The Mississippi Sound is an intensely protected and studied ecosystem with extensive and unique onshore, offshore, and marsh habitats. The economy of several northern Gulf of Mexico states relies on the health and productivity of this estuarine basin, as the marshes that span from Louisiana to Alabama are historical hatcheries and nurseries as well as storm buffers and tourist industry hotspots. Global climate change threatens this ecosystem on the waterfront, with sea level rise (SLR) and irregular flooding causing decreases in marsh coverage as open water coverage increases and encroaches upon the shoreline. Marsh ecosystems survive SLR via vertical accretion through mineral deposits and organic matter accumulation; the rate of vertical accretion is strongly dependent on location, sediment deposition, yearly storm activity, and vegetation productivity.
Using linear mixed effects models or ordinary regression, we evaluated how belowground biomass from 0 to 30 cm depth in Hancock County, MS marshes (HC) and Grand Bay National Estuarine Research Reserve (GBNERR) responded to soil porewater salinity and elevation at mean high water datum (a proxy for inundation). The field sampling was conducted in summer 2020, summer 2021 (peak growth), and winter 2021 (die-off). The results show that belowground biomass was significantly affected by salinity, elevation, and their interaction in all three sampling seasons at GBNERR and two at HC. In summer 2020 at HC, only salinity significantly affected belowground biomass. As the relation between biomass and salinity is in quadratic functions, there existed an optimum salinity at which belowground biomass reached maximum.
 

Sea level rise is an escalating threat to saltmarsh ecosystems as increased inundation is a known stressor for marsh plants, with consequences of decreased biomass, lowered productivity, and plant death. Another potential stressor is elevated nitrogen, which has a controversial impact on belowground biomass, potentially affecting the stability of saltmarshes and is relevant due to additional nitrogen brought into coastal regions via freshwater diversions. Our objective is to examine the combined effects of inundation and nitrogen on common saltmarsh plants (Spartina alterniflora and Spartina patens). We set up two marsh organs with six rows and eight replicates in each row, one planted with Spartina alterniflora, the other with Spartina patens. We randomly selected four replicates in each row to add 25 g/m2 of nitrogen in the form of ammonium nitrate every two or three weeks in the growing season. With the same frequency, we collected morphological characteristics such as plant height, leaf count, and stem count to represent vegetation conditions in different dimensions. We developed multilevel Bayesian models to evaluate how inundation and nitrogen affected these characteristics. The results show plants with the nitrogen addition generally have higher productivity when compared to non-fertilized plants. Additionally, the different plant characteristics show various responses to inundation, with plant height being the lowest and leaf counts the highest in the intermediate inundation, indicating some tradeoff at horizontal and vertical directions. This work will facilitate more-informed restoration and conservation efforts in coastal wetlands while accounting for climate change and sea-level rise.

Freshwater runoff into tidal creeks has been shown to increase with coastal watershed development, leading to increased variability of salinity. To evaluate potential development effects, we examined 12 tidal creeks along the Alabama and west-Florida coast across an urban watershed gradient. Using field data and watershed models, we examined creek response to watershed development by measuring changes in salinity variation, gross primary production (GPP), ecosystem respiration (ER), and resident fish abundance, diet, and caloric density. As predicted, salinity in more developed tidal creeks was more variable and flashier (as measured using a modified Richard-Baker index) (p < 0.01, r‑2 = 0.39). Further, salinity flashiness was related to decreased creek GPP (p < 0.01, r2 = 0.44) and ER (p < 0.01, r2 = 0.31) (n=6). Through seasonal trapping of resident fish, we found that Fundulus grandis (Gulf killifish) was the most common species and its catch per unit effort decreased with salinity flashiness (p = 0.03, r2= 0.18) and modelled estimates of NO3- concentration (p = 0.05, r2 = 0.11)- both measures of watershed development. F. grandis diets were broad and dominated by fish but no relationship to watershed development was detected. Likewise, F. grandis caloric density was not related to development. As coastal urbanization continues in the region, research on the effects of runoff is still needed to improve management and protections designed to minimize urban effects.

Per- and poly- fluorinated chemicals (PFAS) are a class of man-made chemicals that are widespread and persistent in the environment, including Mobile Bay, AL. They have a high potential to bioaccumulate in many aquatic organisms. Oysters are chronically exposed to PFAS through filtering activities, which calls into question the health of wild and farmed populations. Depuration of contaminants has been shown to be efficient but energetically expensive in some bivalves, with previous studies primarily focusing on single compounds rather than mixtures. In this study we investigate whether oysters can efficiently depurate an ecologically relevant mixture of PFAS compounds and whether depuration is energetically expensive with potential negative effects on organismal health. Eastern oysters(Crassostrea virginica)were exposed to a mixture of PFAS (PFPeA, PFHxA, PFBS, PFOA, and PFOS) at an ecologically relevant cumulative concentration (< 2 ug/L) to estimate bioaccumulation during exposure and depuration after being transferred to clean water. Optical respirometry was used to assess energetic costs associated with exposure and subsequent depuration. Results show that at ecologically relevant concentrations, PFAS did bioaccumulate at low levels, but compounds were depurated below detection limits within 24 hours of being placed in clean water. We found no evidence for increased energetic costs related to exposure and/or depuration. It is unlikely that the mixtures of dominant PFAS compounds recently detected in and near Mobile Bay are negatively affecting the energetic health of oysters. Oysters appear to have the capacity to quickly and efficiently depurate ecologically relevant mixtures of PFAS when transferred to clean water.