Florida Bay Research Articles

The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow

The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ34S, δ18O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates.

Description of the Late Holocene South‐east Saline Everglades, Florida palustrine depositional environment with comparisons to other Holocene environments

AbstractA transgressive palustrine depositional model is described for the South‐east Saline Everglades, Florida. The origin, development and termination of freshwater carbonate mud (marl) deposition along the very low gradient Late Pleistocene carbonate ramp are responses to changing rates of rising sea level during the Late Holocene. The onset of the Late Holocene is defined by a decrease in the rate of sea‐level rise from between 2 and 3 to <1 mm year−1. Freshwater marl deposition began with this decrease ca 3165 ± 187 year BP, in a shallow (<0.3 m deep), ephemeral wetland that developed landward of a fringing mangrove forest and is maintained by seasonal Everglades water delivery. Sedimentation kept pace with sea‐level rise forming a 1.2 m thick wedge shaped, landward thinning deposit. The rate of global sea‐level rise began to accelerate ca 1900, the Anthropocene Marine Transgression, and presently the regional rate is 9.4 mm year−1. Saltwater encroachment rates >80 m year−1 are driven by sea‐level rise. Saltwater encroachment resulted in retreat and transformation of coastal communities and their biogenic facies, resulting in a decrease in freshwater wetlands and marl production. Inundation ponding, mangrove overstep and the beginning of submergence are the responses to the accelerating rate of sea‐level rise, however, small scale topographic and tidal ingress differences create considerable variability between Biscayne Bay and Florida Bay coastal basins. The freshwater marl producing habitat will probably be lost within 55 years, and submergence within the next century at the present rate of sea‐level rise. The unique South‐east Saline Everglades depositional environment is compared to other Holocene palustrine depositional environments.

Long-term patterns and trends in water column biogeochemistry in a changing environment

Water column nutrient concentrations and autotrophy in oligotrophic ecosystems are sensitive to eutrophication and other long-term environmental changes and disturbances. Disturbance can be defined as an event or process that changes the structure and response of an ecosystem to other environmental drivers. The role disturbance plays in regulating ecosystem functions is challenging because the effect of the disturbance can vary in magnitude, duration, and extent spatially and temporally. We measured changes in total nitrogen (TN), dissolved inorganic nutrient (DIN), total phosphorus (TP), soluble reactive phosphorus (SRP), total organic carbon (TOC), and chlorophyll-a (Chl-a) concentrations throughout the Everglades, Florida Bay, and the Florida Keys. This region has been subjected to a variety of natural and anthropogenic disturbances including tropical storms, fires, eutrophication, and rapid increases in water levels from sea-level rise and freshwater restoration. We hypothesized that the rate of change in water quality would be greatest in the coastal ecotone where disturbance frequencies and marine P concentrations are highest, and in freshwater marshes closest to hydrologic changes from restoration. We applied trend analyses on multi-decadal data (1996–2019) collected from 461 locations distributed from inland freshwater Everglades (ridge and slough) to outer marine reefs along the Florida Keys, USA. Total Organic Carbon decreased throughout the study area and was the only parameter with a systematic trend throughout the study area. All other parameters had spatially heterogeneous patterns in long-term trends. Results indicate more variability across a large spatial and temporal extent associated with changes in biogeochemical indicators and water quality conditions. Chemical and biological changes in oligotrophic ecosystems are important indicators of environmental change, and our regional ridge-to-reef assessment revealed ecosystem-specific responses to both long-term environmental changes and disturbance legacies.

