The Higher Trophic Levels (HTLs) Plan is designed to address Question #5 of the Florida Bay Interagency Strategic Science Plan, "What is the relationship between environmental change, habitat change and the recruitment, growth, and survivorship of higher trophic level species?" In this context, the term "Higher Trophic Levels" includes zooplankton, benthic invertebrates such as mollusks and crustaceans (particularly decapods), fishes, marine mammals, marine reptiles, and water birds.

    The objectives of the Florida Bay Higher Trophic Levels Plan are as follows:

• Build scientific knowledge about the higher trophic levels of Florida Bay and adjacent coastal systems and the processes and environmental factors connecting these systems to each other and their watershed.

• Provide the scientific knowledge, biological indicators, performance measures, and evaluation tools about higher trophic levels needed to protect and restore the dynamic ecosystems of Florida Bay, the reef tract, and the coastal shelf in water management and other planning processes.

    The evolving approach of the HTL Plan to addressing Question #5 of the Florida Bay Science Program is to address the following topics:

1. Determine human influences (e.g., water management, fishing) and major natural influences on biological processes affecting growth, survival, and recruitment;
2. Determining the major factors that influence HTL distribution and abundance patterns and community and trophic structure;
3. Identifying major pathways, mechanisms, and influencing factors in the transport of pre-settlement stages of offshore-spawning species onto Bay nursery grounds; and
4. Determining ecological processes influenced by HTL species distributions or community and trophic structure.

    A series of questions are posed relative to these topics.

    A main responsibility of the Florida Bay Science Program is to develop the scientific knowledge and tools to support the Comprehensive Everglades Restoration Plan (CERP). CERP is led by the U. S. Army Corps of Engineers and the South Florida Water Management District but involves many other Federal and State agencies, as well as local governments and Native American Tribes.

    CERP proposes to restructure the intricate system of canals and control structures by which flows of fresh water to Florida Bay and all South Florida estuaries are managed. A primary CERP goal is to restore South Florida’s public wetlands and estuaries by restoring a more natural quantity, timing, and distribution of freshwater inflows. The CERP implementation process is designed for guidance by science-based ecological criteria. Knowledge about Florida Bay in relation to freshwater inflow will be needed throughout planning, design, and implementation phases of CERP. Modeling will be used to predict biological effects when selecting among alternative components and designs, and monitoring will be used to "take the pulse of the system" as each project component is implemented. An adaptive assessment process is being developed to coordinate and integrate the input of scientific information and to ensure that modeling and monitoring results lead to improvements in the Plan. The selection of appropriate biological indicators and formulation of performance measures relative to these indicators is a crucial element of this process. Scientific input about Higher Trophic Level species in the Bay is critical to a successful restoration of Florida Bay and associated coastal ecosystems. Higher trophic level species are ecologically and economically important and are viewed as important by the public. Furthermore, higher trophic level species tend to integrate the condition of the ecosystem and reflect it in their responses to environmental change.

    Deteriorating conditions in Florida Bay were a major factor prompting the legislation that led to CERP. Indications in Florida Bay of an ecosystem in poor health have included (1) a decline in catch rates of commercial and recreational species that depend on the Bay as juvenile nursery habitat, (2) algal blooms in western Florida Bay and central Florida Bay, (3) massive seagrass die-offs in western Florida Bay, (4) sponge mortalities in southwestern Florida Bay, and (5) declines in mangroves on islands and shorelines of the Bay. While some seagrass areas have recovered since the original die-offs observed in 1987, new seagrass die-off areas have appeared.

    The shortest and most direct pathway of effects of water management on the higher trophic levels of Florida Bay is through the effects of freshwater flow on salinity and the effects of salinity on survival, growth, and reproduction. Salinity affects physiological processes that may influence growth, survival, and reproduction of many higher trophic level species. The appropriate flow regime to restore the Bay ecosystem must be determined by linking the salinity requirements of key indicator species and communities to the freshwater inflows required to maintain these salinities in the specific locations where other suitable habitat conditions (e.g., bottom type, depth, shoreline type) are found. These areas must also be accessible to pre-settlement stage immigrants.

    Another possible pathway for water management effects is through the establishment of gradients of salinity and/or organic compounds that provide directional clues or stimuli for early life stages migrating into Florida Bay. Except for brief experimental work on pink shrimp postlarvae and juveniles conducted by Hughes (1967a, b), there has not been any work on this topic specific to Florida Bay, however information from other areas suggests that this factor could be of great importance in determining settlement of HTL species in the Bay.

    Secondary effects of water management on higher trophic level organisms, as, for example, through effects on important benthic habitat such as seagrass and sponges, may occur (e.g., possibly through salinity effects, nutrient effects, turbidity effects, etc.), and these effects must also be evaluated.

    In addition, loads of mercury and other contaminants related to freshwater inflow must be determined in relation to water management, and effects on indicator organisms predicted.

    The CERP process extends beyond Florida Bay to encompass interactions between Florida Bay and the Florida Keys Reef Tract and the human-influenced factors that affect the Bay, the reef tract, and their interactions. In particular, as part of CERP, a Florida Bay-Florida Keys Feasibility Study is underway by the Corps of Engineers that will require further scientific input about the factors that influence higher trophic level species of Florida Bay and coastal waters. Many higher trophic level species range between the Bay and coastal reefs within their life cycle. The development of scientific knowledge about higher trophic level species of the Bay, therefore, must extend beyond Florida Bay to address the greater ecosystem that supports these species. This includes the Florida Current, the Tortugas Gyre, and their influence on Florida Bay. Investigations also should address possible higher trophic level effects on the reef tract of discharges from the water management system and water exchanges with Florida Bay, as well as the long term higher trophic level effects in Florida Bay of the existing overseas highway connecting the Keys to the mainland.

