Developing performance measures of mangrove wetlands using simulation models of hydrology, nutrient biogeochemistry, and community dynamics

The goal of mangrove restoration projects should be to improve community structure and ecosystem function of degraded coastal landscapes. This requires the ability to forecast how mangrove structure and function will respond to prescribed changes in site conditions including hydrology, topography, and geophysical energies. There are global, regional, and local factors that can explain gradients of regulators (e.g., salinity, sulfides), resources (nutrients, light, water), and hydroperiod (frequency, duration of flooding) that collectively account for stressors that result in diverse patterns of mangrove properties across a variety of environmental settings. Simulation models of hydrology, nutrient biogeochemistry, and vegetation dynamics have been developed to forecast patterns in mangroves in the Florida Coastal Everglades. These models provide insight to mangrove response to specific restoration alternatives, testing causal mechanisms of system degradation. We propose that these models can also assist in selecting performance measures for monitoring programs that evaluate project effectiveness. This selection process in turn improves model development and calibration for forecasting mangrove response to restoration alternatives. Hydrologic performance measures include soil regulators, particularly soil salinity, surface topography of mangrove landscape, and hydroperiod, including both the frequency and duration of flooding. Estuarine performance measures should include salinity of the bay, tidal amplitude, and conditions of fresh water discharge (included in the salinity value). The most important performance measures from the mangrove biogeochemistry model should include soil resources (bulk density, total nitrogen, and phosphorus) and soil accretion. Mangrove ecology performance measures should include forest dimension analysis (transects and/or plots), sapling recruitment, leaf area index, and faunal relationships. Estuarine ecology performance measures should include the habitat function of mangroves, which can be evaluated with growth rate of key species, habitat suitability analysis, isotope abundance of indicator species, and bird census. The list of performance measures can be modified according to the model output that is used to define the scientific goals during the restoration planning process that reflect specific goals of the project.

Relações ecologicas entre caranguejos e composição arbórea em bosques de mangue naturais e restaurados no nordeste brasileiro

This study aimed to compare the development of crab and tree communities of two restored mangrove areas, one planted with Rhizophora mangle and the other naturally recovered, and also to compare the predation of Grapsid crab Goniopsis cruentata and the Ocypodid Ucides cordatus over the propagules of three mangrove trees: Rhizophora mangle, Avicennia schaueriana e Laguncularia racemosa. Specifically, we tested the hypothesis that Goniopsis predation is more important that Ucides predation, and that these consumers have antagonist effects over propagule consumption. In each area, 10 quadrates were selected at random to analyze tree richness, diameter, height, tree biomass and crab richness and density five years after restoration experiment start. Results show that tree height, biomass and crab density were significantly higher in artificially restored area. No significant differences were observed in crab species richness between areas, but higher tree richness was observed in self-recovered area. Results suggest that planting propagules of Rhizophora can significantly increase tree recovering if the aim was increase tree biomass and crab density, which can accelerate return of ecological functionality. Goniopsis is a more important propagule predator than Ucides both in natural and restored areas. The effects of Goniopis were higher in absence of Ucides, due to negative interactions among these two predator species. The preference of Goniopsis by Avicennia and Laguncularia can favor the dominance of Rhizophora observed in Neotropical mangroves. This study suggests that propagule predation by Goniopsis should be controlled in restoration programs, if dominance of Rhizophora is undesirable respect to more rich tree communities

Secondary succession impairment in restored mangroves

In this work it was hypothesized that secondary succession on sites that have been managed by single planting of mangrove species is compromised by residual stressors, which could reduce the ecosystem's structural development and lower its functions. Forest structure and environmental characteristics of three planted mangrove stands are compared with reference sites. Structural attributes showed significant differences in the comparison of planted and reference stands. Avicennia schaueriana was the dominant species within both natural regeneration and old-growth stands in terms of basal area (99.2 and 99.4 %, 69.6 and 84.5 %, and 59.0 and 87.1 % for Itacorubi, Saco Grande, and Ratones, respectively). Restoration stands were dominated by Laguncularia racemosa (80.6 and 94.2 % for Saco Grande and Ratones, respectively), except at one site (Itacorubi), where A. schaueriana prevailed (99.7 %). Even though restoration and regeneration stands at Itacorubi showed similar species composition and dominance, cohort sorting revealed an inferior regeneration potential in the restoration stand. Multiple correlation analysis indicated that variables related to elevation disruptions (p (w) = 0.521) were the environmental drivers responsible for the differences observed in forest structure. At restoration sites an impaired pattern of secondary succession was observed, indicating that single species plantings may be ineffective if characteristics of the site, as well as of the area surrounding it, are not considered. The inadequate management of restoration sites can therefore have implications for both immediate and long-term large-scale ecosystem services.