Reduced seagrass resilience due to environmental and anthropogenic effects may lead to future die-off events in Florida Bay

Coastal systems often depend on foundation species such as seagrasses that are supported by self-facilitation. Seagrass meadows, however, are threatened worldwide due to climate change and local human impact, disrupting self-facilitation leading to system instability. Florida Bay is a large seagrass dominated coastal ecosystem that suffered from multiple seagrass mortality events over the last half century driven by hypoxia, high water temperatures, hypersalinity, and high biological oxygen demand. These conditions reduce the amount of photosynthetically-derived oxygen in the plant causing sulphide intrusion into meristematic tissues. Using a bay-wide sampling design and long-term monitoring trends of seagrass condition, we investigated the current state of the meadows, sediment characteristics (e.g., organic matter, sulphide, nutrients) and discuss how climate stressors interact with plant and sediment oxygen dynamics. Our survey revealed that at sites where seagrass had been previously denuded by die-off, the dominant seagrass Thalassia testudinum had not recovered, while the pioneering seagrass Halodule wrightii recolonized the impacted areas. Organic matter and sulphide levels were higher at the impacted sites, apparently a persistent characteristic of the formerly dense T. testudinum meadows in central and western Florida Bay. These sediment conditions promote sulphide intrusion of T. testudinum belowground tissue under anoxic conditions. Plant oxidation initially buffers sulphide intrusion, but disruption of this oxidation mechanism due to changing environmental conditions results in widespread mortality and seagrass community collapse. Climate change cannot be fully mitigated by local management, however, attempts can be made to control critical salinity and oxygen levels by increasing freshwater input, reducing hypersalinity and aiming to keep the internal seagrass oxidation feedback intact. Our study shows that the Florida Bay seagrass ecosystem is still recovering four years post die-off and continues to be susceptible to future climate change and system degradation.

Freshwater microbial mud: Punctuated diagenesis during marine transgression in the Florida Everglades, USA

AbstractThis manuscript documents the diagenetic progression from deposition to early burial of freshwater low‐Mg calcite mud within a Holocene sequence of the Everglades and Florida Bay (Florida, USA). During initial, in situ burial, the texturally‐complex, organic‐rich mud, exhibits high susceptibility to alteration, within a primarily dissolution‐driven realm. Seaward, a brackish‐water transitional burial environment currently displays evidence of mixed precipitation and dissolution. This brackish stage burial alteration may be due to fluid exchange (a relatively high fluid‐to‐rock ratio) in a submerged estuary setting. Lastly, the burial environment in Florida Bay records a transgression from freshwater to near‐normal marine conditions. This island setting currently exhibits a diagenetic trend towards low‐Mg calcite precipitation in intervals of both the marine and freshwater mud. Burial of freshwater mud beneath nearly 3 m of marine mud during rising sea level appears to have preserved a considerable amount of original textures, as compared with younger freshwater deposits now within the transitional brackish‐water setting. Geochemical and textural data within the freshwater mud sections suggest that complex early diagenesis begins shortly after burial at the site of formation, and perhaps even during deposition. The findings herein document three major implications for coastal zone paludal carbonates: (i) that incipient textural diagenesis in low‐Mg calcite crystals can be extremely early and the stability and petrographic fidelity of these deposits are vulnerable due to the open, trellis‐like structure of the crystals; (ii) relatedly, the stable isotope signature of the original low‐Mg calcite crystals is also vulnerable to alteration by secondary precipitation within the open crystal structure; and (iii) during marine transgression, the paludal calcite crystals likely experience a shift from interstitial fluids that are dissolution‐dominated (freshwater) to more precipitation‐dominated as marine fluids overtake the pore fluid regime. Because palustrine deposits are used as palaeoenvironmental archives, it is important to understand their diagenetic and preservation potential. This study has implications for those concerned with the deposition, reactivity and preservation potential of continental and microbial carbonates.

Seroprevalence of West Nile Virus in Tampa Bay Florida Patients Admitted to Hospital during 2020-2021 for Respiratory Symptoms.

