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.

Excerpt from Introduction: The Florida Department of Health (FDOH) has set acceptable Enterococcus levels in the environment for determination of human health at 70 MPN/100 mL which is known as the Beach action value or BAV (Florida Department of Health in Bay). Values which exceed this amount result in warnings to the public on the quality of conditions within the waterways and advisory to avoid water contact (Florida Department of Health in Bay). Monitoring at Navarre Park on Highway 98 by Florida Department of Health has shown poor water quality based on high levels of Enterococcus from multiple samples which has resulted in advisories (FDOH website). Poor and moderate conditions have been most prominent in summer months with better conditions during the colder winter months (Florida Department of Health). Thus, identifying possible contamination sources to Santa Rosa Sound in this region is critical. To identify potential sources, we collected samples at multiple locations in creeks entering the Sound near Navarre as well as a stormwater outfall and Santa Rosa Sound water at Navarre Park between January and March 2024.

Seagrass beds provide key ecosystem services in the protected, shallow coastal zone. They are usually characterized by a diverse faunal community and support commercially and recreationally important fish and shellfish species (Orth and Heck 2023). These species find refuge, food or nursery areas in these beds which are particularly important for endangered species such as manatees and sea turtles. Carbon fixation by seagrasses, macroalgae or microalgae including epiphytes, benthic microalgae or phytoplankton is a carbon source for higher trophic levels and may be stored in sediments, the “blue carbon” which represents a sink for carbon dioxide (Orth and Heck 2023). Nutrient cycling in seagrass includes recycling, burial of organic material in sediments and the processes of nitrification, denitrification and nitrogen fixation.

Lagoonal systems in the Gulf of Mexico contain extensive seagrass beds. In the Pensacola Bay system, the first estimates of the extent of seagrass beds began in 1974 with Escambia Bay Recovery Report (EPA 1975). Since then, other aerial photographic surveys (Schwenning et al. 2007, Harvey et al. 2015, Byron et al. 2018) and monitoring of seagrass beds in Gulf Islands National Seashore have occurred (Heck and Byron 2014, Byron et al. 2018).

UWF along with Sea Grant Extension agents began this Seagrass monitoring program in 2017. Sea Grant and the Bream Fishermen Association help to identify and train volunteers on how to monitor seagrasses. Two goals of this program are to increase community awareness of the importance of seagrass and SAV habitats and to develop long-term monitoring of seagrasses in the Pensacola Bay system.

We used the same adaptation of the UF “Eyes on Seagrass” protocols as last year in Big Lagoon and Santa Rosa Sound where volunteers go out monthly along a transect (Caffrey et al. 2024). Volunteers collecting in the urban bayous (Bayou Texar) or Pensacola Bay followed protocols described in Caffrey et al. (2023). This report describes results from 2024.

Seagrass beds are important to the health of estuaries around the world, and often these grasses are keystone species for their environments. Water quality conditions controlling light availability such as total suspended solids (TSS), phytoplankton biomass, and the color of the water are important in understanding seagrass health. Six locations from the Pensacola Bay System in Santa Rosa Sound and Big Lagoon with extensive seagrass beds were sampled monthly between May and October 2023. Water quality was measured, and surveys of seagrass beds were conducted at each site. Linear models were developed to attempt to explain K d from water color, phytoplankton biomass, and TSS, as well as their impact on the percent cover of the seagrasses. Seagrass cover increased over the growing season. K d varied between 0.3 /m and 1.8 /m, and across all study sites only color was significantly (p < 0.1) related to light attenuation, although it could not explain much variability (R 2 =0.08). While water depth was significantly related to percent cover of Halodule wrightii and Thalassia testudinum, depth integrated values of light available and factors related to light attenuation explained little variability in percent cover despite significance levels (p < 0.1). Sites in Santa Rosa Sound and Big Lagoon were similar. Larger scale surveys with more opportunistic sampling (e.g. following rain events) in addition to planned collection days, might provide data with clearer relationships to light attenuation and seagrass cover. Surveys that extend to the deepwater edge of the seagrass beds should also be done in the future to provide a clearer picture of the habitat and changes in the beds.