Shifting N and P limitation along a north-south gradient of mangrove estuaries in South Florida

A multivariate statistical analysis was applied to a 10 year, multiparameter data set in an effort to describe the spatial dependence and inherent variation of water quality patterns in the mangrove estuaries of Ten Thousand Islands – Whitewater Bay area. Principal component analysis (PCA) of 16 water quality parameters collected monthly resulted in five groupings, which explained 72.5% of the variance of the original variables. The “Organic” component (PCI) was composed of alkaline phosphatase activity, total organic nitrogen, and total organic carbon; the “Dissolved Inorganic N” component (PCII) contained NO 3 − , NO 2 − , and NH 4 + ; the “Phytoplankton” component (PCIII) was made up of total phosphorus, chlorophyll a, and turbidity; dissolved oxygen and temperature were inversely related (PCIV); and salinity and soluble reactive phosphorus made up PCV. A cluster analysis of the mean and SD of PC scores resulted in the spatial aggregation of the 47 fixed stations into six classes having similar water quality, which we defined as: Mangrove Rivers, Whitewater Bay, Gulf Islands, Coot Bay, Blackwater River, and Inland Waterway. Marked differences in physical, chemical, and biological characteristics among classes were illustrated by this technique. Comparison of medians and variability of parameters among classes allowed large scale generalizations as to underlying differences in water quality in these regions. A strong south to north gradient in estuaries from high N - low P to low N - high P was ascribed to marked differences in landuse, freshwater input, geomorphology, and sedimentary geology along this tract. The ecological significance of this gradient discussed along with potential effects of future restoration plans.

Pink shrimp as an indicator for restoration of everglades ecosystems

The pink shrimp, Farfantepenaeus duorarum, familiar to most Floridians as either food or bait shrimp, is ubiquitous in South Florida coastal and offshore waters and is proposed as an indicator for assessing restoration of South Florida's southern estuaries: Florida Bay, Biscayne Bay, and the mangrove estuaries of the lower southwest coast. Relationships between pink shrimp and salinity have been determined in both field and laboratory studies. Salinity is directly relevant to restoration because the salinity regimes of South Florida estuaries, critical nursery habitat for the pink shrimp, will be altered by changes in the quantity, timing, and distribution of freshwater inflow planned as part of the Comprehensive Everglades Restoration Project (CERP). Here we suggest performance measures based on pink shrimp density (number per square meter) in the estuaries and propose a restoration assessment and scoring scheme using these performance measures that can readily be communicated to managers, policy makers, and the interested public. The pink shrimp is an appropriate restoration indicator because of its ecological as well as its economic importance and also because scientific interest in pink shrimp in South Florida has produced a wealth of information about the species and relatively long time series of data on both juveniles in estuarine nursery habitats and adults on the fishing grounds. We suggest research needs for improving the pink shrimp performance measure.

Factors affecting the concentration and flux of materials in two southern Everglades mangrove wetlands

Concentrations and fluxes of C, N, and P were measured in dwarf and fringe mangrove wetlands along the Taylor River, Florida, USA from 1996 to 1998. Data from these studies revealed considerable spatial and temporal variability. Concentrations of C, N, and P in the dwarf wetland showed seasonal trends, while water source was better at explaining concentrations in the fringe wetland. The total and dissolved organic carbon (TOC and DOC), total nitrogen (TN), and total phosphorus (TP) content of both wetlands was higher during the wet season or when water was flowing to the south (Everglades source). Concentrations of nitrate plus nitrite (NOx –), ammonium (NH4 +), and soluble reactive phosphorus (SRP) in the fringe wetland were all highest during the dry season or northerly flow (bay source). Nutrient concentrations most effectively explained patterns of flux in both wetlands. Increased wetland uptake of a given constituent was usually a function of its availability in the water column. However, the release of NOx – from the dwarf wetland was related to the NH4 + concentration, suggesting a nitrification signal. Nitrogen flux in the dwarf wetland was also related to surface water salinity and temperature. Our findings indicate that freshwater Everglades marshes are an important source of dissolved organic matter to these wetlands, while Florida Bay may be a source of dissolved inorganic nutrients. Our data also suggest that temperature, salinity, and nutrient concentrations (as driven by season and water source) influence patterns of materials flux in this mangrove wetland. Applying long-term water quality data to the relationships we extracted from these flux data, we estimated that TN and TP were imported by the dwarf wetland 87 ± 10 and 48 ± 17% of the year, respectively. With Everglades restoration, modifications in freshwater delivery may have considerable effects on the exchanges of nutrients and organic matter in these transitional mangrove wetlands.

