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1: Ecoysystems and Populations

Karen M. Balentine1, Ginger Tiling1, and Thomas J. Smith III2

1 Jacobs Technology, Florida Integrated Science Center, St. Petersburg, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

Fiddler (Uca spp) and mud (Eurytium spp) crabs are among the most common and abundant animals in mangrove forests. Their burrows are an important functional component of sediment structure. This study investigates the importance of crab burrows in mangrove forests and their impact on sediment structure. Burrow density and entry-hole diameters were measured from 60 0.25m2 plots. Casts collected from a sub sample of burrows within the plots were used to calculate burrow length and volume.

Based on our measurements the volume of crab burrows ranged 3 to 6 L/m2 in the upper 25 cm of sediment. Density of burrows ranged from 4 to 180 per m2. Assuming burrow volume represents the total volume of sediment redistributed by crab burrowing activities, and all re-mobilized sediment is available for deposition on the soil surface, the maximum potential contribution of crab burrowing to sediment surface elevation in these mangrove forests is 0.3 - 0.6 cm. This result raises questions for future research: How long did it take for this volume of burrows to be constructed and what is the potential rate of soil deposition related to crab burrowing activity? What is the rate of burrow turnover? Is remobilized sediment removed from the system by tidal action? and What is the influence of burrowing on nutrient availability and hydrology in mangrove forests? By answering these questions scientists will be able to understand the role of burrowing crabs in mangrove forests.

Contact Information: Thomas J. Smith III, U.S. Geological Survey, Florida Integrated Science Center, 600 4th St. South, St. Petersburg, FL 33701; phone: 727-803-8747; email: tom_j_smith@usgs.gov

Timothy W. Green1, Daniel H. Slone1, Kenneth G. Rice1, Melinda Lohmann2, Eric D. Swain2, Michael S. Cherkiss3, and Frank J. Mazzotti3

1 U.S. Geological Survey, Florida Integrated Science Center, Gainesville, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida
3 University of Florida IFAS Research and Education Center, Ft. Lauderdale, Florida

As part of the U.S. Geological Survey’s Priority Ecosystems Science (PES) initiative to provide the ecological science required during Everglades restoration, we are integrating regional hydrology models with American Crocodile (Crocodylus acutus) research and monitoring data. The result will be a model of the impact of various CERP restoration scenarios on the American crocodile.

A list of indicators was created by the Restoration Coordination and Verification (RECOVER) component of the Comprehensive Everglades Restoration Plan (CERP) to help determine the success of interim restoration goals. The American crocodile was established as an indicator of the ecological condition of mangrove estuaries due to its reliance upon estuarine environments characterized by low salinity and adequate freshwater inflow.

The spatial and age-structured population model for the American crocodile is based on code from the recently developed landscape-level CERP Alligator Population Model. The model couples local age-structured models into a spatial dispersal model incorporating crocodile movement behavior. A crocodile habitat suitability index and spatial parameter maps that reflect salinity, water depth, habitat, and nesting locations are used as driving functions to construct crocodile finite rate of increase maps under different management scenarios.

The crocodile simulation model makes use of the new application of FTLOADDS (Flow and Transport in a Linked Overland/Aquifer Density Dependent System) to TIME (Tides and Inflows in the Mangroves of the Everglades). TIME has the capability to link to the SFWMM (South Florida Water Management Model), which is the primary regional tool used to assess CERP restoration scenarios. By applying the crocodile model to proposed restoration alternatives and predicting population responses, we can choose alternatives that approximate historical conditions, enhance habitat for multiple species, and identify future research needs. Future modeling efforts include the incorporation of the Biscayne and Florida Bay model to assess climate change scenarios throughout the entire range of crocodiles in south Florida.

