STRATEGIC PLAN FOR THE

INTERAGENCY

FLORIDA BAY SCIENCE PROGRAM

Prepared by Florida Bay Program Management Committee

U. S. DEPARTMENT OF THE INTERIOR- NATIONAL PARK SERVICE
  Dr. Tom Armentano* (Everglades National Park) - Co-Chair
  Robert J. Brock- (Everglades National Park)- Research Coordinator

FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION
  John Hunt*- (Florida Marine Research Institute)- Co-Chair

ENVIRONMENTAL PROTECTION AGENCY
  Dr. Bill Kruzynski

SOUTH FLORIDA WATER MANAGEMENT DISTRICT
  Dr. David Rudnick*

U.S. ARMY CORPS OF ENGINEERS
  Steven Traxler- Jacksonville District

U.S. DEPARTMENT OF COMMERCE - NATIONAL OCEANIC AND ATMOSPHERIC
  ADMINISTRATION
  Dr. Nancy Thompson* (National Marine Fisheries Service)
  Dr. Peter Ortner* (Atlantic Oceanographic and Meteorological Laboratory)

U.S. DEPARTMENT OF INTERIOR - FISH &;WILDLIFE SERVICE
  Kalani Carnes

U.S. DEPARTMENT OF THE INTERIOR - GEOLOGICAL SURVEY
  Dr. Michael Robblee* (Biological Resources Division)
  Dr. Robert Halley* (Geologic Division)

*- Writing Team

INTRODUCTION

The following Strategic Plan for the Interagency Science Program in Florida Bay has been developed by the interagency Florida Bay Program Management Committee (PMC) to focus the resources of the member agencies on a research strategy to provide science information critical to the restoration of Florida Bay. The plan is built around five central questions. The goal of the science program is to produce data and models essential for understanding the Bay as an ecosystem functioning within a regional system that is strongly influenced by human forces. This document: (1) summarizes the background, objectives and organizational function of the PMC, (2) defines the five central questions, and (3) describes the current and planned research program in each area.

Background

In early 1994, scientists from five agencies presented a draft Interagency Science Plan for Florida Bay (Armentano, et al. 1994) for review by managers of local, state and federal agencies and representatives from non-government institutions. The managers and representatives, meeting as an interagency working group, endorsed the plan and agreed to accept it as a guidance document for establishing an integrated science program for the Bay. The program was developed around the need to build a strong scientific information and modeling base as an essential component in plans for the restoration of Florida Bay. To assure that the many individually funded science projects were integrated into a comprehensive program addressing key research issues , the plan called for the formation of the PMC, guided by an independent science oversight panel. In the next two years, many new projects were initiated, each directed towards one of the 72 questions identified by the science plan as essential for advancing our knowledge of the Florida Bay ecosystem.

A strategic science plan is critical to achieving the major programmatic goals that the PMC and its oversight panel have established for the interagency program. The PMC's mission continues to be assuring that a comprehensive scientific understanding of Florida Bay is made available to management in a timely fashion as restoration actions are undertaken. To accomplish this role the PMC directs and coordinates a broad range of scientific activities encompassing the Florida Bay Research Program. The principal functions of the PMC are:

• Develop and implement a research strategy designed to merge scientific understanding of the Bay with management's decision making process
• Facilitate a consensus-based process for determining science needs and priorities
• Promote funding of critical science needs
• Develop and maintain an open and scientifically sound review process for evaluating research results and for advancing the program
• Communicate research results and program progress to the management and scientific community

A Scientific Program for the Restoration of Florida Bay

The 1994 interagency science plan describes a general restoration goal of "restoring Florida Bay to a naturally functioning ecosystem", but the goal needs to be expressed within a quantitative framework and in relation to a general restoration goal. Defining a restoration target is likely to be an iterative process and to extend beyond strictly scientific considerations. It depends on understanding what events, conditions and processes produced the changes in Florida Bay that have led to the call for restoration. A major programmatic goal of the interagency program, is, therefore, to develop a quantitative understanding of the major factors and their interactions that have changed the Bay, both those that can be modified by human actions such as the flows of fresh water into the Bay, and those due solely to forces beyond management control such as storms and sea level rise. The objective of the interagency science program is to provide this knowledge and combine it with data on biological responses to help define restoration goals, to predict system response to management actions, and to establish success criteria.

Although most of the projects funded by our program are unfinished and others have just begun, some results have emerged, including those presented at the 1st and 2nd Annual Florida Bay Science Conferences held in 1995 and 1996. These conferences, sponsored by the PMC, and other meetings as well as written reports, have emphasized to the PMC and its oversight panel the need to strengthen the program's focus on a research strategy while preserving the continuity set in motion by the projects already underway. In organizing the program around five central research and modeling areas, the PMC has chosen to shift focus towards questions of causality and mechanism while continuing essential surveys and monitoring. This approach will assure that we continuously monitor the changes in the physical, chemical, and biological status of Florida Bay so as to establish a spatio-temporal record of trends in the basic ecological components. Simultaneously, however, we will now direct more resources towards understand ing the mechanisms underlying the trends. Only by such a dual approach, coupled with simulation modeling, can we hope to explain the causes for the dramatic declines in seagrass cover, water clarity and the other signals of ecological change that are of primary concern.

Regional Context

Florida Bay is contained within the much larger South Florida region which is the focus of the South Florida Restoration Task Force. The Bay drains much of the adjacent mainland and receives flows of freshwater from both marshes and canals in the region. Clearly then, restoration decisions on the mainland will affect Florida Bay. Fortunately the regional context of restoration incorporates Florida Bay as an important part of the system. Besides re-engineering of the entire water management network in South Florida, large scale land purchases and control of non-point source pollution are underway. Although no specific restoration target has been defined for Florida Bay per se, most of the Bay is within Everglades National Park and much of the rest within the Florida Keys National Marine Sanctuary. Protection of these environments is mandated by federal legislation.

Although restoration of the Bay to any specific historic condition may not be possible, restoration to a state generally characterizing the Bay prior to the recent period of alteration is a reasonable goal. Central to this target is the establishment of annual salinity variations characteristic of the pre-alteration period of the Bay. The physical sub-program (organized around central question # 1) in conjunction with upstream hydrological modeling will determine the extent to which water management can influence Florida Bay salinity patterns. The general physical, chemical, and biological features of this earlier state will be defined by paleoecological and geochemical studies of sediments (central question #1), as well as from research on salinity tolerances of key plant and animal species (central questions #3-#5).

Assuming that findings from these studies and models are supportive, management of salinity might be expected to favor a mix of seagrass and benthic algal species in place of a grass community dominated by a single species as seen in the 1980s. Subsequent water column clarity in many areas of the Bay then would be expected to improve as pioneer seagrasses colonize die-off areas. However, this response may not follow in portions of the Bay where turbidity is a natural feature of some areas of the Bay. Studies of turbidity (central question #2), water quality (central question #2), and ecological processes (central questions #3-#5) would be designed to define those areas and the processes responsible for the variable turbidity regime.

As stated, the Florida Bay Program is a scientific component of the much larger South Florida Ecosystem Restoration initiative, headed by a Task Force consisting of state and federal agency heads and representatives from other stakeholders. Reporting to the Task Force are a group of regional managers of those agencies responsible for managing the environmental resources in South Florida and carrying out the restoration activities. This Working Group has established among other committees a Science Subgroup responsible for defining and developing plans to provide the scientific and information needs of the Working Group. In doing so it has divided south Florida into a series of subregions one of which includes Florida Bay. The Science Subgroup has delegated to the Interagency Florida Bay PMC the responsibility of managing the program of research, monitoring, and modeling activities conducted in Florida Bay and its environs. Results of the PMC efforts are communicated to the Working Group and its subgroups through the annual Florida Bay science conferences, joint membership of some PMC members on the Science Subgroup, and by direct briefing of agency managers.

The PMC has adopted several approaches to integrating the broad range of projects it supports and in assuring their scientific adequacy. These approaches, described below, are conducted in addition to those that individual agencies carry out. Each of the sub-programs being developed around critical questions has relied on one or more of the approaches and will so continue.

