Technical Synthesis of Sarasota Bay 

# Technical Synthesis of Sarasota Bay Page 1 of 17

by David A. Tomasko, Ph.D. Sarasota Bay National Estuary Program

Mark Alderson Ernest Estevez, Ph.D. Peter Clark Michael Hey1 James Culter Susan Lowrey Kellie Dixon Y. Peter Sheng, Ph.D. Randy Edwards, Ph.D. John Stevely 

## Table of Contents

l Executive Summary

l Impacts of Pollutants on Sarasota Bay

l Water Clarity

l Dissolved Oxygen

l Present and Future Habitat

l Literature Cited 

## Executive Summary
Much has been learned from the technical work conducted on Sarasota Bay (from Anna Maria Sound to Venice Inlet) during the past few years. The extent and severity of the problems within Sarasota Bay are more substantial than originally believed, particularly in regard to the levels of toxic contaminants found in tributaries and the degree of habitat loss. In addition, recent evidence suggests that the extent of eutrophic conditions is most probably underestimated throughout the Bay. The nomination document supporting entrance to the National Estuary Program stated that the majority of problems in Sarasota Bay were related to overuse of its rather limited resources, At that time, it was believed that habitat loss and overuse were the most pressing issues. However, data collected through the Program indicate larger-scale problems than originally perceived. Metals contamination, as well as contaminants from pesticides and PCB’s, is believed to be a significant issue in Hudson Bayou, Cedar Hammock Creek, Bowlees Creek, Whitaker Bayou and Phillippi Creek. In addition, the potential exists for contamination in the unsampled upstream portions of other tributaries. While such areas comprise a relatively small proportion of the total area of Sarasota Bay, they make up a large proportion of the extremely important low-salinity nursery habitat for Sarasota Bay’s fisheries. Data also indicate that vitally important tidal wetlands, some of them located in contaminated tributaries, have declined by approximately 39 percent during the past 40 years, with equally dramatic declines occurring in freshwater wetlands.

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Oysters from tributaries with sediment contamination showed elevated levels of copper and zinc compared to other sites in Florida, and were greatly elevated in lead when compared to both state and national data sets. This information indicates that metals contamination, the product of stormwater runoff and illicit point-source discharges, is an important issue in Sarasota Bay. Stormwater pollution is also the major source of nutrient loadings, accounting for approximately 47 percent of the nitrogen and phosphorus entering the Bay. Data collected for the Program suggest that nutrient pollution is an important issue, since Sarasota Bay currently receives approximately three times as much nitrogen as would be loaded from a pristine, undeveloped watershed M . Heyl,personal communication). It is also apparent that Bay circulation and flushing patterns, as well as sediment resuspension and transport, play an important role in determining the magnitude of water-quality degradation associated with nutrient over-enrichment. In some areas of Sarasota Bay, anecdotal information and preliminary studies indicate that the animal communities found in seagrassmeadows have reduced species diversity, perhaps due to recurrent hypoxia associated with algal blooms. Algal blooms, which are not uncommon in parts of the Bay with reduced circulation, appear to be related to nutrient over-enrichment, Persistent and noxious algal blooms can indicate water-quality problems that might require large-scale, potentially expensive remedies. Preliminary data from continuous monitoring of dissolved oxygen (D.O.) and faunal-utilization studies suggest that parts of the Bay are more degraded than is indicated by the State of Florida’s Trophic State Index (TSI).The TSI classifies almost all of Sarasota Bay as “good,” with only Little Sarasota Bay ranking as “fair.” However, the index does not contain a specific term for critical pre-dawn D.O. sags. Given the well documented importance of recurrent low D.O. levels on species diversity and abundance within estuarine locations, including preliminary information from Sarasota Bay, it might prove useful to incorporate such information into a modified TSI. 

## Impacts of Pollutants on Sarasota Bay

Metals Habitats located outside the mouths of the tributaries to Sarasota Bay do not appear to be heavily impacted by metals contamination (Dixon, 1992; Lowrey, 1992). The data from the sediment- and shellfish-contamination studies indicate that elevated metals concentrations appear primarily in the tributaries, with anthropogenic enrichment typically increasing as one progresses upstream. Areas ofnotable metals enrichment include Hudson Bayou, Cedar Hammock Creek, Phillippi Creek, Whitaker Bayou and Bowlees Creek, as well as areas near points of substantial stormwater runoff. Levels of mercury (the only regulated metal) were below federal action limits for health and safety, but metals concentrations in shellfish were well above Florida averages for lead, zinc and copper. For metals, the routes of entry into Sarasota Bay vary Most of the zinc entering Sarasota Bay comes from direct atmospheric deposition and precipitation, while most lead enters via stormwater runoff (CDM, 1992). Metals deposited on paved surfaces by direct atmospheric deposition would then be incorporated into stormwater runoff. The routes of entry for metals other than lead and zinc have not been determined for Sarasota Bay, but they might be expected to behave in similar manners as have been documented in other major estuaries, specifically Chesapeake Bay. Data from Chesapeake Bay indicate that in addition to zinc, significant amounts of lead, copper and cadmium enter the Bay via direct precipitation on the open