    The Florida Bay food web includes herbivores, detritivores, planktivores, and piscivores at three to four trophic levels (Figure 1) (Browder et al. 1998). The primary producers that are the food-web base include phytoplankton, epiphytes, benthic algae, seagrass, and mangroves. Although seagrass communities dominate much of the bay, stable-isotope analysis of food web structure and sources of primary production indicate that the hard-bottom communities of southern Florida Bay function more or less independently of seagrass, with most energy derived from benthic macroalgae or phytoplankton (Behringer and Butler, 1999). Within the Bay, the food web has two major branches, pelagic (water-column) and benthic (on or near the bottom). These branches may converge at the highest trophic levels. The following information is summarized from the March, 1998, Higher Trophic Levels Group Report.

    In the pelagic branch, zooplankton and filter-feeding planktonic stages of fishes, crustaceans, mollusks, and other taxa feed on phytoplankton (e.g., copepods, velliger larvae, etc.) in the water column and are preyed upon by small schooling pelagic fish such as bay anchovy and hardhead silversides. The benthic branch includes filter feeders (e.g., sponges, bivalve molluscs, ascidians, polychaetes, etc.) and demersal grazers or detritivores such as amphipods, harpacticoid copepods, polychaetes, striped mullet, and post-settlement stages of mollusks and other invertebrates. The next level of benthic consumers includes a host of small demersal fish and macroinvertebrates that feed on small invertebrates. Dominant members of this group include gulf toadfish, goldspotted killifish, rainwater killifish, dwarf seahorse, dusky pipefish, gulf pipefish, spotfin mojarra, silver jenny, white grunt, pigfish, pinfish, and silver perch (Thayer et al. 1999). Pink shrimp and many taxa of small caridean and penaeoidean shrimp also are numerically abundant in the Bay (Robblee pers. comm.). Juvenile spiny lobster are abundant in the southwest portion of the bay, south of major mudbank barriers (Field and Butler 1994, Herrnkind et al. 1997). Information on the food habits of these species in Florida Bay is limited (Ley et al. 1994), although Schmidt (1993) provides information for some species in the Whitewater Bay and Shark River estuary, and some information is available from studies elsewhere. This information suggests that most of these demersal fish are generalists and eat a variety of benthic invertebrates. A few studies employing stable-isotope analysis have also identified certain trophic relationships in Florida Bay’s seagrass (Zieman 1981) and hard-bottom communities (Behringer and Butler 1999).

    Small fish and macroinvertebrates are the prey of larger fish, including game fish and sharks. Within the Florida Bay area, gray snapper and red drum eat primarily shrimp and crabs, whereas barracuda, sea trout, and snook eat more fish than crustaceans (Marshall 1954, Croker 1960, Yokel 1966, Fore and Schmidt 1973, Rutherford et al. 1983, Harrigan et al. 1989, Hettler 1989, Schmidt 1989, 1986). Of the abundant forage fishes, those that appear to be important in the diet of some piscivorous fishes are gulf toad fish (lemon shark), pinfish (lemon shark and snook), hardhead silversides (snook), goldspotted killifish (barracuda), and rainwater killifish (barracuda and sea trout). In southern Florida Bay, juvenile lobster constitute a large fraction of the diets of a variety of fish: nurse shark, bonnethead shark, southern stingray, bonefish, permit, and gulf toad fish (Smith and Herrnkind 1992). Small mollusks are abundant in Florida Bay and probably are fed on by rays and fish such as sheepshead. Nurse sharks and bonnethead sharks, as well as large rays, are commonly seen in Florida Bay on aerial surveys (S. Bass, pers. comm.).

    The many piscivorous water birds that live in the Bay seasonally or year-around also eat small fish and macroinvertebrates such as crabs and shrimps, although this is poorly documented. Piscivorous birds in the Bay include double-crested cormorants, brown pelicans, red-breasted mergansers, laughing gulls, ring-billed gulls, royal terns, and many wading bird species, as well as bald eagles and osprey. The most abundant wading bird species in the Bay seasonally are White Ibis and Great Egrets (Browder et al. in prep). The Bay is a major habitat for the Great White Heron, Roseate Spoonbill, and Reddish Egret. All of these species feed in the Bay proper or in shallow ponds on the Bay’s islands.

    The bottlenose dolphin is another high-level predator in Florida Bay and, based on studies elsewhere in South Florida, probably feeds on fish at several trophic levels. The American crocodiles that occur in the northern Bay and the American alligators that penetrate the northern Bay during wet years also are predators on the Bay’s small fish populations.

    West Indian manatees and green and loggerhead sea turtles occur in Florida Bay, although they do not appear to be numerically abundant in the Bay. As large herbivores, the manatees and adult green sea turtles may have once been an important ecological force in the Bay. Their numbers in the Bay today may be too limited for them to have much influence on the ecosystem.

    The relationship of HTL species to freshwater inflow is complex. The HTL species group of Florida Bay is made up of many species with different life histories; dietary and energy needs; abundance, distribution and movement patterns; and habitat and salinity requirements. Many animal species of Florida Bay (e.g., pink shrimp, spiny lobster, gray snapper) are spawned offshore, then migrate to Florida Bay in early life stages to grow to maturity in shallow, relatively protected and food-rich nursery grounds, after which they leave the Bay to renew the offshore spawning. Other species (e.g., spotted sea trout and most caridean shrimps) live their entire lives in the Bay, but have different dietary, energy, salinity, and habitat requirements in their various life stages. Still other species are transients that move between the Bay and the nearby reef tract in response to daily or seasonal rhythms.

Fisheries

    Major fisheries operate in the coastal waters of South Florida, contributing strongly to the economic base of the area as direct production, "value added", and purchases generated in support industries such as tourism, restaurants, fishing supply stores, and dive shops. Many of the coastal fisheries have ecological connections to Florida Bay. The Florida reef tract supports both commercial and recreational fisheries for snapper and grouper.

