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Benthic primary production in Florida Bay is mainly driven by mangroves, seagrass, peryphiton, and macroalgae. The nutrient dynamics and salinity regimes at Florida Bay are strongly influenced by marine waters from the Gulf of Mexico, oceanic waters from the Atlantic Ocean and fresh waters from the Everglades creating a complex estuary with oligohaline ecotones. Marine and groundwater are sources of P and are expected to decline with increased freshwater inflow (Childers et al. 2006a; Price et al. 2006). The Taylor Slough ecotone, (TS/Ph), which flows into the Bay, is characterized by small tidal influence and clear seasonal variability in water source and quality (Davis et al. 2003; Sutula et al. 2001), receives P from shallow groundwater inputs (Price et al. 2006).Therefore the amount of freshwater inputs from the Everglades will affect salinity, water residence times, and the sources, availability, and flux of organic and inorganic nutrients on Florida Bay. As a consequence gradients of N and P concentrations are characteristic in the Bay with expected low concentration of P and high N on the fresh water end, contrasting with higher levels of P and lower of N towards the marine section of the Bay. This gradient in P concentrations is expected to reflect in differences in both primary production and biomass along the TS/Ph ecotone. One of the Everglades LTER scientist general hypothesis is "that increasing inputs of freshwater will enhance oligotrophy in nutrient-poor coastal systems, as long as the inflowing water has low nutrient content; this dynamic will be most pronounced in the oligohaline ecotone" (LTER program). In this context we expect to have a differential production of calcareous macroalgae along the TS-Ph transect which reflect the P gradient with low productivity towards the fresh water influenced sites close to the Everglades increasing towards the marine section of the Bay. We document the primary production of calcareous green macroalgae along the TS-Ph transect including three contrasting environments at Florida Bay. The transect include site TS-Ph 9 located near Duck Key in oligotrophic northeastern Florida Bay; TS-Ph 10 is located near Bob Allen Keys in the oligotrophic center Florida Bay and TS-Ph 11 is located near Sprigger Bank at the western open boundary between Florida Bay and the Gulf of Mexico.In order to survey the temporal and spatial variability in production of calcareous marine macroalgae, a monitoring survey was started in 2007 on the three TS-Ph transect. In each site 3 hazard selected quadrats were sampled for biomass, CaCO3 production and species ID, and abundance using Braun Blanquet Index. Surveys are conducted bimonthly.Results show a significant difference on production with a high abundance and biomass at Sprigger Bank (Ts-Ph11) compared with lower values at Bob Allan Key and Duck Key. Seasonal changes show a higher production in summer compared with winter periods. The long term trend shows a decline on production in Sprigger Bank. Thalli CaCO3 content has a linear relation with biomass (carbon content) indicating a constant relationship between CaCO3 fixation and algae size-biomass. As a general trend we document a higher calcareous green macroalgae production towards the marine sites, consistent with the fact that the TS-Ph transect shows an enhanced productivity in the TS/Ph toward the marine end of the Bay (Fourqurean et al., 1992). A decline in calcareous green macroalgae at Sprigger Bank is reported based on 4 years of survey, which might have consequences on sand production for this site, moreover this will eventually change the sediment characteristics of this site. Our long term data set is a base line that will allow us detect potential changes in CaCO3 fixation by calcareous green macroalgae as a consequence of predicted acidification of the oceans.