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water (Haberman et at, 1983). Lead, along with cadmium, is incorporated into stormwater runoff via dry deposition of automobile exhaust onto paved surfaces, as well as through the deterioration of brakes and tires (Haberman et al., 1983). Another source of metals contamination comes from marine activities. In Chesapeake Bay, copper loadings related to boater’s uses of antifouling bottom paints were thought to equal loadings from industrial and municipal sources (Haberman et at, 1983). With more than 30,000 registered boats in Manatee and Sarasota counties, the potential role of antifouling paints on copper loading into Sarasota Bay deserves further attention. In addition, the use of copper-containing herbicides for weed control along roads may be associated with elevated copper levels found in stormwater-control structures (Lowrey, personal communication). In some tributaries, problems with metals enrichment are exacerbated by contamination from pesticide residues and PCBs(Dixon, 1992; Lowrey, 1992). The synergism between different metals, or metals and pesticide residues, is mostly unknown. Consequently, more detailed investigations would seem appropriate to determine the biological effects of sediment contamination by multiple factors. Low-salinity habitats are essential for juvenile snook, redfish, tarpon, spotted seatrout, striped mullet and pink shrimp (Edwards, 1991). As these areas become increasingly contaminated by metals, both lethal and sub-lethal effects would act to reduce the sizes of future populations of recreationally and commercially important species (Haberman et at, 1983).
Role of Nutrients The nutrients nitrogen and phosphorus play important roles in determining the trophic status of Sarasota Bay. Under conditions of increased nutrient availability, one would expect elevated levels of phytoplankton (with reduced water clarity), elevated levels of epiphytic algae (which would shade seagrasses) and greater amounts of drift algae (capable of shading seagrasses and producing recurrent low pre-dawn dissolved-oxygen levels). With lower nutrient loads, less algae can be supported. Nitrogen, rather than phosphorus, appears to be the primary limiting nutrient for phytoplankton in Tampa Bay (Johansson, 199 l),and nitrogen is most probably the limiting nutrient for phytoplankton, epiphytic algae on seagrassblades and drift macroalgae in Sarasota Bay (see review in Lapointe et al., 1992a). However, even low levels of phosphorus enrichment might be sufftcient to stimulate algal blooms in freshwater ponds and streams throughout the watershed (Taylor, 1967). Baywide, approximately half of all nitrogen and phosphorus loadings come from stormwater runoff, and roughly one-quarter of loadings come from direct atmospheric deposition (CDM, 1992). The remaining nutrient loads are divided among baseflow(groundwater contributions to tributaries), septic tanks and point sources.
Wastewater Point sources of pollution can cause localized water-quality problems, but the overall status of water quality in Sarasota Bay does not seem to be strongly impacted by point sources of pollution (CDM, 1992). In addition, many point sources of nutrient pollution have been upgraded in recent years. The documented reduction over time of phosphorus and nitrogen levels in waters offshore of Whitaker Bayou (Lowrey, 1992) may be associated with the upgrade to nutrient-removal technology at the City of Sarasota’s wastewater-treatment plant. While not prominent Baywide, septic systems play a significant role in nitrogen loading in Bay segments whose watersheds have concentrations of septic tanks (i.e., Roberts Bay, Little Sarasota

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Bay, Blackbum Bay), While properly functioning septic systems do not pose health problems, their primary function is that of minimizing health risks through reducing bacterial contamination, rather than the removal ofnitrogen and phosphorus in effluent. For the soils characteristic of the Sarasota Bay region, carbonate-binding sites generally prevent groundwater transport of phosphorus to nearby surface waters (IFAS, 1985). In contrast, the processes of absorption, biological uptake, denitrification and volatilization might remove only 20-40 percent of the nitrogen load before septic-tank effluent reaches groundwater (IFAS, 1985). Once in the groundwater, nitrate is relatively free to travel, as opposed to ammonium, which might still absorb onto binding sites, The method used in the CDM study (1992) for calculating the impact of septic tanks on nitrogen loadings is the best effort to date for the Sarasota Bay area, as it was locally calibrated using data on nutrient concentrations in receiving waters. Given that Sarasota County contains approximately 45,000 septic tanks -the vast majority of systems in the Bay watershed- it is essential that their impacts on nutrient loadings be documented. In parts of the Bay watershed, particularly in Sarasota County, package sewage-treatment plants are common. The levels of treatment and means of effluent disposal for these plants vary. Plants with direct surface discharge must meet advanced wastewater-treatment (AWT) levels for biological oxygen demand, total suspended solids, total nitrogen and total phosphorus; respectively, 5, 5, 3, 1 (mg/l). In contrast, several plants treat effluent only to secondary levels, with up to seven times the nitrogen concentration of AWT effluent (approximately 20 mg/l), and four times the phosphorus concentration of AWT effluent (approximately 4 mgA). If percolation ponds are used for these secondary-treatment plants, the nutrient-loading potential for these plants might be best estimated using information on groundwater migration of nutrients within septic-tank effluent streams. Package plants with secondary treatment and percolation ponds would be a more condensed source of nutrient pollution compared to an equivalent number of customers using septic tanks. Consequently, replacing septic systems with secondary- treatment plant using percolation ponds may exacerbate problems in some areas, and might not result in any reductions in totalnutrient loadings to nearby surface waters. Connecting septic systems to secondary plants with re-use of efIIuent, or to advanced wastewater-treatment plants with or without re-use, would be the only way to ensure a decline in nutrient loads associated with wastewater

Stormwater Stormwater loadings of nitrogen and phosphorus would be expected to decrease if agricultural land is replaced by residential land uses. However, if natural areas are developed for housing, stormwater loadings of nutrients would be expected to increase (data from CDM, 1992). Estimates of nutrient-removal efficiencies of wet detention ponds, the most efficient stormwater-treatment systems, average only 30-percent removal for nitrogen, and only SO-percent removal for phosphorus (Heyl, 1992). Currently, stormwater-control structures are required only for new developments involving the subdivision of land, not for development of single homes on single lots. Approximately 40 percent of the Bay’s watershed is in residential land use (CDM, 1992). Due to extensive use of lawn fertilizers, the nutrient concentration of runoff from these residential areas is second only to various agricultural land uses (CDM, 1992). As such, it seems obvious that source control of nutrient runoff(e.g., educating homeowners about the impacts of lawn fertilizers on Bay waters) would be an essential tool for improving water quality in Sarasota Bay.

9~28~48 AM

### Land-Use Patterns WBhfn the Watershed of Hudson Bayou



## Land-Use Patterns Within the Watershed of North Creek3 0

### Technical Synthesis of Sarasota Bay PageSof

Management options must consider the diversity of land-use patterns that occur throughout our watershed. Figure 1 shows the difference in land-use patterns among Hudson Bayou (an urbanized watershed), North Creek (a rural watershed) and Phillippi Creek (intermediate between urban and rural). As such, management strategies for stormwater control must be designed on a watershed-by-watershed basis. Connections Between Nutrient Lords and Water Quality 

### The recently completed nutrient-loading evaluation provides useful data on the sources and quantities of nutrient loading on a watershed-by-watershed basis. However, the model cannot predict changes in water quality associated with increased or decreased nutrient loads. Factors such as circulation and sediment-nutrient fluxes need to be taken into account.

