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Although position within the estuarine landscape is known to influence structural characteristics and ecological functioning of many habitats, the influence of position on subtidal oyster reef characteristics and functioning is relatively understudied. This study assessed habitat provision by oysters and benthic macrofauna on subtidal bar and patch oyster reefs within the northwestern Gulf of Mexico estuary. Bar reefs had greater and more variable oyster density, biomass, and volume, as well as dead shell material, compared to patch reefs. Benthic macrofaunal community composition differed between reef types, with bar reefs hosting 11× and 30× higher biomass of Porcellanidae and Ampithoidae crustaceans, and patch reefs supporting 34× and 47× higher biomass of Eunicidae annelids and Leptocheliidae crustaceans. The environmental variables most highly correlated with macrofaunal communities on both bar and patch reefs were sediment chlorophyll-a, volume of dead oyster shells, and depth. Despite differences in structural characteristics and position within the estuarine landscape, subtidal oyster reefs are often managed as a single habitat type. Our findings emphasize the importance of considering location in oyster reef conservation and restoration efforts to better predict and optimize faunal provision outcomes. [ABSTRACT FROM AUTHOR]

Low inflows cause predominantly hypersaline conditions in Baffin Bay, TX (USA), which are inhospitable for oysters, the dominant reef-builder in other northern Gulf of Mexico estuaries. Instead, extensive biogenic reefs contain dense aggregations of the ubiquitous tube-building serpulid worm, Hydroides dianthus. The distribution and size of these reefs have declined over the last several decades. Although serpulid reef habitats have increased in conservation importance, there is a need for ecological knowledge to inform resource management and habitat restoration planning. This study examined spatial and temporal recruitment patterns of serpulid worms and other encrusting species over an 18-month-long period, using recruitment tiles, and live serpulid reef as a reference. Recruitment of H. dianthus occurs year-round; however, the greatest recruitment occurs between September and December. No consistent differences in serpulid recruitment were detected among locations within Baffin Bay, which could be because salinity and temperature were similar among locations, and/or because sampling replication was low. H. dianthus cover was greater on the lower surface of horizontally oriented recruitment tiles (28% cover), whereas Amphibalanus eburneus (barnacle) cover dominated the upper surface of tiles (34% cover). Furthermore, there is no evidence that predation by megafauna (> 1 cm) is hindering serpulid recruitment. There is sufficient larval supply of H. dianthus to suggest that the restoration of serpulid reefs can be successful by providing additional substrate with appropriate microhabitat complexity. Study findings can be used to support planning and successful implementation of serpulid reef restoration. [ABSTRACT FROM AUTHOR]

Biogenic reefs provide important ecological functions and services to coastal and marine environments, supplying high levels of biodiversity, providing refuge and foraging habitat, and supporting fisheries. Serpulid reefs are a relatively uncommon habitat in coastal ecosystems globally that provide habitat for a diverse community of organisms, and have become a target for conservation and management efforts due to habitat degradation and loss. Baffin Bay, Texas, USA, is known for exceptionally productive commercial and recreational fisheries that are thought to be supported by Serpulid reef benthic macrofauna, particularly during regular periods of hypersalinity. This study compared the functioning of Serpulid reef habitats with nearby soft sediment areas using quantitative faunal and food web analyses. Serpulid reefs support a unique benthic macrofaunal community with 191 times greater abundance, 97 times greater biomass, and twice the number of species than in soft sediments. In contrast to soft-sediment macrofauna, Serpulid reef macrofaunal abundance and biomass were not correlated with any measured water quality variables. Isotope compositions of both suspension and deposit-feeding macrofauna from both habitats (i.e., Serpulid reefs and soft sediments) were close to organic matter from the sediment, demonstrating connectivity and the importance of primary production in the sediment to both habitat types. Abundant macrofauna inhabiting Serpulid reefs likely serve as an important food source for sport fish and other higher trophic-level fauna, particularly in hypersaline periods when soft-sediment macrobenthic food resources are scarce. Given the substantial loss of Baffin Bay's Serpulid reef habitat compared to historic levels, conservation actions may be warranted to protect and restore Serpulid habitat and food resources. The results of this study can be used to increase the success of such efforts. [ABSTRACT FROM AUTHOR]