Seagrasses protect coastlines from erosion, improve the water quality, shelter juvenile marine species, and are an important part of the estuarine environment. Seagrasses are responsible for nutrient cycling within the estuary, such as carbon fixation and burial, and nitrification and denitrification. Pensacola Bay System’s seagrasses were studied to see how seagrass coverage, water quality, and nutrient concentrations changed during the 2024 growing season. Three locations in Santa Rosa Sound, home to the most seagrass coverage, were used to collect samples. Measurements of seagrass cover and water quality were made, along with samples for overlying water and pore water. The average seagrass cover
at these locations was 57% with Halodule wrightii dominating in shallow water and Thalassia testudinum dominating in deeper water. Porewater was analyzed for dissolved inorganic phosphate (DIP), sulfide, iron, and ammonium. Ammonium and DIP concentrations from May and June had consistently lower overlying water concentrations compared to the porewater. DIP was in excess compared to ammonium assuming Redfield stoichiometry, perhaps due to seagrasses taking up nitrogen from the porewater. This data will be used to find how seagrass growth effects the nutrient concentrations of estuarine sediment.

Seagrass beds provide numerous services, including coastal protection, erosion control, carbon sequestration, and habitat for ecologically and economically important species. Many factors influence the growth of seagrasses, with one of the main factors being nutrient availability. The aims of this study are to quantify the recycling of key nutrients such as nitrogen, phosphorus, iron, copper, zinc and manganese by 3 dominant faunal species from different trophic levels found in seagrass beds in Santa Rosa Sound, FL and Grand Bay, MS. Fecal samples were collected from spotted seatrout (Cynoscion nebulosus), pinfish (Lagodon rhomboides), and blue crabs (Callinectes sapidus) from each location and analyzed for carbon, nitrogen, and phosphorus, along with sediment and seagrass samples from each location. Trace metal analyses were also conducted on all samples. Results from this study provide a
method for identifying ecologically important species that contribute to the health and continued growth of seagrass beds.

Seagrasses are essential in coastal ecosystems by providing important ecological benefits, including improved water quality, support for complex food webs, and stabilization of sediments which can reduce shoreline erosion. Increased nutrient concentrations can cause seagrass decline through light reduction caused by the overgrowth of epiphytes, macroalgae, or phytoplankton. Previous research has shown significant epiphyte biomass, nitrogen fixation and diazotroph abundances associated with seagrasses. Phytoplankton contain unique combinations of chlorophyll compounds. Chlorophyll analysis can provide biomass and be used to estimate general phyla information based on presence and abundance of certain chlorophyll compounds. This study will examine biomass, abundance and community composition of epiphytes associated with two species of seagrasses, Thalassia testudinum and Halodule wrightii.

Introduction: The Citizen Science Seagrass monitoring program began in 2017 to engage local citizens and train them in seagrass monitoring as part of an effort to develop a long-term monitoring program of seagrasses in the Pensacola Bay system. Periodic estimates of the extent seagrass beds began in 1974 with Escambia Bay Recovery Report (EPA 1975) and have continued with other aerial photographic surveys (Schwenning et al. 2007, Harvey et al. 2015, Byron et al. 2018). Monitoring of seagrass beds in Gulf Islands National Seashore began 1993 and has continued periodically (Heck and Byron 2014, Byron et al. 2018). The Pensacola and Perdido Bays Estuary Program has expanded on the existing programs in 2023 using aerial, satellite and Tier 2 boat surveys (Darnell et al. 2023)
Many shallow, clear lagoonal systems in the Gulf of Mexico contain extensive seagrass beds. Commercially and recreationally important fish and shellfish species find refuge, food or nursery areas in these beds as do a diverse faunal community including endangered species such as manatees and sea turtles. Biogeochemical cycling such as the fixation of carbon and nutrient transformations provides carbon to higher trophic levels and storage in sediments, the “blue carbon” which is a sink for carbon dioxide. Nutrient removal occurs by direct uptake by plants and burial into sediments. Seagrass can also enhance microbial nutrient removal by the processes of nitrification and denitrification or enhance nutrient inputs by nitrogen fixation.
This year protocols similar to UF “Eyes on Seagrass” were implemented for Big Lagoon and Santa Rosa Sound (https://www.flseagrant.org/citizenscience/eyes-on-seagrass/). Citizens collecting in the urban bayous or Pensacola Bay followed our previous protocols used between 2017 and 2022 (Caffrey et al. 2023). This report describes results from 2023.

Excerpt - The project provided key baseline information about the shallow continental shelf environment in the northeastern Gulf of Mexico. This area is poorly studied compared to other continental shelves such as the South Atlantic Bight. Colonization of benthic invertebrates increased secondary production. This in turn supports higher trophic levels, particularly the commercially important reef fishes such as snapper, triggerfish and sheepshead. Results from this work represent one of the few studies of primary production, biogeochemical cycling, and the implications to fisheries production in the northeastern Gulf of Mexico. With the increasing deployment of artificial reefs in Florida, this provides key information for management of these habitats.