Figures 2. 3. 4 For instance, when nitrogen loadings from various watersheds are plotted against the annual average total Kjeldahl nitrogen (organic N plus ammonium; TKN) concentration within receiving waters, no clear pattern appears (Figure 2). The same lack of correlation occurs when phosphorus loadings are plotted against annual average-water-column total phosphorus (TP) levels, and when nitrogen loadings are plotted against annual average-water- column chlorophyll a concentrations (Figure 3). Reasons for this lack of correlation include differences in the segment volumes to which loads are applied as well as differences in flushing rates of various segments and potential differences in nutrient cycling associated with dissimilar sediment dynamics. As such, areas degraded by elevated loading

8/l/97 9.3R.4R A MTechnical Synthesis of Sarasota Bay Page 6 of 17 would not necessarily be found in the immediate vicinity of the loading point, but possibly would be some distance away. As an example of the tenuous relationship between nutrient loading and segment-wide water quality, Little Sarasota Bay has much poorer water quality (higher TKN and TP, lower clarity, shallower depths for its seagrassmeadows) than both Roberts Bay and Blackbum Bay, even though Roberts Bay and Blackburn Bay receive considerably greater nitrogen loads than Little Sarasota Bay. A likely reason for this apparent discrepancy is the location of Little Sarasota Bay in the null zone for circulation within this region, as well as the proximity of Roberts Bay and Blackburn Bay to Big Pass and the Venice inlet, respectively, which provide better flushing (Sheng and Peene 1992). Similarly, recently obtained current and salinity data indicate that water quality in Anna Maria Sound and Palma SolaBay is influenced by the Manatee River and Tampa Bay (Sheng and Peene, 1992). This influence might result in poorer water quality than that produced by the nutrient-loading estimates for the watersheds directly draining into these areas. Within a given area, with hydraulic variables remaining similar from measurement to measurement, water quality can correlate well with loadings. A plot of nitrogen loadings versus chlorophyll a levels in Hillsborough Bay (a part of Tampa Bay) shows a clear pattern over a period of 22 years (Figure 4). The Sarasota Bay data set, on the other hand, is from a single year, and represents the initial stages of developing specific relationships between water quality and nutrient loads on a segment-by-segment basis. Water quality in areas of Sarasota Bay with reduced flushing would probably be slower to respond to nutrient-loading reductions, due to the higher residence times and the increased importance of nutrient release from sediments, which would be less likely to be transported to other locations. In the cases of Little Sarasota Bay and Palma SolaBay, water quality might not improve as quickly and/or dramatically after reducing land-based pollution as would be expected to occur in areas such as Roberts Bay, Blackburn Bay and the areas offshore of Bowlees Creek and Tidy Island. Without a coupled circulation/water-quality model, only limited qualitative forecasts can be made as to the expected benefits of implemented management options. Although we cannot at present predict the exact response of the Bay’s waters to reductions in nutrient loading, much evidence exists as to the expected positive benefits associated with reduced nutrient loadings. In the Potomac River, a 95percent reduction in point-source loads of both total phosphorus and biological oxygen demand was brought about mainly by upgrading municipal sewage-treatment plants to AWT standards (Alderson, 1988). Aquatic grass habitat in the Potomac River has dramatically increased during the past few years, with much of this increase attributed to reduced water-column chlorophyll levels and increased water clarity (Carter and Rybicki, 1986). Similarly, 80- to go-percent reductions in point-source phosphorus loading into Lake Erie and Lake Ontario have led to declines in water-column phosphorus levels and decreased abundances of nuisance algae in these phosphorus-limited systems (Alderson, 1988). Johansson (1992) has documented the improvements in water quality in Tampa Bay that have accompanied reduced nutrient loading by the fertilizer industry and the upgrading of the City of Tampa’s main wastewater-treatment plant to Advanced Wastewater Treatment (AWT). Increased water quality has allowed seagrasses to return to areas where they had previously been killed off by poor water quality (Johansson, 1992). In the part of Sarasota Bay near the mouth of Whitaker Bayou, seagrasses were thought to be

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eliminated in the past due to the discharge of secondarily treated sewage from the City of Sarasota’s wastewater-treatment plant (Dr. Robert Orth, personal communication). Perhaps associated with the implementation of nutrient-removal technology at this plant, declines in water- column nitrogen and phosphorus have been detected in this region (Lowrey, 1992). As a test case using seagrasstransplants as bio-indicators of improved water quality, shoal grass (Halodule wrightii) was transplanted into an area just south of Whitaker Bayou in October 1991. The majority of these transplants had survived at least until March 1992, indicating water quality sufficient to maintain shoal grass in that area. At that time, an older established seagrassbed merged with the transplants. The loss of plot markers made continued monitoring impossible (Tomasko, unpublished data). 