Restoration efforts will likely cause changes to salinity levels throughout the habitat of the American crocodile. The response of the crocodile to restoration efforts will provide a quantifiable measure of restoration success. This modeling effort will examine how CERP restoration alternatives that allow greater freshwater flow into Florida Bay during the critical post-hatching period (Sept-Dec) will affect:

• Growth and survival rates of hatchling and juvenile crocodiles
• Hatchling dispersal distance to suitable nursery habitat
• Survival rates of hatchlings originating from nests within Florida Bay
• Overall crocodile density and distribution

Contact Information: Timothy W. Green, U.S. Geological Survey, Florida Integrated Scien ce Center, 2201 NW 40th Terrace, Gainesville, FL 32605; phone: 352-264-3556, email: tgreen@usgs.gov

George R. Kish, U.S. Geological Survey, Florida Integrated Science Center, Tampa, Florida

Plant phenology is increasingly recognized as a vital aspect of understanding how ecosystems will respond to climatic change. Climate variability has been closely linked to spatially extensive patterns of observed phenological changes; several studies have demonstrated a trend of earlier leaf emergence and bloom dates over the last several decades for lilac and cloned lilac species in the northern U.S.

The USA National Phenology Network (USA-NPN) has been established to integrate phenological event observations on a national level with remotely-sensed weather and vegetation data. The network focuses on the north-central portions of the continental U.S. An extension of the USA-NPN is underway for the southeastern U.S. to provide a link to the national network and a framework for addressing climate change effects unique to the Southeast.

The Intergovernmental Panel on Climate Change (IPCC) projections applicable to the southeastern U.S. indicate future periods of warmer summer maximum temperatures, higher evapotranspiration, and more intense rainfall periods with longer dry periods between rainfall events.

Projected climate change effects of particular importance to ecosystems for the southeastern U.S. are:

1. accelerated wildfire frequency – a warmer climate encourages wildfires through a longer dry season,
2. reduced availability of soil moisture to plants,
3. increased insect epidemics in southern forest stands by pine bark beetles, and
4. changes in ecosystem community dynamics.

The Southeastern Coastal Plain is relatively flat; a significant portion of the landscape serves as water-storage areas in the form of swamps, marshes, and wetlands in floodplains of slow-moving streams. Plant community structure and ecosystem dynamics have developed around the availability of water close to the land surface. Prolonged droughts, warmer summer maximum temperatures, and higher evapotranspiration may stress plant communities resulting in shifts in the range of sensitive species, changes in community structure along hydrologic gradients, and changes in diversity and ecosystem function.

Establishing the network in the southeastern United States is of utmost importance as the Southeast is probably the most difficult of regions in the United States to distinguish regional climate change effects from the variability imposed by local weather effects. Climate change effects in the Southeast will likely be less dramatic than in colder regions, but no less important to ecosystem dynamics.

A plant phenology network for the southeastern U.S. will consist of a tiered approach consistent with the USA-NPN:

1. intensive sites focused on process studies,
2. spatially extensive environmental networks focused on standardized observations,
3. scientific networks with educational components (college campuses, nature preserves with educational programs, etc.), and
4. remote-sensing products that can be assimilated to extend surface observations.

Contact Information: George Kish, U.S. Geological Survey, Florida Integrated Science Center, The University Center for Business, 10500 University Center Drive, Suite 215, Tampa, FL 33612; phone: 813-975-8620; email:gkish@usgs.gov

Carole C. McIvor1, William F. Loftus2, and David P.J. Green3,4

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida
3 Audubon of Florida, Tavernier Science Center, Tavernier, Florida
4 Florida Gulf Coast University, Department of Marine and Ecological Sciences, Ft. Myers, Florida

Southern Florida is the focus of a major hydrological restoration of a vast wetlands ecosystem, the Greater Florida Everglades. The overriding principle of this restoration is that reconstruction of the basic hydrological patterns of water quality and flow will facilitate ecological recovery of populations and communities of freshwater and estuarine animal consumers. A major goal of restoration is to prolong the period of low-salinity conditions in the upper reaches of tidal rivers and streams, a condition historically correlated with the occurrence of large numbers of nesting colonial wading birds in riverine headwater reaches. Given that estuarine trophic pathways are, in part, driven by salinity regimes, we collected baseline data on food-web relationships along a salinity gradient in Shark River, a major conduit of freshwater outflow from the Greater Everglades Ecosystem.

Using stable isotopes of carbon and nitrogen, our objectives were to:

1. identify the major sources of organic matter for representative consumers along the salinity gradient;
2. determine if the relative contribution of organic-matter sources differs over seasons and years; and
3. identify those pathways and sites most likely to reflect trophic changes that could conceivably occur with modified freshwater inflow.

