Ref. No. [UMCES]CBL 98-123

Annual Report to the United States Geological Service Biological Resources Division University of Miami Coral Gables, FL 33124

Network Analysis of Trophic Dynamics in South Florida Ecosystem, FY 97: The Florida Bay Ecosystem

Robert E. Ulanowicz, Cristina Bondavalli, Michael S. Egnotovich

University of Maryland System, Chesapeake Biological Laboratory, Solomons, MD 20688-0038

E-mail: ulan@cbl.umces.edu
Tel: (410) 326-7266
FAX: (410) 326-7378

May 29, 1998

EXECUTIVE SUMMARY

A 125- component budget of the carbon exchanges occurring during the wet and dry seasons in Florida Bay has been assembled. These trophic networks are the most highly-resolved and complete foodweb ever to have been assembled for any ecosystem. They will serve as independent benchmarks against which the performance of the ATLSS multi-model, now under construction, will be assessed.

As is the case with such detailed, quantitative descriptions of ecosystems, the overall configuration of trophic transfers yields numerous clues as to how the ecosystem is functioning. An analysis of indirect contributions reveals, for example, that seagrasses are the ultimate source of carbon for the system during the wet season, however, epiphytic periphyton becomes the foundation that sustains system activity during the dry period. These primary producers fuel ecosystem activity mostly via indirect routes involving passage through detrital links. There is some 37% more trophic activity during the wet season, as compared with the dry interval that follows. Nevertheless, more species appear to feed higher on the trophic ladder during the dry season than they do during the wet period. The taxon feeding highest on the trophic ladder are the raptors, which, on average, feed at level 4.6. Such averages hide the existence of some very long trophic feeding chains, which in a few instances reach 15 transfers in length. Such long concatenations, however, move only an insignificant amount of carbon along their whole length.

A remarkably high percentage of carbon is recycled by the Florida Bay ecosystem. Over 26% of total system activity involves recycling (a proportion exceeded only by coral reef ecosystems), and, quantitatively, most of these processes are carried out by the pelagic and benthic flagellates. The topology of the Florida Bay ecosystem is remarkably stable throughout the year.

PAST WORK

This report covers work done during the second year of a four year task under ATLSS to quantify the trophic processes in South Florida ecosystems. Last year, a 69-compartment network of trophic exchanges in the cypress wetlands was constructed and analyzed. The results were communicated in last year’s report to USGS/BRD and were elaborated in two manuscripts now under peer review for publication in the scientific literature. In particular, "Beneficial predators: The case for the American alligator" is in review with Ecosystems, and "Insights into whole ecosystem behavior of South Florida wetlands" has been completed and will be sent for review to the journal Oecologia. These manuscripts are being forwarded to USGS/BRD along with this report.

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