Search

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.

International audience

Assessments based on monetary valuation of ecosystem services have been increasingly used as a tool to highlight the connection between ecosystems and society. The dissemination of this approach is leading to difficulties and ambiguities related to the use of such assessments in the socio-political realm. Such limits can be stressed using the case study of intertidal bare mudflats. These coastal habitats indeed provide many ecological functions—several being related to the high production of benthic microalgae—but also remain poorly known for some other aspects. The major users of these habitats (i.e. oyster farmers) are still unaware about the trophic role of benthic microalgae, limiting contingent valuation survey methods. Moreover, economic valuation cannot take into account the potentials of mudflats (i.e. undescribed functions) like positive feedbacks related to shellfish farming and provision of bioactive compounds. The lack of physical boundaries in marine systems also strongly reduces the effectiveness of assessments. Lastly, there are concerns that monetary valuation can lead to a commodification of the nature or to the economization of the environment (e.g. appropriation of the environment by users, creation of artificial thresholds). The evaluation of the functions of a socio-ecosystem should not only be restricted to a monetary assessment of its ecosystem services, as this framework may be more reductive than integrative. Some other descriptors—not based on currencies—should be used for ecosystem description.

Oyster reef restoration has become a principal strategy for ameliorating the loss of natural Crassostrea virginica populations and increasing habitat provision. In 2014, a large‐scale, high‐relief, 23‐ha subtidal C. virginica reef was restored at the historically productive Half Moon Reef in Matagorda Bay, TX, using concrete and limestone substrates. Encrusting and motile fauna were sampled seasonally until 17 months postrestoration at the restored reef and at adjacent unrestored sites. Restored oysters developed rapidly and were most abundant 3 months postrestoration, with subsequent declines possibly due to interacting effects of larval settlement success on new substrate versus post‐settlement mortality due to competitors and predators. Oyster densities were 2× higher than in a restored oyster population in Chesapeake Bay that was reported to be the largest reestablished metapopulation of native oysters in the world. Resident fauna on the restored reef were 62% more diverse, had 433% greater biomass, and comprised a distinct faunal community compared to unrestored sites. The presence of three‐dimensional habitat was the most important factor determining resident faunal community composition, indicating that substrate limitation is a major hindrance for oyster reef community success in Texas and other parts of the Gulf of Mexico. There were only minor differences in density, biomass, and diversity of associated fauna located adjacent (13 m) versus distant (150 m) to the restored reef. The two substrate types compared had little influence on oyster recruitment or faunal habitat provision. Results support the use of reef restoration as a productive means to rebuild habitat and facilitate faunal enhancement.

Oyster reefs are important foundational habitats and provide many ecosystem services. A century of habitat degradation has resulted in substantial reductions in the extent and quality of oyster reefs in many estuaries, thus spurring restoration efforts. In this study, a 1.5 ha oyster reef complex was constructed in Copano Bay, Texas to restore habitat for oysters and associated fauna. Oysters and resident and transient fishes and crustaceans were monitored at the restored reef as well as at nearby natural oyster reef and unrestored bottom (i.e., dense mud with shell hash) habitats for two years following reef construction. The restored reef had substantial oyster recruitment and growth, with oyster abundance and size comparable to nearby habitats within the first year. Resident and transient fauna communities recruited to the restored reef within six months post-construction, and abundance and diversity were comparable to nearby habitats. Significant changes observed in oyster densities between the first and second year post-restoration demonstrate the importance of monitoring over multiple years to capture multiple recruitment cycles and growth to market size. Nekton densities did not change significantly after the first year, but changes in community assemblages were observed through the end of the study. The high densities of oysters and resident nekton relative to other studies indicate that this restoration project was successful in restoring suitable habitat. The design of the reef complex, consisting of relatively high-relief reef mounds and deeper corridors, likely contributed to the relatively high oyster and nekton densities observed in this study. Overall, the restored reef in this study showed tremendous near-term success in providing important ecological functions associated with habitat provision and oyster production.

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.

Recently, greater interest in the resilience of coastal habitat ecosystem services in the northern Gulf of Mexico has emerged due in part to an expansion of mangroves into areas previously dominated by salt marshes. To operationalize coastal wetland ecosystem services for decision-making, there is a need to clarify how salt marshes and mangroves function in this region. The goal of this research is to operationalize blue carbon (carbon stored in coastal habitats) within the Mission-Aransas National Estuarine Research Reserve, TX by documenting what we know about blue carbon within the study area, identifying data gaps and future research needs, and using available knowledge to inform management and decision-making within the Reserve. Our research shows that there is a lack of data within the Reserve on mangrove aboveground biomass, belowground biomass and soil carbon and on salt marsh soil carbon. There is also a dearth of information on wetland carbon sequestration and emission rates within the Reserve, making it challenging to inform management and develop a market for blue carbon.