Localized contamination from research-related activities and its effects on macrofauna communities in the marine environment were investigated at Palmer Station, a medium-sized Antarctic research station. Relatively low concentrations of polycyclic aromatic hydrocarbons (PAHs; 32–302 ng g-1) and total petroleum hydrocarbons (TPHs; 0.9–8.9 μg g-1) were detected in sediments adjacent to the sewage outfall and pier, where most human activities were expected to have occurred, and at even lower concentrations at two seemingly reference areas (PAHs 6–30 ng g-1, TPHs 0.03–5.1 μg g-1). Elevated concentrations of PAHs in one sample taken in one reference area (816 ng g-1) and polychlorinated biphenyls (353 ng g-1) and dichloro-diphenyl-trichloroethane (3.2 and 25.3 ng g-1) in two samples taken adjacent to the sewage outfall indicate spatial heterogeneity of localized sediment contamination. Limpet (Nacella concinna) tissues collected adjacent to Palmer Station had high concentrations of PAHs, copper, lead, zinc and several other metals relative to outlying islands. Sediment and limpet tissue contaminant concentrations have decreased since the early 1990s following the Bahía Paraíso spill. Natural sediment characteristics affected macrofaunal community composition more than contamination adjacent to Palmer Station, presumably because of the low overall contamination levels. [ABSTRACT FROM AUTHOR]

Estuaries exist across a large climatic gradient in the northwestern Gulf of Mexico, capturing a range of hydrologic conditions and estuarine functioning. We examined freshwater inflow, salinity, and stable isotope compositions (δ13C, δ15N) of oysters, suspended particulate organic matter (SPOM), and surface sediment organic matter (SSOM) from five estuaries across the hydrologic gradient. All five estuaries experienced large decreases in freshwater inflow over the last 40 yr, with three estuaries being subject to freshwater inflow reductions of more than 85%. Generally, these freshwater inflow decreases were associated with estuarine salinity increases. Across the spatial gradient, average salinity generally increased from northeast to southwest estuaries. SPOM in the northeastern, lower salinity estuaries generally contained more continental organic matter and was of higher quality (i.e., lower C/chlorophyll a ratio), as compared to southwestern, higher salinity estuaries. Similarly, both SSOM and oyster δ13C values were positively correlated with salinity, further highlighting that food webs in lower salinity estuaries are more greatly influenced by continental organic matter than those in higher salinity estuaries. A decrease in the connectivity between continental and coastal habitats may have broad consequences for flows of organic matter, and estuarine function and health. Conducting studies across large‐scale hydrologic gradients can provide a useful approach to informing and predicting shifts in estuarine functioning. [ABSTRACT FROM AUTHOR]

Human activities and regional-scale climate variability drive changes in the ecology of coastal and marine ecosystems. Ecological restoration has emerged as a best-management practice to combat habitat degradation and restore lost ecological functions. However, relatively short project monitoring timeframes have limited our understanding of the effects of interannual climate cycles on water quality and restoration dynamics. We collected measurements on a 23-ha oyster reef constructed in the Gulf of Mexico to determine the relationship between El Niño Southern Oscillation (ENSO)-driven climate variability and local salinity patterns, and to evaluate the effects of this climate variability and salinity on oyster population dynamics and faunal community composition over a medium-term (five-year) timeframe. The role of ENSO-driven climate variability on local salinity patterns (primarily from changes in precipitation and evaporation) and faunal dynamics was investigated using the Oceanic Niño Index (ONI). Salinity was negatively correlated with ONI with an approximately 4-month lag. Higher ONI values (El Niño periods) were followed by reductions in salinity, increases in oyster recruitment and density, and reductions in resident motile fauna density and species richness. Lower ONI values (La Niña periods) had higher and less variable salinities, and higher areal coverage of restoration substrates by large oysters. ENSO-driven salinity reductions in the second year after reef construction coincided with a shift in resident motile faunal community composition that was maintained despite a second strong salinity reduction in year 5. Our results indicate that it is important to expand the typical monitoring timeframes to at least five years so that resource managers and restoration practitioners can better understand how both short-term environmental variability and longer-term climate cycles can affect the outcomes of restoration actions. [ABSTRACT FROM AUTHOR]

