invasive lionfish detected in estuaries in the northern Gulf of Mexico using environmental DNA

Environmental Biology of Fishes - Invasive lionfish are considered to be one of the worst marine invaders primarily due to their threat as predators to native species. The distribution of lionfish...