Recent research revealing the extent of marine habitat degradation has ignited a surge of restoration efforts globally. Restoration of estuarine habitats became a priority in the United States with the Estuary Restoration Act (ERA) of 2000. In the present study, a synthesis of data from the National Estuaries Restoration Inventory (NERI), developed in response to ERA requirements to track and disseminate project data, was conducted in order to analyze U.S. oyster reef restoration efforts. From 2000–2011, more than $45 million was invested in 187 projects to restore over 150 ha of oyster reef habitat, with projects most heavily concentrated in the Chesapeake Bay area and Florida Gulf coast. Trends over time indicate that projects are being implemented at larger scales, increasing from an average of less than 0.4 ha in 2000 to over 1 ha on average in 2011. Costs per unit decreased from an average of more than $2.1 million per ha in 2000 to just over $500,000 per ha in 2011. However, our analysis confirms one major problem hindering the field of restoration ecology: a lack of monitoring data or project-specific assessments of success. Habitat restoration has become an increasingly common effort in the policy sector, and gaps identified through this analysis can help inform future policy making and implementation. Better facilitation of data dissemination and further research on economies of scale in restoration projects are two key areas for improvement. As the field of restoration ecology continues to grow, it is critical that both new and current restoration practitioners, scientists, and decision-makers are able to learn from past projects and apply that collective knowledge to future restoration efforts.

Understanding the effects of freshwater inflow on estuarine fish habitat use is critical to the sustainable management of many coastal fisheries. The Baffin Bay Complex (BBC) of south Texas is typically a reverse estuary (i.e., salinity increases upstream) that has supported many recreational and commercial fisheries. In 2012, a large proportion of black drum (Pogonias cromis) landed by fishers were emaciated, leading to concerns about the health of this estuary. In response to this event and lacking data on black drum spatial dynamics, a 2-year acoustic telemetry study was implemented to monitor individual-based movement and seasonal distribution patterns. Coupled with simultaneous water quality monitoring, the relationship between environmental variables and fish movement was assessed under reverse and “classical” estuary conditions. Acoustic monitoring data suggested that the BBC represents an important habitat for black drum; individuals exhibited site fidelity to the system and were present for much of the year. However, under reverse estuary conditions, fish summertime distribution was constrained to the interior of the BBC, where food resources are limited (based on recent benthic sampling), with little evidence of movement across the system. Out of eight environmental variables used to model fish movement using multiple linear regression, the only significant variable was salinity, which exhibited a negative relationship with movement rate. These findings suggest that prolonged periods of hypersalinity, which are detrimental to other euryhaline species due to increased osmoregulatory costs, reduce black drum distribution patterns and can limit the species’ access to benthic habitats supporting abundant prey resources.

Improved waste management at McMurdo Station, Antarctica beginning in the 1980s has been followed by decreases in polycyclic aromatic hydrocarbon (PAH) and metal contamination in the adjacent marine sediments. However, determining the effect of the decreased contamination on marine ecological indicators (macrobenthic fauna) is confounded by concurrent changes in climate cycles and other physical forces. Between 2000 and 2013, there was a decrease in concentrations of some contaminants including mercury, copper, organochlorines, and PAHs in marine sediments adjacent to McMurdo Station. PAH concentrations in Winter Quarters Bay decreased an order of magnitude from 2000/2003 to 2012/2013 and were within an order of magnitude of reference area concentrations by 2013. Macrobenthic communities did not indicate any sign of recovery and have not become more similar to reference communities over this same period of time. Temporal changes in macrobenthic community composition during the study period had higher correlations with climatic and sea ice dynamics than with changes in contaminant concentrations. The Interdecadal Pacific Oscillation climatic index had the highest correlation with macrobenthic community composition. The Antarctic Oscillation climatic index, maximum ice extent and other natural environmental factors also appear to influence macrobenthic community composition. Despite large improvements in environmental management at McMurdo Station, continuing environmental vigilance is necessary before any noticeable improvement in ecological systems is likely to occur. The effects of climate must be considered when determining temporal changes in anthropogenic effects in Antarctica. Maintaining long-term monitoring of both contaminants and ecological indicators is important for determining the localized and global influences of humans on Antarctica, which will have implications for the whole planet.

More than four decades of alkalinity and pH data (late 1960s to 2010) from coastal bays along the northwestern Gulf of Mexico were analyzed for temporal changes across a climatic gradient of decreasing rainfall and freshwater inflow, from northeast to southwest. The majority (16 out of 27) of these bays (including coastal waters) showed a long-term reduction in alkalinity at a rate of 3.0-21.6 μM yr(-1). Twenty-two bays exhibited pH decreases at a rate of 0.0014-0.0180 yr(-1). In contrast, a northernmost coastal bay exhibited increases in both alkalinity and pH. Overall, the two rates showed a significant positive correlation, indicating that most of these bays, especially those at lower latitudes, have been experiencing long-term acidification. The observed alkalinity decrease may be caused by reduced riverine alkalinity export, a result of precipitation decline under drought conditions, and freshwater diversion for human consumption, as well as calcification in these bays. A decrease in alkalinity inventory and accompanying acidification may have negative impacts on shellfish production in these waters. In addition, subsequent reduction in alkalinity export from these bays to the adjacent coastal ocean may also decrease the buffer capacity of the latter against future acidification.