Spatial and temporal expansion of the freshwater and low-salinity zones of the estuary would be expected to be reflected in the pool of dissolved inorganic carbon, and thus the phytoplankton carbon isotopic values. Additionally, nitrogen isotopic values in phytoplankton might also display enrichment as a result of increased nitrogen availability in inflow. This Priority Ecosystem Science study provided information on the structure of that food web, including such basic questions as: what species use the fringing forests, what groups constitute the major biomass pools, and which primary producers support those communities.

We collected representative plant and animal taxa from three fixed locations along the salinity gradient on Shark River three times a year, from 2005-2007. All samples originated from fringing mangrove forests or adjacent subtidal waters. Following initial processing, all samples were sent to the stable isotope laboratory at Florida International University for analysis.

Preliminary analyses across river locations indicate that both red mangroves and BMA (benthic microalgae) were enriched in δ15N and depleted in δ13C at the most upriver site at Tarpon Bay (mean annual salinity = 5 psu). These unique values at the upriver site are indicative of its location at a salinity ecotone where freshwater influence dominates marine influence. The major in situ primary producers (red mangrove, benthic microalgae) overlapped considerably in both δ13C and δ15N at the upriver location, making it impossible to tease apart the relative contributions of the two identified potential organic matter sources there. Preliminary data indicate that inferences will be possible at the two downriver locations, however, as the values of the two sources are consistently different at those locations.

At the upriver location, the overlapping potential sources of organic matter (red mangrove, BMA) appear to be incorporated into resident killifishes, grass shrimp, and mud crabs, as well as into young life-history stages of snook and gray snapper, both recreational-fishing species. At the upriver location, both fish and invertebrate data suggest the presence of an unidentified source of organic matter that is much depleted in δ13C and enriched in δ15N relative to both red mangroves and BMA. The source is hypothesized to be phytoplankton. This source appears to be incorporated into pink shrimp, water-column forage fish (anchovies), and filter-feeding clams.

Invertebrates from the upriver site were predictably intermediate in δ15N values, an indication of a trophic level between plants and fishes. An exception was grass shrimp (Palaemonetes spp.) which had relatively enriched (high) values. Grass shrimp in other south Florida systems are one of the highest trophic-level invertebrates, indicating a diet rich in animal material. There were four consumer levels at the upriver location. Low-level consumers included filter-feeding clams and combination detritivorous-herbivorous amphipods and coffee bean snails. Second-level consumers included mud crabs, blue crabs, pink shrimp, grass shrimp and the small killifish, mangrove rivulus. Gray snappers and juvenile snook constituted the top-level consumers.

• These data provide baseline data on fringing-mangrove-forest food webs that will be useful for post-CERP restoration comparisons.
• Salinity regimes of coastal habitats will be altered because of increased freshwater flow or because of saltwater encroachment from sea-level rise. Changes in salinity will alter aquatic-community structure and therefore food webs.
• Top predators in the food web associated with the mangrove forest were gray snapper and snook, important gamefish species.

Contact Information: Carole C. McIvor, U.S. Geological Survey, Florida Integrated Science Center, 600 Fourth Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: carole_mcivor@usgs.gov

James R. Snyder and Beyte Barrios

U.S. Geological Survey, Florida Integrated Science Center, Ft. Lauderdale, Florida

The Cape Sable Seaside Sparrow (CSSS) is a federally listed endangered species whose habitat is the south Florida short-hydroperiod grassland known as marl or muhly prairie. Wildfire is a natural and necessary phenomenon in muhly prairies, but the interactions of fire and flooding can have profound effects on vegetation structure and composition. If fire is followed by flooding, high mortality of plants that normally resprout vigorously may result. Even though prescribed burning has been practiced in these seasonally flooded grasslands for many years, little research has been done to determine the importance of season of burning on post-fire recovery.

We were interested in observing the response of muhly prairie vegetation to experimental burns before, during, and after the CSSS nesting season to examine both community-level responses of vegetation and species-specific responses of sawgrass and muhly grass, often the dominant species. Large-scale prescribed burns are difficult and expensive to use in replicated experimental treatments; instead, we performed a series of micro-burns inside a cylindrical sheet-metal barrier (1.2 m diameter x 0.7 m tall) to constrain the burn area. This procedure enabled us to do a large number of burns in a single day.

