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).
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?
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.
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.