Macroalgae Production in Florida Bay (FCE LTER), South Florida, USA, May 2007 - April 2023

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.

佛罗里达湾（Florida Bay）的底栖初级生产力（benthic primary production）主要由红树（mangroves）、海草（seagrass）、周丛生物（periphyton）与大型藻类（macroalgae）驱动。佛罗里达湾的营养盐动态与盐度格局（salinity regimes）深受墨西哥湾（Gulf of Mexico）海水、大西洋（Atlantic Ocean）外海水体以及大沼泽地（Everglades）淡水的共同影响，由此形成了包含寡盐生态交错带（oligohaline ecotones）的复杂河口生态系统。海水与地下水是磷（P）的来源，随着淡水输入量增加，该磷来源预计会有所减少（Childers等，2006a；Price等，2006）。

注入佛罗里达湾的泰勒斯劳生态交错带（Taylor Slough ecotone，缩写TS/Ph）潮汐影响微弱，其水源与水质具有显著的季节波动特征（Davis等，2003；Sutula等，2001），其磷来源为浅层地下水输入（Price等，2006）。因此，大沼泽地的淡水输入量会影响佛罗里达湾的盐度、水滞留时间（water residence times）以及有机与无机营养盐的来源、可利用性与通量。

由此，氮（N）与磷（P）的浓度梯度成为佛罗里达湾的典型特征：淡水端磷浓度较低、氮浓度较高，而朝向海湾海洋区段则磷浓度升高、氮浓度降低。这种磷浓度梯度预计会体现在TS/Ph生态交错带沿线的初级生产力与生物量差异上。

大沼泽地长期生态研究（Long-Term Ecological Research, LTER）项目的科学家提出的一般性假说为："若输入淡水的营养盐含量较低，则淡水输入增加会加剧贫营养沿海系统的寡营养化状态，这一效应在寡盐生态交错带中最为显著"（LTER项目）。在此背景下，我们推测TS-Ph样带沿线的钙化大型藻类（calcareous macroalgae）生产力存在差异：靠近大沼泽地、受淡水影响的站点生产力较低，而朝向海湾海洋区段的站点生产力逐步升高，这一差异正反映了磷浓度梯度。

本研究记录了佛罗里达湾TS-Ph样带沿线钙化绿色大型藻类的初级生产力，涵盖三种截然不同的生境。该样带包含三个站点：TS-Ph 9位于佛罗里达湾东北部寡营养水域的达克礁（Duck Key）附近；TS-Ph 10位于佛罗里达湾中部寡营养水域的鲍勃·艾伦礁群（Bob Allen Keys）附近；TS-Ph 11位于佛罗里达湾与墨西哥湾西部开放边界的斯普里格浅滩（Sprigger Bank）附近。

为调查钙化海洋大型藻类生产力的时空变异，研究团队于2007年针对这三个TS-Ph样带站点启动了监测工作。每个站点随机选取3个样方（quadrats），采用布朗-布朗凯多度指数（Braun Blanquet Index）进行物种鉴定、多度统计，并取样测定生物量与碳酸钙（CaCO3）生产量。监测工作每两个月开展一次。

研究结果显示，各站点的藻类生产力存在显著差异：斯普里格浅滩（TS-Ph11）的藻类多度与生物量较高，而鲍勃·艾伦礁群与达克礁的相关数值较低。季节变化特征表现为夏季生产力显著高于冬季。长期趋势显示，斯普里格浅滩的藻类生产力呈下降趋势。藻体（Thalli）的碳酸钙含量与生物量（以碳计）呈线性相关，表明碳酸钙固定量与藻类体型-生物量之间存在恒定关系。

总体而言，我们观测到朝向海洋站点的钙化绿色大型藻类生产力更高，这与TS/Ph生态交错带朝向海湾海洋区段的生产力提升的研究结果一致（Fourqurean等，1992）。基于4年的监测数据，我们报道了斯普里格浅滩钙化绿色大型藻类的衰退现象，这可能对该站点的沙源产生影响，并最终改变该站点的沉积物特征。本研究的长期数据集可作为基准，用于监测因海洋酸化预测事件导致的钙化绿色大型藻类碳酸钙固定量的潜在变化。