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1. Tropical estuarine ecosystem change under the interacting influences of future climate and ecosystem restoration

   https://doi.org/10.1111/gcb.16868  

   Smith, Mason ; Chagaris, David ; Paperno, Richard ; Markwith, Scott ( July 2023 , Global Change Biology)

   One of the largest restoration programs in the world, the Comprehensive Everglades Restoration Plan (CERP) aims to restore freshwater inputs to Everglades wetlands and the Florida Bay estuary. This study predicted how the Florida Bay ecosystem may respond to hydrological restoration from CERP within the context of contemporary projected impacts of sea‐level rise (SLR) and increased future temperatures. A spatial–temporal dynamic model (Ecospace) was used to develop a spatiotemporal food web model incorporating environmental drivers of salinity, salinity variation, temperature, depth, distance to mangrove, and seagrass abundance and was used to predict responses of biomass, fisheries catch, and ecosystem resilience between current and future conditions. Changes in biomass between the current and future scenario suggest a suite of winners and losers, with many estuarine species increasing in both total biomass and spatial distribution. Notable biomass increases were predicted for important forage species, including bay anchovy (+32%), hardhead halfbeak (+19%), and pinfish (+31%), while decreases were predicted in mullet (−88%), clupeids (−55%), hardhead silverside (−15%), mojarras (−117%), and Portunid crabs (−16%). Increases in sportfish biomass included the angler‐preferred spotted seatrout (+9%), red drum (+10%), and gray snapper (+8%), while decreases included sheepshead (−40%), Atlantic tarpon (−73%), and common snook (−507%). Ecosystem resilience and fisheries catch of angler‐preferred species were predicted to improve in the future scenario in total, although a localized decline in resilience predicted for the Central Region may warrant further attention. Our results suggest the Florida Bay ecosystem is likely to achieve restoration benefits in spite of, and in some cases facilitated by, the projected future impacts from climate change due to the system's shallow depth and detrital dominance. The incorporation of climate impacts into long‐term restoration planning using ecosystem modeling in similar systems facing unknown futures of SLR, warming seas, and shifting species distributions is recommended.

    

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2. Florida mangrove saltmarsh reference surface soils

   https://doi.org/10.6073/pasta/0e08cbe07c84488cb7b9dd16669946d0  

   Lewis, David Bruce ( January 2021 , Environmental Data Initiative)