    Many fishery species associated with the Florida Keys Reef Tract and the waters near the Dry Tortugas spend some part of their life cycle in Florida Bay. This includes not only pink shrimp, spiny lobster, and gray snapper but also sparids, grunts, other snappers, and possibly groupers (although the population levels of groupers in the Bay are low). Shelf waters near the Dry Tortugas islands are the most important commercial fishing grounds for pink shrimp in Florida, and Florida Bay is a major pink shrimp nursery ground. Florida Bay also contains important spiny lobster nursery habitat, and Everglades National Park is a fishing-free sanctuary for spiny lobster.

    Recreational fishing is an expanding sport in the Florida Keys, Tortugas waters, and Florida Bay, both within and outside the boundaries of Everglades National Park.. Commercial and recreational fishing for Spanish mackerel, spiny lobster, and other species takes place in the greater Florida Bay area outside the Park.

    The growing demand for fish and popularity of fishing have increased the pressure on fishery populations in South Florida. This pressure is especially reflected in declining sizes and densities of snappers and groupers and changes in the trophic structure of fish assemblages on reefs (Ault et al. 1998). These changes are apparent even in the Tortugas area and are consistent with similar changes previously detected in the Florida Keys (Schmidt et al. 1999).

    Florida Bay is bordered on the north by the Florida mainland, on the west by the nearshore coastal shelf, and on the east by the Florida Keys, which partially separate the Bay from the nearshore reef. A series of embayments and coastal lakes connected to Florida Bay form the Bay’s border with the mainland. The intercoastal waterway circumscribes the Bay and defines the boundaries of the Bay portion of Everglades National Park.

    Florida Bay is a spatially complex system. The Bay is made up of many sub-basins partially separated from each other by a network of banks, which are broadest in the west but more effective barriers to water flow in the east. Tides are propagated from the west to the east, and tidal amplitude decreases from over 35 cm in the west to virtually zero in the east (Smith 1997). The annual variation in sea level (~15 cm in Key West) is a more important determinant of water depths in the eastern Bay than tidal variation (Smith 2000). Wind has a major influence on water levels in the Bay. Benthic habitats in Florida Bay include seagrass meadows (both mixed and monotypic), open sand bottom, mudbanks, and hard-bottom areas supporting sponges, octocorals, corals, and extensive stands of macroalgae.

    Circulation patterns near the boundaries of the Bay have been well studied (Lee et al. 1994, 1999, 2000; Wang and Monjo 1995), but mixing patterns within the Bay are poorly known. Wind is thought to be a more important influence on mixing than tide, especially in the Bay’s interior. Net water flow across the western boundary of the Bay is from west to east, from the Gulf to the Atlantic, except along the western boundary’s most southerly reaches, where the net flow is in the opposite direction (Smith 2000).

    Freshwater inflows to the various parts of the Bay differ. Fresh water enters the eastern Bay through Taylor Slough and many coastal creeks that empty into small coastal embayments connected to the Bay. Fresh water enters western Florida Bay after mixing with coastal waters off southwest Florida, which receive the main flow of the Everglades and Big Cypress. The northcentral Bay receives freshwater inputs less frequently than eastern and western Bay areas because of a natural coastal berm that retards flow to the Bay. Fresh water enters the northcentral Bay when an as yet unknown threshhold water level in the southern Everglades is exceeded. Rainfall on the Bay is the main source of fresh water to the Bay, however salinity patterns in the northern and western Bay indicate an influence of freshwater inflow.

    A major feature of Florida Bay is an area of hypersalinity in the northcentral Bay that appears intermittently, can persist for years, and can expand to the western and southern Bay (Fourqurean et al. 1989, Klein 199?). A nucleus of hypersalinity, sometimes greater than 50 ppt, occurs in the northcentral Bay. Not only are freshwater flows to this area restricted by the coastal berm, but mixing with waters of adjacent areas is restricted by island chains to the east and broad shallow banks to the west. Low species diversity and low biomass are usually associated with extreme hypersalinity, although some tolerant species can be highly abundant.

    Florida Bay lies between the Atlantic Ocean and the Gulf of Mexico and is connected to both of these bodies through regional-scale circulation and exchange processes and the oceanic boundary currents that influence these processes. The southwest Florida Shelf to the west and the Keys coastal zone to the east and south of Florida Bay interact with each other and the Bay through the tidal channels between the Keys and also by means of their boundary currents (Herrnkind and Butler 1994, Lee et al. 2000). A dominant process potentially affecting water transport and the transport of eggs and larvae to Florida Bay is the strong coherent response to alongshore wind forcing, coupled with seasonal stratification in response to variation in wind-mixing, air-sea exchange, and river runoff along the nearshore western shelf. Boundary current dynamics and eddy processes are also critical larval transport mechanisms that operate both on the regional and local scales. Transport response to prevailing easterly winds may vary along the Florida Keys as a result of the curvature of the coastline (Lee et al. 2000), Easterly winds are expected to favor onshore larval transport between the Lower Keys and the Dry Tortugas where the coastline is east-west oriented. Onshore convergence of the Florida Current can also facilitate transport into the coastal zone of the Keys, and this occurs mainly in the upper Keys where the shelf narrows and curves northwards.

    Frontal eddies of the Loop Current in the Gulf of Mexico that propagate southward along the outer edge of the western shelf may be trapped and develop into persistent gyres off the Dry Tortugas. The subsequent arrival of another frontal eddy or the abrupt retreat of the Loop Current may dislodge the gyre, which then moves eastward along the southeastern shelf off the Florida Keys in the form of a transient coastal eddy. The Tortugas gyre provides a retention mechanism for periods of weeks to up to 3 months. The area of the Dry Tortugas is an important spawning site for penaeid shrimps, spiny lobsters, and some species of snappers and groupers (Limouzy-Paris et al. 1997). Coastal eddies originating from the Dry Tortugas and propagating downstream may be a mechanism to deliver pre-settlement stages from spawning site to nursery site.

