Spatial variability in Florida Bay particulate organic matter composition: combining flow cytometry with stable isotope analyses

Abstract

Long-term management plans for restoration of natural flow conditions through the Everglades increase the importance of understanding potential nutrient impacts of increased freshwater delivery on Florida Bay biogeochemistry. Planktonic communities respond quickly to changes in water quality, thus spatial variability in community composition and relationships to nutrient parameters must be understood in order to evaluate future downstream impacts of modifications to Everglades hydrology. Here we present initial results combining flow cytometry analyses of phytoplankton and bacterial populations (0.1-50 lm size fraction) with measurements of d 13 C and d 15 N composition and dissolved inorganic nutrient concentrations to explore proxies for planktonic species assemblage compositions and nutrient cycling. Particulate organic material in the 0.1-50 lm size fraction was collected from five stations in Northeastern and Western Florida Bay to characterize spatial variability in species assemblage and stable isotopic composition. A dense bloom of the picocyanobacterium, Synechococcus elongatus, was observed at Western Florida Bay sites. Smaller Synechococcus sp. were present at Northeast sites in much lower abundance. Bacteria and detrital particles were also more abundant at Western Florida Bay stations than in the northeast region. The highest abundance of detritus occurred at Trout Creek, which receives freshwater discharge from the Everglades through Taylor Slough. In terms of nutrient availability and stable isotopic values, the S. elongatus population in the Western bay corresponded to low DIN (0.5 lM NH 4 + ; 0.2 lM NO 3 ) ) concentrations and depleted d 15 N signatures ranging from +0.3 to +0.8&, suggesting that the bloom supported high productivity levels through N 2 -fixation. d15 N values from the Northeast bay were more enriched (+2.0 to +3.0&), characteristic of N-recycling. d13 C values were similar for all marine Florida Bay stations, ranging from )17.6 to )14.4&, however were more depleted at the mangrove ecotone station ()25.5 to )22.3&). The difference in the isotopic values reflects differences in carbon sources. These findings imply that variations in resource availability and nutrient sources exert significant control over planktonic community composition, which is reflected by stable isotopic signatures.

Baselines and Degradation of Coral Reefs in the Northern Line Islands

“…It is interesting that the concentration of nutrients (DIN and SRP) around all four of the northern Line Islands surveyed are higher than the hypothesized thresholds for outbreaks of macroalgal blooms [68] and are well within the range for polluted Florida Bay (e.g., 0.7 to 10.7 µMol for DIN) [69] . Nevertheless, macroalgal blooms are absent at Kingman and Palmyra, which suggests that grazing activity on unpopulated reefs may control macroalgal abundance even at high inorganic nutrient concentrations.…”

Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA

“…Phytoplankton blooms dominated by Synechococcus spp. were first observed in 1992 and also continue intermittently, primarily in the north-central and eastern regions of the bay (Phlips et al 1999;Evans et al 2006).…”

Distribution of foraging habitats of male loggerhead turtles (Caretta caretta) as revealed by stable isotopes and satellite telemetry

“…Food web baseline signatures along the latitudinal gradient used by loggerheads are scarce; however, nitrogen isotopic signatures of particulate organic matter (proxy for primary producer) are available for the Florida Keys (»25°N) and coastal waters of Virginia and Delaware (»37° and 39°N, respectively). Nitrogen values range from ¡0.9 (Macko et al 1984) to 3.6‰ in waters of the Florida Keys (Behringer and Butler 2006; Evans et al 2006;Lamb and Swart 2008) and 7.2-7.7‰ in near-shore waters oV Virginia and Delaware (McKinney et al 2010). Hence, although we did not assess the isotopic signatures of loggerhead prey items in all the geographic locations visited by the turtles, the results indicate that the variation in the 13 C and 15 N of male loggerheads is due to geographic location.…”