2. Food Webs
FCE scientists discovered that decomposing plant material, rather than the plants
themselves, supports the freshwater food web. When exported to coastal waters, this
material also supports substantial marine plant and animal life.
Michael Heithaus, FCE Co-PI, prepares to place a GPS tag on an alligator. Using these, and much smaller acoustic transmitters, FCE researchers have been able to show that some alligators commute from marine waters where they feed to the ecotone, possibly moving important nutrients upstream.
Credit: Photo by Jeff Rauch
Determining the sources, fate, and transport of dead organic matter is an important aspect
of understanding the linkages between freshwater and marine environments in estuaries such
as the Everglades. Comparative work among aquatic sites in the LTER network has shown that
the dissolved form of organic matter is abundant in the Everglades but less biologically
available compared to other estuaries. However, particulate organic matter, found as a
detrital layer above the soil surface, is formed in unusual quantities in the freshwater
Everglades and moves slowly as bedload into estuaries. FCE researchers have shown that this
material, rather than the living or dissolved form, forms the base of the Everglades food
web. Large mobile consumers, such as bull sharks and alligators, may play a role in
transporting nutrients upstream from the Gulf of Mexico. Although they reside primarily in
low-salinity areas particular individual alligators and bull sharks will commute to the
coastal oceans to feed before returning back upstream. Alligators in particular may link
the marshes, estuaries, and coastal ecosystems through their movements and feeding patterns.
Exposure of flocculent material to sunlight causes the generation of significant amounts of dissolved organic carbon and nitrogen. This process can potentially influence nutrient dynamics in this oligotrophic environment.
Source: Oliva Pisani; PhD Dissertation work.
In addition, when detrital material meets the estuary, metabolic rates are high, suggesting
its importance to nutrient regeneration and biogeochemical cycling. The particulate matter
was found to be highly reactive upon exposure to sunlight, resulting in the release not only
of high levels of dissolved carbon, but also nutrients. These processes have implications
for Everglades' restoration, as expected increases in freshwater inflows should increase
detrital transport to estuaries, increasing nutrient availability via diverse
For further reading:
Maie, N., J.N. Boyer, C. Yang, R. Jaffe. 2006. Spatial, geomorphological, and seasonal variability of CDOM in estuaries of the Florida Coastal Everglades. Hydrobiologia 569: 135-150.
Boyer J.N., S.K. Dailey, P.J. Gibson, M.T. Rogers, D. Mir-Gonzalez. 2006. The role of dissolved organic matter bioavailability in promoting phytoplankton blooms in Florida Bay. Hydrobiologia 569:71-85.
Jaffe, R., D. McKnight, N. Maie, R. Cory, W.H. McDowell, J.L. Campbell. 2008. Spatial and temporal variations in DOM composition in ecosystems: The importance of long-term monitoring of optical properties. Journal of Geophysical Research - Biogeosciences 113: G04032.
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