    Observed crustacean larval distribution patterns in the Florida Keys coastal zone corroborate many of the predictions based on key coastal transport processes. Early-stage phyllosomata (<2 mo old) were concentrated within or at the boundaries of a gyre, in the pattern hypothesized for passive drifters (Yeung and Lee. In prep.). However, the abundance of strong swimming spiny lobster postlarvae is not highly correlated with wind-driven currents that can affect the coastal transport of more passive drifters (Acosta and Butler 1997) . High concentrations of pink shrimp larvae were found in the Tortugas Gyre in late spring-early summer (Criales and Lee 1995). High densities of larvae and postlarvae of 10 different shrimp families were found off Looe Key during the presence of a gyre (Criales and McGowan 1993, 1994).

    The Florida Keys Reef Tract, which extends, with only minor interruption, along the entirety of the Florida Keys and is the core component of the Florida Keys National Marine Sanctuary, is affected by the same large (regional)-scale and local-scale oceanic processes that affect Florida Bay. The reef tract is populated by a great diversity of life associated to varying degrees with coral reef structure. Animal populations at all trophic levels depend upon nearby seagrass beds, low-relief hardbottom, and algal turf for feeding. Reef tract populations are replenished not only by local spawning but also by spawning upstream. The upstream distance limit is primarily determined by current velocity and larval development rate, which ranges from two weeks in some invertebrates and fish to up to 12 months in spiny lobster. Recruitment of some species to the Florida Keys Reef Tract from as far away as the western Caribbean has been postulated. The argument for multiple upstream larval sources for the Florida spiny lobster population is especially strong, given the wide geographic range of the species and its extraordinarily long planktonic larval life (Lyons 1980, Yeung et al. 2000), and is supported by mtDNA analysis (Silberman et al. 1994). Recent studies, however, support the potential importance of more local sources of recruitment in maintaining reef fish populations.

    The lower southwest shelf in the vicinity of the Dry Tortugas is one potential source of recruitment to the Florida Keys Reef Tract and Florida Bay. The islands of the Dry Tortugas and surrounding shallow waters, now both a national park and part of the Florida Keys National Marine Sanctuary, lie roughly 70 miles west of Key West and are known for remoteness and relatively unspoiled marine richness. The coastal shelf in the vicinity of the Dry Tortugas is the major spawning ground for pink shrimp in Florida. Recent research is uncovering luxuriant, previously unknown and unmapped coral reefs near the Dry Tortugas, as well as near the Marquesas, which lie between the Dry Tortugas and Key West.

    A risk assessment conceptual model was prepared by the Florida Bay PMC in collaboration with CERP to encapsulate the best available scientific knowledge and most likely hypotheses about the major sources and stressors potentially affecting Florida Bay, major Bay attributes expected to be affected, and the pathways and processes through which effects occur (Figure 2). Performance measures were then formulated to reflect the responses of each attribute. Water quality condition, the seagrass community, mollusks and filter feeders, pink shrimp, the fish community, and fish-eating birds were identified as attributes in this model. This model is a product of a series of workshops involving scientists with current knowledge of Florida Bay and is consistent with recent reviews and plans, although some details or omissions may not be consistent with the opinions of every contributor.

    The stated purpose of this model is to "identify restoration goals and success criteria and the minimum measurements required to determine whether these criteria are being met." The principal immediate goal of risk assessment conceptual model development is to provide the basis for designing a monitoring program funded by the U.S. Army Corps of Engineers and the South Florida Water Management District under CERP. This is the reason for its relatively narrow definition of attributes and performance measures. This model is a living document that will undergo periodic revision and update, at which time new understanding about the system, including new attributes, will be incorporated. The HTL Program should not be constrained to building knowledge about only what is included in this model because continuing research may identify other relevant connections and attributes. Furthermore, there are other funding sources to broaden the science to support Florida Bay ecosystem restoration. However it is useful at this time to know where some emphasis should be placed to ensure that immediate identified science needs of CERP are met.

    The "Factors" model in Figure 3 was developed as part of the March, 1998, Report of the original HTL Science Planning Group. It is a comprehensive overview of the HTL components of the Bay and the internal and external factors that influence those components. There are three HTL components in the model: benthos community structure, forager community structure, and predator community structure. Life cycles and processes such as grazing, predation, and movement patterns are internal influences on these components. External forces are organized into two categories: climatic variability and anthropogenic effects. Freshwater inflow is included in both categories because rainfall on the watershed and water management both affect freshwater inflow to Florida Bay. Further, there is a direct rainfall input of freshwater to Florida Bay. Other anthropogenic effects include fishing pressure, habitat alteration, and inputs of nutrients and contaminants. Except for fishing, which affects HTLs directly, the external forcing functions affect HTLs primarily through their effects on habitat, salinity, water clarity, and water and sediment concentrations of nutrients and contaminants.

    A strategic conceptual model to help guide Florida Bay HTL research is shown in Figure 4. The model incorporates the following major concepts:

1. The scope of research on HTLs of Florida Bay must include within-bay, cross boundary, and greater coastal ecosystem processes, and these processes should be examined at time scales from seasons to decades;
2. Higher trophic level processes and patterns potentially affected by water management occur at the population, community/trophic, and ecosystem level;
3. HTL responses to water management are expected to occur through water management effects on salinity, the area of co-occurence of biologically favorable salinity and habitat, the condition of biological habitat (e.g., seagrass, sponge, coral), animal movements, and loading of nutrients or toxicants;
4. Intrinsic factors potentially influencing responses to water management include physiological salinity requirements, dietary and energy requirements, and trophic relationships, all of which may differ by species, life stage, and spawning and migration characteristics;
5. At the bay scale, other potential influencing factors on HTLs include salinity-temperature interactions, toxicant concentrations in freshwater inflow, and fishing;
6. At the shelf scale, other potentially influencing factors include temperatures on spawning grounds, larval transport processes, and fishing.