As illustrated in Figure 4, the circulation, water quality, and ecological models being developed in the Bay rely considerably on modeling being conducted outside the Bay itself. These include the regional circulation models of the Gulf of Mexico and Florida Straits, hydrological models of the Everglades, and regional atmospheric models. Outputs from these models provide input to the Bay models. Results of the Florida Bay program are expected to provide vital information to managers of the Florida Keys National Marine Sanctuary, located downstream of Florida Bay, although programs conducted in the Sanctuary are not within the purview of the PMC.

Scientific Advisory Panels

Integral to the implementation of the Florida Bay Research Program is independent expert review. This need has been served by the Florida Bay Scientific Oversight Panel as defined in the interagency science plan (Armentano et al. 1994). The plan defines the Panel's role as providing regular, broad, technical and management review of agency plans, of PMC strategies for program development, of the scientific quality of research, modeling and monitoring, and of research results and inferences. The Panel consists of seven senior scientists with significant experience in major estuarine restoration programs but without involvement in Florida Bay projects. The Panel participated in both annual conferences by formally leading question and answer sessions and by providing a written report to the PMC presenting critical review and recommendations for advancing the program.

Additionally, the Panel has, at the request of the PMC, arranged for ad hoc advisory panels of experts in specialized subject areas to participate in workshops where critical research issues and questions are addressed. These workshops also lead to written recommendations that the PMC accepts as guidance in coordinating the interagency program as described above. To date, substantive workshops have included: circulation modeling (April 17-18, 1996), nutrients (July 1-2, 1996), and water quality modeling (October 22-24, 1996). The PMC will continue to involve the Florida Bay Science Oversight Panel with the Florida Bay Research Program as described above. Based on the advice of its panels, the PMC will create a standing modeling advisory group from the expert panels convened for the circulation and water quality workshops but also including modelers connected to the developing ecological program.

Research Teams

The success of the integrated science program will depend on regular communication between the scientists conducting research in the Bay. To promote and coordinate communication, the PMC will organize researchers and modelers into teams. Five teams are considered necessary: circulation/hydrology, water quality/algal blooms, seagrasses and benthic habitat, higher trophic levels, and model integration. Additional teams will be created if needed. Teams will consist of formally appointed team leaders, a PMC member, and modelers and empirical researchers working in Florida Bay. The team leaders will be modelers or empirical researchers with extensive experience and knowledge of the subject area, as well as of the research and management issues affecting Florida Bay. If appropriate, a PMC member can serve as the team leader, however, the PMC member assigned to the team will also serve as liaison to the PMC and facilitate team activities. PMC members are not prohibited from participating within teams as researchers, but function primarily as committee members within the Florida Bay program. Modelers and researchers not actively working in the Bay are welcome to participate and to contribute to team deliberations. Each research team will conduct a session at the Florida Bay Annual Conference and provide the PMC with a written annual report.

The responsibilities of each team within its subject area are to: (1) synthesize available information by developing conceptual models and specific hypotheses; (2) determine needs for monitoring, and research in support of numerical modeling ; and (3) evaluate new information for the need to revise hypotheses and modify the priorities of present and future tasks.

Program Integration

Conceptual models will synthesize our understanding of Florida Bay, and help formulate critical hypotheses about the Bay's response to upstream hydrology, water quality or other restoration actions. Models will identify information needs and assist in prioritizing those needs and identifying research tasks. Ultimately, numerical models used in a predictive mode will link research understanding of the Florida Bay ecosystem to environmental management decisions by predicting the likely outcomes of various management alternatives on the Bay. These predictions then become hypotheses about the results of management actions, which will be testable with monitoring.

The PMC envisions the need to create a full-time science program manager or executive officer position devoted to providing leadership in program integration. The manager would be an experienced marine scientist with strong quantitative skills, research project management experience and knowledge of computer modeling. The manager would take general direction from the PMC, and lead one or more of the integration teams. The position probably would operate within one of the line agencies. Funding for the position is presently being sought from FY97 funds.

The model integration research team serves a critical role in program integration, particularly because the research strategy of the Florida Bay Program calls for an integrated package of simulation models. This team will develop the interface through which these models communicate. The Florida Bay models must be linked with upstream landscape and ecosystem models and upstream hydrological models such as the South Florida Water Management Model and the Natural System Model. A model integration team would assure that this connection is made.

Agency Implementation Plans

A principal function of the PMC is to see that critical research needs are funded. As set forth in the 1994 interagency plan, agencies, within areas of institutional strength, develop implementation plans for review by the PMC with the requirement that they be consistent with needs expressed in the interagency plan. In the future, agency implementation plans will be based on written recommendations of the Florida Bay Science Review Panel, the expert panels, and the individual research teams. These teams, with PMC and advisory panel input, will then recommend program needs and priorities.

Communication

Communication of scientific results, and progress is a high priority of the Florida Bay Science Program. Following are written science reports provided by the PMC:

• An annual book of extended abstracts from the Annual Florida Bay Program Conferences.
• An annual report of the Science Oversight Panel on progress with recommendations
• Reports from each research team
• Reports from special topic workshops, including both a workshop report and, if convened with the workshop, a report of the advisory panels.

In addition, the following initiatives are being carried out by the Florida Sea Grant and Everglades National Park:

• The quarterly Florida Bay newsletter produced by Everglades National Park for the general public.
• A local Florida Bay Science Radio Station operated with limited broadcasting, by Florida Sea Grant.

Further means of outreach to the public have been proposed by Florida Sea Grant and Everglades National Park but planning for them is not yet completed as of the date of release of this plan.

All technical reports will be included on the Florida Bay PMC web page, or be available on request from Everglades National Park. Metadata connected with PMC-funded research projects, in both spatial and non-spatial formats, will be added to the Florida Bay web page.

On the advice of the Florida Bay Science Oversight Panel, the PMC has defined a series of core or central research questions to provide a framework for establishing program priorities. The five questions posed are discussed below in terms of the information and modeling needs considered critical for program success. All are tied to achieving a comprehensive knowledge of the Bay as a complex ecosystem that has undergone profound changes in its recent past. Each question is introduced with a brief discussion of critical knowledge already acquired, followed by a brief discussion of the critical missing information. The PMC approach is then presented with lead funding agencies noted.

The sub-programs connected to each question differ widely in maturity. Thus projects being conducted to address question #1 have already been identified, funded, and most are underway. In contrast, work for addressing the other questions is only partially underway and key projects have not begun because of funding limits.

How and at what rates do storms, changing freshwater flows, sea level rise, and local evaporation/precipitation influence circulation and salinity patterns within Florida Bay and the outflow from the Bay to adjacent waters?

What is known?

1. Florida Bay circulation is a complex function of tidal and wind forcing and sea level slopes across the Bay's ocean boundaries. Both large-scale flow and local bathymetry influence water movements.
2. Mean flows are to the southeast with considerable exchange both along the western boundary and through inlets between the Keys. Residence times within the northeastern Bay are considerably longer than in the central or western Bay. This difference may have been exacerbated both by construction of the Overseas Highway and by a sediment accumulation resulting from an absence of hurricanes over the last few decades.
3. Freshwater inputs to the Bay include surface and groundwater from the adjacent peninsula as well as intense seasonal and episodic rainfall events.
4. Mean salinity and seasonal hypersalinity may have increased within the Bay as a result of water management practices, although historical variations in salinity are large.
5. Restoration of the South Florida Ecosystem is certain to include hydrological manipulations that can cause changes in Bay salinity, water quality, and circulation.

What do we need to know?