A conceptual model of ecological interactions in the mangrove estuaries of the Florida Everglades

A brackish water ecotone of coastal bays and lakes, mangrove forests, salt marshes, tidal creeks, and upland hammocks separates Florida Bay, Biscayne Bay, and the Gulf of Mexico from the freshwater Everglades. The Everglades mangrove estuaries are characterized by salinity gradients that vary spatially with topography and vary seasonally and inter-annually with rainfall, tide, and freshwater flow from the Everglades. Because of their location at the lower end of the Everglades drainage basin, Everglades mangrove estuaries have been affected by upstream water management practices that have altered the freshwater heads and flows and that affect salinity gradients. Additionally, interannual variation in precipitation patterns, particularly those caused to El Nin˜o events, control freshwater inputs and salinity dynamics in these estuaries. Two major external drivers on this system are water management activities and global climate change. These drivers lead to two major ecosystem stressors: reduced freshwater flow volume and duration, and sea-level rise. Major ecological attributes include mangrove forest production, soil accretion, and resilience; coastal lake submerged aquatic vegetation; resident mangrove fish populations; wood stork (Mycteria americana) and roseate spoonbill (Platelea ajaja) nesting colonies; and estuarine crocodilian populations. Causal linkages between stressors and attributes include coastal transgression, hydroperiods, salinity gradients, and the ‘‘white zone’’ freshwater/estuarine interface. The functional estuary and its ecological attributes, as influenced by sea level and freshwater flow, must be viewed as spatially dynamic, with a possible near-term balancing of transgression but ultimately a long-term continuation of inland movement. Regardless of the spatio-temporal timing of this transgression, a salinity gradient supportive of ecologically functional Everglades mangrove estuaries will be required to maintain the integrity of the South Florida ecosystem.

Seasonal fish community variation in headwater mangrove creeks in the southwestern Everglades: an examination of their role as dry-down refuges

The connectivity between the fish community of estuarine mangroves and that of freshwater habitats upstream remains poorly understood. In the Florida Everglades, mangrove-lined creeks link freshwater marshes to estuarine habitats downstream and may act as dry-season refuges for freshwater fishes. We examined seasonal dynamics in the fish community of ecotonal creeks in the southwestern region of Everglades National Park, specifically Rookery Branch and the North and watson rivers. Twelve low-order creeks were sampled via electrofishing, gill nets, and minnow traps during the wet season, transition period, and dry season in 2004-2005. Catches were greater in Rookery Branch than in the North and watson rivers, particularly during the transition period. Community composition varied seasonally in Rookery Branch, and to a greater extent for the larger species, reflecting a pulse of freshwater taxa into creeks as marshes upstream dried periodically. The pulse was short-lived, a later sample showed substantial decreases in freshwater fish numbers. No evidence of a similar influx was seen in the North and watson rivers, which drain shorter hydroperiod marshes and exhibit higher salinities. These results suggest that head-water creeks can serve as important dry-season refugia. Increased freshwater flow resulting from Everglades restoration may enhance this connectivity.

The Role of the Everglades Mangrove Ecotone Region (EMER) in Regulating Nutrient Cycling and Wetland Productivity in South Florida

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height <3 m cover 49% of the EMER, particularly in the SE region. These scrub/dwarf mangroves are the result of a combination of low soil phosphorus (P < 59 μg P g dw−1) in the calcareous marl substrate and long hydroperiod. Phosphorus limits the EMER and its freshwater watersheds due to the lack of terrigenous sediment input and the phosphorus-limited nature of the freshwater Everglades. Reduced freshwater delivery over the past 50 years, combined with Everglades compartmentalization and a 10 cm rise in coastal sea level, has led to the landward transgression (1.5 km in 54 years) of the mangrove ecotone. Seasonal variation in freshwater input strongly controls the temporal variation of nitrogen and P exports (99%) from the Everglades to Florida Bay. Rapid changes in nutrient availability and vegetation distribution during the last 50 years show that future ecosystem restoration actions and land use decisions can exert a major influence, similar to sea level rise over the short term, on nutrient cycling and wetland productivity in the EMER.