## Water Clarity
Water Clarity and Seagrasses Water clarity varies from region to region throughout Sarasota Bay. Nearshore areas are more heavily influenced by terrestrial runoff and bottom resuspension due to currents and wave action (Sheng and Peene, 1992), with concomitant increases in suspended and dissolved substances. Suspended substances increase both the scattering and absorption of photosynthetically active radiation (PAR), while dissolved substances increase the absorption of PAR mostly in the region of blue light (McPherson and Miller, 1987). Areas closer to passes are exposed to water more characteristic of the Gulf of Mexico, with greater water clarity. The availability of light, as modified by various light attenuators, is the primary abiotic factor controlling the area1 extent and productivity of seagrasscommunities (see review in Dennison, 1987). Seagrasses, which cover nearly 26 percent of Sarasota Bay’s bottom (83 19 acres; Culter, 1992), are indispensable for the roles they play in nutrient cycling, primary production, sediment stabilization and fisheries utilization (see reviews in Zieman, 1982; Thayer et al., 1984). Accordingly, it is crucial that we understand the relationships between various light attenuators, water clarity and the health of seagrasssystems within the Bay. Many studies have documented the decline of seagrassassociated with degraded water clarity (es., Cambridge and McCoomb,1984; Orth and Moore, 1984; Giesen et al., 1990). In addition, a limited amount of information exists on the resurgence of seagrasses associated with improvements in water clarity in Australia (Shepard et al, 1989) and in Tampa Bay (Johansson, 1992). The shallow slope of the bottom of Sarasota Bay would allow for dramatic increases in seagrass coverage with minimal increases in water clarity. According to bathymetric data for Sarasota Bay (Sheng et al., in preparation), roughly 46 percent of Little Sarasota Bay is less than two feet deep at Mean Lower Low Water (approximately three feet at Mean Sea Level). This depth is equal to the deep edge of grassbeds in the central portion of Little Sarasota Bay. If water clarity in Little Sarasota Bay were to improve to values typically found in Roberts Bay, seagrasses could grow to one more foot of water depth. In Little Sarasota Bay, that would result in an increase in potential acreage from 986 acres of Bay bottom to 1,434 acres, a possible increase in seagrasshabitat of 448 acres (equal to 45 percent of existing habitat). Light availability not only delimits most seagrassmeadows at their deep edges, it can also regulate the biomass and productivity of seagrasses within meadows. Short (1990) has shown a linear response between light levels and the biomass of seagrasses grown under controlled conditions. Hall et al.

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The state of the science in seagrassbiology has not progressed much beyond the point where it can be stated that increased water clarity is good and decreased water clarity is bad. This information does little to aid resource managers in determining how improvements in water clarity can be achieved. If the relative importance of various light attenuators (i.e., color, turbidity, chlorophyll a) is not known, it is difficult to devise appropriate courses of action to increase water clarity. Knowledge of which factors are most responsible for light attenuation can be used to draft specific resource-management options. For instance, previous work on the east coast of Florida has shown that boat wakes can create sufficient sediment resuspension to increase turbidity values, thus decreasing water clarity (U.S.F.W.S., 1979). Information from the water-quality monitoring program has been used to determine which light attenuators are most closely associated with variation in water clarity in Sarasota Bay. Based on information from multiple-regression analysis, turbidity does not seem to be an overly important contributor to light attenuation in those segments of the Bay where this association was examined. The data suggest that variation in turbidity accounts for only two to five percent of the variation in light penetration for waters in various parts of the Bay. However, these data were not collected during weekends, when boating activity increases. It might be that only at such times would a relationship emerge between turbidity and light attenuation. A linkage between water-column chlorophyll values and light attenuation does exist for various parts of the Bay, where variation in chlorophyll a accounts for 23-47 percent of the variation in water clarity. As phytoplankton populations (the source of water-column chlorophyll a) are most probably limited by nitrogen loading in these areas (Johannson, 1992), locating the dominant sources of nitrogen loading could result in management activities designed to reduce loading. A predicted consequence would be less chlorophyll a, greater water clarity and increased acreage of seagrass habitat. Variation in the amount of dissolved substances (color) in any particular segment of the Bay is related to variation in circulation patterns and the relative importance of freshwater flows to a segment. In areas where dissolved organic substances are dominant light attenuators, few options other than increased circulation/flushing would be sufftcient to improve water clarity. The data on circulation and transport in Sarasota Bay showed poor tidal flushing in Palma SolaBay and Little Sarasota Bay (Sheng and Peene, 1992); these same two areas are in the lower 25 percent of all Bay segments for a variety of light-related water- quality variables (Lowrey et al., 1992). The improvement in water quality achieved by increased circulation, however, must be evaluated in context with possible increases in salinity, and any potential reductions in low-salinity habitats. 

## Dissolved Oxygen
Critical Levels of Dissolved Oxygen Dissolved oxygen (D.O.) plays a critical role in regulating the health of estuarine systems. Unfortunately, low dissolved oxygen has become increasingly common in a variety of estuarine and marine areas, from Denmark and Sweden to Chesapeake Bay and the Gulf of Mexico (e.g., Turner and Allen, 1972; Rosenberg, 1990; Rossignol-Strick, 1985; Stachowitsch, 1984). Typically, low dissolved-oxygen levels are the result of human-induced nutrient enrichment of nearshore waters, often referred to as cultural eutrophication (Ryther and Dunstan, 1971; Officer et al., 1984; Rosenberg, 1985).

8/l/97 9128149 AMTechnical Synthesis of Sarasota Bay Page 10 of 17 Physiological effects of hypoxia (less than or equal to 2 ppm D.O.) on fishand shellfish are well-known (Butler et al., 1978; Kapper and Stickle, 1987; DeFur et al., 1990). Behavioral changes in marine organisms can also be induced by hypoxia (Hagerman and Szaniawska, 1986; Kramer, 1987). If marine organisms cannot evade hypoxic waters, as in blue-crab migrations (Bailey and Jones, 1989), they must be able to adapt to conditions or perish. The eggs and larvae of bay anchovies, Anchoa mitchilli, are extremely susceptible to hypoxic conditions (Chesney, 1989), and their survival and geographic distribution within estuarine systems might be somewhat controlled by hypoxia. Dissolved Oxygen Levels in Sarasota Bay Little information currently exists to suggest that low D.O. plays an important role in reducing the vitality of habitats in Sarasota Bay. Excepting some of the tributary stations, few areas have reported problems with hypoxia and/or anoxia (0 ppm D.O.) during the daylight hours typically sampled. As related to the problems of hypoxia and anoxia in Sarasota Bay, the maxim “an absence of evidence does not constitute evidence for absence” should be kept in mind. When water-quality sampling efforts are undertaken later in the day (accurate measurements of water clarity require the sun to be nearly overhead), D.O. levels can be much higher than their daily minimum in areas subject to eutrophication.