West Nile virus (WNV) is an arbovirus spread primarily by Culex mosquitoes, with humans being a dead-end host. WNV was introduced to Florida in 2001, with 467 confirmed cases since. It is estimated that 80 percent of cases are asymptomatic, with mild cases presenting as a non-specific flu-like illness. Currently, detection of WNV in humans occurs primarily in healthcare settings via RT-PCR or CSF IgM when patients present with severe manifestations of disease including fever, meningitis, encephalitis, or acute flaccid paralysis. Given the short window of detectable viremia and requirement for CSF sampling, most WNV infections never receive an official diagnosis. This study utilized enzyme-linked immunosorbent assay (ELISA) to detect WNV IgG antibodies in 250 patient serum and plasma samples collected at Tampa General Hospital during 2020 and 2021. Plaque reduction neutralization tests were used to confirm ELISA results. Out of the 250 patients included in this study, 18.8% of them were IgG positive, consistent with previous WNV exposure. There was no relationship between WNV exposure and age or sex.

Impacts of Freshwater Sources on Salinity Structure in a Large, Shallow Estuary

Florida Bay, a large and shallow estuary, serves as a vital habitat for a diverse range of marine species and holds significant environmental, commercial, and recreational value. The salinity structure of the bay plays a key role in the bay’s ecosystem. Florida Bay receives 45% of its freshwater directly from rainfall, the largest source of freshwater, while the Taylor River is the second largest source. A hydrodynamic model was applied to determine if doubling the Taylor River flow, as currently planned, is adequate to meet salinity performance measures and protect the bay’s ecosystem health. Model-predicted salinity indicated that rainfall caused the largest reduction (10–15 ppt) followed by Taylor River discharges, and none of the predicted salinity scenario means exceeded 38 ppt. The salinity restoration target was achieved more than 70% of the time, by doubling the Taylor River freshwater discharges, only for the existing bay conditions. To protect Florida Bay’s ecosystem health and counterbalance saltwater intrusion in the Everglades wetlands, caused by future sea-level rise, additional freshwater sources needs to be identified. Yet, the question becomes, do we have enough available freshwater sources to achieve the restoration target and protect the bay’s ecosystem health now and for future sea-level rise?

Hydrodynamic Modeling of a Large, Shallow Estuary

Florida Bay, a large and shallow estuary, serves as a vital habitat for a diverse range of marine species and holds significant environmental, commercial, and recreational value. The Florida Bay ecosystem is under extensive stress due to decades of increased nutrient loads. Based on the Environmental Fluid Dynamics Code (EFDC), a hydrodynamic model was developed in this study. The model was calibrated with a comprehensive dataset, including measurements over 7 years from 34 tidal stations, 42 current stations, and 14 temperature and salinity stations. Key findings include the following: (1) the bay exhibits a shift in the tidal regime, transitioning from macro-tidal in the western region to micro-tidal in the central and eastern/northeast regions; (2) local winds and the subtidal variations from the coastal ocean are the primary drivers for the hydrodynamic processes in the eastern and central regions; (3) salinity changes in the bay are primarily controlled by three processes: the net supply of freshwater, the processes that drive mixing within the estuary (e.g., wind, topography, currents), and the exchange of salinity with the coastal ocean. This hydrodynamic model is essential for providing a comprehensive tool to address environmental challenges and sustain the bay’s ecosystem health.

Rings of power: evidence of mud ring feeding performed by Guiana dolphins

Abstract To capture prey more efficiently, cetaceans can display a wide range of foraging tactics to separate individual prey. Barrier feeding tactics are performed to restrict prey movements, using natural and non-natural barriers and some species can even create barriers with their own bodies. Mud ring feeding has been observed in bottlenose dolphins in Florida Bay and in Chetumal-Corozal Bay, where ring-maker dolphins create ring-shaped mud plumes to encircle fish schools. Here, we document for the first time Guiana dolphins performing the mud ring feeding behaviour in the Cananéia estuarine system, in the southern portion of the state of São Paulo, Brazil. A total of 11 dolphins were recorded in four expeditions through aerial footage engaging in the behaviour. These findings expand our knowledge about the behavioural plasticity of the species and builds upon existing records of mud ring feeding behaviour in cetaceans.

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

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.