• Salinity has direct effects on health and growth and survival of higher trophic levels.

• The carrying capacity of Florida Bay nursery areas for pink shrimp, spiny lobster, American crocodiles, and other HTL speciesis related to the overlap of favorable salinity and favorable bottom or shoreline habitat.

• Changes in water management that affect the areal coverage, intensity, and duration of hypersalinity radiating out from the interior of Florida Bay affect recruitment of shrimp, lobster, and other species.

• The timing and amount of freshwater releases to coastal wetlands adjacent to Florida Bay affects the nesting success of wading birds in northeastern Florida Bay.

• Fishing on the reef tract, in the Tortugas, and throughout the Bay affects the population structure and abundance of predator fish species in Florida Bay.

• Abrupt and out-of-season releases of large volumes of freshwater into Florida Bay and coastal waters affect benthic fauna and fish, shrimp, and lobster recruitment.

• Salinity, which is influenced by water management, has been shown to affect the growth of spotted sea trout and the growth and survival of pink shrimp, lobster, and crocodiles. Salinity optima or threshholds have been determined for each of these species and occur within the range of salinity found in Florida Bay (lobsters: Field and Butler 1994). Models of growth and survival, as influenced by salinity, have been developed for each of these species (Browder 1999, ?? & Butler 1999, in review, Richards in prep., Wuenschel et al. 2001, Powell et al. 2001).

• A spatially-explicit individual-based model that accounts for variation in bottom habitat has been developed for spiny lobster (Butler 1994, Butler et al. in press).

• Differences in spatial distributions of mollusks between 1994 and 1995 appear to reflect differences in salinity patterns in the two years (Lyons 1999).

• A major increase in he percent abundance of the mollusk Brachidontes exustus has occurred over the last 30 years in cores from the northern transitional zone, eastern, and central Florida Bay. Molluscan fanal diversity and evenness declined during this same time period. Brachidontes is a euryhaline mollusk tolerant of relatively poor water quality and fluctuating salinities. The increase in this mollusk in recent years may be related to water management practices (Brewster-Wingard, in review).

• The molluscan fauna from a core at the mouth of Taylor Creek indicates gradually increasing salinity, an increase in euryhaline molluscan fauna, and a decline in mesohaline molluscan fauna during the last century (Brewster-Wingard, in review).

• Statistical analyses have found significant separate relationships between indices of pink shrimp abundance on the Tortugas fishing grounds and various indices of freshwater inputs to Florida Bay, including Royal Palm rainfall (near Taylor Slough in Everglades National Park), water releases into Everglades National Park at the Tamiami Trail, and salinity in interior and western Florida Bay. (Browder 2000).

• Mean water levels at fish sampling sites in coastal wetlands immediately north of Florida Bay were found to be lower than 12.5 cm during successful Roseate Spoonbill nesting periods and higher than 12.5 cm during failed nesting periods. Furthermore, during successful nestings, prey availability at the sites was twice that of failed periods. (Lorenz 19??)

• The modal length of gray snapper (Lutjanus griseus) along mangrove shorelines is substantially larger in the Crocodile Sanctuary of Everglades National Park, where fishing has been excluded since 1980, than in other parts of Everglades National Park and nearby Biscayne National Park, where fishing is allowed. Modal lengths were 25-30 cm TL in the Crocodile Sanctuary vs. 15-20 cm TL elsewhere. (Faunce et al. ??)

• An analysis of ENP catch and effort data suggests that fishing activity in the Park affects the abundance of apex predator species in Florida Bay (Schmidt et al. ??)).

• Functional relationships between habitat and fish assemblage structure will be determined and a spatially explicit GIS data base will be developed from data being acquired within mangrove habitats of Biscayne Bay, Key Largo, and northeast Florida Bay. Size, abundance, and distribution of fishes are being monitored on a seasonal basis. (Faunce et al. 2001).

• Statistical model preparation for multiple species in the small forage fish community by means of a meta-analysis that integrates data from several multi-year field studies in Florida Bay (Johnson et al. 2001). The models relate variation in density over space and time to salinity, habitat, and other variables.

• Refinement of existing individual HTL species models (Butler et al. 2001).

• Experimental studies of the effects of salinity on growth and survival of sponges and selected hard-bottom invertebrates. (Butler et al. 2001).

• Determination of red drum nursery grounds in Florida Bay (Powell et al. 2001).

• Development of individual-based models for wading birds (DeAngelis et al. 2001).

• Development of an individual-based bioenergetic model for spotted sea trout (Wuenschel 2001).

• Investigation of lethal viral disease in spiny lobster and its relationship to lobster densities and locations (Behringer et al. 2001).

• Chione cancellata shells are being used to develo a historical record of seasonal-scale salinity changes. The shells from cores and modern monitoring sites are sectioned and analyzed using the SHRIMP (High resolution ion microprobe) (Wardlaw and Brewster-Wingard 20??).

• Key species of mollusks are being grown in tanks under controlled salinity conditions to determine survival rates and tolerance limits in terms of minimum and maximum salinities and in terms of tolerance to rate of fluctuation. This work prepares for the use of these species as indicators.

• Development of new spatially explicit, individually based models for spotted sea trout and other HTLs.

• Growth and survival rates of other fishery species as a function of changing salinity regimes.

• Further development of statistical models for HTL species.

• Further development of existing individual HTL species models.

• Determination of the timing and rate of movement of fishery species between Florida Bay and adjacent waters.

• Determination of the ultimate sources of immigrants to Florida Bay and the Crocodile Sanctuary and destination of emigrants from the Bay and the Sanctuary (e.g., do gray snapper from the Crocodile Sanctuary spawn on the reef tract, in the Tortugas, or somewhere else?).