While the set of relevant physical processes affecting Bay circulation and salinity can be enumerated, their relative importance and dynamic interactions are not known. We need to be able to make accurate quantitative predictions of how the physical (and dependent chemical) conditions in the Bay will change as with the implementation of upland hydrological modifications and other restoration efforts. The effects of natural forces such as hurricanes and sea level rise also must be quantitatively known. At the moment the general patterns of circulation are known, not the details. Exchanges with surrounding waters that produced the above patterns are poorly understood, as are the forcing mechanisms and the Bay's response. Knowledge of these details is critical if we are to relate circulation to water quality and living resources which are distributed inhomogeneously in the Bay. Better understanding of the source, magnitude, and variability of the observed net southeastward mean flow is also critical to our knowledge of relationships between the Bay and the downstream coral reefs.

General approach

Answering central question # 1 requires complementary and closely integrated modeling, empirical studies, monitoring and historical data analysis. These will be pursued simultaneously and modified interactively as necessary through collaboration and communication. The eventual product will be a fully verified regional physical model supported by continuing data acquisition (monitoring). A Florida Bay hydrodynamic model would underpin water quality and ecosystem models. Uncertainties in model outputs would be carefully delimited so that restoration scenarios (and progress) can be evaluated and predictions (with error estimates) reported to restoration managers.

Program Elements

The elements of the research program designed to address this central question are described below.

Given the complexity of the system there is no question that rigorous prediction requires a circulation model. Efforts to design and implement such a model have already been initiated by the Waterways Experiment Station (WES) in collaboration with other agency field scientists and modelers. The PMC has, through COE/Jacksonville, requested that WES report on progress in modeling including timetables and explicit discussion of present and planned use of NOAA physical data and models and of USGS bathymetric data.

The first step will be a barotropic finite-element model (RMA2). Currently efforts are underway to analyze the sensitivity of this model to the coarseness of the network and to incorporate the requisite modern bathymetric data. The boundaries of the model have been expanded as advised by our outside review panel, both along the western boundary and along the Florida Keys. Efforts are already underway to use the NOAA regional circulation model (see below) outputs to provide appropriate boundary conditions (tides, sea level, currents and water properties). Similarly realistic wind fields and rainfall inputs will eventually be incorporated (see below). If the two-dimensional and finite-element formulation is insufficient either because fundamental system aspects (e.g.-baroclinic forcing and/or density stratification) are not incorporated or because it is not amenable to integration with a water quality model, WES has indicated that they will adopt a more appropriate approach. In fact, as a result of discussions at the water quality modeling workshop, a fixed grid formulation, Ch3D will probably be used in the water quality model. Its adequacy will be evaluated by comparison with the full finite element model.

The goals of this project are to produce a conceptually simple mass-balance ("box") model of Florida Bay. The model incorporates current assumptions about processes controlling salinity and circulation. The preliminary model version simulates temporal salinity trends in north-central Florida Bay, but requires further calibration and testing that will be completed in the second year of the two year study. When finished the model can be used to parameterize the complex hydrodynamic and water quality models, and serve as a screening device in evaluating water management scenarios. The U.S. Geological Survey (Biological Resources Division) has identified this as a high priority for FY97 funding.

This project began in the summer of 1995. Investigators are applying the Princeton Ocean Model to the oceanic waters adjacent to the Bay to provide oceanographic boundary conditions and forcing to the Bay circulation model. A two-dimensional vertically integrated model with 5km resolution has been developed which uses the highest resolution coastline and bathymetry data available. After calibration of the 2-D model for tides, wind-forcing was incorporated to predict coastal water levels that can be compared to available tidal gauge data for a simulation test period. The model is now being extended to a 3-D (baroclinic) version and the effects of Loop Current and eddy shedding to provide an estimate of the importance of baroclinicity on coastal circulation and the requisite boundary information on temperature and salinity fields.

This project began in FY94 and is well- developed. It has two principal objectives: episodic wind field reconstruction and mesoscale atmospheric modeling. Mesoscale atmospheric modeling is an essential contribution relative to wind-forcing of the Bay circulation model and input of freshwater to the peninsula and directly to Florida Bay. Explicit attention to episodic events is essential since the South Florida ecosystem can be dramatically affected by seasonal but episodic tropical storms and/or hurricanes. Recent storms have been analyzed and the results made available on the internet site of the Atlantic Oceanic and Meteorological Laboratory (AOML). A high resolution of the ARPS (advance regional prediction) model has been configured for the south Florida peninsula and adjacent waters with appropriate horizontal and vertical resolution to force the oceanographic models. The effort is well underway to further improve the realism of the atmospheric model by initializing runs with the operational National Weather Service model, incorporation of rain/ice microphysics, and high resolution land cover, use, soil, and vegetation data.

This project began in the summer of 1995, and the first flights were made in the early fall. Its objective is the tuning of radar algorithms so that the NEXRAD data now being collected in Miami and soon to be collected in Key West can be used to accurately characterize rainfall amount and distribution over the peninsula and Florida Bay. The present rain gauge network provides insufficient spatialand temporal integration of the highly variable rainfall of south Florida. Given the highly convective nature of rainfall events in this system, the NEXRAD approach offers the best way to obtain the requisite data. NOAA has taken the lead to date. Over the next year (or two) as this effort changes from a research to an operational prediction mode, the SFMWD would assume the lead.

Numerical experiments have strongly suggested that seemingly subtle changes in land surface can cause dramatic, persistent changes in the spatial distribution of rainfall. Considerable land surface change can be expected to occur as result of hydrological changes associated with restoration. The question is how and to what degree these changes will affect rainfall distribution and intensity within the South Florida peninsula. This effort would represent an explicit NOAA/SFWMD collaboration. Each agency would support its own scientific participants, and funds have been identified in the FY97 NOAA budget.

7. Energy and Freshwater Cycles in Florida Bay - development of a seasonal (monthly) climatology (NOAA)

Our advisory panels have highlighted the need for better estimates of evaporation because the difference between precipitation and evaporation, not precipitation alone that is the critical parameter for modeling. Considerable physical data has been accumulated (albeit on a relatively coarse time and space scale) in Florida Bay and the adjacent areas. However it has not yet been fully analyzed nor integrated to address this issue. A comparatively modest analysis and integration of available salinity, temperature, radiative flux, and rainfall data should improve this estimate or at least set more reasonable boundaries for its parameterization in the Bay hydrodynamics model. Funds for this initiative have been identified within the FY98 NOAA budget.

This effort began in the summer of 1995, and the first sampling cruises were made in the summer of 1996. Lagrangian Drifters, current meter moorings, and small boat surveys are being used to define circulation and exchange in the Bay and the surrounding waters. Current meter moorings have been established along the western boundary of the Bay and seaward of the tidal inlets at the Florida Keys. Expansion of this field program in FY97 and beyond will emphasize the linkage between the west Florida Shelf and the western Bay, immediately offshore of the Keys and the southeastward flow connecting the Bay to the reef tract. As stated by the Circulation Model Panel in regard to Bay modeling, "boundary conditions are inadequately addressed at this time...that the western boundary be extended over the shelf and northward of the Shark River inflow point and ... (possibly) offshore of the keys". The expansion would involve additional shipboard sampling (Acoustic Doppler Current Profile (ADCP) and ThermoSalinograph), bottom-mounted moorings (ADCP and Conductivity/ Temperature) and Lagrangian float deployments. These field studies would be closely integrated with the COE modeling effort and (along with ongoing monitoring studies supported by EPA and the SFMWD) provide the requisite physical data for parameterizing and validating Bay (and to a lesser degree regional) hydrodynamics models. Funds to markedly extend this work have been identified in the FY97 NOAA budget.

Three levels of sediment elevation data are being collected by the USGS. These data form a set of nested surveys with increasing precision in support of sedimentation studies. High resolution GPS ( ca.10 cm vertical resolution) bathymetric surveys in selected basins of the Bay began during the summer of 1995 and continue with completion anticipated for most basins by 1998. Bathymetry is being extended to electronically leveled profiles (resolution of ca. 2 cm) across selected mudbanks. In addition, along the profiles are meter-square survey sites with sediment elevations measured to ca. 3 mm. These surveys provide the basis for updating century-old charts for hydrodynamic models as well as establishing baseline elevations for determining sediment accumulation and erosion rates. Bathymetry data will be used to quantify sedimentation in the Bay on time scales that vary from those of individual catastrophic storms to those continuous processes occurring over decades.