Algal bloom ties: Systemic biogeochemical stress and Chlorophyll-a shift forecasting

Algae are deemed to be the highest carbon drawdown contributors in the world. Almost half of the world’s organic carbon is fixed by marine phytoplankton, especially during algal blooms, despite accounting for less than one percent of the total photosynthetic biomass on Earth. Nonetheless, there are growing concerns about the rise of harmful algal blooms in terms of their persistence and distribution that is a fingerprint of both global climate and local anthropogenic pressure.A novel forecasting model – combining transfer entropy network inference and a forecasting convolution neural-network – is used to predict bloom and non-bloom epidemic regimes, and their environmental determinants to define bloom sources, causes and systemic risk. The model shows high forecasting skills by extracting salient ecosystem features even without spatial dependencies. We defined a 2D entropic ecosystem mandala where the ecological impact, manifested by the distribution’s randomness of Cyanobacteria-driven chlorophyll-a (CHL-a), is proportional to the systemic environmental pressure/stress determined by a set of erratic ocean/climate and coastal/nutrient factors. Originally, a spatial risk was defined based on CHL-a magnitude, persistence and shifts. Considering the temporal variability of CHL-a in Florida Bay (FL Bay) as a case-study, we show how shifts in algal blooms are becoming more persistent in shallow areas with higher dinoflagellate/diatom ratio. This emphasizes the likely key role of cyanobacteria disorganization into phytoplankton organization, and thus the role of land discharge into the marine microbiome balance. This presents major challenges considering the increasing potential causality of green–blue algal blooms (river-dominated) for harmful red-tides with cascading socio-ecological effects, including carbon cycling alteration and ingrained eutrophication in coastal ecosystems. A universal threshold on the top 20% Pareto CHL-a extremes clearly defines bloom and non-bloom regimes independently of being endemic or epidemic, underpinned by distinct eco-environmental interactions, where the largest biogeochemical stress is structurally scale-free with CHL-a as the hub.Forecasting algal bloom in short- and long-term is indispensable for quantifying ecosystem health considering coastal-marine habitats, species and humans, as well as impacts into environmental processes such as carbon sequestration capacity. However, the increasing disorganization of biogeochemical stress decreases our forecasting ability of algal blooms except during outbreaks when is too late for prevention. This has impacts for investigating and controlling eco-environmental determinants of undesired algal bloom emergence and spread.

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

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.

A large aerobic scope and complex regulatory abilities confer hypoxia tolerance in larval toadfish, Opsanus beta, across a wide thermal range

Few studies have been performed on early-life stage toadfish, and none have addressed their tolerance to temperature and hypoxia despite large seasonal temperature fluctuations and daily hypoxia in their natural environment. The first directed captive breeding of Opsanus beta allowed the examination of larval oxygen demands and hypoxia tolerance across the range of their environmental temperatures (23–33 °C). Larval toadfish exhibited a surprisingly large aerobic scope across the tested temperature range. In response to progressive hypoxia, larval toadfish showed early metabolic depression and a low regulation index (RI), while juveniles had higher regulatory abilities but, unexpectedly, a lower aerobic scope. Larval and juvenile toadfish survived hours of severe hypoxia, but larval fish had a higher excessive post-hypoxia oxygen consumption, yet their metabolic rate returned to RMR in the same timeframe as the juveniles, likely due to their higher aerobic scope. We defined hypoxia tolerance using a physiological trait, p50, the oxygen tension in which oxygen uptake is reduced to 50 % of the metabolic rate at rest and determined it at all tested temperatures. Comparing these p50 values to environmental conditions in Florida Bay using hourly temperature and oxygen measurements from January 2014–October 2021 revealed that larval toadfish rarely experience < p50 conditions (11 % of events). Further, the median duration of these events was 3 h. The metabolic performance of larval toadfish combined with temperature and oxygen observations from their natural environment reveals the fascinating strategy in which larval toadfish survive diel hypoxia across seasons.

