Spatial patterns of fish communities along two estuarine gradients in southern Florida

In tropical and subtropical estuaries, gradients of primary productivity and salinity are generally invoked to explain patterns in community structure and standing crops of fishes. We documented spatial and temporal patterns in fish community structure and standing crops along salinity and nutrient gradients in two subtropical drainages of Everglades National Park, USA. The Shark River drains into the Gulf of Mexico and experiences diurnal tides carrying relatively nutrient enriched waters, while Taylor River is more hydrologically isolated by the oligohaline Florida Bay and experiences no discernable lunar tides. We hypothesized that the more nutrient enriched system would support higher standing crops of fishes in its mangrove zone. We collected 50 species of fish from January 2000 to April 2004 at six sampling sites spanning fresh to brackish salinities in both the Shark and Taylor River drainages. Contrary to expectations, we observed lower standing crops and density of fishes in the more nutrient rich tidal mangrove forest of the Shark River than in the less nutrient rich mangrove habitats bordering the Taylor River. Tidal mangrove habitats in the Shark River were dominated by salt-tolerant fish and displayed lower species richness than mangrove communities in the Taylor River, which included more freshwater taxa and yielded relatively higher richness. These differences were maintained even after controlling for salinity at the time of sampling. Small-scale topographic relief differs between these two systems, possibly created by tidal action in the Shark River. We propose that this difference in topography limits movement of fishes from upstream marshes into the fringing mangrove forest in the Shark River system, but not the Taylor River system. Understanding the influence of habitat structure, including connectivity, on aquatic communities is important to anticipate effects of construction and operational alternatives associated with restoration of the Everglades ecosystem.

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g−1 vs. 107 μg g−1, respectively) and soil TP (284 μg g−1 vs. 145 μg g−1). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m−2). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly

Hydrologic Dynamics of the Ground-Water-Dependent Sian Ka’an Wetlands, Mexico, Derived from InSAR and SAR Data

The 5,280 km2 Sian Ka’an Biosphere Reserve includes pristine wetlands fed by ground water from the karst aquifer of the Yucatan Peninsula, Mexico. The inflow through underground karst structures is hard to observe making it difficult to understand, quantify, and predict the wetland dynamics. Remotely sensed Synthetic Aperture Radar (SAR) amplitude and phase observations offer new opportunities to obtain information on hydrologic dynamics useful for wetland management. Backscatter amplitude of SAR data can be used to map flooding extent. Interferometric processing of the backscattered SAR phase data (InSAR) produces temporal phase-changes that can be related to relative water level changes in vegetated wetlands. We used 56 RADARSAT-1 SAR acquisitions to calculate 38 interferograms and 13 flooding maps with 24 day and 48 day time intervals covering July 2006 to March 2008. Flooding extent varied between 1,067 km2 and 2,588 km2 during the study period, and main water input was seen to take place in sloughs during October–December. We propose that main water input areas are associated with water-filled faults that transport ground water from the catchment to the wetlands. InSAR and Landsat data revealed local-scale water divides and surface water flow directions within the wetlands.

Nutrient impacts on epifaunal density and species composition in a subtropical seagrass bed

The capacity of epifauna to control algal proliferation following nutrient input depends on responses of both grazers and upper trophic level consumers to enrichment. We examined the responses of Thalassia testudinum (turtle grass) epifaunal assemblages to nutrient enrichment at two sites in Florida Bay with varying levels of phosphorus limitation. We compared epifaunal density, biomass, and species diversity in 2 m2 plots that had either ambient nutrient concentrations or had been enriched with nitrogen and phosphorus for 6 months. At the severely P-limited site, total epifaunal density and biomass were two times higher in enriched than in unenriched plots. Caridean shrimp, grazing isopods, and gammarid amphipods accounted for much of the increase in density; brachyuran crabs, primary predatory fish, and detritivorous sea cucumbers accounted for most of the increase in biomass. At the less P-limited site, total epifaunal density and biomass were not affected by nutrient addition, although there were more caridean shrimp and higher brachyuran crab and pink shrimp biomass in enriched plots. At both sites, some variation in epifaunal density and biomass was explained by features of the macrophyte canopy, such as T. testudinum and Halodule wrightii percent cover, suggesting that enrichment may change the refuge value of the macrophyte canopy for epifauna. Additional variation in epifaunal density and biomass was explained by epiphyte pigment concentrations, suggesting that enrichment may change the microalgal food resources that support grazing epifauna. Increased epifaunal density in enriched plots suggests that grazers may be able to control epiphytic algal proliferation following moderate nutrient input to Florida Bay.