• Determination the settlement and post settlement habitat and locations of snapper, grouper, and grunts by determining the spatial and temporal distribution of young-of-the-year snapper, grouper, and grunts within the Bay and adjacent waters.

• Integration of individual HTL species models with seagrass and hydrodynamic models, as these are developed.

• Paleoecological analyses of cores from additional locations within Florida Bay to define the spatial pattern of molluscan distribution, abundance, and diversity over the last 200 years based on historical information..

• Increased freshwater inflow to northeastern Florida Bay will increase the load of mercury entering the Bay and the body burden of mercury in Bay HTLs.

• Methylmercury formation is linked with denitrification in the sediments of eastern Florida Bay.

• Mercury body burdens are greater in northeastern Florida Bay than either downstream (central and western Florida Bay) or upstream in the Northern Transition zone adjacent to the Everglades.

• Highest mercury body burdens in fish are not associated uniquely with either mangrove-based or seagrass-based foodwebs, but with an intermediate mixture of the two or, alternatively, with a phytoplankton-based (water column) food web.

• Higher mercury concentrations in gray snapper, spotted sea trout, and red drum are associated with higher * ¹⁵N ratios.

• The South Florida Water Management District (SFWMD) and NOAA’s Beaufort Laboratory have begun a COP funded collaborative study "Linking Everglades Restoration and Enhanced Freshwater Flows to Elevated Concentrations of Mercury in Florida Bay Fish." Total mercury and methylmercury concentrations in water and sediments are being measured in two transects from the the freshwater Everglades into eastern Florida Bay. Samples are taken seasonally to capture periods of high and low freshwater flows. Preliminary results by SFWMD have identified non-conservative gradients with maximum total and methylmercury concentrations in the transition zone near the mouth of Taylor River and a creek flowing into Joe Bay. (Rumbold et al., 2000)

• Forage and game fish are being collected along the transects for mercury analysis which will be related to mercury exposures from water and sediments. Fish and invertebrates are being analyzed for stable isotopes of carbon, nitrogen and sulfur to identify the contributions of different habitats and food web structures to elevated mercury concentrations. (Evans and Crumley, 2000)

• Measure gross mercury methylation rates in different habitats along the Everglades to Florida Bay transition to assess local methyl mercury sources..

• Develop a mass balance budget to assess mercury loading to Florida Bay.

• Integrate mercury flux measurements with existing hydrology and water quality models as a basis for a new mercury transport-fate-bioaccumulation model in Florida Bay. Apply the model to predict potential impacts from increased or redirected flows during restoration.

• Apply observed and predicted methylmercury concentrations in fish to an ecological risk assessment of higher trophic level organisms in Florida Bay.

• Initiate long term monitoring of mercury concentrations in fish to evaluate possible human health risks and consumption advisories during the period of the restoration transition.

• Incorporate other persistent bioaccumulative contaminants in the transport-fate-bioaccumulation model and evaluate them under an ecological risk assessment framework. (Scott et al., 1998)

• Changes in community composition are related directly to changes in salinity and benthic habitat influenced by water management, although the effect of natural variables such as tidal exposure, rainfall, and oceanographic events may need to be filtered out to see these effects.

• Spatial and temporal patterns in trophic pathways vary depending on salinity, water quality and abundance of seagrass.

• Fishing reduces the number and size of some apex predators, causing shifts in community structure.

• Bottlenose dolphins are good indicators of the distribution of forage fish and quality of fish habitat.

• Frequent, intense, and persistent cyanobacteria blooms are associated with sponge mortalities, resulting in change in hard-bottom community and loss of spiny lobster habitat.

• Echinoderm grazing reduces seagrass biomass, affecting benthic community structure and water quality.

• Cores from the northern transition zone, eastern, and central Florida Bay have indicated that patterns of dominance and abundance of individual species of mollusks has changed over the last 200 years. The changes have not been so profound, however, that complete displacement of assemblages has occurred. For example, we do not find an assemblage typical of the western Bay today occurring in central Florida Bay 100 years ago.

• The molluscan assemblages in the Taylor Creek core show a decline in mesohaline fauna over time.

• Between 1910 and 1930, distinctive changes occurred in the molluscan assemblage at Russell bank (core RB 19B). Anomalocardia auberiana, a typical northern transition zone species that was consistently present in low perentages prior to 1920, completely disappeared from the site after that time.

• At Bob Allen mudbank (core BA7A) a dramatic change in faunal asemblages ocurred between 1900 and 1910, from a Transennella sp. dominated assemblage to a Brachidontes exustus-dominated assemblage.

• From 1930 to 1980, dramatic shifts in percent abundance of different species within the Brachidontes assemblage occurred at Bob Allen mudbank and Russell Bank cores.

• Greater species diversity occurred on banks in the Bay’s interior in the 1990s than in the 1980s and may have been due to the increase in benthic species following seagrass die-off or the greater habitat heterogeneity created by seagrass die-off and gradual recovery (Matheson et al. 1999).

• Study results are equivocal concerning the effect of seagrass die-off and recovery on seagrass canopy species. The pattern of annual variation in densities of canopy fish species in Florida Bay found in one (Powell et al. abstract) study does not support the hypothesis that the abundance of these species was affected by seagrass die-off and recovery. Another study (Robblee et al. abstract) indicates that caridean shrimp, pink shrimp, and certain fishes declined substantially from the period before die-off (1985), when Johnson Key Basin was dominated by Thalassia, and the period after die-off (1995), when Halodule and bare bottom replaced some Thalassia and all Syringodium. For bank habitats, locations experiencing significant declines in seagrass cover between the 1980s and 1990s generally had dramatic declines of canopy associated fishes and decapods and increases in benthic species (Matheson et al. 1999). Differences in study area or the number of years of data analyzed may account for some of the inter-study differences, which may be resolved with further analyses of existing data.

