Negative relationships between the nutrient and carbohydrate content of the seagrass Thalassia testudinum

This study documents relationships between plant nutrient content and rhizome carbohydrate content of a widely distributed seagrass species, Thalassia testudinum, in Florida. Five distinct seagrass beds were sampled for leaf nitrogen, leaf phosphorus, and rhizome carbohydrate content from 1997 to 1999. All variables displayed marked intra- and inter- regional variation. Elemental ratios (mean N:P ± S.E.) were lowest for Charlotte Harbor (9.9 ± 0.2) and highest for Florida Bay (53.5 ± 0.9), indicating regional shifts in the nutrient content of plant material. Rhizome carbohydrate content (mean ± S.E.) was lowest for Anclote Keys (21.8 ± 1.6 mg g−1 FM), and highest for Homosassa Bay (40.7 ± 1.7 mg g−1 FM). Within each region, significant negative correlations between plant nutrient and rhizome carbohydrate content were detected; thus, nutrient-replete plants displayed low carbohydrate content, while nutrient-deplete plants displayed high carbohydrate content. Spearman\u27s rank correlations between nutrient and carbohydrate content varied from a minimum in Tampa Bay (ρ = −0.2) to a maximum in Charlotte Harbor (ρ = −0.73). Linear regressions on log-transformed data revealed similar trends. This consistent trend across five distinct regions suggests that nutrient supply may play an important role in the regulation of carbon storage within seagrasses. Here we present a new hypothesis for studies which aim to explain the carbohydrate dynamics of benthic plants

Biomass and Productivity of Thalassia testudinum in Estuaries of the Florida Panhandle

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

Optical Variability along a River Plume Gradient: Implications for Management and Remote Sensing

Effective assessment and management of seagrass distributions require a thorough understanding of the water environment, in particular the inherent optical properties (IOPs) of the water column, and the linkage with environmental forcing such as coastal run-off. Coastal waters off the Suwannee and Steinhatchee rivers in the northeastern Gulf of Mexico where seagrass is abundant were sampled regularly in 2010 and 2011 during periods ranging from normal spring flooding to record-low flow conditions associated with widespread drought. Relationships between surface salinities, chlorophyll a concentrations (Chl-a), and IOPs were examined to characterize the optical variability of this region as well as its connection with river discharge and wind forcing. Significant spatial and temporal variability was observed for Chl-a (0.285–14.4 mg m−3), colored dissolved organic matter (CDOM) absorption at 443 nm, aCDOM(443), (0.042–7.53 m−1), and particulate backscattering at 660 nm, bbp(660), (0.002–0.067 m−1) with gradients evident between nearshore (riverine) and offshore (oceanic) waters. Overall, CDOM was the dominant optically significant constituent (OSC), contributing ∼74–75 ± 11% to total (non-water) absorption at 443 nm and 555 nm. CDOM was mainly controlled by river flow, with an inverse correlation observed between aCDOM(443) and salinity (r2 = 0.66). Chl-a showed less direct dependence on flow, exhibiting elevated concentrations (\u3e5 mg m−3) mainly during the summer. Particulate backscattering in this region was relatively low and largely controlled by non-algal particles, as was evident by the strong relationship between bbp(660) and detrital absorption at 443 nm, ad(443) (r2 = 0.71). Compared with other coastal waters in the eastern Gulf of Mexico, aCDOM(443) was ∼3–5 times higher and bbp(660) was ∼50% lower, making the study region very dark. Given that the optical properties of coastal waters in this region are strongly influenced by CDOM derived from terrestrial discharge, remote-sensing algorithms for determining long-term Chl-a trends should focus on utilizing wavebands less influenced by CDOM

Florida Gulf Bay Scallop (Argopecten Irradians Concentricus) Population Genetic Structure: Form, Variation, and Influential Factors

Knowledge of changes in the interdependence of a species\u27 populations for continued existence (connectivity) and of the forces driving connectivity patterns is critical for management and conservation of the species. Population genetics can be used to investigate population connectivity. Combining population genetics with climatic, environmental, and biological (external) factors that can influence population structure and connectivity can lead to a greater understanding of the forces influencing population dynamics. We deciphered the population genetic structure and connectivity patterns of bay scallops (Argopecten irradians concentricus Lamarck) from Florida Gulf of Mexico waters using allozyme-locus and mitochondrial DNA population genetics data from samples representing four consecutive generations. We evaluated bay scallop population genetic relationships within the context of habitat, hydrodynamic, and environmental variation, and concomitant spatial patterns in the abundance of adult and recently recruited scallops to infer the influence of these factors on bay scallop population structure. Florida Gulf bay scallops form a hierarchical, mixed-model, source-sink metapopulation with intergenerational variation in connectivity that seems to be influenced by the factors we considered. An El Niño event that occurred during 1 y caused climatic and environmental change that greatly reduced subpopulation connectivity, allowing us to understand more completely the potential relative importance of the other external factors on change in metapopulation connectivity over time. Our study illustrates the value of using multiple genetic markers, sampling for multiple years, and integrating data from multiple external factors for understanding the population genetic structure of species for adaptive management