Dr. Jane M Caffrey

Nitrogen fixers can enhance nitrogen availability for seagrass communities that may be nitrogen limited. However, the role of epiphytic diazotrophs, particularly cyanobacteria, in seagrass communities is not well understood. We measured nitrogen fixation rates, epiphyte biomass, and relative abundances of epiphytic diazotrophs on the leaves of Thalassia testudinum and Halodule wrightii in the northern Gulf of Mexico. Greater accumulation of epiphyte biomass and diazotrophs may occur in T. testudinum due to lower leaf turnover than found in H. wrightii , particularly during periods of seagrass dormancy. Nitrogen fixation rates were determined using the acetylene reduction assay, while quantitative polymerase chain reaction was used to measure relative abundances of three cyanobacterial diazotroph groups in epiphyte DNA. Nitrogen fixation and epiphyte biomass were higher on T. testudinum leaves than on H. wrightii leaves. The lowest average fixation rates occurred in August when leaf turnover was high. Three phylotypes of nifH genes were detected in most samples, but overall, Crocosphaera ‐like Group B cyanobacteria (UCYN‐B) were present on all leaves during all seasons. Relative abundance of this group was positively correlated with nitrogen fixation rates on both species ( r = 0.59, p = 0.02). At one of the four study sites, heterocystous cyanobacterial symbionts in the Richelia‐ like (Het‐1) and Calothrix‐ like (Het‐3) groups accounted for similar relative abundances to those observed with UCYN‐B nifH genes. Because T. testudinum and H. wrightii are dominant in shallow tropical and subtropical ecosystems, understanding the role that diazotrophic epiphytes play in providing nitrogen to these vital ecosystems is critical.

Florida’s low elevation and geographic location make it particularly vulnerable to climate change effects such as sea level rise, increased intensity and frequency of storm events, and altered precipitation. Climate change is expected to exacerbate hydrological cycling with potential widespread implications for estuarine habitats that thrive under specific salinity regimes. We used historical data from sites in the eastern Gulf Coastal Plain, USA to examine trends and trend variability of several climatic, hydrologic, and estuarine water quality variables which have implications on seagrass and oyster habitat extent in downstream estuarine environments. We analyzed temperature, precipitation, low-flow and high-flow metrics (including the highest or lowest daily, 7-day average, and 30-day average) for each season annually over the period 1985–2020. We also analyzed estuarine water clarity metrics and salinity within waterbody segments of four estuary systems within the study area. Hydroclimate results showed that temperature increased at most sites. While there was variation in streamflow, the overall trend was declining streamflow. Declining trends were observed in most water clarity metrics, indicating improved clarity, especially in winter. Salinity generally declined across the study area. While overall streamflow decreased, main river stems to the estuaries had increasing trends in maximum streamflow characteristics, likely contributing to the decrease in estuarine salinity across the region. These results indicate that trends in streamflow (both magnitude and timing) in the watershed affect downstream estuarine water quality. These results have important implications on seagrass and oyster restoration and management efforts in the region, indicating that it is important to understand changing climatic and hydrologic conditions and how they may impact the estuarine resources.

Thalassia testudinum often dominates seagrass meadows of the Florida panhandle but few measurements of productivity, biomass, density, turnover or leaf area index in this region have been made. We targeted 5 estuaries located at similar latitudes, 30⁰ ± 0.3⁰N: Big Lagoon, Santa Rosa Sound, St. Andrew Bay, St. Joseph Bay, and St. George Sound. This study was one component of a collaborative partnership of state and local researchers examining factors preventing recovery in panhandle estuarine areas that had historically contained seagrass in the 1940s and 1950s. Measurements were made twice in 2016, once in June and then again in summer or fall, except in Santa Rosa Sound where measurements were made 3 times. In the estuaries sampled for the second time in July or August, aboveground productivity was greater than in June. St. Joseph Bay had the highest aboveground productivity (4.3 g/m2/d) and 1—sided leaf area index (4.2) while St. George Sound had the lowest values (0.41 g/m2/d and 1.0). Principal component analysis suggested that St. Andrew Bay, Big Lagoon and Santa Rosa Sound were the most similar, with higher values for shoot densities and leaf turnover and lower salinities and watershed:water ratios. St. Joseph Bay had high aboveground productivity and salinity, and low turbidity. St. George Sound had low aboveground productivity, high total suspended solids and the highest watershed:water ratio. These baseline productivity estimates will be useful to assess the success of restoration efforts targeting seagrasses in the Florida panhandle and evaluate impacts of climate change on seagrasses.

