Everglades National Park is known for the numerous water resource problems assailing the integrity of its marine and freshwater ecosystems. Maintenance of the health and function of these systems is a central focus of the South Florida Restoration Program. This project documents fish and invertebrate community composition in western Florida Bay in order to assess the bay's response to seagrass and environmental changes over time. Florida Bay is a subtropical lagoon located between mainland Florida and the Florida Keys. The Bay is the largest of the Park's marine systems and is recognized as critical fishery habitat supporting prominent south Florida fisheries. The Bay is considered to be the principal nursery ground for the Tortugas pink shrimp fishery. Hard bottom habitats serve as critical nursery habitat for the spiny lobster. The pink shrimp and spiny lobster fisheries are recognized as the two largest commercial fisheries in Florida. Florida Bay also supports an extensive recreational hook and line fishery which is critical to the economy of the Florida Keys.

In the fall of 1987, a widespread, rapid die-off of turtle grass (Thalassia testudinum) began in Florida Bay. Die-off occurred in areas of dense seagrass cover and, principally, in western Florida Bay. Apparently linked to the loss of seagrass cover, increasingly extensive and persistent turbidity and algal blooms, have characterized western and central Florida Bay since 1991. Abrupt changes of this magnitude have not been observed previously in Florida Bay nor have similar occurrences been reported in the scientific literature for other tropical seagrass systems. In Florida Bay these changes were hypothesized to threaten the bay's water quality, sport fishery, and nursery function. In the short-term, grass canopy loss and declining environmental conditions may lead to shifts in species composition and reduced abundance of grass canopy dependent organisms. Over a longer-term increasing seagrass habitat heterogeneity may result in enhanced secondary productivity.

Roughly coincident with these habitat changes in the bay have been declines in the offshore Tortugas pink shrimp fishery and a die-back of sponges, critical habitat for the spiny lobster (Nance, 1994; Butler and others, 1995). Within the bay, abundance and species composition of seagrass associated fish and invertebrates, including the pink shrimp, have been shown to be lower in areas of seagrass die-off when compared to adjacent undamaged or recovering seagrass habitats (Robblee and DiDomenico, 1992).

A detailed quantitative data base, initially developed by the National Park Service (NPS), has evolved since the early to mid-1980's prior to seagrass die-off describing prominent faunal elements (pink shrimp, caridean shrimp, and fish) characteristic of seagrass habitats in Johnson Key Basin in western Florida Bay. This data base has been expanded over time. The NPS added additional data between May 1989 and August 1991, a period following the advent of seagrass die-off in Johnson Key Basin but prior to the extensive and persistent plankton blooms which have characterized western and central Florida Bay since 1991. More recently, within a multiagency Decadal Comparison Program, data were added when the experimental design used originally between October 1984 and April 1987 was duplicated between October 1994 and April 1997. This was a multiagency program involving the Florida Marine Research Institute; the National Marine Fisheries Service; and the U.S. Geological Survey, Biological Resources Division (Matheson and others, in press; Thayer and others, in press). Since April 1997, this project has continued routine sampling of long-term monitoring stations in Johnson Key Basin in order to extend this detailed biological record.

Distinct differences in the species composition of fish and caridean shrimp communities were evident in Johnson Key Basin in the mid-1990's when compared to the mid-1980's. Rainwater killifish (Lucania parva) and the caridean shrimp (Thor floridanus), once the most dominant communities in the seagrasses of Johnson Key Basin prior to seagrass die-off in 1985, decreased by over 62 and 93 percent, respectively, by 1995. However, other species increased in abundance--the code goby, (Gobiosoma robustum), the bay anchovy (Anchoa mitchilli), and the burrowing caridean shrimp (Alpheus herterochaelis), were found in greater numbers in 1995. The appearance of the bay anchovy and also the Spanish sardine (Sardinella aurita), observed for the first time in throw trap collections in 1995, is thought to be in response to the persistent increase of algal blooms.

Funding for this research was provided from the U.S. Department of the Interior, South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service); and, in part, from the U.S. Geological Survey, Florida Caribbean Science Center for the "Empirical and Modeling Studies in Support of Florida Bay Ecosystem Restoration Program."

REFERENCES

Butler, M.J., IV, Hunt, J.H., Herrnkind, W.F., Childeress, M.J., Bertelsen, R., Sharp, Matthews, T., Field, J.M., and Marshall, H.G., 1995, Cascading disturbances in Florida Bay, USA--Cyanobacterial blooms, sponge mortality, and implications for juvenile spiny lobsters Panulirus argus: Mar. Ecol. Prog. Ser., v. 129, p. 119-125.

Matheson, R.E., Jr., Camp, D.K., Sogard, S.M., and Bjorgo. K.A., (in press) Changes in seagrass-associated fish and crustacean communities on Florida Bay mud banks: The effects of recent ecosystem changes?: Estuaries v. 22.

Nance, J.M., 1994, A biological review of the Tortugas pink shrimp fishery through December 1993: Unpublished report of the Galveston Laboratory, Southeast Fisheries Science Center, National Marine Fisheries Service, Galveston, Texas, 2 p., 9 figures.

Robblee, M.B,. and DiDomenico, W.J., 1992, Seagrass die-off in Florida Bay, Everglades National Park: Park Science, v. 11, no. 4, p. 21-23.

Thayer, G.W., Powell, A.B., and Hoss, D.E., (in press) Composition of larval, juvenile and small adult fishes relative to changes in environmental conditions in Florida Bay: Estuaries.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)

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