Advancing parcel-level hurricane regional loss assessments using open data and the regional resilience determination tool

Hurricanes are a major driver of losses in the United States and thus are the focus of risk assessment capacity building efforts in the public and private sectors, as well as in the scholarly community. Capabilities for loss modeling have been particularly advanced through the development of open-source scientific workflows that conduct site-specific, building-specific, and even component-level loss assessments across entire regions. Notable among these is the Natural Hazards Engineering Research Infrastructure's Computational Modeling and Simulation Center's (NHERI SimCenter) Regional Resilience Determination (R2D) tool. However, the modular architecture of R2D's computational scaffolding has only been described and illustrated through testbed applications thus far. This study presents the first replication and extension of the R2D tool to conduct parcel-level and component-level hurricane performance assessments outside of the SimCenter's testbed locations. The study first details how building inventories that capture time-evolving building characteristics and regional construction practices can be generated using updated heuristic rulesets that guide the integration of tax assessor data with other open data sources. These rulesets and supporting data are then utilized to generate building inventory information for a set of single family homes located in Florida's Bay County, the landfall site of Hurricane Michael in 2018. HAZUS-compatible, parcel-level damage and loss assessments are then conducted, considering Hurricane Michael's peak gust wind speeds. Finally, a set of custom fragilities, empirically-derived from multiple regional post-disaster datasets, are incorporated into R2D to conduct the first component-level damage assessment of buildings under hurricanes using the SimCenter's regional loss modeling workflows. In total, this represents an important first step in operationalizing replicable regional risk assessments down to the parcel level to provide more granular risk information to key stakeholders.

Algal Bloom Ties: Spreading Network Inference and Extreme Eco-Environmental Feedback

Coastal marine ecosystems worldwide are increasingly affected by tide alterations and anthropogenic disturbances affecting the water quality and leading to frequent algal blooms. Increased bloom persistence is a serious threat due to the long-lasting impacts on ecological processes and services, such as carbon cycling and sequestration. The exploration of eco-environmental feedback and algal bloom patterns remains challenging and poorly investigated, mostly due to the paucity of data and lack of model-free approaches to infer universal bloom dynamics. Florida Bay, taken as an epitome for biodiversity and blooms, has long experienced algal blooms in its central and western regions, and, in 2006, an unprecedented bloom occurred in the eastern habitats rich in corals and vulnerable habitats. With global aims, we analyze the occurrence of blooms in Florida Bay from three perspectives: (1) the spatial spreading networks of chlorophyll-a (CHLa) that pinpoint the source and unbalanced habitats; (2) the fluctuations of water quality factors pre- and post-bloom outbreaks to assess the environmental impacts of ecological imbalances and target the prevention and control of algal blooms; and (3) the topological co-evolution of biogeochemical and spreading networks to quantify ecosystem stability and the likelihood of ecological shifts toward endemic blooms in the long term. Here, we propose the transfer entropy (TE) difference to infer salient dynamical inter actions between the spatial areas and biogeochemical factors (ecosystem connectome) underpinning bloom emergence and spread as well as environmental effects. A Pareto principle, defining the top 20% of areal interactions, is found to identify bloom spreading and the salient eco-environmental interactions of CHLa associated with endemic and epidemic regimes. We quantify the spatial dynamics of algal blooms and, thus, obtain areas in critical need for ecological monitoring and potential bloom control. The results show that algal blooms are increasingly persistent over space with long-term negative effects on water quality factors, in particular, about how blooms affect temperature locally. A dichotomy is reported between spatial ecological corridors of spreading and biogeochemical networks as well as divergence from the optimal eco-organization: randomization of the former due to nutrient overload and temperature increase leads to scale-free CHLa spreading and extreme outbreaks a posteriori. Subsequently, the occurrence of blooms increases bloom persistence, turbidity and salinity with potentially strong ecological effects on highly biodiverse and vulnerable habitats, such as tidal flats, salt-marshes and mangroves. The probabilistic distribution of CHLa is found to be indicative of endemic and epidemic regimes, where the former sets the system to higher energy dissipation, larger instability and lower predictability. Algal blooms are important ecosystem regulators of nutrient cycles; however, chlorophyll-a outbreaks cause vast ecosystem impacts, such as aquatic species mortality and carbon flux alteration due to their effects on water turbidity, nutrient cycling (nitrogen and phosphorus in particular), salinity and temperature. Beyond compromising the local water quality, other socio-ecological services are also compromised at large scales, including carbon sequestration, which affects climate regulation from local to global environments. Yet, ecological assessment models, such as the one presented, inferring bloom regions and their stability to pinpoint risks, are in need of application in aquatic ecosystems, such as subtropical and tropical bays, to assess optimal preventive controls.