The eastern oyster Crassostrea virginica is a commercially and ecologically important organism found throughout the western North Atlantic and Gulf of Mexico. Morphological differences in shell shape of eastern oysters are known to arise from environmental, genetic, and husbandry‐related factors. Here, live eastern oysters were collected from 17 sites along the U.S. Gulf of Mexico coast from Texas to Florida to examine morphological differences among geographic samples. Six morphological metrics were recorded for each individual, and four different composite ratios commonly used to describe oyster shape (fan, cup, volume ratio, and weight ratio) were calculated. Principal component analysis was used to demonstrate geographic differences in ordinated shape ratios, correlating roughly with eastern (Florida), northern (Alabama, Louisiana, north Texas), and western (south Texas) samples. In Texas, differences in shape were correlated with previously described genetic population boundaries, indicating that populations north versus south of Aransas Bay had different overall shell shapes. On a broader scale, shell shape variation correlated roughly with previously described genetic population boundaries throughout the Gulf of Mexico as well as tide depth (intertidal versus subtidal reefs). Among the various factors that might act as drivers of shell shape, individual variation is important, but population structure and tide height are also significant predictor variables of shape in this species. [ABSTRACT FROM AUTHOR]

The Baffin Bay estuary is a hypersaline system in the Gulf of Mexico that supports an important recreational and commercial fishery for black drum Pogonias cromis, a benthic predator. Seasonal measurements of water quality variables, benthic macrofauna densities and biomass, and determination of P. cromis food sources using stomach‐content and stable‐isotope analyses were carried out to determine how P. cromis food sources change with water quality and how this may affect P. cromis diet. Gut‐content analysis indicated P. cromis selectively consumed bivalves Mulinia lateralis and Anomalocardia auberiana. Isotope compositions demonstrated that P. cromis relied on these benthic food resources produced in the Baffin Bay estuary year‐round. Biomass and densities of these bivalves were influenced by changes in water quality variables, particularly salinity and dissolved oxygen. Thus, this paper demonstrates the relationship between water quality variables, benthic macrofauna, and their use as food resources by a carnivorous fish species, and emphasizes the need for integrated assessments when studying the effects of water quality on ecosystem function. Holistic approaches such as these can provide important information for management and conservation of fishery resources and can improve predictions of ecosystem response to climate variability. [ABSTRACT FROM AUTHOR]

Habitat reconstruction is commonly employed to restore degraded estuarine habitats and lost ecological functions. In this study, we use a combination of stable isotope analyses and macrofauna community analysis to compare the ecological structure and function between a recently constructed Spartina alterniflora salt marsh and a natural reference habitat over a 2-year period. The restored marsh was successful in providing habitat for economically and ecologically important macrofauna taxa; supporting similar or greater density, biomass, and species richness to the natural reference during all but one sampling period. Stable isotope analyses revealed that communities from the natural and the restored marshes relied on a similar diversity of food resources and that decapods had similar trophic levels. However, some generalist consumers (Palaemonetes spp. and Penaeus aztecus) were more 13C-enriched in the natural marsh, indicating a greater use of macrophyte derived organic matter relative to restored marsh counterparts. This difference was attributed to the higher quantities of macrophyte detritus and organic carbon in natural marsh sediments. Reduced marsh flooding frequency was associated with a reduction in macrofaunal biomass and decapod trophic levels. The restored marsh edge occurred at lower elevations than natural marsh edge, apparently due to reduced fetch and wind-wave exposure provided by the protective berm structures. The lower elevation of the restored marsh edge mitigated negative impacts in sampling periods with low tidal elevations that affected the natural marsh. The results of this study highlight the importance of considering sediment characteristics and elevation in salt marsh constructions. [ABSTRACT FROM AUTHOR]