Major channels discharging flows into northern Florida Bay are being instrumented by the USGS and NPS with acoustic velocity profiling meters, water-level recorders, and specific conductance sensors to determine ratings for quantifying inflow volumes. Significant channels along the southwest coast discharging flows from upland areas of the Everglades National Park and Big Cypress Preserve into the Gulf of Mexico are also being similarly instrumented. In addition to providing data for model calibration and for use as boundary conditions for conducting numerical simulations, these efforts to quantify inflows coupled with synoptic measurements of critical water-quality parameters, will enable scientists to evaluate nutrient loads and thereby investigate their impact on the Bay. Additional USGS project efforts focused on the enhancement of generic hydrologic and hydrodynamic models include studies to evaluate and develop improved representations of evapotranspiration effects, frictional resistance effects of vegetation, wind forcing mechanisms, seepage and precipitation gains/losses, and canal/wetland exchange mechanisms. These project efforts, supplemented by field measurements of time-varying upland and Bay inflows, together with precise measurements of land-surface elevations and vegetation characteristics also being conducted by USGS, will facilitate the development of improved models for investigating flow mechanisms governing the transport of nutrients into the Bay.

What is the relative importance of the influx of external nutrients and of internal nutrient cycling in determining the nutrient budget of Florida Bay? What mechanisms control the sources and sinks of the Bay's nutrients?

The exchange of nutrients between Florida Bay and adjacent regions ("external" dynamics) and the cycling of nutrients within Florida Bay ("internal" dynamics) influence the entire Bay's ecological structure and function, including the occurrence of algal blooms, seagrass growth and mortality, and the sustenance of critical species. Through a program of monitoring and research, including computer modeling, the question of how human activity is affecting the nutrient dynamics of Florida Bay and how future restoration actions will alter these dynamics is being addressed.

What is known?

1. The waters of eastern and central Florida Bay are rich in nitrogen, but poor in phosphorus. However phosphorus concentrations increase and nitrogen decreases towards western Florida Bay. Through a water quality monitoring program that began in 1991, the temporal and spatial variations of nutrient concentrations in Florida Bay waters have been quantified.

2. Inorganic P (SRP) is extremely sparse in these waters, with a mean concentration below 0.1 µM. Total P is higher, but still averages only 0.5 µM. Nitrogen concentrations are higher throughout the Bay, such that the Bay-wide molar TN:TP ratio averages about 170. Spatially, N:P decreases from east to west, averaging over 200 in the eastern Bay to under 80 in the western Bay.

3. The N:P pattern indicates that the productivity of much of the Bay, particularly in eastern and central portions, is likely to be limited by the availability of P. This inference is supported by the N:P ratios of seagrass leaves in the Bay, which have been found to be among the highest found in the world. However bioassays of phytoplankton growth have shown the increasing importance of nitrogen towards the west.

4. Bay waters have high ammonium concentrations (Bay-wide mean of 6 µM), which may indicate a bottleneck in the process of nitrification. As denitrification depends on nitrification, N loss via denitrification may be lower than in other relatively nitrogen- rich estuaries.

5. An area of the Bay near the north-central coast has been identified as a "core" region where water column nutrients (both organic and inorganic) are higher than in any other region of the Bay. This region, which includes Rankin Lake, Garfield Bight, Terrapin Bay, and Whipray Basin, is also where Thalassia die-off was first noticed in the late 1980s and where algal blooms have been sustained since 1991. Furthermore, salinity maxima found in this region during drought years have exceeded 70 ppt, higher than elsewhere in the Bay.

6. Sediments and their associated seagrass beds contain a large reservoir of organic and inorganic nutrients. Likewise, the mangrove forests on the north coast and islands of the Bay and on the Gulf coast contain a large nutrient pool in living tissue and sedimentary detritus.

7. Loading of nutrients from the Everglades to Florida Bay has not been fully quantified. Estimates of nutrient inputs to the upstream wetlands of Everglades National Park indicate that N and P inputs increase with increasing water flow, but that the water is relatively poor in P, with molar N:P exceeding 200.

8. Because of the relatively high concentrations of P in Gulf of Mexico waters, and the net flow of water from northwest to southeast along the Bay's western boundary, the Gulf may be an important nutrient source for the Bay.

9. The Keys may be a primary source of anthropogenic nutrients affecting the Bay. Because of the high transmissivity of the limestone beneath the Keys, waste nutrients (particularly from septic tanks) can readily move into the Bay as a result of the tidal pumping of groundwater. The geographic extent to which the Bay is affected by this input is uncertain.

What do we need to know?

The main information needs relative to nutrient cycles in Florida Bay are an understanding of the factors that triggered and maintain the mass mortality of seagrasses and the persistent phytoplankton blooms. Also critical is sufficient understanding to enable us to assess the impact of various environmental management strategies being considered for Bay restoration. In particular, we need to accurately predict the sensitivity of the Bay's nutrient cycles to changing fresh water flow to the Bay, and the resultant change in the Bay's salinity regime. For much of the Bay, any factor that increases P availability either by increasing sources or decreasing removal, is likely to exacerbate the current problems of the Bay. Recent evidence also indicates that algal blooms in the central and western Bay are also stimulated by N enrichment. Thus we need thorough understanding of the Bay's nutrient cycles. Questions that the current monitoring and research program must address in order to meet these needs are as follows.

1. What are the sources of nutrients that sustain algal blooms?

Understanding the mechanisms that have triggered and are sustaining algal blooms in the Bay is fundamental to restoration decision making. This understanding entails quantifying the nutrient demands of these algae and how these nutrients are supplied.

2. What effect does changing seagrass community dynamics have on nutrient availability in the Bay? Has seagrass mortality only increased nutrient availability by releasing nutrients from this detrital source, or has seagrass mortality also caused other less direct changes, such as a decrease in the capacity of the sediments to sequester nutrients?

The lag of several years between the onset of seagrass mass mortality and the occurrence of algal blooms in the Bay argues against the hypothesis that only nutrients released from dead seagrass tissue fuel the blooms. However, the increase in nutrients from this detrital source, combined with a net decreased uptake capacity associated with seagrass mortality, may explain the bloom's temporal patterns. Thus, estimates are needed of net benthic nutrient uptake or release rates, over a range of seagrass growth rates, mortality rates, and detrital decomposition rates for different seagrass species. The accuracy of such estimates may largely depend upon understanding sedimentary nutrient transformations, including how seagrass roots affect nutrient mobility and how such processes change with seagrass mortality.

Additionally, seagrass mortality may have indirectly affected nutrient cycles in the Bay. For example, sediment resuspension increases with decreasing seagrass density, and P associated with this suspended sediment may be available to phytoplankton.

3. How will changing fresh water flow directly and indirectly alter the supply and availability of nutrients in the Bay? What effect does changing salinity have on nutrient availability in the Bay?

With fresh water flow expected from restoration of the Everglades and Florida Bay, increasing nutrient loading from the Everglades watershed also will probably increase. While the magnitude of this expected increase is unknown, this direct input may be less important than the indirect effect of an altered salinity regime caused by increased freshwater influx. Altered salinities can affect internal nutrient cycling by: (1) altering community structure, such as changing seagrass species dominance, thus changing nutrient storage and cycling, and (2) modifying specific processes, such as P surface reactions and sulfate reduction.

4. What is the effect of major events, such as hurricanes and freezes, on the Bay' s nutrient cycles? Has the absence of a major hurricane in the Bay during the past 30 years resulted in the apparent nutrient enrichment of the Bay?

For a shallow estuary like Florida Bay, hurricanes can profoundly affect the distribution of sediments and of nutrients stored in the sediments as well as the status of vegetation. Large hurricanes may export large quantities of sediment and associated nutrients, perhaps removing much of the exogenous nutrients that annually accumulate in the Bay. The recent absence of large hurricanes may have thus enabled nutrients to accumulate.

