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.

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.

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.