• Concentrations of recently spawned spotted seatrout larvae and juveniles in the interior of the Bay appeared greater in the 1990s than in the 1980s (Thayer et al. 1999, Powell et al. In prep., Colvocoresses, pers. comm.)

• Mollusk distributions differed from wet season to dry season and between the wet season of a wet and a dry year and appeared to reflect salinity regime (Lyons et al. 19??).

• Bay anchovies, which were rare in Florida Bay in the mid 1980s, dominated the ichthyofauna in the early 1990s, were rare again in 1998, and became moderately abundant in 1999-2000. This pattern suggests a response to factors that vary over time rather than those having a long-term trend (e.g., chlorophyll-a concentrations, are dynamic and spatially variable) (Thayer et al. 1999, Ortner et al. 2001, Powell et al. 2001).

• The recent history of phytoplankton, zooplankton, and planktivorous fish abundance provides little or no support for the concept of a fundamental and persistent shift from an ecosystem based on demersal benthic production to one based on pelagic water column production (Ortner et al. 2001).

• Stable isotope analyses (carbon, nitrogen, and sulfur) for seagrasses and invertebrate and vertebrate populations across Florida Bay from 1997-1999 indicate that the current trophic structure within the Bay is strongly seagrass (benthic) based. Outer Bay stations trend toward a more water-column-based system (Chasar et al. 2001).

• Stable isotope analyses from another study suggests a mangrove foodweb base in the Northern Transition Zone and a mixed foodweb base in the Eastern Zone that includes a significant water-column source (Evans et al. 2001).

• Stable isotope analysis indicates that hard-bottom communities in southwestern Florida Bay are largely dependent on endogenous energy derived from macroalgae (Behringer and Butler 1999, in prep.)

• The number of forage fish associated with the mangrove prop roots in northeastern Florida Bay is low, and the number of juvenile carnivorous fish in this habitat is low in comparison to the Bahamas and Puerto Rico (Dennis and Sulak 2001).

• The relative density of forage fish is greater in the vicinity of feeding bottlenose dolphin than in other areas (Read et al. 2001).

• Two independent preliminary trophic network models have been prepared for the Bay as a whole and have shown serious gaps in information needed for ecosystem modeling (Ulanowich ??, Acosta et al. 199??).

• Stomach contents examination, pigment measurements, and stable isotope analysis of pink shrimp fed nocturnally indicated the main prey species of pink shrimp is the seagrass shrimp Thor floridanus. Plant detritus made only 15 to 6 % of the stomach contents.

• Multiple stable isotope analyses are being conducted on preserved specimens.to look at temporal and spatial variation with respect to salinity and other variables. (Chasar et al. 2001).

• Descriptive ecology of destructive grazing of seagrass by urchins in western Florida Bay.

• Quarterly characterization of hard-bottom sessile community structure (e.g., sponges, octocorals, corals, macroalgae, lobsters, etc.) at selected sites in southwestern Florida Bay in comparison with other sites throughout the Florida Keys (Butler, Herrnkind, and Hunt 2001).

• The relationship between seagrass distribution and molluscan diversity and abundance is being examined by Brewster-Wingard and collaborators.

• Current focus is on Whipray Basn in a continuing analysis of cores collected in Florida Bay by Brewster-Wingard and collaborators.

• Identification of the information/data gaps suggested by the preliminary trophic network models.

• Acquisition of information/data identified by the trophic network models.

• Further work with the trophic network models, including models specific to each major region of the Bay.

• Analyses and modeling of trophic dynamics in relation to salinity, habitat, and other environmental variables.

• Integration of Florida Bay and offshore species and trophic models.

• Feeding ecology of caridean shrimp and other small crustaceans that are major components of the Bay macrofauna and a major prey of pink shrimp and forage and juvenile fishes.

• Empirical investigations of the impact of changes in nursery habitat structure (e.g., seagrass density, macroalgal abundance) on settlement of key species and integration of these results in spatial models.

• Transport and detrainment of pre-settlement stages into the coastal zone of the Florida Keys are caused by coastal eddies.

• Spawning and nursery sites for pink shrimp, spiny lobsters, and some snappers are linked through the evolution of the coastal eddies from the Tortugas gyre.

• The formation of the Tortugas gyre is enhanced by a well-developed Loop Current (high latitudinal intrusion). Loop Current dynamics may be modulated by climatic shifts.

• Year class strength of six snapper species is enhanced by increased larval retention and nutrient-enrichment of the pelagic larval habitat via gyre-induced upwelling when this coincides with the seasonal occurrence of adult snapper spawning aggregations off the Dry Tortugas.

• Snapper larvae entering Florida Bay largely originate from adult spawning stocks that form seasonal aggregations off the Dry Tortugas.

• High density influxes of presettlement stages of lobsters, pink shrimp, and six snapper species into Florida Bay occur in the channels of the middle and Lower Keys during the presence of a coastal eddy and associated countercurrent nearshore (Yeung et al. In review).

• The influx of spiny lobster postlarvae in the lower Keys is poorly correlated with wind shear (Acosta et al. 1997) and has little correspondence among sites stretching from Key Largo to Key West, conforming best to a random supply model (Butler et al. in press). High concentrations of spiny lobster postlarvae are also of significantly poorer nutritional condition than at other times, as determined from C/N analyses and survival bioassays (Butler et al. unpub. data).

• The influx of pink shrimp postlarvae into the Florida Bay area through two intertidal channels in the Middle Keys was much lower during the 1997-1998 El Nino event than during the 1998-1999 La Nina (Criales et al. In prep.).

• Correlation was found between pink shrimp abundance on the Tortugas grounds and sea level difference between Naples and Key West. (Ehrhardt, in prep.)