Figure 7

1 &~;;‘;

--__--_-_----___. IFigure

8 Daily variation in D.O. is illustrated (Figure 7) using data obtained by continuous recording devices placed in Little Sarasota Bay by the University of Florida. Figure 8, which is a rearrangement of the same data as in Figure 7, demonstrates the typical relationship between hours of sunlight and D.O. levels. For most of Sarasota Bay, the evaluation of the extent of hypoxic conditions will require monitoring efforts at pre-dawn times, or the use of continuously recording instrumentation. Pre-dawn D.O. sags are probably the most important water- quality variable affecting species diversity and abundance in estuarine locations. Reliance on D.O. sampling during daylight hours biases water-quality classification schemes to the point where optimistic evaluations of water quality are oflen unwarranted. Preliminary data from an ongoing study on fauna1 utilization of various grassbeds indicate that

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### I kTechnical Synthesis of Sarasota Bay Page 11 of 17 “pristine” and “impacted” seagrassbeds (subjectively classified as such) have quite different fauna1 assemblages and levels of species diversity, despite occurring in areas of equal status according to the Trophic State Index (Leverone and Marshall, 1992). Indeed, impacted meadows of shoal grass contained only a small fraction of the numbers of caridean shrimp as were found in healthier meadows of shoal grass. Results from Culter (1992) indicate that approximately 4,800 acres of Bay bottom (15 percent of the total area) are “disturbed,” with many of these locations being anoxic sinks for fine sediments. However, it is not known if hypoxic conditions in Sarasota Bay are persistent enough to cause substantial differences in animal communities. 

## Present and Future Habitat

Status and Trends of Various Habitats
Much has been written about the value of freshwater and tidal wetlands in terms of shoreline stabilization, wildlife utilization and filtering of runoff. From 1950 to 1990, Sarasota Bay lost an estimated 1,609 acres of tidal wetlands, a 39-percent decline (Estevez, 1992); freshwater wetlands show a similarly dramatic decline during that time (Beaman, 1992). Also, more than 75 percent of freshwater wetlands within the Bay’s watershed are altered to some degree by dredge-and/or-fill activities (Beaman, 1992). The spatial variation in patterns of wetlands loss can be summarized as follows: Manatee County has lost proportionally more of its original freshwater wetlands than Sarasota County, and Sarasota County has lost proportionally more of its original tidal wetlands than Manatee County. This configuration of wetlands loss reflects dissimilar demographic trends and agricultural practices within the watershed (Estevez 1992). Although seagrasses have declined approximately 30 percent Baywide compared to historical coverage (Mangrove Systems, Inc., 1988) areas such as Longboat Pass and New Pass show positive trends for coverage. In the Longboat Pass area, it appears that seagrassincreases may be due to growth on flood-tidal shoals created by pass dredging (Darryl Hatheway, personal communication), In the New Pass area, better water quality (Lowrey, 1992) appears to be allowing seagrasses to grow into deeper areas that were previously unvegetated (Culter, 1992). In Little Sarasota Bay, data indicate significant shifts in the species composition of seagrassmeadows (Culter, 1992). Areas previously vegetated with turtle grass (Thalassia testudinum) are now mainly vegetated with shoal grass (Halodule wrightii) and widgeon grass (Ruppia maritima). As shoal grass oftenreplaces turtle grass in areas of degraded water-quality (Reyes and Merino, 1991): Tomasko and Lapointe, 1991; Lapointe et al., 1992b), this species shift would indicate significant changes in water quality in portions of Little Sarasota Bay.
Functions of Wetland Habitats Mangrove ecosystems have been shown to play an important role in shoreline stabilization (see reviews in Odum et al., 1985). Although salt-marsh grasses are important shoreline stabilizers in higher latitudes, they have not been extensively studied in west-central Florida (Estevez and Mosura, 1985). Regardless, it can be stated with confidence that the extensive decline in tidal wetlands, both in area and edge, produced concurrent declines in shoreline stability. Unstable shorelines erode more easily, with resultant increased sediment resuspension, increased turbidity and decreased water clarity. Freshwater wetlands perform similar functions in terms of shoreline stabilization along creeks and

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“pristine” and “impacted” seagrassbeds (subjectively classified as such) have quite different fauna1 assemblages and levels of species diversity, despite occurring in areas of equal status according to the Trophic State Index (Leverone and Marshall, 1992). Indeed, impacted meadows of shoal grass contained only a small fraction of the numbers of caridean shrimp as were found in healthier meadows of shoal grass. Results from Culter (1992) indicate that approximately 4,800 acres of Bay bottom (15 percent of the total area) are “disturbed,” with many of these locations being anoxic sinks for fine sediments. However, it is not known if hypoxic conditions in Sarasota Bay are persistent enough to cause substantial differences in animal communities. 

## Present and Future Habitat

Status and Trends of Various Habitats
Much has been written about the value of freshwater and tidal wetlands in terms of shoreline stabilization, wildlife utilization and filtering of runoff. From 1950 to 1990, Sarasota Bay lost an estimated 1,609 acres of tidal wetlands, a 39-percent decline (Estevez, 1992); freshwater wetlands show a similarly dramatic decline during that time (Beaman, 1992). Also, more than 75 percent of freshwater wetlands within the Bay’s watershed are altered to some degree by dredge-and/or-fill activities (Beaman, 1992). The spatial variation in patterns of wetlands loss can be summarized as follows: Manatee County has lost proportionally more of its original freshwater wetlands than Sarasota County, and Sarasota County has lost proportionally more of its original tidal wetlands than Manatee County. This configuration of wetlands loss reflects dissimilar demographic trends and agricultural practices within the watershed (Estevez 1992). Although seagrasses have declined approximately 30 percent Baywide compared to historical coverage (Mangrove Systems, Inc., 1988) areas such as Longboat Pass and New Pass show positive trends for coverage. In the Longboat Pass area, it appears that seagrassincreases may be due to growth on flood-tidal shoals created by pass dredging (Darryl Hatheway, personal communication), In the New Pass area, better water quality (Lowrey, 1992) appears to be allowing seagrasses to grow into deeper areas that were previously unvegetated (Culter, 1992). In Little Sarasota Bay, data indicate significant shifts in the species composition of seagrassmeadows (Culter, 1992). Areas previously vegetated with turtle grass (Thalassia testudinum) are now mainly vegetated with shoal grass (Halodule wrightii) and widgeon grass (Ruppia maritima). As shoal grass oftenreplaces turtle grass in areas of degraded water-quality (Reyes and Merino, 1991): Tomasko and Lapointe, 1991; Lapointe et al., 1992b), this species shiftwould indicate significant changes in water quality in portions of Little Sarasota Bay.
Functions of Wetland Habitats Mangrove ecosystems have been shown to play an important role in shoreline stabilization (see reviews in Odum et al., 1985). Although salt-marsh grasses are important shoreline stabilizers in higher latitudes, they have not been extensively studied in west-central Florida (Estevez and Mosura, 1985). Regardless, it can be stated with confidence that the extensive decline in tidal wetlands, both in area and edge, produced concurrent declines in shoreline stability. Unstable shorelines erode more easily, with resultant increased sediment resuspension, increased turbidity and decreased water clarity. Freshwater wetlands perform similar functions in terms of shoreline stabilization along creeks and