General Approach

In keeping with the general approach of the entire Florida Bay research program, answering the questions outlined above entails a combination of monitoring, research, and modeling. The development of a water quality model for the Bay is central to this effort, because such a model not only provides a tool for environmental managers to assess the consequences of their plans and actions, but also provides a means for scientists to integrate existing information and focus future monitoring and research. Monitoring includes a continued commitment to measure water column nutrients throughout the Bay and adjacent waters, and to measure nutrient pools that influence the Bay's nutrient cycles, such as sediments and seagrasses. Long-term measurements of nutrient dynamics, such as sediment-water fluxes, atmospheric inputs, and exchange of nutrients at the Bay's boundaries, are also essential for documenting the status and trends of the Bay's nutrient budget. Finally, experiments that explore the mechanisms that control the current nutrient cycles in the Bay are required to understand cause and effect relationships and distinguish natural causes from human induced causes of change in the Bay.

Program Elements

1. Water Quality Model (COE/WES)

Along with the hydrodynamic modeling that is underway, a water quality model coupled to the hydrodynamic model is needed. A workshop held in October 1996 provided the framework for a conceptual structure of the water quality model. Building on workshop recommendations, the ACOE is preparing a water quality model development work plan. The model will include water column nutrient dynamics, sediment dynamics, water column and benthic algae and at least two seagrass components. We expect that the model, along with simpler box models, will be an organizational tool that helps focus our research on those components and processes that are central to understanding the Bay's nutrient cycles.

2. Mass Balance Model (USGS/BRD)

An immediate requirement is a mass balance model to estimate the Bay's nutrient budget and evaluate the relative importance of data on components of N and P nutrient budgets. Funding for completion of a mass balance model has been obtained by USGS/BRD and is part of the COE work plan for water quality modeling.

3. Monitoring and estimating external nutrient exchanges (SFWMD, NPS/ENP and NOAA)

Water column nutrient concentrations have been monitored in Florida Bay by FIU scientists (with SFWMD and ENP support) since early 1991. This monitoring network has since expanded to include the nearshore waters from Cape Sable to Ten Thousand Islands and, with FKNMS support, the Florida Keys. Water quality monitoring within the Everglades wetlands also continues with support from the SFWMD and NPS/ENP.

4. Regional monitoring network has provided baseline information, and continues to be essential in our efforts to understand patterns of ecological change in the Bay. However, at this time, monitoring needs to be expanded from "snapshots" of water column concentrations to measurements that enable us to estimate net nutrient imports into and exports from the Bay. This largely entails monitoring flows of water and nutrients across the Bay's boundaries, including exchanges on the western boundary with the Gulf, the northern boundary with the Everglades, and the southern boundary through the Keys' passes and with ground water under the Keys. Coupled physical-chemical-biological studies of nutrient exchange along the western boundary are being solicited in a NOAA RFP to be issued in November 1996.

5. Atmospheric monitoring should be expanded such that wet and dry deposition of nutrients in the Bay can be estimated accurately. Estimation of atmospheric inputs was included in a NOAA RFP in November 1996. FY97 funding has already been identified. The temporal and spatial scales at which all these measurements of nutrient inputs and exchanges should be made will be decided based on the development of hydrodynamic and water quality models for the Bay.

6. Systematic measurements of the stock of nutrients in pools other than in the water column are currently lacking. In particular, Bay-wide measurements of sedimentary nutrients are needed. Likewise, nutrients in other large pools, such as in living seagrass and mangroves, should be measured on a regular basis.

Measuring internal nutrient fluxes and process rates (SFWMD, NPS/ENP and DEP/FMRI)

Given the shallow depth and restricted circulation of Florida Bay, internal cycling and transformations of nutrients probably have a strong influence on the structure and productivity of Bay communities. These nutrient pathways and transformations have not been well studied. Essential measurements include nutrient uptake by primary producers (especially seagrass and phytoplankton), the exchange of nutrients between the sediments and the water-column, the diagenesis of nutrients within the sediments (especially P - carbonate reactions and N transformations), and microbial and inorganic reactions within the water column (such as nitrification and P sorption to, and removal, from suspended sediment).

7. Ongoing measurements of nutrient fluxes from sediments to the water column as measured in benthic chambers and modeled from porewater gradients will continued for selected basins in 1997 and 1998. Existing discrepancies between the results of these two approaches need to be investigated. NPS/ENP and DEP/FMRI support this work.

8. Studies of water column nutrient dynamics, including microbial processes and interaction with suspended sediments were solicited in a NOAA RFP in November 1996. FY97 funding has already been found.

9. Turbidity and Sediment Resuspension (USGS/GD and COE)

Turbidity and sediment resuspension are important aspects of water quality that directly affect light penetration and probably nutrient cycles. The USGS is documenting long-term changes in turbidity using AVHRR imagery. More than 1500 images spanning the last seven years have been processed and 600 have been selected for a database. In addition, these images can be used to constrain predictions of turbidity from current wave modeling efforts. In response to advisory panel recommendation, a USGS project has characterized physical properties of bottom sediments and estimated seagrass cover to produce a map of the Bay floor that predicts the susceptibility to sediment resuspension. As part of the study, the potential for resuspension will be measured using a device that relates turbulence to sediment resuspension in cores of selected sediment types. The results of these studies will be used to help calibrate turbidity predictions in the water quality model being developed by the COE. The USGS and COE support this work.

10. Understanding cause and effect relationships

The factors that influence the loading of nutrients into Florida Bay, and the availability of nutrients within the Bay are not well understood. In particular, we need to understand the effect that potential environmental management actions, such as increasing fresh water flow and decreasing salinity, will have on the Bay's nutrient transformations and fluxes. Experiments on suspended sediment particles and on factors that may influence the mobilization and immobilization of P in carbonate sediments are critical. Given the unusually high ammonium concentrations of the Bay and the potential for N limitation the western Bay, experiments on factors that may influence key N transformations, such as nitrification and denitrification are also needed. Experiments that explore how nutrient cycling is altered by changing seagrass community structure and physiological condition (particularly below-ground nutrient changes) is also important, but are yet to be done. Funding for this suite of studies is being explored among several agencies but has not yet been fully defined.

What regulates the onset, persistence and fate of planktonic algal blooms in Florida Bay?

Over the past 6 years Florida Bay has been subjected to extensive phytoplankton blooms contrasting earlier reports of high water column clarity. Although there is anecdotal evidence of algal blooms in the past, frequent and pervasive blooms lagged seagrass die-off by several years. Although not clearly established, nutrient release to the water column caused by remineralization of dying seagrass and suspension of bottom sediments appears to have stimulated algal bloom development. As a consequence, recurrent blooms have repeatedly developed in localized areas and spread into other areas of the Bay. Under the right conditions, phytoplankton-rich water from Florida Bay flows through the major passes in the Keys to the reef tract and beyond.

1. Except for rare situations, resuspended sediments are a major component of the turbidity produced during the microalgal blooms. Increases in phytoplankton are a function of growth of cells as well as repeated suspension into the water column of benthic sediments. Both components can contribute to the "microalgal blooms" of the Bay.

2. Regularly scheduled areal surveys, as well as extensive monitoring (chlorophyll biomass,suspended particulate matter, nutrients, species abundances and composition) and process measurements of nutrient utilization and primary production, are used to map regions of the Bay where blooms tend to initiate, develop and spread. Extensive blooms occur predominantly in the fall/winter and can spread throughout the Bay. Eventually they may spread into the far western regions of the lower Keys and shelf, as well as through the Keys channels onto the reef tract.

3. The species composition of blooms varies throughout the Bay. Communities in the western regions reflect the strong contribution of the southwest Florida shelf, with diatom species predominating. Dominant diatom genera include Rhizosolenia, Chaetoceras,Cyclotella, and Thalassosira. In the central region, where high salinities are found, the composition is numerically dominated by small species such as the blue green alga Synechococcus elongatus, several other blue green species, and very small (<5 µm) eukaryotic picoplankton. Diatoms are also found in the central region of the Bay and, in certain periods, dominate in terms of biomass. Although other species are present throughout the Bay, one consistent component includes the numerous microflagellates of various size classes which are abundant in all regions, particularly near the mainland. The abundance of microflagellates may be correlated with the amount of freshwater runoff. Although nearly continuously turbid, the eastern sector of the Bay is noted as having few phytoplankton blooms, perhaps reflecting its relative isolation from the rest of the Bay.