   Site description. This data package consists of data obtained from sampling surface soil (the 0-7.6 cm depth profile) in black mangrove (Avicennia germinans) dominated forest and black needlerush (Juncus roemerianus) saltmarsh along the Gulf of Mexico coastline in peninsular west-central Florida, USA. This location has a subtropical climate with mean daily temperatures ranging from 15.4 °C in January to 27.8 °C in August, and annual precipitation of 1336 mm. Precipitation falls as rain primarily between June and September. Tides are semi-diurnal, with 0.57 m median amplitudes during the year preceding sampling (U.S. NOAA National Ocean Service, Clearwater Beach, Florida, station 8726724). Sea-level rise is 4.0 ± 0.6 mm per year (1973-2020 trend, mean ± 95 % confidence interval, NOAA NOS Clearwater Beach station). The A. germinans mangrove zone is either adjacent to water or fringed on the seaward side by a narrow band of red mangrove (Rhizophora mangle). A near-monoculture of J. roemerianus is often adjacent to and immediately landward of the A. germinans zone. The transition from the mangrove to the J. roemerianus zone is variable in our study area. An abrupt edge between closed-canopy mangrove and J. roemerianus monoculture may extend for up to several hundred meters in some locations, while other stretches of ecotone present a gradual transition where smaller, widely spaced trees are interspersed into the herbaceous marsh. Juncus roemerianus then extends landward to a high marsh patchwork of succulent halophytes (including Salicornia bigellovi, Sesuvium sp., and Batis maritima), scattered dwarf mangrove, and salt pans, followed in turn by upland vegetation that includes Pinus sp. and Serenoa repens. Field design and sample collection. We established three study sites spaced at approximately 5 km intervals along the western coastline of the central Florida peninsula. The sites consisted of the Salt Springs (28.3298°, -82.7274°), Energy Marine Center (28.2903°, -82.7278°), and Green Key (28.2530°, -82.7496°) sites on the Gulf of Mexico coastline in Pasco County, Florida, USA. At each site, we established three plot pairs, each consisting of one saltmarsh plot and one mangrove plot. Plots were 50 m^2 in size. Plots pairs within a site were separated by 230-1070 m, and the mangrove and saltmarsh plots composing a pair were 70-170 m apart. All plot pairs consisted of directly adjacent patches of mangrove forest and J. roemerianus saltmarsh, with the mangrove forests exhibiting a closed canopy and a tree architecture (height 4-6 m, crown width 1.5-3 m). Mangrove plots were located at approximately the midpoint between the seaward edge (water-mangrove interface) and landward edge (mangrove-marsh interface) of the mangrove zone. Saltmarsh plots were located 20-25 m away from any mangrove trees and into the J. roemerianus zone (i.e., landward from the mangrove-marsh interface). Plot pairs were coarsely similar in geomorphic setting, as all were located on the Gulf of Mexico coastline, rather than within major sheltering formations like Tampa Bay, and all plot pairs fit the tide-dominated domain of the Woodroffe classification (Woodroffe, 2002, "Coasts: Form, Process and Evolution", Cambridge University Press), given their conspicuous semi-diurnal tides. There was nevertheless some geomorphic variation, as some plot pairs were directly open to the Gulf of Mexico while others sat behind keys and spits or along small tidal creeks. Our use of a plot-pair approach is intended to control for this geomorphic variation. Plot center elevations (cm above mean sea level, NAVD 88) were estimated by overlaying the plot locations determined with a global positioning system (Garmin GPS 60, Olathe, KS, USA) on a LiDAR-derived bare-earth digital elevation model (Dewberry, Inc., 2019). The digital elevation model had a vertical accuracy of ± 10 cm (95 % CI) and a horizontal accuracy of ± 116 cm (95 % CI). Soil samples were collected via coring at low tide in June 2011. From each plot, we collected a composite soil sample consisting of three discrete 5.1 cm diameter soil cores taken at equidistant points to 7.6 cm depth. Cores were taken by tapping a sleeve into the soil until its top was flush with the soil surface, sliding a hand under the core, and lifting it up. Cores were then capped and transferred on ice to our laboratory at the University of South Florida (Tampa, Florida, USA), where they were combined in plastic zipper bags, and homogenized by hand into plot-level composite samples on the day they were collected. A damp soil subsample was immediately taken from each composite sample to initiate 1 y incubations for determination of active C and N (see below). The remainder of each composite sample was then placed in a drying oven (60 °C) for 1 week with frequent mixing of the soil to prevent aggregation and liberate water. Organic wetland soils are sometimes dried at 70 °C, however high drying temperatures can volatilize non-water liquids and oxidize and decompose organic matter, so 50 °C is also a common drying temperature for organic soils (Gardner 1986, "Methods of Soil Analysis: Part 1", Soil Science Society of America); we accordingly chose 60 °C as a compromise between sufficient water removal and avoidance of non-water mass loss. Bulk density was determined as soil dry mass per core volume (adding back the dry mass equivalent of the damp subsample removed prior to drying). Dried subsamples were obtained for determination of soil