Florida Coastal Everglades Long Term Ecological Research
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Trophic Dynamics & Community Structure Working Group
(Phase II, 2007-2012)

Hypotheses and Proposed Work for FCE II (2006-2012)

General Question: What are the implications of increased inputs of freshwater and detrital organic matter for consumers in the oligohaline ecotone, and how does this impact food webs in the greater estuary?

Specific Research Question 1: Do large consumers transport nutrients between the oligohaline ecotone and freshwater marshes or downstream marine/estuarine environments (Florida Bay and the Gulf of Mexico)?

Approach - We will use passive acoustic telemetry to determine residency times and fine-scale movements of Florida gar (Lepisosteus platyrhincus) and aligators (Alligator mississippiensis), which may migrate seasonally between freshwater marshes and the ecotone during wet seasons, and snook (Centropomus undecimalis) and juvenile bull sharks (Carcharhinus leucas), which are generally found in higher salinities but may also be found in freshwater. In the SRS ecotone, we will deploy ca. 40 stationary acoustic monitoring stations (VEMCO VR2) along the main channel. These units record the identity and time of every transmitter that passes within range (1.2-1.4 km detection diameter). We will thus be able to almost continuously monitor movements of tagged individuals from almost 30km upstream to the mouth of the estuary. We will track 40 bull sharks and alligators in the ecotone and at least 10 gar and snook. We will use our hydrologic and water quality data to determine how salinity, water flow, and tidal inundation affect movements of these 2 species.

Specific Research Question 2: How does fish community structure (standing crops and species composition) in the oligohaline ecotone change in response to increased freshwater inflow?

Approach - We will continue our sampling of fish standing stocks and species composition at FCE sites to enhance interpretation of movement data. Samples will be collected by 1-m2 throw trap at freshwater sites (Jordan et al 1997) and 9-m2 drop trap at mangrove sites (Lorenz et al. 1997). These two methods produce indistinguishable fish density and composition estimates when used side by side (Trexler and Lorenz, unpubl. data). Drop-trap sampling will be stratified by habitat type; 3 traps will be placed in wetlands and 3 in adjacent creek habitats at sites TS/Ph-3 and 6, and SRS-4 and 5. Seven throw trap samples will be collected at randomly identified locations in three 100 m by 100 m plots at select freshwater site (TS/Ph-2; SRS-2 and 3). Samples will be collected at least three times per year at each site (February, April, and October/November).

We also will continue our studies in the upstream regions of the Shark River Slough using electrofishing. Samples will be collected at least three times a year to determine how hydrological conditions, especially marsh dry-down, and predator-prey interactions impact the abundance and composition of fish communities in mangrove creeks adjacent to marshes.

Specific Research Question 3: How are food webs in the oligohaline ecotone affected by changes in water source, nutrient and "floc" supply, and tidal energy?

Approach - In FCE II, we will continue bi-annual sampling of isotopic composition of sailfin mollies, eastern mosquitofish, and juvenile Mayan cichlids at our ecotone sites. We will expand this work to include fish from our estuarine sites and samples of primary consumers (zooplankton and benthic invertebrates), submerged aquatic vegetation (SAV), mangrove leaves, and "floc" from all sites. We will non-destructively sample tissues from snook and Florida gar that “participate” in our movement studies. These stable isotope data will be used to assess the origins and major routes of energy flow, including the potential for allochthonous transport by these mobile predators (Post 2002). We will also continue lab and field studies on how salinity affects isotope assimilation in these fish species.
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National Science Foundation logo This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DEB-1237517, #DBI-0620409, and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
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