4. Phytoplankton growth rates can exceed one doubling per day with primary productivity and chlorophyll concentrations occasionally attaining values reported for highly productive estuaries of cooler temperate zones ( 30 ug/L) and 1 g C/m2/d, respectively).

5. The blooms are in part a function of the nutrients required to support them. Initiation and maintenance of the Florida Bay microalgal blooms must rely on a supply of nutrients, primarily nitrogen, phosphorus and silica (for diatoms) as well as essential trace elements. Iron limitation also has been reported. Data on nutrient concentrations in the Bay and results of nutrient bioassays suggest that the Bay is a primarily a phosphorus- limited system although the western and, sometimes the central portions, can be nitrogen-limited.

6. Bloom formation depends on the difference between population growth and loss, the latter primarily resulting from zooplankton and benthic filter-feeder grazing. Copepods like Acartia spp. are capable of utilizing the bloom species and producing eggs with appreciable hatching success. Limited experiments suggest that most daily primary production is utilized by zooplankton grazers in the water column. Microzooplankton rather that macrozooplankton account for most of this grazing.

II. What we need to know

1. Continued surveillance of bloom dynamics through a synoptic monitoring study is required. This need not be extensive but should include enough observations to evaluate if the blooms are increasing, decreasing, or generally changing. Synoptic monitoring also will be also necessary to evaluate any mitigating efforts of restoration.

2. The factors supplying the essential nutrients such as phosphorus, nitrogen and silica required for bloom formation have to be identified and their rates quantified.

3. The light and nutrient requirements and the potential growth rates of the dominant competing bloom taxa need to be determined in order to predict which species form blooms.

4. The suitability of bloom species as food and their susceptibility to grazing by benthic, macro- and microzooplankton grazers must be evaluated to determine the impact of the phytoplankton blooms on trophic structure and the potential for grazing to balance microalgae growth.

5. Finally, a model is needed to analyze nutrient and bloom dynamics within the context of larger ecosystem models needed to assess management strategies for Florida Bay.

The required knowledge suggests four general approaches. First, the continued acquisition and evaluation of field data is required to fully define the history, present status and possible future trends of algal blooms in Florida Bay. The second focuses on the study of key bloom species and their particular characteristics which allow them to successfully compete in the Florida Bay environment and adapt to the changing regimes. The third emphasizes investigation of the trophodynamic structure of algal blooms. The fourth, involves the quantitative elaboration of critical bloom processes using mathematical models. Since for the most part, rate coefficients for sub-tropical estuarine systems are rare, a critical need is to provide meaningful coefficients for basic processes which are essential to building useful models.

Program Elements

1. Monitoring of Bloom Status (DEP/FMRI and NOAA)

Continued selected monitoring is essential to determine the present status of the Bay blooms. This monitoring will continue as part of the FMRI research program, the long-term FIU monitoring program, the Florida Sea Grant special studies and NOAA.

2. Physiological Rate Measurements (DEP/FMRI and NOAA)

Physiological rate measurement studies are needed of key phytoplankton species involved in the blooms of Florida Bay. Well defined experimental protocols will define the capacity of phytoplankton species to grow, assimilate nutrients, photosynthesize, produce toxins and overcome competing species. Autecological and carefully controlled whole community "competition" experiments are essential to understand which species which bloom under which conditions. Advanced physiological/biochemical methods are necessary to the elucidate the role of nutrient cycling.

3. Trophodynamic Studies (NOAA)

Trophic studies are needed to define rates of assimilation, utilization and eventual success of subsequent trophic levels utilizing the bloom phytoplankton species. Trophodynamic studies of macro- and microzooplankton utilization of phytoplankton, including bloom species is being emphasized in the FY97 NOAA field program. Effects of blooms on finfish community structure (e.g., variable recruitment success and effects on obligate planktivore abundance) and potential toxic algal bloom species will be investigated.

4. Phytoplankton Modeling Studies (NOAA, DEP/FMRI, USGS/BRD)

Plankton models will be supported to simulate the response of the phytoplankton community to varying environmental conditions (salinity, temperature, nutrients and light), and to shifts in nutrient processes (recycling, resuspension, adsorption, etc.) The modeling will proceed in coordination with the water quality model and the planned seagrass ecosystem model. NOAA FY97 funds will support work on a plankton dynamics model focusing on nutrient availability, taxonomic differences, grazing pressure effects, benthic-pelagic coupling and trophodynamic consequences. DEP/FMRI, USGS/BRD, and NOAA will all support field studies contributing to the modeling.

In the fall of 1987, seagrasses in dense grass beds, primarily in western Florida Bay, began dying for as yet unknown reasons. The onset of extensive and persistent turbidity/algal blooms followed several years after the initial seagrass die-off events in 1987. Die-back of seagrasses continues today, now probably largely as a result of decreased light, though limited seagrass die-off is still being observed. Seagrass die-off very likely triggered the changes observed in the Bay over the last six years and needs to be understood.

1. Prior to seagrass die-off in 1987, Florida Bay was a clear water, Thalassia dominated marine lagoon which was often hypersaline. Corresponding to gradients of water depth, sediment depth, and nutrient availability, seagrass community development was greatest on bank tops and decreased from west to east across the Bay.

2. The seagrass community in Little Madeira Bay and other northern bays, responding to extreme annual and seasonal fluctuations in salinity, was early successional, poorly developed, and ephemeral prior to seagrass die-off and remains so now.

3. Beginning in the fall of 1987, seagrass in dense grass beds, primarily in western Florida Bay, began dying. The process was rapid, possibly occurring primarily in late summer and fall. The size of the areas affected varied greatly; whole basins were affected (Rankin Lake), sub-basins were affected (Rabbit Key Basin), and patch- sized areas were affected (Johnson Key Basin).

4. Records indicate that only a few "seagrass die-off" events have been reported previously in Florida Bay. Most recently in 1975 and in 1983, periods when the Bay exhibited hypersaline and marine/estuarine conditions, respectively. Both events were observed in Whipray Basin in central Florida Bay, both were small in extent and short in duration and therefore not necessarily similar to recent die-off. Small, confirmed die-offs of seagrass were also observed in the 1950's and attributed to hypersaline conditions.

5. Observations indicate that isolated die-off continues today. However, die-back of Thalassia today is assumed to be more a result of decreased light than seagrass die-off.

6. The small scale pattern of die-off, square meter sized patches coalescing into larger and yet larger areas, suggests the role of a pathogen. Four strains of the slime mold, Labyrinthula sp., the same genus thought to be the causal agent in the wasting disease affecting Zostera, were isolated from Florida Bay. One of the four strains was able to infect Thalassia but not kill it under experimental conditions. However, lesions associated with Labyrinthula correlate with observed patterns of seagrass decline in the Bay today.

7. Thalassia standing crop in areas affected by seagrass die-off has decreased from 200 g dry wt/m2 in 1989 to 50 g dry wt/m2 in 1995. In Johnson Key Basin (western Florida Bay) aboveground biomass of Thalassia had decreased 72% by 1995 relative to 1985, Syringodium had disappeared totally, but there had been no change in biomass of Halodule. Production of Thalassia had generally declined over time. At stations where long-term data are available, areal productivity has decreased from 2 g dry wt/m2/d in 1989 to 1 g dry wt/m2/d in 1995. Control sites are more constant.

8. Since initial seagrass die-off events in the Bay, density and dominance of Thalassia has declined in western Florida Bay. An expansion of Halodule into areas formerly dominated by Thalassia and the presence of previously absent mud bottom has resulted in increased habitat heterogeneity in areas affected by die-off.

