Microbial diversity and community structure in sediments associated with the Seagrass (Thallassia testudinum) in Apalachicola Bay, Florida

Seagrass is an angiosperm which provides many ecosystem services in coastal areas, such as providing food, shelter and nurseries for many species, and decreasing the impact of waves on shorelines. A global assessment reported that 29% of known seagrass meadows are in a state of decline due to the effects of human activity. Seagrass is commonly found in shallow marine waters where they form meadows containing a microbiome that plays an important role in providing nutrients for seagrass growth, though little is known about the microorganisms within the seagrass meadow sediments. Our project collected sediments from seagrass meadows and adjacent unvegetated areas around Apalachicola Bay, Florida. We sequenced the bacterial communities present and compared the communities, which provided data that indicated that the differences in bacterial communities were primarily between sites and that vegetated and unvegetated plots within the same collection site were similar

Patterns of Dispersion, Movement and Feeding of the Sea Urchin Lytechinus variegatus, and the Potential Implications for Grazing Impact on Live Seagrass

The sea urchin Lytechinus variegatus is a known grazer of both living and dead tissue of turtlegrass, Thalassia testudinum, occasionally denuding large areas of seagrass. Field studies have attempted to assess effects of herbivory on seagrass by enclosing urchins at various densities. However, it is unclear how unrestricted urchins affect seagrass at lower densities more typically observed in the field. This study describes movement, feeding, and distribution of L. variegatus within beds of T. testudinum in St. Joseph Bay, Florida (USA) to quantify this urchin’s impact as a seagrass grazer. Urchins were absent from portions of seagrass beds closest to shore, present at low densities midway across the bed, and at highest densities (up to ~5 individuals/m2) at the offshore edge of the bed. Urchins tended not to aggregate, moved twice as rapidly where seagrass cover was reduced, and moved \u3e 20X faster when placed in areas of open sand. Dead seagrass tissue occurred 4—30X more frequently on oral surfaces than living seagrass tissue. Fecal pellets with dead seagrass tissue were \u3e 3X more common than pellets with live seagrass tissue. Injury to seagrass leaves was more common along dead leaf sections than live sections (\u3e 2—10X). Overall, spatial distributions, movement, and diet indicate that L. variegatus at densities observed in this study would tend to have minimal effects on living seagrass. Episodic periods of denuding grassbeds reported in the literature suggest L. variegatus switches to live seagrass tissue as dead tissue becomes scarce during times of high urchin density

Spatial and temporal variation in the development of epiphytic diatom communities on the eelgrass, Zostera marina L.

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 79-83). Description: viii, 83 leaves : ill., map ; 29 cm

Examining the Effects of Non-Native Seagrass Species on Sediment Chemistry in Jobos Bay, PR.

Seagrasses provide a variety of essential ecosystem services such as erosion prevention, carbon storage, processing water column nutrients, and providing food and habitat for endangered species. These services are invaluable to humans and must be studied to determine how seagrasses may be a link in achieving the overall goal of fighting climate change and preserving earth’s coastal and marine ecosystems. Jobos Bay, Puerto Rico hosts a wide variety of marine habitats but is vulnerable to ecosystem damage from human activities. This research was conducted to investigate how the presence of non-native Halophila stipulacea impacts the nitrogen cycle, nutrient availability, and dissolved ammonium pool in Jobos Bay. In March 2023, a total of forty-eight sediment cores were collected from four different habitat types across three different locations in Jobos Bay. Porewater was extracted from the cores and will be examined spectrophotometrically to determine porewater ammonium concentration and exchangeable ammonium concentration. An analysis of variance will be used to compare the concentrations of ammonium among the different habitat types. Due to higher refractory carbon composition in the biomass of Thalassia testudinum, more burial and less decomposition is expected in seagrass beds containing T. testudinum than those with H. stipulacea. I predict that this lower decomposition rate will be detected as lower sediment porewater ammonium concentration. Differences in porewater ammonium concentration associated with these species could indicate changes in the availability of nitrogen for microbial metabolism and nitrogen recycling within the ecosystem

Landscape Monitoring and Biological Indicators for Seagrass Conservation In Texas Coastal Waters : final report