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ponds. Page 12 of 7

In addition to stabilizing shorelines and functioning as wildlife habitat (see reviews in Odum et al., 1985; Lewis and Estevez, 1988) wetlands filter runoff before it enters creeks, ponds and the Bay itself Due to differences in funding sources and research directions, tidal wetlands are better understood than freshwater wetlands in terms of shoreline stabilization, but freshwater wetlands are better understood than tidal wetlands as relates to filtering of stormwater runoff.

Figure 9 Dense vegetation along creek banks slows the velocity of runoff, thus increasing the infiltration of water into surface soils and groundwater. As a result, the “first flush” of runoff is dampened, and metals and nutrients are more likely to be absorbed onto soil particles and/or incorporated into plant biomass. In the absence of filtering vegetation, stream velocities are initially elevated compared to natural systems; in addition, after the “first flush” stream velocities drop off more rapidly in the absence of filtering vegetation figure 9 9. Streams and creeks without vegetative cover exhibit a pattern of “feast or famine.” When rains occur, velocities and pollutant loads are magnified; when dry weather dominates, creeks have reduced flow and volume. In that estuarine areas exhibit decreased productivity with both too much and too little freshwater inflow (see review in Browder, 1991) wetlands habitats should be protected and restored to the fullest extent if only for their function as filters of stormwater runoff. The critical importance of reestablishing natural patterns of freshwater input into estuarine areas is evidenced by the priority consideration granted it by the Task Force on Resource- Based Water Quality in Tampa Bay (Agency on Bay Management, 1990). Even if all remaining wetlands could be completely protected from loss due to development (an unlikely scenario), Sarasota Bay would still be left with but a fraction of its original wetlands habitat. Those few remaining wetlands exhibit various levels of disturbance, due to ditching, invasive species, pruning, insect damage and freeze damage (Estevez, 1992). Accordingly, increased wetlands, brought about by restoration and/or creation activities, would seem to be an appropriate course of action. With limited funds for such activities, a prioritization of properties for wetlands restoration/creation could be appropriate. Such a ranking of areas could be based on a holistic approach to estuarine functioning. In addition to preserving remaining wetlands and restoring/creating wetlands to ameliorate the effects of past losses, strategies must be developed to deal with anticipated future losses. One can easily foresee additional declines in wetlands due to continued development throughout the watershed. Although the rate of wetlands destruction due to development may be slowed by current and future legislation, it seems reasonable to assume that both freshwater and tidal wetlands will continue to be lost. In addition, an accelerated rate of sea-level rise, associated with global climate change, might produce additional losses of wetlands. Wetlands issues connected with accelerated sea-level rise include the following: 1) hardened shorelines

full97 9.28:49 AMTechnical Synthesis of Sarasota Bay Page 13 of 17 and development of upland areas might eliminate the possibility of landwardmigration of wetlands; 2) encroachment of invasive species might hinder landwardmigration of wetlands; 3) sediment-accumulation rates in wetlands might be insufficient to accommodate elevated rates of sea-level rise. Although uncertainties abound in predicting global climate change and sea-level rise, a prudent course of action might include a variety of activities. Purchasing acreage upland from existing wetlands might alleviate the problems associated with wetlands migration in areas with appropriate slopes and land-use patterns. Wetlands delimited at their upland edges by seawalls, causeways and/or extensive reaches of invasive species might be very expensive to maintain with an elevated rate of sea-level rise. Relationships Between Recreation and Habitat Recreational activities are varied in their dependence on habitat quality. Some activities, such as boating or cruising, can take place just as easily, and be just as enjoyable, regardless of the location in Sarasota Bay. The level of enjoyment of other activities, such as fishing, snorkeling and bird-watching, are dependent upon the health of the Bay at that particular location. Recreational anglers engage in various types of fishing. Individuals who use cast nets to capture mullet can do quite well in locations where adults of other species are more difficult to catch. Consequently, recreational fishing can be a quite diverse activity, with various people requiring various habitats; one person’s fishing hole may be viewed as a lifeless void by other anglers. A problem that arises with characterizing the various habitats in Sarasota Bay is the emphasis placed on determining the “value” of such habitats. While the area around the former Midnight Pass seems to be functioning as a nursery for various juvenile fish (Edwards, 1992), seasonal aggregations of sought-after species

-as are typical of open pass areas

- no longer occur. As a result, this area is no longer a focal point for recreational fishing. A question arises, both in this example and in many others, as to the type of habitats we are aspiring to preserve, enhance or create. While one may argue the merits of maintaining a mosaic of estuarine habitats, others might argue for maximizing the area of those habitats in shortest supply. In turn, identifying habitats in shortest supply depends on what species are being considered. Pass-type communities are obviously very different from quiescent, lagoonal environments. Both these areas are important, but which is most vital depends on what species are being considered, which might also vary with the age of the targeted species. As shown in the chapter on Fisheries, the primary issue affecting recreational fishing in Sarasota Bay is that of more people fighting for their slice of a diminishing pie. A tenfold increase in population during the last 40 years has greatly increased fishing pressure. During the same period, dramatic declines in fisheries habitat have occurred (an approximate 39- percent decline in mangrove area, and a 30-percent decline in seagrassarea). A relationship appears to exist among declines in habitat, increased fishing pressure and the finding that the average angling experience is less productive than it used to be. Based on this scenario, it seems that protecting remaining fisheries habitats, although essential, is not sufficient. To truly increase the level of enjoyment of recreational angling, new fisheries habitat must be created on a continuing basis. 