organic matter (SOM), mineral texture composition, and extractable and total carbon (C) and nitrogen (N) within the following week. Sample analyses. A dried subsample was apportioned from each composite sample to determine SOM as mass loss on ignition at 550 °C for 4 h. After organic matter was removed from soil via ignition, mineral particle size composition was determined using a combination of wet sieving and density separation in 49 mM (3 %) sodium hexametaphosphate ((NaPO_3)_6) following procedures in Kettler et al. (2001, Soil Science Society of America Journal 65, 849-852). The percentage of dry soil mass composed of silt and clay particles (hereafter, fines) was calculated as the mass lost from dispersed mineral soil after sieving (0.053 mm mesh sieve). Fines could have been slightly underestimated if any clay particles were burned off during the preceding ignition of soil. An additional subsample was taken from each composite sample to determine extractable N and organic C concentrations via 0.5 M potassium sulfate (K_2SO_4) extractions. We combined soil and extractant (ratio of 1 g dry soil:5 mL extractant) in plastic bottles, reciprocally shook the slurry for 1 h at 120 rpm, and then gravity filtered it through Fisher G6 (1.6 μm pore size) glass fiber filters, followed by colorimetric detection of nitrite (NO_2^-) + nitrate (NO_3^-) and ammonium (NH_4^+) in the filtrate (Hood Nowotny et al., 2010,Soil Science Society of America Journal 74, 1018-1027) using a microplate spectrophotometer (Biotek Epoch, Winooski, VT, USA). Filtrate was also analyzed for dissolved organic C (referred to hereafter as extractable organic C) and total dissolved N via combustion and oxidation followed by detection of the evolved CO_2 and N oxide gases on a Formacs HT TOC/TN analyzer (Skalar, Breda, The Netherlands). Extractable organic N was then computed as total dissolved N in filtrate minus extractable mineral N (itself the sum of extractable NH_4-N and NO_2-N + NO_3-N). We determined soil total C and N from dried, milled subsamples subjected to elemental analysis (ECS 4010, Costech, Inc., Valencia, CA, USA) at the University of South Florida Stable Isotope Laboratory. Median concentration of inorganic C in unvegetated surface soil at our sites is 0.5 % of soil mass (Anderson, 2019, Univ. of South Florida M.S. thesis via methods in Wang et al., 2011, Environmental Monitoring and Assessment 174, 241-257). Inorganic C concentrations are likely even lower in our samples from under vegetation, where organic matter would dilute the contribution of inorganic C to soil mass. Nevertheless, the presence of a small inorganic C pool in our soils may be counted in the total C values we report. Extractable organic C is necessarily of organic C origin given the method (sparging with HCl) used in detection. Active C and N represent the fractions of organic C and N that are mineralizable by soil microorganisms under aerobic conditions in long-term soil incubations. To quantify active C and N, 60 g of field-moist soil were apportioned from each composite sample, placed in a filtration apparatus, and incubated in the dark at 25 °C and field capacity moisture for 365 d (as in Lewis et al., 2014, Ecosphere 5, art59). Moisture levels were maintained by frequently weighing incubated soil and wetting them up to target mass. Daily CO_2 flux was quantified on 29 occasions at 0.5-3 week intervals during the incubation period (with shorter intervals earlier in the incubation), and these per day flux rates were integrated over the 365 d period to compute an estimate of active C. Observations of per day flux were made by sealing samples overnight in airtight chambers fitted with septa and quantifying headspace CO_2 accumulation by injecting headspace samples (obtained through the septa via needle and syringe) into an infrared gas analyzer (PP Systems EGM 4, Amesbury, MA, USA). To estimate active N, each incubated sample was leached with a C and N free, 35 psu solution containing micronutrients (Nadelhoffer, 1990, Soil Science Society of America Journal 54, 411-415) on 19 occasions at increasing 1-6 week intervals during the 365 d incubation, and then extracted in 0.5 M K_2SO_4 at the end of the incubation in order to remove any residual mineral N. Active N was then quantified as the total mass of mineral N leached and extracted. Mineral N in leached and extracted solutions was detected as NH_4-N and NO_2-N + NO_3-N via colorimetry as above. This incubation technique precludes new C and N inputs and persistently leaches mineral N, forcing microorganisms to meet demand by mineralizing existing pools, and thereby directly assays the potential activity of soil organic C and N pools present at the time of soil sampling. Because this analysis commences with disrupting soil physical structure, it is biased toward higher estimates of active fractions. Calculations. Non-mobile C and N fractions were computed as total C and N concentrations minus the extractable and active fractions of each element. This data package reports surface-soil constituents (moisture, fines, SOM, and C and N pools and fractions) in both gravimetric units (mass constituent / mass soil) and areal units (mass constituent / soil surface area integrated through 7.6 cm soil depth, the depth of sampling). Areal concentrations were computed as X × D × 7.6, where X is the gravimetric concentration of a soil constituent, D is soil bulk density (g dry soil / cm^3), and 7.6 is the sampling depth in cm. 