In 2006, we carried out three seasonal burning treatments of winter (dry season), spring (transition from dry to wet season), and summer (wet season) burns at three sites in Everglades National Park. At one site, we included three additional burn treatments during the spring to increase the chances of burning near the beginning of the summer rains. Each treatment consisted of burning 15 prairie points and 15 muhly plants at each site. We measured the height of resprouting sawgrass (in the prairie points) and muhly weekly. Post-burn growth rates varied by site and season of burning. Muhly had more rapid initial post-fire regrowth than sawgrass. Sawgrass regrowth was more sensitive to drought than muhly, and muhly regrowth was more sensitive to flooding than sawgrass. Following the 2006 burns, we observed no mortality from flooding so, in 2007, we carried out a second series of eight microburn treatments from February to June at one site. There was little evidence of stress following burns from February through mid May, but there was 80% mortality of muhly plants burned on June 12 because the site was flooded by 12 cm of water within a week of the burn. At the community level, burns during a very dry period in 2006, and those followed soon by flooding in 2007, resulted in reduced total vegetation cover one to two years after burning. Because rapid recovery of vegetation cover after burning is beneficial to the CSSS, prescribed burning should generally avoid the spring, when prairies are likely to get flooded.

Contact Information: James R. Snyder, U.S. Geological Survey, Florida Integrated Science Center, Big Cypress National Preserve Field Station, 33100 Tamiami Trail E., Ochopee, FL 34141; phone 239-695-1180; email: jim_snyder@usgs.gov

Pamela A. Telis1 and Heather Henkel2

1 U.S. Geological Survey, Florida Integrated Science Center, Jacksonville, Florida
2 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

Successful restoration of the Everglades depends, in part, on restoring more natural volume, timing, and distribution of sheet flow in the wetlands and the corresponding response of the natural system to these changes. A primary product of the REstoration COordination and VERification (RECOVER) Monitoring and Assessment Plan (MAP) integrated hydrology monitoring effort is the Everglades Depth Estimation Network (EDEN), which provides much of the hydrologic data that underpins many of MAP’s restoration hypotheses. Water depth and hydroperiod are important ecological drivers, and EDEN data and tools are used to retrieve, investigate, assess, and compare hydrologic data.

EDEN presents data for an integrated network of 253 gages that records the surface-water levels throughout Big Cypress National Preserve (BCNP), Everglades National Park (ENP), and the Water Conservation Areas (WCA) 1, 2 and 3. Data from multiple agencies, BCNP, ENP, and South Florida Water Management District (SFWMD) are combined with data from the USGS in the USGS National Water Information System (NWIS) database and then served near real-time to scientists, managers and the general public. Water-level data are also used to simulate daily water surfaces covering the greater Everglades. These water surfaces are available as GIS layers from January 1, 2000 through the 2008. These data, along with corresponding documentation, are available on the EDEN website (http://sofia.usgs.gov/eden/):

• Daily water surfaces are generated from daily median water level gage data
• Surfaces are created on a 400m by 400m grid in NetCDF and GeoTiff formats
• Water level surfaces are in units of centimeters
• Vertical datum is North American Vertical Datum of 1988 (NAVD 88)

By combining the daily water-level surfaces and the ground surface generated by the EDEN digital elevation model (DEM), a full suite of hydrologic data and formats for the Everglades are made available to scientists and others:

• Water depth
• Hydroperiod (computation of days since last dry)
• Water-surface slope
• Surfaces and landscape transects animated over time

Principal users are biologists and ecologists examining trophic- and landscape-level responses to hydrodynamic changes in the Everglades. EDEN can also be used to inform policy makers, planners, and decision-makers of the potential effects of water management and restoration scenarios on the natural resources of the Everglades.

Contact Information: Pamela A. Telis, U.S. Geological Survey, Florida Integrated Science Center, c/o U.S. Army Corps of Engineers, 701 San Marco Blvd., Jacksonville, Florida 32207; phone: 904-232-2602; email: patelis@usgs.gov