How do ambient conditions and management actions affect manatee movements and habitat use?

AbstractKings Bay in northwest Florida, USA, is an important winter home of the largest aggregation of Florida manatee (Trichechus manatus latirostris), and the only location in the United States where visitors legally swim and interact with manatees. In addition to ambient conditions, visitors to the area and management actions have the potential to influence manatee behaviors. We tracked 32 manatees with satellite‐linked global position system (GPS) telemetry tags in Kings Bay from 2006 to 2018. Also, personnel at Crystal River National Wildlife Refuge collected manatee counts at Three Sisters Springs from 2014 to 2017. Our objectives were to document the use of springs and other habitat components in Kings Bay relative to ambient water temperature, time of day, tide stage, and management actions within Three Sisters Springs and other manatee sanctuaries in the bay. Manatees that we tagged in Kings Bay spent a median 87% of the winter within the local study area, compared to 47% for animals that we tagged in the Florida Panhandle. Manatees showed preferences for King and Magnolia springs basins at low tide, indicating that they function as tidal refuges, when other locations may be less accessible; we also recorded within spring basin movements. Magnolia Spring Basin showed a significant diel pattern overall, and within basins, King Spring, Tarpon Hole, and Three Sisters Springs were used more during the night than during the day. All areas outside Kings Bay were used more at warmer ambient gulf water temperatures, while all of the springs basins were used more when gulf temperature was colder, especially Three Sisters Springs Basin. Management of Three Sisters Springs had an influence on manatee use during times of cold ambient gulf water temperatures; manatees used the springs more when the spring was closed to visitors, versus when the springs were completely open or when the spring lobes alone were closed. Manatee decisions were consistent with avoiding human interactions.

Resilience of recruiting seagrass (Thalassia testudinum) to porewater H2S in Florida Bay

Major seagrass die-off events (>50 km2) are occurring globally with mortality frequently linked to hypoxia and exposure to sediment-derived hydrogen sulfide (H2S), a well-known phytotoxin. While H2S intrusion into shoot meristematic tissue is considered a leading cause of seagrass mortality events, H2S effects on subsequent recruitment is unclear. Our research examined if porewater H2S limits the dominant tropical Atlantic-Caribbean, habitat-forming seagrass, T. testudinum, from recruiting into unvegetated sediment. Florida Bay provides an excellent case-study site due to high porewater H2S and expansive unvegetated areas adjacent to intact meadows that are recolonized by T. testudinum recruits following morality events. Our approach was 2-fold (1) examine δ34S of leaf, meristem, rhizome, and root tissue to establish tissue exposure to H2S in new recruits, and (2) measure internal H2S and O2 dynamics in leaves and meristems of new recruits. Our data show recruiting shoot resistance to H2S exposure is linked to (1) adequate oxidation of internal tissue during the day through late afternoon, (2) internal plant oxidation via water column diffusion at night, driven by tidal subsidy, and (3) limited belowground root development that potentially constrains microbial community development and a decrease in H2S intrusion from roots into growing shoot meristems. Our results provide confidence that T. testudinum can successfully recruit following die-off events due to biomass partitioning during early development, young root structure, and an ability to efficiently oxidize internally which lowers H2S exposure; however, recovery of meadows can take a decade.