• The influx pattern of six species of snapper larvae at Long Key and Whale Harbor channels (1997-1999) showed the majority (ca. 75%) of the total snapper catch occurred at Long Key, suggesting offshore linkage to Florida Bay may be more important at this site for these species (Jones et al. 2001). Additionally, significantly more larvae entered Florida Bay during the first summer sampled (1997), a time coincident which greater development of the Loop Current (and likely increased frequency and duration of gyre events.)

• Backcalculated spawning dates of snapper postlarvae collected in Florida Keys passes suggest a spawning date and origin consistent with the occurrence of known spawning aggregations off the Dry Tortugas (Richards et al. 2001).

• Biological sampling experiments to test the influence of coastal eddies on the supply of pre-settlement stages into Florida Bay in the Middles and Lower Keys, with resolution of coastal current structure to enable modeling particle trajectories using in-situ current meters, remote sensing instruments, and a shore-based Ocean Surface Current Radar (OSCR) system (Yeung et al. 2001).

• Monthly monitoring of spiny lobster postlarval supply from Key Largo to Key West to examine potential quantitative relationships between oceanographic conditions, postlarval supply, and postlarval condition. In conjunction with these measures of postlarval supply, quarterly sampling of changes in juvenile spiny lobster population structure (abundance, size distribution), juvenile dynamics (growth, mortality), and hard-bottom habitat structure are being conducted at 28 sites throughout the Florida Keys and southwest Florida Bay (Butler et al. 2001).

• Investigate the roles of two upstream processes in the transport and ecology of local and upstream larval recruits in the South Florida Ecosystem: (1) the Tortugas gyre and (2) dynamics of the Loop Current (Yeung et al. In review) through two potential approaches: (1) explore correlations using historical physical and biological/fishery data time series; (2) hypothesis testing using new empirical biological and physical data in conjunction with ocean circulation models.

• A freshwater signal, represented by a gradient in salinity or some olfactory substance, guides and enhances immigration of pre-settlement stages of shrimp and other offshore-spawned species into Florida Bay.

• Pink shrimp post larvae enter Florida Bay from three directions: west (across the southwest shelf), southeast (through the Lower Keys), and east (through the Upper Keys). These pathways vary in importance and are differentially affected by physical oceanographic factors and tides.

• Sufficient pink shrimp larvae enter the Bay’s interior for the interior Bay to be a significant source of recruits to the fishery during years of favorable conditions.

• Snappers settle outside Florida Bay but near the boundary and enter Florida Bay as juveniles.

• The abundance of Bay-dependent species that are spawned offshore is lower in northeastern Florida Bay because of weak transport into northeastern Florida Bay.

• The transport of spiny lobster postlarvae into the interior of Florida Bay is severely restricted by the presence of mudbanks, inappropriate salinity, and scarcity of hard-bottom settlement habitat (Field and Butler 1994). In southwestern Florida Bay, the transport and pattern of settlement of postlarvae is highly dependent on the location of red macroalgae (Laurencia) and crevice shelters, and planktonic postlarval abundance (Herrnkind and Butler 1994).

• Pink shrimp postlarvae entering Florida Bay from the Gulf of Mexico side are slightly larger in total length and number of rostral spines than those entering the Bay through the Middle Keys (Browder et al. 2001). This result may suggest that those on the west grow faster and, therefore, conditions are more favorable on this transport route; or, alternatively, that these larvae are older.

• Pink shrimp postlarvae were identified in plankton samples from interior Florida Bay (Whipray Basin), demonstrating that they are transported into the interior of the Bay, although larval concentrations there were lower than in the western Bay (Browder et al. 2001).

• The density influx of pink shrimp postlarvae through two channels 30 km apart differed in intensity and seasonal pattern. Long Key in the Middle Keys showed a seasonal pattern with peaks in late spring-early summer. Long Key peaks were related to sea surface temperature, and wind stress that usually enhances countercurrent transport. Conversely, postlarval influx further up the Keys, through Whale Harbor, showed both summer and winter peaks that may be associated with eddy-induced countercurrent (Criales et al. In prep.).

• Abundance of pre-settlement stages of reeffish species that settle in mangrove proproot areas is low in northeastern Florida Bay compared to a control site on the bayside of Key Largo, nearer to the source of ichthyoplankton, suggesting that the low density of juveniles in the northeastern Bay may be caused by lack of influx of ichthyoplankton spawned outside the Bay (Dennis and Sulak 2001).

Present Research

• Pink shrimp postlarvae influx on western, southern, and eastern pathways (Criales et al. 2001, Browder et al. 2001).

Needed New Research

• Recruitment and survivorship of snapper and grunts from the western Florida shelf into Florida Bay.

• Expansion of pink shrimp postlarvae sampling sites further into the interior of Florida Bay.

• Field studies to determine the influx of ichthyoplankton into Florida Bay.

• Analysis of existing of depth-discrete night-collected ichthyoplankton samples from the western Florida shelf.

• Experimental tests on pink shrimp and other species of gradient detection for salinity and olfactory materials.

Critical Research Hypotheses

 

Recent Progress

• A dense aggregation of the variegated sea urchin (Lytechinus variegatus) caused severe localized defoliation of a seagrass bed in outer Florida Bay during 1997-98. The population dynamics of this aggregation has been described, and the short-term effect of this aggregation on the benthic community has been assessed (Macia & Lirman 1999, Rose et al. 1999). Subsequent monitoring of the aggregation during 1998-99 revealed that urchin densities progressively declined, as did their impact on seagrass biomass. However, little regrowth of seagrass was observed in the most severely defoliated portion of the seagrass bed. By late 1999, smaller, presumably younger, urchins were found within the remnants of the original aggregation, foreboding continued impacts on the seagrass community.

 

Present Research

 

Needed New Research

• What is the ecological role of sponges in the ecosystem? What does the loss of sponges in southwestern Florida Bay and an increasing fishery for some sponge species portend?

 

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