Subtroprical wetland fish assemblages and changing salinity regimes: Implications for everglades restoration

During the 1960s, water management practices resulted in the conversion of the wetlands that fringe northeastern Florida Bay (USA) from freshwater/oligohaline herbaceous marshes to dwarf red mangrove forests. Coincident with this conversion were several ecological changes to Florida Bay’s fauna, including reductions in the abundances of top trophic-level consumers: piscivorous fishes, alligators, crocodiles, and wading birds. Because these taxa rely on a common forage base of small demersal fishes, food stress has been implicated as playing a role in their respective declines. In the present study, we monitored the demersal fishes seasonally at six sites over an 8-year time period. During monitoring, extremely high rainfall conditions occurred over a 3.5-year period leading to salinity regimes that can be viewed as “windows” to the area’s natural past and future restored states. In this paper, we: (1) examine the changes in fish communities over the 8-year study period and relate them to measured changes in salinity; (2) make comparisons among marine, brackish and freshwater demersal fish communities in terms of species composition, density, and biomass; and (3) discuss several implications of our findings in light of the intended and unintended water management changes that are planned or underway as part of Everglades restoration. Results suggest the reduction in freshwater flow to Florida Bay over the last several decades has reduced demersal fish populations, and thus prey availability for apex consumers in the coastal wetlands compared to the pre-drainage inferred standard. Furthermore, greater discharge of freshwater toward Florida Bay may result in the re-establishment of pre-1960s fauna, including a more robust demersal-fish community that should prompt increases in populations of several important predatory species.

Regional processes in mangrove ecosystems: spatial scaling relationships, biomass, and turnover rates following catastrophic disturbance

Physiological processes and local-scale structural dynamics of mangroves are relatively well studied. Regional-scale processes, however, are not as well understood. Here we provide long-term data on trends in structure and forest turnover at a large scale, following hurricane damage in mangrove ecosystems of South Florida, U.S.A. Twelve mangrove vegetation plots were monitored at periodic intervals, between October 1992 and March 2005. Mangrove forests of this region are defined by a −1.5 scaling relationship between mean stem diameter and stem density, mirroring self-thinning theory for mono-specific stands. This relationship is reflected in tree size frequency scaling exponents which, through time, have exhibited trends toward a community average that is indicative of full spatial resource utilization. These trends, together with an asymptotic standing biomass accumulation, indicate that coastal mangrove ecosystems do adhere to size-structured organizing principles as described for upland tree communities. Regenerative dynamics are different between areas inside and outside of the primary wind-path of Hurricane Andrew which occurred in 1992. Forest dynamic turnover rates, however, are steady through time. This suggests that ecological, more-so than structural factors, control forest productivity. In agreement, the relative mean rate of biomass growth exhibits an inverse relationship with the seasonal range of porewater salinities. The ecosystem average in forest scaling relationships may provide a useful investigative tool of mangrove community biomass relationships, as well as offer a robust indicator of general ecosystem health for use in mangrove forest ecosystem management and restoration.

Comparison of community structure of mangrove and riprap rock habitats along urban coastlines of south Florida

Globally, mangrove ecosystems have substantially declined, largely a result of human impacts. Mangroves provide a number of ecosystem services such as shoreline stabilization and nursery habitat for fish species. As declines continue, many of these ecosystem services are lost or altered. The need for shoreline stabilization has become increasingly apparent when chronic erosion wear away coastlines once mangroves are removed. Limestone boulders called riprap have been employed to offset continued erosion associated with mangrove clearing. In urban coastal areas adjacent to Biscayne Bay, Florida, as much as 80 percent of mangroves have been lost. More recently, riprap has been used in conjunction with mangroves to restore wetlands throughout the Bay. This riprap-mangrove habitat provides structure for marine organisms to colonize. However, fish assemblages and benthic composition could vary between this hybridized habitat and natural mangrove systems. Comparisons of fish and benthic community structure were made, to determine if abundance, species richness, and overall diversity differed between the two habitat types. Visual census and benthic quadrat surveys were conducted in vi mangrove and mangrove-riprap sites within two regions of Biscayne Bay. Total fish abundance was greater in mangroves, but the effect of habitat type on species richness varied between regions. The community structure of fishes and benthic composition differed significantly between mangroves and riprap habitats. Because species composition is so distinct, it is likely that the two communities do no function in the same manner. In areas with cleared shorelines, it may be important to consider the function of added anthropogenic structure for ecological communities.