Air–sea gas exchange in a seagrass ecosystem – results from a 3He ∕ SF6 tracer release experiment

Abstract. Seagrass meadows are some of the most productive ecosystems in the world and could help to mitigate the increase of atmospheric CO2 from human activities. However, understanding the role of seagrasses in the global carbon cycle requires knowledge of air–sea CO2 fluxes and hence knowledge of the gas transfer velocity. In this study, gas transfer velocities were determined using the 3He and SF6 dual tracer technique in a seagrass ecosystem in south Florida, Florida Bay, near Bob Allen Keys (25.02663∘ N, 80.68137∘ W) between 1 and 8 April 2015. The observed gas transfer velocity, normalized for CO2 in freshwater at 20 ∘C, k(600), was 4.8 ± 1.8 cm h−1, which was lower than that calculated from published wind speed/gas exchange parameterizations. The deviation in k(600) from other coastal and offshore regions was only weakly correlated with tidal motion and air–sea temperature difference, implying that wind is the dominant factor driving gas exchange. The lower gas transfer velocity was most likely due to wave attenuation by seagrass and limited wind fetch in the study area. A new wind speed/gas exchange parameterization is proposed (k600=0.143u102), which might be applicable to other seagrass ecosystems and wind-fetch-limited environments.

Examining the performance of alternative harvest regulations for short-lived taxa: A case study of Florida Bay scallop management

The life history schedule of short-lived species compresses the temporal window available for harvest and exacerbates harvest timing decisions. For annual species whose populations are made up of a single year class, it is challenging yet essential to limit harvest to a level that will allow sufficient spawning escapement to sustain the population. Unexpectedly, intense harvest prior to reproduction could extirpate a population in a single season. Larger-scale commercial fisheries for annual or semelparous species are often managed using sophisticated pre-season abundance forecasts or in-season depletion estimates combined with intensive monitoring of catches and enforcement of catch limits. However, sufficient monitoring and harvest control are rarely feasible in recreational fisheries. We demonstrate the use of an age-structured simulation model to identify robust management regulations for recreational harvest season and bag limits applied to the Florida bay scallop fishery. We compared the outcomes of current harvest regulations with a suite of alternative harvest regulations in a recreational fishery for Florida bay scallops. To account for uncertainty in the stock status and dynamics of the fishery, we evaluated alternative harvest options across three levels of initial stock exploitation and two scenarios for future fishing effort. Our results show that biologically-informed regulations which allowed for more bay scallops to spawn prior to harvest, such as a later harvest season and daily harvest limit increasing over the season, performed well across all treatments and outperformed many of the current regulations when the initial stock state was more exploited, as well as when future effort doubled. These results suggest that (1) harvest regulations that more closely match the biology and life history are likely to perform better for short-lived, annual taxa than simpler regulations that may not explicitly consider these factors, and (2) simpler regulations can perform well, but require precise, annual monitoring to prevent potentially catastrophic overharvest or costly underutilization.

Cyanobacteria blooms induced precipitation of calcium carbonate and dissolution of silica in a subtropical lagoon, Florida Bay, USA

In recent decades, annual cyanobacteria blooms in Florida Bay displayed spatial and temporal patterns that are consistent with changes in alkalinity and dissolved silicon in water. In early summer, the blooms developed in the north–central bay and spread southward in fall. The blooms drew down dissolved inorganic carbon and increased water pH, causing in situ precipitation of calcium carbonate. Dissolved silicon concentrations in these waters were at minimum in spring (20–60 µM), increased during summer, and reached an annual maximum (100–200 µM) during late summer. The dissolution of silica as a result of high pH in bloom water was first observed in this study. During the peak of blooms, silica dissolution in Florida Bay varied from 0.9 × 107 to 6.9 × 107 mol per month over the study period, depending on the extent of cyanobacteria blooms in a given year. Concurrent calcium carbonate precipitations in the cyanobacteria bloom region are between 0.9 × 108 and 2.6 × 108 mol per month. It is estimated that 30–70% of atmospheric CO2 uptake in bloom waters was precipitated as calcium carbonate mineral and remainders of CO2 influx were used for the production of biomass.