Salinity and Chlorophyll a as Performance Measures to Rehabilitate a Mangrove-Dominated Deltaic Coastal Region: the Ciénaga Grande de Santa Marta–Pajarales Lagoon Complex, Colombia

Salinity, water temperature, and chlorophyll a (chl-a) biomass were used as performance measures in the period 1999–2001 to evaluate the effect of a hydrological rehabilitation project in the Ciénaga Grande de Santa Marta (CGSM)–Pajarales lagoon complex, Colombia where freshwater diversions were initiated in 1995 and completed in 1998. The objective of this study was to evaluate how diversions of freshwater into previously hypersaline (>80) environments changed the spatial and temporal distribution of environmental characteristics. Following the diversion, 19 surveys and transects using a flow-through system were surveyed in the CGSM–Pajarales complex to continuously measure selected water quality parameters. Geostatistical analysis indicates that hydrology and salinity regimes and water circulation patterns in the CGSM lagoon are largely controlled by freshwater discharge from the Fundacion, Aracataca, and Sevilla Rivers. Residence times in the CGSM lagoon were similar before (15.5 ± 3.8 days) and after (14.2 ± 2.0 days) the rehabilitation project and indicated that the system is flushed regularly. In contrast, chl-a biomass was highly variable in the CGSM–Pajarales lagoon complex and not related to discharge patterns. Mean annual chl-a biomass (44–250 μg L−1) following the diversion project was similar to values recorded since the 1980s and still remains among the highest reported in coastal systems around the world owing to its unique hydrology regulated by the Magdalena River and Sierra Nevada de Santa Marta watersheds and the high teleconnection to the El Niño Southern Oscillation (ENSO). Our results confirm that the reduction in salinity in the CGSM lagoon and Pajarales complex during 1999–2000 was largely driven by high precipitation (2500 mm) induced by the ENSO–La Niña rather than by the freshwater diversions.

Adventures and Misfortunes in Macondo: Rehabilitation of the Cienaga Grande

We describe trajectories of selected ecological indicators used as performance measures to evaluate the success of a mangrove rehabilitation project in the Ciénaga Grande de Santa Marta (CGSM) Delta-Lagoon complex, Colombia, as result of freshwater diversions initiated in 1995. There is a significant reduction in soil and water column salinity in all sampling stations following the hydraulic reconnection of the Clarín and Aguas Negras channels to the Magdalena River. Soil intersticial water salinity (depth: 0.5 m) (7 stations) and water column salinity (0.5 m) (10 stations) values declined significantly (soil <30 g kg-1; water <10 g kg-1) from 1994 to 2000. During 1994 soil interstitial water salinity ranged from 40 g kg-1 (Rinconada) to 100 g kg-1 (KM 13), while water column salinity fluctuated between 25-35 g kg-1 for most of the sampling stations. This salinity reduction increased mangrove forest regeneration promoting a net gain of 99 km2 from 1995 to 1999. The high precipitation recorded in 1995 and 1999 caused by El Niño-La Niña (ENSO), coinciding with the channels rehabilitation, influenced rapid mangrove regeneration. The lack of economic investment in the maintenance of the diversion structures from 2001 to 2004 caused a salinity increase affecting negatively already restored vegetation. A sustainable effort from the international community and the Colombian government is needed to maintain the strategic social and economic benefits reached until 2000 in the CGSM region.

Patterns of nutrient exchange in a riverine mangrove forest in the Shark River Estuary, Florida, USA

This study aimed to evaluate tidal and seasonal variations in concentrations and fluxes of nitrogen (NH4 +, NO2+NO3, total nitrogen) and phosphorus (soluble reactive phosphorus, total phosphorus) in a riverine mangrove forest using the flume technique during the dry (May, December 2003) and rainy (October 2003) seasons in the Shark River Estuary, Florida. Tidal water temperatures during the sampling period were on average 29.4 (± 0.4) oC in May and October declining to 20 oC (± 4) in December. Salinity values remained constant in May (28 ± 0.12 PSU), whereas salinity in October and December ranged from 6‒21 PSU and 9‒25 PSU, respectively. Nitrate + nitrite (N+N) and NH4+ concentrations ranged from 0.0 to 3.5 μM and from 0 to 4.8 μM throughout the study period, respectively. Mean TN concentrations in October and December were 39 (±0.8) μM and 37 (±1.5) μM, respectively. SRP and N+N concentrations in the flume increased with higher frequency in flooding tides. TP concentrations ranged between 0.2‒2.9 μM with higher concentrations in the dry season than in the rainy season. Mean concentrations were <1. 5 μM during the sampling period in October (0.75 ± 0.02) and December (0.76 ± 0.01), and were relatively constant in both upstream and downstream locations of the flume. Water residence time in the flume (25 m2) was relatively short for any nutrient exchange to occur between the water column and the forest floor. However, the distinct seasonality in nutrient concentrations in the flume and adjacent tidal creek indicate that the Gulf of Mexico is the main source of SRP and N+N into the mangrove forest.