Part I: Given the threats to coastal resources, implementation of a seagrass monitoring program in Texas is a top priority; however, to achieve maximum effectiveness, the program design should both detect changes in seagrass distribution, abundance, and condition as well as identify causative factors that drive those changes. Therefore, monitored habitat quality or stressor indicators should be strongly related to seagrass characteristics so that the seagrass condition at a site may be adequately characterized based on values of stressor indicators. We examined numerous abiotic and biotic variables at 40 sites in seagrass beds of Redfish Bay and East Flats to determine the strength of their relationship with seagrass biomass, density, cover and community composition. Strong relationships would suggest possible stressors as well as identify potential indicators of current and future seagrass condition. Both univariate and multivariate statistical analyses were used to assess these relationships and identify candidate variables for inclusion in a monitoring program.Part II: In support of the Texas Seagrass Monitoring Program, aerial remote sensing research has been performed to evaluate automated methods for monitoring landscape changes in seagrass beds indicative of human stressors and/or natural disturbances. This report discusses the integration of high resolution aerial color film photography, color space transformation, pixel threshold models, and geographic information system (GIS) technology to detect, assess, and monitor 1-m ground feature changes and landscape disturbances within Coastal Bend seagrass beds.Part III: This report outlines an implementation program for monitoring Texas seagrasses following protocols that evaluate seagrass condition based on landscape-scale dynamics. We recommend a hierarchical strategy for seagrass monitoring in order to establish the quantitative relationships between physical and biotic parameters that ultimately control seagrass condition, distribution, and persistence. The monitoring protocols are based on conceptual models that link: (1) light and nutrient availability to seagrass condition indicators and landscape level dynamics, including patchiness and depth limit distributions, and (2) physico-mechanical stressors, including hydrodynamic processes and human activities, to landscape feature indicators of seagrass bed degradation. The three-tiered approach follows a broad template adopted by several federal and state agencies across the country, but which is uniquely designed for Texas. This plan accommodates the immense hydrographic diversity in the State’s estuarine systems and its associated seagrass habitats, recent advances in seagrass monitoring techniques, and current economic constraints associated with long-term studies. Based on this approach, we describe a multiscale monitoring protocol that, when implemented, integrate plant condition indicators with landscape feature indicators to detect and interpret seagrass bed disturbances.Contract No. 0627Coastal Bend Bays & Estuaries Program Executive Director: Ray AllenMarine Scienc

Relative Contributions of DNRA and Denitrification to Nitrate Reduction in Thalassia testudinum Seagrass Beds in Coastal Florida (USA)

Seagrass beds are vulnerable to eutrophication (nutrient loading) and declining worldwide. To quantify the fate of nitrogen (N) inputs, intact sediment cores were incubated in a continuous-flow system with 15N enrichments to compare N consumption and efflux pathways within and near seagrass (Thalassia testudinum) beds in St. Joseph Bay, Florida. Sediment oxygen demand and total ammonium (NH4+) efflux were greater (p \u3c 0.001) in vegetated versus unvegetated sediments, suggesting that seagrasses enhance organic matter remineralization. Denitrification rates were 2–20× greater than estimates of potential dissimilatory nitrate reduction to ammonium (DNRA). The effect of vegetation on denitrification rates was inconsistent. Direct denitrification of overlying water nitrate and N fixation rates were low, suggesting tight coupling between remineralization, nitrification, and denitrification. DNRA rates were lower than denitrification and consistently greater in vegetated sediments. DNRA rate measurements are conservative if sediment cation exchange decreases the fraction of 15NH4+ reaching overlying water, especially in vegetated sediments, where rates of nitrate-induced ammonium fluxes were observed. Coupled nitrification-denitrification was the major N loss pathway in this system, as evidenced by the lack of 15N-labeled N2 production in isotope-enriched cores. Using measured sediment oxygen demand and NH4+ fluxes as an indicator of organic matter quality and quantity, these results are consistent with previous work showing that labile organic matter helps regulate the balance between N removal and internal recycling pathways in seagrass systems, which has implications for coastal management strategies to address eutrophication

The Effects of Anthropogenic Pressure on Estuarine Cyanobacteria Levels

Estuaries are transitional ecosystems that merge river and sea. The brackish waters are home to a large variety of plant and animal species making estuaries highly productive environments. Dissolved oxygen levels in estuaries vary depending on season and temperature. However, dissolved oxygen levels are also affected by the eutrophication of nutrients (e.g., phosphorus and nitrogen) which are caused by agricultural and industrial practices within the estuary’s watershed. These hypoxic events allow organisms, such as cyanobacteria, to multiply at high rates producing blue-green algae blooms of cyanobacteria to occur within the ecosystem. As a result, “dead zones” or areas of extremely low dissolved oxygen are created that can have deadly effects on the plant and animal species inhabiting the area. For this study, water samples were collected from three Georgia estuaries: Wassaw Sound, Ossabaw Sound, and Doboy Sound. Deoxyribonucleic acid (DNA) was extracted from water filters using a DNA purification kit. The quantitative polymerase chain reaction (qPCR) method was utilized to investigate cyanobacteria diversity among the three estuaries. Our preliminary results display a difference in cyanobacteria species among the three sampling locations