Relating Freshwater Flow with Estuarine Water Quality in the Southern Everglades Mangrove Ecotone

Florida Bay is more saline than it was historically, and reduced freshwater flows may lead to more phosphorus inputs to the mangrove ecotone from the marine end-member. This is important given plans to restore freshwater flow into eastern Florida Bay. We investigated the relationships between salinity, nutrients, and hydrologic variables in the mangrove ecotone of Taylor Slough. We expected that total phosphorus (TP) would increase with salinity, reflecting a downstream marine source, while total nitrogen (TN) would increase with flow in the mangrove ecotone. Despite expectations of increased flows improving the ecological health of lower Taylor Slough and Florida Bay, total nitrogen (TN) and total phosphorus (TP) dynamics may shift in response to new conditions of flow and salinity as well as organic carbon, N, and P availability. Our results showed that TP concentrations are more discharge-driven while TN is more variable and potentially derived from different sources along the flow path from the freshwater Everglades marshes to Florida Bay. Increased flow of freshwater through Taylor Slough will likely decrease TP concentrations in this historically oligotrophic and P-limited ecosystem. However, more studies along the mangrove ecotone is needed to understand how increased flows will affect nitrogen dynamics relative to phosphorus.

Ecohydrology, evapotranspiration and hydrogeochemistry of carbonate mangrove wetlands

Coastal environments can be highly susceptible to environmental changes caused by anthropogenic pressures and natural events. Both anthropogenic and natural perturbations may directly affect the amount and the quality of water flowing through the ecosystem, both in the surface and subsurface and can subsequently, alter ecological communities and functions. The Florida Everglades and the Sian Ka'an Biosphere Reserve (Mexico) are two large ecosystems with an extensive coastal mangrove ecotone that represent a historically altered and pristine environment, respectively. Rising sea levels, climate change, increased water demand, and salt water intrusion are growing concerns in these regions and underlies the need for a better understanding of the present conditions. The goal of my research was to better understand various ecohydrological, environmental, and hydrogeochemical interactions and relationships in carbonate mangrove wetlands. A combination of aqueous geochemical analyses and visible and near-infrared reflectance data were employed to explore relationships between surface and subsurface water chemistry and spectral biophysical stress in mangroves. Optical satellite imagery and field collected meteorological data were used to estimate surface energy and evapotranspiration and measure variability associated with hurricanes and restoration efforts. Furthermore, major ionic and nutrient concentrations, and stable isotopes of hydrogen and oxygen were used to distinguish water sources and infer coastal groundwater discharge by applying the data to a combined principal component analysis-end member mixing model. Spectral reflectance measured at the field and satellite scales were successfully used to estimate surface and subsurface water chemistry and model chloride concentrations along the southern Everglades. Satellite imagery indicated that mangrove sites that have less tidal flushing and hydrogeomorphic heterogeneity tend to have more variable evapotranspiration and soil heat flux in response to storms and restoration. Lastly, water chemistry and multivariate analyses indicated two distinct fresh groundwater sources that discharge to the phosphorus-limited estuaries and bays of the Sian Ka'an Biopshere Reserve; and that coastal groundwater discharge was an important source for phosphorus. The results of the study give us a better understanding of the ecohydrological and hydrogeological processes in carbonate mangrove environments that can be then be extrapolated to similar coastal ecosystems in the Caribbean.

Do the crabs Goniopsis cruentata and Ucides cordatus compete for mangrove propagules? A field-based experimental approach

Mangroves are under threat worldwide by deforestation, overexploitation and climate change. The availability and consumption rates of propagules influence mangrove recruitment and can play a major role in their viability and restoration potential. We assess the potential trophic competition between Goniopsis cruentata and Ucides cordatus, two dominant crab species in the New World, by experimentally comparing herbivory levels between forest stands with varying crab abundance. We hypothesize that herbivory rates (HR) of G. cruentata will be lower in mangroves where it coexists with U. cordatus than in mangroves where U. cordatus is absent. The removal of Rhizophora mangle propagules was very rapid, and HR were overall high and increased through time. However, HR did not differ significantly between mangroves with and without the potential trophic competitor U. cordatus. Our study did not support previous literature indications of food competition between these two crab species, which seem to have developed strategies for competition avoidance.