## Literature Cited

Agency on Bay Management. (1990). Goals and strategies for Tampa Bay -Results of the forum. Tampa Bay Regional Planning Council, Task Force on Resource-Based Water Quality.

8/l/97 9:28:49 AMTechnical Synthesis of Sarasota Bay Page 14 of 17

Alderson, M. (1988). "Saving Bays and Estuaries: A Handbook of Tactics." U.S. Environmental Protection Agency. Bailey, B., Jones. R.B. (1989). Association between advected hypoxic water and crab wars in the lower Potomac River.

(Abstract) In Tenth Biennial International Estuarine Research Conference, Baltimore, MD. Estuarine Research Federation, P. 4
Beaman, R.D. (1992). Trends and status of freshwater wetlands. Sarasota Bay National Estuary Program "1992 Framework for Action". Browder, J.A (1991). Watershed management and the importance of freshwater flows to estuaries. Pp 7-22. In: Treat, S.F., Clark, PA., eds. Proceedings, Tampa Bay Area Scientific Information Symposium 2. February 27

-March 1, 1991; Tampa, FL 528 P. Butler, P.J., Taylor, E.W., McMahon, R.R. (1978). Respiratory and circulatory changes in the lobster (Homarus vulgarus) during long-term exposure to moderate hypoxia. J. Exp. Biol. 73: 131- 146. Cambridge, M.L., McComb, A.J. (1984). The loss of seagrass in Cockburn Sound, Western Australia I. The time course and magnitude of seagrass decline in relation to industrial development. Aquat. Bot. 20: 229-243.
Camp, Dresser, and McKee, Inc. (1992). Point-/non-point-source pollution-loading assessment. Phase 1. Final Report to Sarasota Bay National Estuary Program. Carter, V., Rybicki, N. (1986). Resurgence of submersed aquatic macrophytes in the tidal Potomac River, Maryland, Virginia and the District of Columbia. Estuaries 9: 368-375. Chesney, E.J. (1989). Laboratory studies on the effect of hypoxic waters on the survival of eggs and yolk-sac larvae of the bay anchovy, Anchoamitchilli. (Abstract) In: Tenth Biennial International Estuarine Research Conference, Baltimore, MD. Estuarine Research Federation, P. 4. Culter, J. (1992). Estuarine bottom assessment. Sarasota Bay National Estuary Program "1992 Framework for Action".

DeFur, P.L., Mangum, C.P., Reese, J.E. (1990). Respiratory responses of the blue crab Callinectes sapidus to long-term hypoxia. Biol. Bull. 178:46-54. Dennison, W.C. (1987). Effects of light on seagrass photosynthesis, growth and depth distribution. Aquat. Bot. 27: 15-26. Dixon, L.K. (1992). Bivalved shellfish of Sarasota Bay. Sarasota Bay National Estuary Program "1992 Framework for Action"
Duarte, C.M (1991 Seagrass depth limits Aquat Bot 40: 363-377. Edwards, R.E. (1991). Nursery habitats of important earlyjuvenile fishes in the Manatee River estuary system of Tampa Bay. PP. 237-252. In: Treat, S.F., Clark, P.A., eds. Proceedings, Tampa Bay Area Scientific Information Symposium 2. February 27

- March 1, 1991; Tampa, FL. 528 P. Edwards, R.E. (1992). Fishery Resource Assessment. Sarasota Bay National Estuary Program "1992 Framework for Action".

s/1/97 9:28:49 AMTechnical Synthesis of Sarasota Bay Page 15 of 17

Estevez, E.D. (1992). Status and trends of Sarasota Bay's tidal wetlands. Sarasota Bay National Estuary Program "1992 Framework for Action".

Estevez, E-D., Mosura, L. (1985). Emergent vegetation. Pp. 248-278. In: S.F. Treat, J.L. Simon, R.R. Lewis III, R.L. Whitman, Jr. (eds). Proceedings, Tampa Bay Area Scientific Information Symposium. Burgess Publishing Co., Inc., Minneapolis, MN. Giesen, W.B.J.T., van Katwijk, M.M., den Hartog, C. (1990). Eelgrass condition and turbidity in the Dutch Wadden Sea. Aquat Bot. 37: 71-85. Haberman, D. Mackiernan, G.B., Macknis, J. (1983). Toxic Compounds. "Chesapeake Bay: A Framework for Action." Chesapeake Bay Program. Hagerman, L., Szaniawska, A. (1986). Behavior, tolerance and anaerobic metabolism under hypoxia in the brackish-water shrimp Crangon crangon. Mar. Ecol. Prog. Set. 34: 125-132. Hall, M.O., Tomasko, D.A., Courtney, F.X. (1990). Responses of Thalassia testudinum to in situ light reduction. Pp. 53-58. In: W.J. Kenworthy, D.E. Haunert (eds.). "The Light Requirements of Seagrasses: Results and Recommendations of a Workshop. South Florida Water Management District. Heyl, M. (1992). Point and nonpoint source loading assessment of Sarasota Bay. Sarasota Bay National Estuary Program "1992 Framework for Action".