Collaborative nonregulatory programs can benefit the long-term sustainability of environmental resources. Such programs benefit from extensive planning and assessment relative to ecological systems as well as public participation. While many programs use adaptive management as a guiding programmatic framework, few programs successfully integrate social and human context into their adaptive management frameworks. While this adaptive governance framework can be successful, many potential challenges arise when incorporating public stakeholders into the adaptive management framework. To reduce those challenges, programs need participation from diverse stakeholder groups that represent multiple communities of interest, place, and identity. The participatory process benefits from a diverse group of stakeholders and can result in successful management of environmental resources. We highlight the participatory co-management process of three newly
developing nonregulatory programs that are modeled after the United States EPA’s National Estuary Program in the Perdido and Pensacola Bay systems, Choctawhatchee Bay, and the St. Andrew and St. Joseph Bay systems (Florida USA). This case study illustrates how collaborative nonregulatory programs can be implemented not only in the United States, but also in other regions of the world.

Seagrass beds are important coastal habitats that are diminishing globally. Nitrogen, a key nutrient, often limits seagrass growth. Nitrogen fixation provides new, bioavailable nitrogen to the plants. This study explores its importance and factors controlling rates in sediments colonized by two dominant taxa in Northwest Florida, Thalassia testudinum and Halodule wrightii, compared to unvegetated sediments. We hypothesized that nitrogen fixation rates would be greater in seagrass colonized sediments, particularly during high growth periods. We expected to observe a positive relationship between rates and porewater sulfide concentrations because sulfate reducers were the dominant diazotrophs in similar studies. Rates were higher in vegetated areas. In H. wrightii beds, nitrogen fixation was driven by the decreased availability of porewater ammonium relative to phosphorus. In T. testudinum beds, rates were highest during winter. Organic matter may be a controlling factor in all substrate types albeit the exact mechanism driving nitrogen fixation differs slightly. During the summer and fall, nitrogen fixation provided between 1–15% of T. testudinum nitrogen demand. Annually, nitrogen fixation provided 4% and 1% of T. testudinum and H. wrightii nitrogen demand, respectively. Nitrogen fixation was an important source of nitrogen during periods of senescence and dormancy when organic matter content was high.

Vibriosis is the general term for human illnesses caused by infection of pathogenic Vibrio species. Vibrio vulnificus (Vv) and parahaemolyticus (Vp) are two problematic waterborne pathogens that have yet to be enumerated in northwest Florida coastal Gulf of Mexico estuaries. In this regionally novel study, we surveyed 43 locations in two subtropical estuarine systems, Perdido Bay and Pensacola Bay, over seven dates in winter 2020. Sampling included three substrate types: surface waters, sediments, and invertebrate biofilms. We determined baseline abundances of presumptive viable Vv and Vp appearing as colonies on CHROMagar (Vv, blue; Vp, purple). Vv was detected in 37 out of 43 water samples, with maximum levels of 3,556 CFU/mL. Vp was only detected in 15 water samples, with a maximum concentration of 8,919 CFU/mL. Sediments contained Vv in all but one sample, with concentrations ranging from 121 to 607,222 CFU/mL. In contrast, Vp were only detected in 33 sediment samples, where concentrations ranged from 28 to 77,333 CFU/mL. Opportunistically-sampled surface swabs (biofilms), collected from shells (either oyster or barnacle) and polychaete worms found in sediment samples, contained on average 7,735 and 1,490 CFU/mL of Vv and Vp, respectively. Surface water Vv abundances covaried with bottom water pH, maximum prior cumulative wind speeds, and tidal coefficient on the day of sampling. Vp surface water abundances negatively correlated with surface water salinity, surface water pH, and bottom water pH and positively correlated with total surface dissolved inorganic and total Kjeldahl nitrogen concentrations, and wind. Spatially, there was large variation in Vibrio densities in surface waters; abundances of both species were strongly correlated with wind, suggesting resuspension was important. Sedimentary abundances of both putative Vv and Vp shared a correlation with one parameter: salinity stratification. Due to the length of this study, temperature was not considered a major factor. This short-term (one month) study was designed not to enumerate pathogenic Vv or Vp, but rather to establish the first winter baseline of Vibrio abundances for this region. Determination of these baseline winter cultivable putative Vibrio abundances will be valuable in predicting relative risk factors in each waterbody of interest.