A limited supply of oyster shell for restoration practices has prompted investigations of alternative substrates used in construction of artificial oyster reefs. The success of oyster reef restoration projects is increasingly focused not only on oyster densities, but also on habitat provisioning for associated fauna. A subtidal oyster reef complex (0.24 km2) was restored in the Mission-Aransas Estuary, Texas, U.S.A., in July 2013 using replicated mounds of concrete, limestone, river rock, and oyster shell substrates. Oyster and reef-associated fauna characteristics were quantified quarterly for 15 months, using sampling trays that were deployed 3 months after construction. The highest densities of oyster spat occurred 9 months after tray deployment (July 2014, 1,264/m2), whereas juvenile oyster densities increased throughout the study period to 283/m2. Concrete (1,022/m2) and limestone (939/m2) supported the highest number of oysters over all dates. Oyster shell (1,533/m2) and concrete (1,047/m2) substrates supported the highest densities of associated motile fauna. Faunal diversity (Hill's N1) did not vary by substrate material, but did show seasonal variation. A simple benefit-cost ratio was used to indicate the localized monetary value for each of the substrates. Oyster shell and concrete substrates returned the highest benefit-cost ratio for motile fauna, while concrete yielded the highest benefit-cost ratio for oyster abundance. Incorporating benefit-cost ratios in restoration planning will allow practitioners to better integrate substrate-specific ecological values with economic considerations and project goals to maximize return on restoration investments. [ABSTRACT FROM AUTHOR]

Eastern oysters ( Crassostrea virginica) in Gulf of Mexico estuaries create complex reefs and provide important habitat for fish and crustaceans. Oyster reefs have suffered historic losses due to overharvest, disease, and degraded water quality, and recent efforts have focused on restoring reefs to benefit nekton populations. Oyster shell is the preferred substrate for oyster reef restoration, but as a consequence of its limited supply, a variety of alternative substrates are being used. We used field experiments to quantify the effects of substrate type (concrete, porcelain, limestone, river rock, and oyster shell) on oyster recruitment, growth, and nekton habitat use in St. Charles Bay, TX. After 4 months, oyster spat recruitment density, nekton density and community structure were similar across substrate types-and analogous to those on natural reefs-but differed from samples collected on bare sediment. To determine refuge value of the alternative substrates, we tested mud crab (Panopeidae) prey mortality with and pinfish ( Lagodon rhomboides) or blue crab ( Callinectes sapidus) predators. Prey mortality was similar across substrate types for both predators, and was significantly lower than no substrate and bare sand controls. Alternative substrates can provide important structural materials to support the development of oyster populations and nekton assemblages, and may be used to promote sustainable management of oyster reef resources via restoration. [ABSTRACT FROM AUTHOR]

Suspension-feeding activities of oysters impart a potentially significant benefit to estuarine ecosystems via reduction of water column nutrients, plankton and seston biomass, and primary productivity which can have a significant impact on human well-being. This study considered nitrogen regulation by eastern oysters Crassostrea virginica in the Mission-Aransas Estuary, Texas, USA, as a function of denitrification, burial, and physical transport from the system via harvest. Oyster reefs were estimated to remove 502.5 kg N km−2 through denitrification of biodeposits and 251.3 kg N km−2 in burial of biodeposits to sediments. Nitrogen is also physically transported out of the estuary via harvest of oysters. Commercial harvest of oysters in the Mission-Aransas Estuary can remove approximately 21,665 kg N per year via physical transport from the system. We developed a transferable method to value the service of nitrogen regulation by oysters, where the potential cost equivalent value of nitrogen regulation is quantified via cost estimates for a constructed biological nutrient removal (BNR) supplement to a wastewater treatment plant. The potential annual engineered cost equivalent of the service of nitrogen regulation and removal provided by reefs in the Mission-Aransas Estuary is $293,993 yr−1. Monetizing ecosystem services can help increase awareness at the stakeholder level of the importance of oysters beyond commercial fishery values alone. [ABSTRACT FROM AUTHOR]