Food Webs

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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.
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.

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 re-mineralization processes.

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.
Oliva Pisani; PhD Dissertation work.
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.
For further information: 
Rudolf Jaffe
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