Artificial reefs have been deployed throughout US coastal waters since the late 1970s, primarily to enhance fisheries. Although numerous studies have examined their effects on fish communities, few have examined interactions between artificial reefs and primary producers or their effects on biogeochemistry of the surrounding water column. Understanding how reefs may alter biogeochemistry and primary producers is key to understanding overall reef productivity. In this study, we examined the relationships among epifauna, algae, and biogeochemical processes on artificial reefs located on the shallow Florida shelf in the Northeast Gulf of Mexico over a year following their deployment. We measured oxygen and nutrient fluxes, attached chlorophyll a, and invertebrate macrofauna. Temporal differences in biomass and chlorophyll a production occurred due to changes in in situ conditions including fluctuations in bottom-water temperature over the year as well as decreasing bottomwater oxygen and increasing chlorophyll a fluorescence during the summer. Invertebrate biomass was greater than micro- or macroalgal biomass. Biomass of the invertebrate epifaunal community increased exponentially during the first 5 months of this study. The reef was net heterotrophic with few differences between oxygen or nutrient fluxes in the light and dark. Positive nitrate
and nitrite fluxes and abundances of amoA genes in the microbiomes of benthic invertebrates indicate significant nitrification associated with the epifaunal community. Reef biogeochemistry was directly related to the composition and biomass of the epifaunal community at the reef sites.

Increased organic loading to sediments from eutrophication often results in hypoxia, reduced nitrification and increased production of hydrogen sulfide, altering the balance between nitrogen removal and retention. We examined the effect of short-term exposure to various oxygen and sulfide concentrations on sediment nitrification, denitrification and DNRA from a chronically hypoxic basin in Roskilde Fjord, Denmark. Surprisingly, nitrification rates were highest in the hypoxic and anoxic treatments (about 5 μmol cm⁻³ d⁻¹) and the high sulfide treatment was not significantly different than the oxic treatment. Denitrification in the hypoxic treatment was highest at 1.4 μmol cm⁻³ d⁻¹ and significantly higher than the high sulfide treatment. For DNRA, the rate in high sulfide treatment was 2 μmol cm⁻³ d⁻¹. This was significantly higher than all oxygen treatments that were near zero. In this system, nitrifiers rapidly recovered from conditions typically considered inhibiting, while denitrifiers had a more muted response. DNRA bacteria appear to depend on sulfide for nitrate reduction. Anammox was insignificant. Thus, in estuaries and coastal systems that experience short-term variations in oxygen and sulfide, capabilities of microbial communities are more diverse and tolerant of suboptimal conditions than some paradigms suggest.

Shallow continental shelves support productive pelagic and benthic communities. This study examined primary productivity at a shallow shelf region in the northeastern Gulf of Mexico focusing on the effect of light on water column and benthic productivity at water depths between 12 and 17 m. Measurements were made between November 2015 and September 2016. Dissolved oxygen fluxes were measured using benthic chambers with four different light levels and used to calculate gross primary production and respiration. Phytoplankton productivity was measured using ¹⁴C-uptake incubations in a laboratory photosynthetron. Organic matter production by benthic microalgae is substantial in this region of northeastern Gulf of Mexico with daily production rates ranging from 0.1 to 0.8 g C m⁻² d⁻¹ in this study. Maximum rates of phytoplankton production up to 2.7 g C m⁻² d⁻¹ occurred in spring. This peak productivity followed wind conditions favorable to upwelling and occurred when bottom water NO₃⁻ concentrations were 11 times greater than on any other sample date during the study. At these shallow depths, benthic microalgae made a significant contribution to total shelf production, averaging about 14% of total production. These results helped characterize benthic and water column production rates prior to planned habitat alterations caused by placement of numerous artificial reef structures in the region.