Crassostrea virginica (the Eastern or American oyster) bioaccumulates pollutants from the water column, and therefore, its tissues can be used as bioindicators of past and present estuarine health. In this pilot project, we decided to investigate whether its tissues would be a suitable medium for toxicity testing using tissues from a variety of southern Texas locations of known and suspected anthropogenically impacted and unimpacted areas. We also conducted toxicity tests on sediments adjacent to oyster reefs using standard protocols for sediment toxicity. We tested the toxicity of tissues and sediments on the luminescent bacteria Vibrio fischeri, whose bioassays are commonly referred to by the trade name Microtox®. Microtox tests are quick, relatively inexpensive and sensitive to a range of contaminants. Evidence from this preliminary study suggests that conducting toxicity tests on oyster tissues may predict localized contamination better than when conducting toxicity tests on subtidal sediment. The refinement of these methods to use oyster tissues to detect contamination may be especially useful for environmental impact studies and/or studies where rapid and inexpensive information is needed.

Characterizing density patterns of fish and crustaceans across estuarine habitat types can provide useful information regarding their relative value. The oyster reef complex within Sabine Lake Estuary is the largest known in the United States with no record of commercial harvest, and it presents a unique opportunity to understand the habitat value of an unfished reef system in comparison with adjacent estuarine habitats. High abundances of relatively large oysters with complex formations were observed throughout the 2-y study period. Average densities of fish and crustaceans were 6 times greater at the marsh edge than the nonvegetated shallow habitats, and 40 times greater than both the oyster reef and nonvegetated deep habitats. Low faunal densities observed in the oyster reef habitat may be the result of spatial configuration and connectivity to surrounding habitats, collection limitation resulting from its large vertical relief (>1 m) and complex 3-dimensional structure, or habitat selection resulting from water depth. Because the majority of crustaceans and resident and transient fish were observed within the marsh edge and nonvegetated shallow habitats, it is difficult to determine whether oyster reefs within Sabine Lake Estuary provide essential habitats for these species. Although low densities of organisms were observed in the oyster reef habitat, multivariate analysis indicates that the unfished reef supports a unique community of fish and crustaceans. Results provide a valuable baseline for future conservation, restoration, and management actions as we seek to understand more completely and to protect important estuarine habitat types.

The aim of this study was to compare the impact of different freshwater inflow volumes on benthic communities and water column dynamics in different estuary classes. Benthic and water column spatial dynamics were contrasted in lagoons (with no direct inflow sources), tidal rivers that empty directly into the Gulf of Mexico, and bar-built bay systems (with direct inflow sources) along the Texas (USA) coast to determine the role of inflow in regulating ecosystem structure and function. Chlorophyll-a and nutrient concentrations were inversely correlated with salinity and were thus highest in the river systems, but lowest in lagoons. All Texas estuary types studied have conservative mixing for silicate and ammonium but are sinks for nitrite plus nitrate and phosphate. Macrobenthic production (abundance and biomass) was lowest in rivers and highest in lagoons. Diversity was low in estuaries with salinities between 1 and 17, but increased with salinities of up to 30, before decreasing in hypersaline conditions. Macrofaunal community structure divided the estuaries into two groups. The first group represented polyhaline communities and contained lagoons (East Matagorda, Matagorda, Christmas, and South Bays). The second group represented oligo-mesohaline community characteristics and contained the secondary bays (Lavaca Bay and Cedar Lakes) and rivers (San Bernard River, Brazos River, and the Rio Grande). The implications of these results for managing freshwater flows is that altered hydrology can change the character of estuarine systems regardless of their classification as bays, lagoons, or tidal rivers.

Freshwater inflow is an important source of physical variability in estuaries. Effects of water flow are dynamic, and it is impossible to sample all conditions as they vary over space and time. Benthos, however, are fixed in place, continuously sample the overlying water conditions, and demonstrate a variety of consistent responses to multiple sources of stress. Benthic indices of biotic integrity (BIBIs) have been particularly useful for assessing aquatic systems. However most indices have focused on assessing effects related to changes in water quality rather than water quantity. This study develops a Freshwater Inflow Biotic Index (FIBI) to determine how changes in freshwater inflow affect benthic populations, which in turn reflect the ecological condition of an estuary. Based on benthic succession theory and long-term data, 12 biotic metrics were chosen that characterized benthic community structure in response to inflow regimes. The metrics were ranked and then reduced to one variable using principal...