IFAS (1985). On-site sewage disposal: Nitrogen behavior. "Notes in Soil Science." Institute of Food and Agricultural Sciences, University of Florida. Johansson, J.O.R. (1991). Long-term trends of nitrogen loading, water quality and biological indicators in Hillsborough Bay, Florida. Pp. 157-176. In: Treat, S.F., Clark, PA., eds. Proceedings, Tampa Bay Area Scientific Information Symposium 2. February 27

-March 1, 1991; Tampa, FL. 528 P. Kapper, M.A., Stickle, W.B. (1987). Metabolic responses of the estuarine gastropod Thais haemastoma to hypoxia. Physiol. 2001. 60: 159-173. Kramer, D.L. (1987). Dissolved oxygen and fish behavior Env Biol. Fishes 18: 81-92. Lapointe, B.E., Littler, M.M., Littler, D.S. (1992a). Nutrient availability to marine macroalgae in siliciclastic versus carbonate-rich coastal waters. Estuaries 15: 75-82. Lapointe, B.E., Tomasko, D.A., MatZie, W. (1992b). Final Report: Eutrophication and trophic structuring of marine plant communities in the Florida Keys. Florida DER Contract # CM-300. Leverone, J.R., Marshall, M.J. (1992). Seagrass bed fauna1 utilization study. Sarasota Bay National Estuary Program. Lewis, R.R. III, Estevez, E.D. (1988). The ecology of Tampa Bay, Florida: an estuarine profile. U.S. Fish. Wildl. Serv. Biol. Rep 85(7.18). 132 pp. Lowrey, S. (1992). Bay water and sediment quality. Sarasota Bay National Estuary Program "1992 Framework for Action". Mangrove Systems, Inc. (1988) Marine Habitat Trend Analysis

8/l/97 9128149 AMTechnical Synthesis of Sarasota Bay Page 16 of 17

McPherson, B.F., Miller, R.L. (1987). The vertical attenuation of light in Charlotte Harbor, a shallow, subtropical estuary, Southwestern Florida. Est. Coast. Shelf Sci. 25: 721-737. Odum, W-E., McIvor, C.C., Smith, III, T.J. (1982). The ecology of the mangroves of south Florida: a community profile. U.S. Fish and Wildlife Service, Office of Biological Services, Washington, DC. FWS/OBS-81/24.144 pp. Officer, C.B., Biggs, R.B., Taft, J.L., Cronin, L.E., Tyler, MA, Boynton, W.R., (1984). Chesapeake Bay anoxia: origin, development, and significance. Science 223: 22-27. Orth, R.J., Moore, K.A. (1984). Distribution and abundance of submerged aquatic vegetation in Chesapeake Bay: an historical perspective. Estuaries 7: 531-540. Reyes, E., Merino, M. (1991). Die1 dissolved oxygen dynamics and eutrophication in a.shallow, well-mixed tropical lagoon (Cancun, Mexico). Estuaries 14: 372-381. Rosenberg, R. (I 985). Eutrophication -the future marine coastal nuisance? Mar. Poll. Bull. 6: 227-231. Rosenberg, R. (1990). Negative oxygen trends in Swedish coastal bottom waters. Mar. Poll. Bull. 21: 335-339. Rossignol-Strick, M.A. (1985). A marine anoxic event on the Brittany Coast, July 1982. J. Coast. Res. 1: 11-20. Ryther, J.H., Dunstan, W.M. (1971). Nitrogen, phosphorus, and eutrophication in the coastal marine environment. Science 171: 375-380. Sheng, Y.P., Peene, S. (1992). Circulation and its effect on water quality. Sarasota Bay National Estuary Program "1992 Framework for Action". Shepard, S.A., McComb, A.J., Bulthuis, D.A., Neverauskas, V., Steffenson, D.A., West, R. (1989). Decline of Seagrasses. Pg. 346-393. In: A.W.D. Larkum, A.J. McComb, S.A. Shepard (Eds.). "Biology of Seagrasses: A Treatise on the Biology of Seagrass with Special Reference to the Australian Region. Elsevier, Amsterdam. Short, F.T. (1990). Light limitation on seagrass growth. Pp. 26-28. In: W.J. Kenworthy, D.E. Haunert (eds.). "The Light Requirements of Seagrasses: Results and Recommendations of a Workshop." South Florida Water Management District. Sogard, S.M., Powell, G.V.N., Holmquist, J.G. (1987). Epibenthic fish communities on Florida Bay banks: relations with physical parameters and seagrass cover. Mar. Ecol. Prog. Set. 40: 25-39. Stachowitsch, M. (1984). Mass mortality in the Gulf of Trieste: the course of community destruction. Mar. Ecol. P.S.Z.N.I. 5: 243-264. Stoner, A.W. (1983). Distribution of fishes in seagrass meadows: role of macrophyte biomass and species composition. Fisheries Bulletin U.S. 81: 837-846. Taylor, A.W. (1967). Phosphorus and water pollution. J. Soil and Water Conserv. 22: 228-231. Thayer, G.W., Bjorndal, K.A., Ogden, J.C., Williams, S.L., Zieman, J.C. (1984). Role of larger herbivores in seagrass

8/l/97 9:28:49 AM

### Technical Synthesis of Sarasota Bay Page 17 of 17

communities Estuaries 7: 351-376

Tomasko, D.A., Lapointe, B.E. (1991). Productivity and biomass of Thalassia testudinum as related to water-column nutrient availability and epiphyte levels: field observations and experimental studies. Mar. Ecol. Prog. Set. 75: 9-17. Turner, R.E., Allen, R.L. (1972). Bottom-water oxygen concentration in the Mississippi River Delta bight. Contrib Mar Sci. 25: 161-172.

U.S. Fish and Wildlife Service. (1979) Turbidity study of the Intracoastal Waterway, Hobe Sound, FL. Unpubl Manuscript. 29 pp + appendices. Vicente, V.P., Rivera, J.A. (1982). Depth limits of the seagrass Thalassia testudinum (Konig) in Jobos and Guayanilla Bays, Puerto Rico. Carib. J. Sci. 17: 73-79. Zieman, J.C. (1982). The ecology of seagrasses of South Florida a community profile. U.S. Fish and Wildlife Services, Office of Biological Services, Washington, DC. FWS/OBS-82/25. 158 pp.



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