A CONCEPTUAL ECOLOGICAL MODEL OF FLORIDA BAY Author(s): David T. Rudnick, Peter B. Ortner, Joan A. Browder, and Steven M. Davis Source: Wetlands, 25(4):870-883. 2005. Published By: The Society of Wetland Scientists DOI: http://dx.doi.org/10.1672/0277-5212(2005)025[0870:ACEMOF]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.1672/0277-5212%282005%29025%5B0870%3AACEMOF %5D2.0.CO%3B2 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. WETLANDS, Vol. 25, No. 4, December 2005, pp. 870±883 q 2005, The Society of Wetland Scientists A CONCEPTUAL ECOLOGICAL MODEL OF FLORIDA BAY David T. Rudnick1, Peter B. Ortner2, Joan A. Browder3, and Steven M. Davis4 1 Coastal Ecosystems Division South Florida Water Management District 3301 Gun Club Road West Palm Beach, Florida, USA 33406 E-mail: [email protected] 2 Atlantic Oceanographic and Meteorological Laboratory National Oceanic and Atmospheric Administration 4301 Rickenbacker Causeway Miami, Florida, USA 33149 3 Southeast Fisheries Science Center National Marine Fisheries Service National Oceanic and Atmospheric Administration 75 Virginia Beach Drive Miami, Florida, USA 33149 4 RECOVER Section South Florida Water Management District 3301 Gun Club Road West Palm Beach, Florida, USA 33406 Abstract: Florida Bay is a large and shallow estuary that is linked to the Everglades watershed and is a target of the Greater Everglades ecosystem restoration effort. The conceptual ecological model presented here is a qualitative and minimal depiction of those ecosystem components and linkages that are considered essential for understanding historic changes in the bay ecosystem, the role of human activities as drivers of these changes, and how restoration efforts are likely to affect the ecosystem in the future. The conceptual model serves as a guide for monitoring and research within an adaptive management framework. Historic changes in Florida Bay that are of primary concern are the occurrence of seagrass mass mortality and subsequent phytoplankton blooms in the 1980s and 1990s. These changes are hypothesized to have been caused by long-term changes in the salinity regime of the bay that were driven by water management. However, historic ecological changes also may have been in¯uenced by other human activities, including occlusion of passes between the Florida Keys and increased nutrient loading. The key to Florida Bay res- toration is hypothesized to be seagrass community restoration. This community is the central ecosystem element, providing habitat for upper trophic level species and strongly in¯uencing productivity patterns, sediment resuspension, light penetration, nutrient availability, and phytoplankton dynamics. An expectation of Everglades restoration is that changing patterns of freshwater ¯ow toward more natural patterns will drive Florida Bay's structure and function toward its pre-drainage condition. However, considerable uncertainty exists regarding the indirect effects of changing freshwater ¯ow, particularly with regard to the potential for changing the export of dissolved organic matter from the Everglades and the fate and effects of this nutrient source. Adaptive management of Florida Bay, as an integral part of Everglades restoration, requires an integrated program of monitoring, research to decrease uncertainties, and development of quantitative models (especially hydrodynamic and water quality) to synthesize data, develop and test hypotheses, and improve predictive capabilities. Understanding and quantitatively predicting changes in the nature of watershed-es- tuarine linkages is the highest priority scienti®c need for Florida Bay restoration. Key Words: ecosystem restoration, estuaries, Florida Bay, Everglades, adaptive management, seagrass, freshwater ¯ow, salinity effects 870 Rudnick et al., FLORIDA BAY CONCEPTUAL ECOLOGICAL MODEL 871 BACKGROUND restoration are presented in Ogden et al. (2005) and Sklar et al. (2005). The format and symbols of the Florida Bay is a triangularly shaped estuary, with Florida Bay model follows that of Ogden et al. (2005) 2 an area of about 2200 km that lies between the south- and the other conceptual models published in this issue ern tip of the Florida mainland and the Florida Keys of Wetlands. Furthermore, the organization of this pa- (Figure 1). About 80% of this estuary is within the per follows the conceptual model diagram, with major boundaries of Everglades National Park and much of sections on drivers and stressors, and ecological attri- the remainder is within the Florida Keys National Ma- butes (generally structural components of the ecosys- rine Sanctuary. A de®ning feature of the bay is its tem) and their links to stressors. A ®nal section con- shallow depth, which averages about 1 m (Schomer siders expectations and uncertainties regarding future and Drew 1982). Light suf®cient to support photosyn- responses to restoration efforts. thesis can reach the sediment surface in almost all ar- This simple model does not address spatial com- eas of the bay, resulting in dominance of seagrass beds plexity in Florida Bay. Florida Bay is, indeed, not so as both a habitat and a source of primary production. much a singular estuary, but a complex array of more The shallowness of Florida Bay also affects its circu- than forty basins, with distinct characteristics, that are lation and salinity regime. Except for basins near the partitioned by a network of mud banks and islands northern coast (near freshwater sources), the bay's wa- ter column is vertically well-mixed and usually iso- (Schomer and Drew 1982, Fourqurean and Robblee haline. In contrast, its complex network of shallow 1999). The structure of vegetative habitats, as well as mud banks restricts horizontal water exchange among water quality and ecosystem processes, vary distinctly the bay's basins and between these basins and the Gulf with this spatial variation. Nevertheless, only a single, of Mexico (Smith 1994, Wang et al. 1994). In areas generic model is described and intended to summarize with long residence times, the salinity of Florida Bay the main characteristics and trends of the bay. While water can rise rapidly during drought periods due to the structure of this model is appropriate for most areas excess of evaporation over precipitation and freshwa- of the bay, the relative importance of model compo- ter in¯ow (Nuttle et al. 2000). Salinity levels as high nents differ considerably among subregions. Any ap- as twice that of seawater have been measured (McIvor plication of this model (e.g., recommendations for a et al. 1994). Another de®ning feature of the bay is that speci®c set of monitoring parameters and guidelines) its sediments are primarily composed of carbonate must accommodate the degree of spatial variability of mud, which can scavenge inorganic phosphorus from the bay. bay waters (DeKanel and Morse 1978). Until the 1980s, Florida Bay was perceived by the public and environmental managers as being a healthy EXTERNAL DRIVERS AND ECOLOGICAL and stable system, with clear water, lush seagrass beds, STRESSORS and highly productive ®sh and shrimp populations. In the mid-1980s, however, catches of pink shrimp de- Following observations of Florida Bay's dramatic creased dramatically (Browder et al. 1999), and in ecological changes in the 1980s, it was commonly as- 1987, a mass mortality of turtle grass (Thalassia tes- sumed that a direct cause of these changes was a long- tudinum Banks & Soland ex. Koenig) beds began term increase in salinity, which in turn was caused by (Robblee et al. 1991). By 1992, the ecosystem ap- the diversion of freshwater away from Florida Bay via peared to change from a clear water system, dominated South Florida Water Management District canals. by benthic primary production, to a turbid water sys- However, subsequent research has indicated that these tem, with algae blooms and resuspended sediments in ecological changes may not be attributable to a single the water column. The conceptual ecological model cause. While decreased freshwater in¯ow and resultant presented here focuses on these changes in seagrass increased salinity have been part of the problem, it communities and water quality as central issues to be appears that other human activities, as well as natural considered by environmental managers. forces, may have also played a role (Boesch et al. The Florida Bay Conceptual Ecological Model is 1993, Armentano et al. 1997, Fourqurean and Robblee one of eleven regional models that are being used as 1999). The conceptual ecological model presented tools for synthesis, planning, assessment, and com- here includes both natural and anthropogenic sources munication