The shift in Florida Bay from a clear water seagrass system to a seagrass system characterized by persistent algal/turbidity blooms followed seagrass die-off. Understanding the dynamics associated with this change and its consequences are critical.At this time the cause(s) of seagrass die-off is unknown but conceptual models exist which can be tested with appropriate techniques. The processes involved with the onset and maintenance of extensive and persistent algal blooms in the bay and the impact these blooms are having on the present day seagrass community (light availability, altered nutrient regimes) should be investigated.

Understanding how manipulation of the quantity, quality, timing, and distribution of freshwater flowing into Florida Bay affects seagrass community structure is critical. The latter relationship is particularly important since restoration is expected to be accomplished by establishing more natural flows into the Bay. Development of a seagrass model is a critical research need. It will be used to evaluate long- and short-term hypotheses on seagrass die-off, the relationship of the seagrass community to the effects of algal blooms, and to evaluate the response of the seagrass community to upstream manipulations of freshwater flows.

The approach to addressing question # 4 centers on development of an ecological model. A conceptual model of seagrass die-off includes both long- and short-term elements and each requires elaboration in a seagrass community model. The fully functioning model should be capable of key processes including those connected with putative causes of the die-off. The hypothesized causes of seagrass die-off are: 1) altered freshwater flows to the Bay, including relationships to hypersalinity; 2)overmaturity and susceptibility of Thalassia beds; 3) reduction in storm-mediated disturbance of the sediments and seagrass beds; 4)altered sediment chemistry such as sulfide build-up and iron limitation; 5) disease spread; 6) unusually severe climatic conditions when die-off began, and 7) an altered nutrient regime.

In western Florida Bay, seagrass beds are hypothesized to have become overmature and thus susceptible to climatic and environmental extremes. The model also must ultimately be capable of simulating realistically the influence of these factors interacting over time and space on seagrass production, succession, and turnover.

An important function of the seagrass model, along with environmental data on hardbottom habitats, is to provide the requisite information for a landscape model within which growth, survival, and recruitment of key benthic species may be simulated.

1. Fisheries-Habitat Assessment (USGS/BRD and DEP/FMRI)

This is an ongoing program to assess status and trends in seagrasses in Florida Bay. The program includes three elements: 1) abundance and distribution; 2) structure and dynamics; and 3) populations dynamics. These study elements provide information for spatial assessment and resolution of both intra- and inter-annual variability in the macrophyte (seagrasses and macroalgae) communities, and will provide spatially explicit change data to monitor response to water management alterations or other restoration activities. The protocols used in this program are also being used in the Florida Keys National Marine Sanctuary thus providing the opportunity for a regional database.

2. Causal Mechanisms for Seagrass Distribution ( USGS/BRD, NPS/ENP and DEP/FMRI)

Progress is being made on understanding the spatial pattern of seagrass distribution and the database must be continued. To begin exploration of causal mechanisms, data from seagrass and physical/chemical monitoring projects will be brought together to examine statistical relationships. Data will be collected for selected reference sites in the northeastern embayment area, the north central area of hypersalinity, and a western site where major die-offs have occurred. Concomitant physical and chemical measurements will be conducted in the selected reference sites if they are not already fully in place. The USGS/BRD and NAPS/ENP have defined the development of a program to address these needs as a high priority for FY97 funds provided from the U.S. Department of Interior.

3. Studies of Seagrass Growth and Survival (NPS/ENP, SFWMD and USGS/BRD)

Experimental and field studies are needed which consider interactions of salinity variation, N and P levels, water temperature, and light attenuation on seagrass growth and survival. The three main seagrass species require study. Among the inadequacies are information on the responses of seagrass growth and demography, effects of epiphytes on seagrass growth, disease etiology associated with seagrass die-off and recovery, and interactions of sediment chemistry. SFWMD, USGS/BRD and NPS/ENP propose to commit funds to support an integrated experimental program.

4. Seagrass Community Model (USGS/BRD and NPS/ENP)

This model will simulate the effects of changing salinity and nutrient conditions on the growth and survivorship of seagrasses in the Atlantic tropical/subtropical carbonate-based system of Florida Bay. The model will simulate seagrass community succession and development, and be used as a tool to explore short- and long-term hypotheses on seagrass die-off. It also will provide habitat input to higher trophic level models. USGS/BRD and NPS/ ENP have identified FY97 funds from the Department of Interior South Florida Science Initiative to hold a workshop for defining model requirements and for subsequently beginning the modeling program.

What is the relationship between environmental and habitat change and the recruitment, growth and survivorship of animals in Florida Bay?

Loss of seagrasses and deteriorating environmental conditions have affected secondary production patterns in Florida Bay by altering conditions controlling the growth and recruitment of many consumer organisms. Key organisms such as sponges, lobsters, pink shrimp and many fish species have been affected. During the mid to late 1980's, for example, sponges in southwestern Florida Bay died raising concern about effects on lobster recruitment. Declines in the Tortugas pink shrimp fishery were observed that roughly corresponded to loss of seagrass habitat and hypersalinity in Florida Bay. The distribution of gamefish within the Bay were reported to have shifted in response to turbidity/algal blooms. Florida Bay is critical nursery habitat supporting both ecologically and commercially important animals, and this function is highly valued in south Florida and as such should be fully understood, especially relative to future water management modifications.

1. Correlated with the advent of extensive phytoplankton blooms in central Florida Bay was a sponge die-off (range of loss 25 to 100%) in hardbottom habitats of central and southwestern Florida Bay. Sponges serve as critical nursery habitat for the spiny lobster, Panulirus argus. Initial predictions of declines in lobster recruitment of from 2-19% were not realized.

2. Mollusk communities in the southern and western areas of the Bay have changed markedly over the past two years, and may have responded positively to the reduced salinity caused by heavy rains in 1994 and 1995. But abundance remains low in the central Bay where blooms thrive, especially in the north-central region.

3. Roughly coincident with the occurrence of seagrass die-off in Florida Bay, the harvest of pink shrimp, Penaeus duorarum, on the Tortugas Grounds declined from an annual average of about 10 million pounds per year to a period-of-record low 2.2 million pounds in the late 1980's. Florida Bay was assumed to be the primary inshore nursery supporting the Tortugas Grounds. Seagrass loss and declining environmental conditions in the Bay have been hypothesized as causing the decline, although shrimp have recovered on the Tortugas Grounds while algal blooms and some seagrass die-off continue in the Bay. Experiments indicate that pink shrimp mortality increases in water with salinities exceeding 40 ppt at temperatures typical of Florida Bay.

4. In Johnson Key Basin (western Florida Bay) the localized effect of habitat loss and change due to seagrass die-off is distinct. Seagrass-associated fish and invertebrates including the pink shrimp were found to be less abundant (<10%) in areas of seagrass die-off compared to adjacent undamaged seagrass habitats. Adjacent areas recovering from seagrass die-off through recolonization by Halodule exhibited intermediate abundances. Community dominants such as the killifish, Lucania parva, and the caridean shrimp, Thor floridanus, were virtually absent from die off areas compared to adjacent undamaged seagrass habitats.

5. Throughout Johnson Key Basin, abundance of fish and invertebrates including the pink shrimp was greater in 1985, prior to seagrass die-off, than in 1995. Caridean shrimp densities have decreased from about 160/m2 to 35/m2. Pink shrimp density in January decreased from a mean of 7/m2 to 3/m2 over the decade, with no difference observed in May. Mean fish densities decreased over the decade from 11/m2 to 4/m2. Distinct differences in species composition were also evident between 1985 and 1995. The caridean shrimp declined by 93% and the killifish declined by 97% . The bay anchovy, Anchoa mitchilli, a planktivore, greatly increased in abundance in 1995 perhaps in response to the presence of the algal bloom.

6. Total fish abundance throughout the Bay did not generally decrease. Decreases did occur in areas of the Bay affected by seagrass die-off and in channel habitats. In contrast, changes in species composition were striking. The fish community was dominated by Lucania parva and Eucinostomus spp. in 1985. Following seagrass die-off and the advent of algal blooms, the bay anchovy dominated the fish community, accounting for 57% of the catch.