Biogeochemistry of Nitrogen Across the Everglades Landscape

Compared to phosphorus (P), nitrogen (N) has received little attention across the Everglades landscape. Despite this lack of attention, N plays important roles in many Everglades systems, including being a significant pollutant in Florida Bay and the Gulf of Mexico, the limiting nutrient in highly P-impacted areas, and an important substrate for microbial metabolism. Storage and transport of N throughout the Everglades is dominated by organic forms, including peat soils and dissolved organic N in the water column. In general, N sources are highest in the northern areas; however, atmospheric deposition and active N2 fixation by the periphyton components are a significant N source throughout most systems. Many of the processes involved in the wetland N cycle remain unmeasured for most of the Everglades systems. In particular, the lack of in situ rates for N2 fixation and denitrification prevent the construction of system-level budgets, especially for the Southern mangrove systems where N export into Florida Bay is critical. There is also the potential for several novel N processes (e.g., Anammox) with an as yet undetermined importance for nitrogen cycling and function of the Everglades ecosystem. Phosphorus loading alters the N cycle by stimulating organic N mineralization with resulting flux of ammonium and DON, and at elevated P concentrations, by increasing rates of N2 fixation and N assimilation. Restoration of hydrology has a potential for significantly impacting N cycling in the Everglades both in terms of affecting N transport, but also by altering aerobic-anaerobic transitions at the soil-water interface or in areas with seasonal drawdowns (e.g., marl prairies). Based on the authors’ understanding of N processes, much more research is necessary to adequately predict potential impacts from hydrologic restoration, as well as the function of Everglades systems as sinks, sources, and transformers of N in the South Florida landscape.

Changes in Community Structure of Sediment Bacteria Along the Florida Coastal Everglades Marsh–Mangrove–Seagrass Salinity Gradient

Community structure of sediment bacteria in the Everglades freshwater marsh, fringing mangrove forest, and Florida Bay seagrass meadows were described based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) patterns of 16S rRNA gene fragments and by sequencing analysis of DGGE bands. The DGGE patterns were correlated with the environmental variables by means of canonical correspondence analysis. There was no significant trend in the Shannon–Weiner index among the sediment samples along the salinity gradient. However, cluster analysis based on DGGE patterns revealed that the bacterial community structure differed according to sites. Not only were these salinity/vegetation regions distinct but the sediment bacteria communities were consistently different along the gradient from freshwater marsh, mangrove forest, eastern-central Florida Bay, and western Florida Bay. Actinobacteria- and Bacteroidetes/Chlorobi-like DNA sequences were amplified throughout all sampling sites. More Chloroflexi and members of candidate division WS3 were found in freshwater marsh and mangrove forest sites than in seagrass sites. The appearance of candidate division OP8-like DNA sequences in mangrove sites distinguished these communities from those of freshwater marsh. The seagrass sites were characterized by reduced presence of bands belonging to Chloroflexi with increased presence of those bands related to Cyanobacteria, γ-Proteobacteria, Spirochetes, and Planctomycetes. This included the sulfate-reducing bacteria, which are prevalent in marine environments. Clearly, bacterial communities in the sediment were different along the gradient, which can be explained mainly by the differences in salinity and total phosphorus.

An assessment of the microbial contribution to aquatic dissolved organic nitrogen using amino acid enantiomeric ratios

There is increasing evidence that certain microbially-derived compounds may account for part of the aquatic dissolved organic nitrogen (DON) pool. Enantiomeric ratios of amino acids were used to assess the microbial input to the DON pool in the Florida Everglades, USA. Elevated levels of d-alanine, d-aspartic acid, d-glutamic acid and d-serine indicated the presence of peptidoglycan in the samples. The estimated peptidoglycan contribution to amino acid nitrogen ranged from 2.8 ± 0.1% to 6.4 ± 0.9%, increasing with salinity from freshwater to coastal waters. The distribution of individual d-amino acids in the samples suggests additional inputs to DON, possibly from archaea or from abiotic racemization of l-amino acids.

