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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]

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]

South Texas has a semi-arid climate with a large interannual variability of freshwater inflows. This study sought to define how changes in freshwater inflow affect the composition, quantity and quality of suspended particulate organic matter (SPOM) in a South Texas estuary: the Mission-Aransas estuary. The study was implemented 1.5 months after a large rain event in September 2010 and continued for 10 months of drought conditions. The composition of SPOM originating from rivers, the Gulf of Mexico and the estuary were determined using stable isotopes (δ 13 C, δ 15 N and δ 34 S). The quantity and quality of SPOM were assessed using organic carbon content, chlorophyll a concentrations and C/chl a ratios. Our results demonstrated that autochthonous phytoplankton was the dominant component of SPOM in the Mission-Aransas estuary during droughts. Benthic organic matter from local primary producers (i.e., seagrass, salt marsh plants, benthic microalgae) did not influence SPOM composition, either as fresh material or as detritus. A comparison with a positive estuary (i.e., Sabine-Neches estuary, TX) indicates that decreases in freshwater inflow may lead to decreases of terrestrial organic matter inputs and to increase the ratio of autochtonous phytoplanktonic material in SPOM. [ABSTRACT FROM AUTHOR]

Ecological restoration has become a widely recognized tool to ameliorate the effects of habitat loss. Half Moon Reef, once a highly-productive 2 km2 Crassostrea virginica oyster reef in Matagorda Bay, Texas, was harvested to depletion in the early 20th century. In 2014, a 0.23 km2 reef complex was created using limestone and concrete substrates to restore oyster populations—one of the largest contiguous oyster reef restoration efforts in the U.S. In the three years post-construction, two large freshwater inflow events provided a unique opportunity to determine the effects of prolonged salinity reductions (<10) on oyster reef faunal community composition and organic matter quality. Oyster size generally increased over the 3-year study period, enhancing habitat provision for reef fauna. Reef-resident and reef-associated species metrics (abundance, biomass, diversity, and species richness) were positively correlated with salinity. Following a large salinity reduction (from ∼26 to ∼9) one year post-construction, the reef-resident faunal community shifted from dominance by small gastropods to larger and more resilient crustaceans. A second, lower magnitude salinity reduction two years post-construction did not elicit the same biotic response. Reef-associated fauna showed no patterns related to distance from the reef (13 m vs. 150 m), indicating limited influence of the restored oyster reef on fauna outside of the physical reef structure. Salinity decreases were associated with 13C-depletion of suspended particulate organic matter, whereas no change in isotopic composition was observed for surface sediment organic matter. Carbon/chlorophyll a and carbon/nitrogen ratios of suspended particulate organic matter indicate the quality of organic matter was higher following low salinity events, likely due to increased autochthonous production facilitated by pulses of freshwater inflow. Oysters assimilated nearly equal proportions of surface sediment organic matter and suspended particulate organic matter. It is important to understand the effects of salinity variability for the effective management of coastal restoration projects because freshwater inflow has a major influence on coastal ecosystems. Image 1 • Freshwater inflow events led to prolonged low salinities on a restored oyster reef. • Macrofaunal abundance, biomass, and diversity were strongly correlated with salinity. • Adult oysters may promote faunal resilience to salinity variability. • Suspended particulate organic matter was 13C-depleted following low salinity events. • Quality of organic matter increased following low salinity events. [ABSTRACT FROM AUTHOR]

Salinity variability can act as a disturbance to communities in estuarine systems. Climate models predict changes in precipitation patterns will increase future hydrological variability, particularly in the southwestern United States. This study used infaunal community characterization, stomach content, and stable isotope analyses to evaluate the functioning of an estuarine food web over a range of wet and dry conditions. Baffin Bay is a predominantly hypersaline system in the semi-arid region of South Texas, USA supporting large populations of Pogonias cromis , black drum, a commercially important benthic predator. Salinity was the best predictor of changes in benthic macrofauna biomass, abundance, and diversity in Baffin Bay. Isotopic analyses of muscle tissues indicate that black drum use resources, particularly deposit-feeding benthic macrofauna, from both Baffin Bay and an adjacent system under normal estuarine salinity (≤35) conditions, but are more constrained to Baffin Bay under hypersaline (>35) conditions. This spatial restriction may be due to the energetic cost of osmotic regulation in hypersaline conditions, which can limit movement of euryhaline fish. Understanding the impacts of salinity change on benthic prey availability and trophic interaction dynamics is critical to determining ecosystem-scale effects of salinity variability. Image 1 • High salinity leads to low benthic prey availability in the Baffin Bay complex. • Deposit feeders compose the majority of Baffin Bay complex benthic predator diet. • Lower salinity conditions favor fish migration for feeding purposes. [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.