7. For the decade 1985-1995, catch-per-unit-effort for the spotted seatrout, redfish, grey snapper, and snook was greatest in the years following seagrass die-off and the onset of persistent turbidity/algal blooms.

Seagrass die-off and the advent of extensive and persistent algal blooms in Florida Bay have affected the base of the food chain. The species composition of the forage fish and seagrass associated invertebrate communities have changed, presumably in response to these habitat changes. A significant zooplankton grazing community has developed in response to algal blooms. We need to understand the implications of these food web changes to higher trophic levels. Florida Bay is perceived as an important nursery habitat in south Florida. We need to understand the effects of upstream water management and salinity conditions in Florida Bay on secondary production (community structure, recruitment, growth, survivorship). Development of appropriate consumer models is a critical research need. These models will be used to evaluate restoration alternatives and to predict ecosystem response.

To understand changes in population dynamics of fishery species, it is critical to differentiate the effects of fishing from environmental factors, and to show how these interact to control stock dynamics. Fishing mortality at the stock level can be me asured and evaluated in the context of environmental change and natural mortality. For key species, the research goal is to quantitatively predict the population-level impact of the environmental changes that have occurred in Florida Bay in the past decade. Achieving a predictive capability will require data on effects of changes in fishing effort and of environmental factors upon growth, survivorship, and recruitment.

Also essential is the need to understand what is meant by "habitat change", and to quantify how the population dynamics of higher trophic level species has been affected historically by such changes. Knowing the environmental factors that affect recruitment, growth, and survival is essential for separating habitat effects from fishing effects and intrinsic, biological factors.

Data on survivorship of larval fishes is a key information need not presently being adequately addressed. Survivorship is presumably based on larvae's ability to capture sufficient prey to allow for adequate growth.

Central question #5 will be addressed by developing ecological models complemented by biological monitoring and empirical studies. An initial conceptual model depicts secondary production within the Bay as dependent on availability of suitable habitat and environmental conditions both of which can be altered by upstream water management. Models of representative species and communities will incorporate community structure, reproductive success, growth, recruitment and survivorship in relationship to habitat and communities. The representative species or communities will be chosen based on one or more criteria: (1) they carry out important Bay functions, (2) they have experienced major declines, (3) because long-term response data (e.g., harvest rates, nesting success and distribution, abundance) are available and, (4) linkages to water management are established or can be strongly inferred. Regular field surveys and experimental work are important components of this sub-program as is integration with other Florida Bay models.

1. Higher Trophic Level Modeling (USGS/BRD, NOAA and NPS/ENP)

As a first step in developing a higher trophic level model, a workshop will be conducted in mid 1997 to develop: (1) conceptual models of consumer processes relative to habitat, environmental conditions, and water management, (2) select representative species for modeling, and (3)determine modeling needs and model focus. The outcome of the workshop will provide the rationale for developing higher trophic level models that address the nursery function of Florida Bay. The models will simulate recruitment, growth, survivorship, and community dynamics of selected sport, commercial, and ecologically important fish and invertebrates. The models will integrate results of empirical studies around the hypothesis that secondary productivity in the Bay is limited by availability of optimal habitat, environmental conditions and water management.

2. Pink Shrimp Nursery Function (USGS/BRD and NOAA/NMFS)

Relationships will be determined between inshore populations of the pink shrimp, Penaeus duorarum, and offshore Tortugas and Sanibel fisheries. This is an ongoing project employing stable isotopes as tracers for the purpose of: 1) determining the relative importance of various inshore source areas to the offshore Tortugas and Sanibel shrimp fisheries; and 2) to determine the source areas supporting the fall and spring recruitment peaks in the Tortugas fishery. These data are important in order to understand the relationship of Florida Bay to the Tortugas Fishery and the possible implications of restoration actions to this fishery.

3. Assessment of Trophic Structure and Response of Fish and Shellfish to Habitat Changes in in Florida Bay (USGS/BRD).

This is an ongoing project due for completion in FY 1997. It's goal is to evaluate fish and invertebrate response to changes in habitat associated with seagrass die-off and algal blooms. The funds requested here are for continuing a contract to process the remaining benthic samples.

4. Analyses of Historical Fisheries Data- (NOAA/NMFS, NPS/ENP and DEP/FMRI)

There is a relatively robust store of historical fishery data suitable for population trend analysis. An important component of the analyses should be to separate population effects (e.g. the effect of parental stock size on recruitment) from "habitat" effects (e.g. the availability of suitable habitat for recruitment). Related research should analyze hatch-date distributions and growth from otoliths of field collected larval and juvenile spotted seatrout to determine if (a) differential survival and growth exists along a salinity gradient from north-central to western Florida Bay and (b) if differential survival exists among cohorts during the spawning season, and if so, what factors could have influenced survival. Results could allow us to understand how spotted seatrout early life history stages will respond to changes during restoration.

5. Collection and Modeling of Fishery Data (NOAA/NMFS and NPS/ENP)

Fishery data collection must be continued and the level of sampling must be species-specific. Stock- based cohort models which incorporate levels of fishing mortality and empirically based estimates of natural mortality incorporating variability and uncertainty will be completed. Results of these models will provide the predictive capability with the intent of evaluating species at risk and levels of risk under different environmental and fishing scenarios.

6. Larval Fish Energetics

Given the difficulty of obtaining data on larval fish feeding habitat in the field, bioenergetic models should be developed which utilize laboratory information on energetics costs such as respiration, egestion and excretion combined with known data. Output from the model would include consumption rates, including possible bottlenecks in food supply at larval stages, age linked growth rates and partitioning of energy into growth, respiration and non-metabolizable materials. No projects are currently funded but are under consideration for future funding by NOAA/NMFS.

The PMC is discussing a separately funded project focused on integration of the biological models (e.g. phytoplankton model, seagrass model, higher trophic level models) with the circulation and water quality models and the creation of an appropriate spatial and temporal framework representing the Florida Bay ecosystem. Linkages would be established with upstream simulation models (e.g. ATLSS, ELM, South Florida Water Management Model, Natural System Model) and the synoptic-scale physical and atmospheric models described under Question #1. The model integration project is still under consideration but is expected to develop procedures for configuring model interfaces providing driving variables from the physical models as input to the biological models. Within this framework, hypotheses on the response of the Florida Bay ecosystem to proposed water management modifications of freshwater flows could be generated and alternatives compared. The results would be provided as information for the management decision-making process. The project would be conducted by a team comprised of a lead modeler with participants drawn from modeling projects and selected major data collection projects. Oversight would be provided by a model integration committee reporting to the PMC. USGS/BRD and NPS/ENP is seeking funding for initiation of this work beginning in FY97 but may seek contributions from other agencies.

LITERATURE CITED

Armentano, T.V., M. Robblee, P. Ortner, N. Thompson, D. Rudnick and J. Hunt. 1994. Science Plan for Florida Bay. 43pp.

Armstrong, N.E., D. DiToro, D. Hansen, H. Jenter, I. P. King, S.C. McCutcheon, D.C. Raney and R. Signell. 1996. Report of the Florida Bay Model Review Panel on the Florida Bay Modeling Workshop. April 17-18, 1996. Submitted to the Florida Bay Program M anagement Committee. 7pp.

Florida Bay Science Conference: A Report by Principal Investigators. Abstracts and Program Sponsored by the Agencies of the Program Managment Committee. October 17-`18, 1996, Gainesville, Fl. 232pp.

Florida Bay Science Oversight Panel ad hoc Committee on Nutrients. 1996. Florida Bay Nutrients. Perspectives on the July 1-2, 1996 Workshop. Submitted to the Florida Bay Program Management Committee. 18pp.

Florida Bay Water Quality Model Evaluation Group. Report on the Worshop on the Design and Specifications for the Florida Bay Water Quality Model. October 22-24, 1996. Submitted to the Florida Bay Program Management Committee.

FIGURES