Molecular characterization of proteinaceous material in the Florida coastal Everglades

Dissolved organic nitrogen (DON) is the least known component of the nitrogen cycle, in part as a result of the lack of adequate analytical methods for its molecular characterization. In this study proteinaceous material in DON, collected at six geomorphologically different sites in the Florida coastal Everglades, was characterized by amino acid analysis and protein gel electrophoresis. The amino acid composition of the samples suggests that the canal DON was more degraded and subject to higher microbial inputs than the mangrove marshwater and marine end-member stations. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) results supported this observation as distinctly different protein profiles were obtained for the canal waters compared to samples collected at other stations. These preliminary results highlight the potential of combining amino acid and intact protein analysis to fingerprint the sources of DON in different aquatic environments, and show SDS-PAGE as a potentially useful method to characterize DON.

One-dimensional and two-dimensional polyacrylamide gel electrophoresis: a tool for protein characterisation in aquatic samples

Dissolved organic nitrogen (DON) represents the least understood part of the nitrogen cycle. Due to recent methodological developments, proteins now represent a potentially characterisable fraction of DON at the macromolecular level. We have applied polyacrylamide gel electrophoresis to characterise proteins in samples from a range of aquatic environments in the Everglades National Park, Florida, USA. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed that each sample has a complex and characteristic protein distribution. Some proteins appeared to be common to more than one site, and these might derive from dominant higher plant vegetation. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) provided better resolution; however, strong background hindered interpretation. Our results suggest that the two techniques can be used in parallel as a tool for protein characterisation: SDS-PAGE to provide a sample-specific fingerprint and 2D-PAGE to focus on the characterisation of individual protein molecules.

Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades

Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations, water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic) and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic, they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton net production of 1.08 mg C AFDW−1 h−1 and periphyton whole system respiration of 0.38 mg C AFDW−1 h−1 rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean biomass over all our study sites was high, 1517.30 g AFDW m−2. Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g−1 and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely low mean water total phosphorus concentrations ( ≤ 0.21 μmol l−1), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows. These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water source.

Modeling seasonal dynamics of small fish cohorts in fluctuating freshwater marsh landscapes

Small-bodied fishes constitute an important assemblage in many wetlands. In wetlands that dry periodically except for small permanent waterbodies, these fishes are quick to respond to change and can undergo large fluctuations in numbers and biomasses. An important aspect of landscapes that are mixtures of marsh and permanent waterbodies is that high rates of biomass production occur in the marshes during flooding phases, while the permanent waterbodies serve as refuges for many biotic components during the dry phases. The temporal and spatial dynamics of the small fishes are ecologically important, as these fishes provide a crucial food base for higher trophic levels, such as wading birds. We develop a simple model that is analytically tractable, describing the main processes of the spatio-temporal dynamics of a population of small-bodied fish in a seasonal wetland environment, consisting of marsh and permanent waterbodies. The population expands into newly flooded areas during the wet season and contracts during declining water levels in the dry season. If the marsh dries completely during these times (a drydown), the fish need refuge in permanent waterbodies. At least three new and general conclusions arise from the model: (1) there is an optimal rate at which fish should expand into a newly flooding area to maximize population production; (2) there is also a fluctuation amplitude of water level that maximizes fish production, and (3) there is an upper limit on the number of fish that can reach a permanent waterbody during a drydown, no matter how large the marsh surface area is that drains into the waterbody. Because water levels can be manipulated in many wetlands, it is useful to have an understanding of the role of these fluctuations.

Science behind management of Shark Bay and Florida Bay, two P-limited subtropical systems with different climatology and human pressures

This special issue on ‘Science for the management of subtropical embayments: examples from Shark Bay and Florida Bay’ is a valuable compilation of individual research outcomes from Florida Bay and Shark Bay from the past decade and addresses gaps in our scientific knowledge base in Shark Bay especially. Yet the compilation also demonstrates excellent research that is poorly integrated, and driven by interests and issues that do not necessarily lead to a more integrated stewardship of the marine natural values of either Shark Bay or Florida Bay. Here we describe the status of our current knowledge, introduce the valuable extension of the current knowledge through the papers in this issue and then suggest some future directions. For management, there is a need for a multidisciplinary international science program that focusses research on the ecological resilience of Shark Bay and Florida Bay, the effect of interactions between physical environmental drivers and biological control through behavioural and trophic interactions, and all under increased anthropogenic stressors. Shark Bay offers a ‘pristine template’ for this scale of study.