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3. Common ecological indicators identify changes in seagrass condition following disturbances in the Gulf of Mexico

   https://doi.org/10.1016/j.ecolind.2023.111090  

   Congdon, Victoria M. ; Hall, Margaret O. ; Furman, Bradley T. ; Campbell, Justin E. ; Durako, Michael J. ; Goodin, Kathleen L. ; Dunton, Kenneth H. ( December 2023 , Ecological Indicators)

   Seagrasses are long-lived, clonal plants that can integrate fluctuations in environmental conditions over a range of temporal scales, from days to years, and can act as barometers of coastal change. There are many estimated seagrass traits and ecosystem parameters that have the potential to reflect ecosystem status, linking seagrass condition to natural and anthropogenic drivers of change. We identified five seagrass indicators and seven metrics that are suitable, affordable and frequently measured by 38 monitoring programs across the Gulf of Mexico (GoM). A specific set of ratings and assessment points were formulated for each measurable metric. We determined metric ratings (Acceptable, Concerning, Alarming) and validated assessment points using long-term monitoring data from Texas and Florida, coupled with existing literature and input from a panel of seagrass biologists. We reported scores using a blue-gray-orange (Acceptable-Concerning-Alarming) scale to summarize information in a format accessible to the public, resource managers, stakeholders, and policymakers. Seagrass percent cover, shoot allometry and species composition were sensitive indicators of large-scale climatic disturbances (droughts, hurricanes). Severe drought led to reductions in total seagrass cover and leaf length in Upper Laguna Madre, Texas, and Florida Bay; however, Syringodium filiforme was disproportionally affected in Texas while Thalassia testudinum beds responded strongly to drought impacts in Florida. Hurricanes Harvey (TX) and Irma (FL) also resulted in loss of seagrass cover and diminished leaf length in the Texas Coastal Bend and Florida Keys; both storms largely impacted T. testudinum and to a lesser extent, S. filiforme. Many of the metrics within these affected bays and basins received either a “Concerning” or “Alarming” rating, driven by the impacts of these disturbances. Our proposed indicators serve as a tool to evaluate seagrass condition at the bay or basin scale. Moreover, the indicators, metrics, and assessment points are amenable to large-scale evaluations of ecosystem condition because they are economically feasible. This framework may provide the foundation for a comprehensive assessment of seagrass status and trends across the entire GoM. 

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4. Physical and Biogeochemical Controls on pH Dynamics in the Northern Gulf of Mexico During Summer Hypoxia

   https://doi.org/10.1029/2019JC015140  

   Jiang, Zong‐Pei ; Cai, Wei‐Jun ; Chen, Baoshan ; Wang, Kui ; Han, Chenhua ; Roberts, Brian J. ; Hussain, Najid ; Li, Qian ( August 2019 , Journal of Geophysical Research: Oceans)

   High‐accuracy spectrophotometric pH measurements were taken during a summer cruise to study the pH dynamics and its controlling mechanisms in the northern Gulf of Mexico in hypoxia season. Using the recently available dissociation constants of the purified m‐cresol purple (Douglas & Byrne, 2017,https://doi.org/10.1016/j.marchem.2017.10.001; Müller & Rehder, 2018,https://doi.org/10.3389/fmars.2018.00177), spectrophotometrically measured pH showed excellent agreement with pH calculated from dissolved inorganic carbon (DIC) and total alkalinity over a wide salinity range of 0 to 36.9 (0.005 ± 0.016,n= 550). The coupled changes in DIC, oxygen, and nutrients suggest that biological production of organic matter in surface water and the subsequent aerobic respiration in subsurface was the dominant factor regulating pH variability in the nGOM in summer. The highest pH values were observed, together with the maximal biological uptake of DIC and nutrients, at intermediate salinities in the Mississippi and Atchafalaya plumes where light and nutrient conditions were favorable for phytoplankton growth. The lowest pH values (down to 7.59) were observed along with the highest concentrations of DIC and apparent oxygen utilization in hypoxic bottom waters. The nonconservative pH changes in both surface and bottom waters correlated well with the biologically induced changes in DIC, that is, per 100‐μmol/kg biological removal/addition of DIC resulted in 0.21 unit increase/decrease in pH. Coastal bottom water with lower pH buffering capacity is more susceptible to acidification from anthropogenic CO₂invasion but reduction in eutrophication may offset some of the increased susceptibility to acidification.

    

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5. Trophic Niche Metrics Reveal Long-Term Shift in Florida Bay Food Webs

   https://doi.org/10.1007/s10021-023-00825-5  

   Calhoun-Grosch, Stacy ; Foster, Emelie M. ; James, W. Ryan ; Santos, Rolando O. ; Rehage, Jennifer S. ; Nelson, James A. ( January 2023 , Ecosystems)

   Seagrass beds in Florida Bay are home to many ecologically and economically important species. Anthropogenic press perturbation via alterations in hydrology and pulse perturbations such as drought can lead to hypersalinity, hypoxia, and sulfide toxicity, ultimately causing seagrass die-offs. Florida Bay has undergone two large-scale seagrass die-offs, the first in the late 1980s and early 1990s and the second in 2015. Post-die-off events, samples were collected for stable isotope analysis. Using historical (1998–1999) and contemporary (2018) stable isotope data, we examine how food webs in Florida Bay have changed in response to seagrass die-off over time by measuring contributions of basal sources to energy usage and using trophic niche analysis to compare niche size and overlap. We examined three consumer species sampled in both time periods (Orthopristis chrysoptera, Lagodon rhomboides, and Eucinostomus gula) in our study. Seagrass production comprised the majority of source usage in both datasets. However, contemporary consumers had a mean increase of 18% seagrass usage and a mean decrease in epiphyte usage of 7%. The shift in trophic niche from epiphyte usage (green pathway) toward seagrass usage (brown pathway) may indicate that food web browning is occurring in Florida Bay. 

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