Seagrass Ecology

1995 Abstracts

Florida Department of Environmental Protection's Fisheries Habitat Assessment Program (FHAP):An Assessment of Macrophyte Distribution and Abundance on a Florida Bay-Wide Scale

M. J.Durako, M.O. Hall, P.R. Carlson, Florida Department of Environmental Protection, Florida Marine Research Institute, 100 Eighth Ave. S.E., St. Petersburg, FL 33701.

Since 1988, research at the Florida Department of Environmental Protection's Florida Marine Research Institute (FMRI) has focused on ecosystem responses and possible causative factors related to the widespread decline and loss of seagrasses in Florida Bay. Early studies examined structural and dynamic changes in the seagrass community associated with seagrass die-off (Durako, 1995). Other studies have, 1) elucidated the roles of hypoxic stress and sulfide toxicity in die-off (Barber and Carlson, 1993; Carlson et al., 1994), 2) examined the physiological effects of infection by the marine slime mold Labyrinthula sp. on the dominant seagrass, Thalassia testudinum (Durako and Kuss, 1994), and 3) have compared changes in Thalassia short-shoot demographics related to die-off (Durako, 1994). In 1994, 33 winter and 108 summer stations, previously sampled in 1983/84 (Zieman et al., 1989), were resampled to compare quantitative changes that have occurred over the last decade in the distribution and abundance of the dominant macrophytes (seagrasses and macroalgae). Preliminary analyses of these data indicate that that the overall distribution patterns of the three dominant seagrasses have exhibited little change, but that abundance and biomass of the three dominant seagrasses has declined dramatically in the central and western regions of the Bay. The areas of greatest decline corresponded to those basins that have experienced the most severe die-off and areas subjected to chronic turbidity due to microalgal blooms and resuspended sediments. Demographic analyses of Thalassia testudinum short-shoots collected from several western basins over a period extending from 1989 to 1994 indicate that this species is in a continuing state of decline, but that the mechanism for the decline has changed. To expand the geographic scope and resolution of information on the distribution and abundance of the dominant macrophytes and the demographics of Thalassia in Florida Bay, FMRI initiated the Fisheries Habitat Assessment Program (FHAP) in 1995. In FHAP, 30-35 stations in each of ten basins will be sampled twice yearly using an EMAP-compatible hexagonal grid system. A combination of Braun-Blanquet frequency/abundance sampling and quantitative, core sampling will be conducted during the spring (low stress period); Braun-Blanquet sampling will also be conducted during the fall (high stress period) in order to examine intra- and inter-annual changes in macrophyte distribution and abundance. Ten short-shoots are collected at each station for determination of occurrence of potential microbial pathogens (especially Labyrinthula). Spatial analyses of cover/abundance data from 332 stations sampled in April of 1995 indicate that Thalassia abundances were lowest (<5-25% cover) along the northern boundary of Florida Bay and that they increased from the northeast to southwest. Halodule exceeded 5% cover only in basins in north central Florida Bay. Syringodium was present only in the southwestern Bay. Drift-red macroalgae and Batophora exhibited highest abundances along the northeastern Bay margin. With present funding, FHAP will continue at least through the summer of 1996.


Barber, T. R., Carlson, P. R. Jr. 1993. Effects of seagrass die-off on benthic fluxes and porewater concentrations of SCO2, SH2S, and CH4 in Florida Bay sediments. In: R. S. Oremland (ed.), Biogeochemistry of Global Change: Radiatively Active Trace Gases, Chapman and Hall, New York, pp. 530-550.

Carlson, P. R. Jr., Yarbro, L. A., Barber, T. R. 1994. Relationship of sediment sulfide to mortality of Thalassia testudinum in Florida Bay. Bull. Mar. Sci. 54(3):

Durako, M. J. 1994. Seagrass die-off in Florida Bay (USA): changes in shoot demography and populations dynamics. Mar. Ecol. Prog. Ser. 110:59-66.

Durako, M.J. 1995. Indicators of seagrass ecological condition: An assessment based on spatial and temporal changes associated with the mass mortality of the tropical seagrass Thalassia testudinum. Pp. 261-266 In: K.R. Dyer and C. F. D'Elia (eds.) Changes in fluxes in estuaries: implications for science to management. Olsen and Olsen, Fredensborg, Denmark.

Durako, M. J. and K. M. Kuss. 1994. Effects of Labyrinthula infection on the photosynthetic capacity of Thalassia testudinum. Bull. Mar. Sci. 54(3):727-732.

Zieman, J. C., Fourqurean, J. W., Iverson, R. L. 1989. Distribution, abundance and productivity of seagrasses and macroalgae in Florida Bay. Bull. Mar. Sci. 44(1): 292-311.

Long-Term Seagrass Monitoring Stations on Cross Bank: The Effects of Long-Term Manipulation of Nutrient Supply on Competition Between the Seagrasses Thalassia Testudinum and Halodule Wrightii in Florida Bay

James W. Fourqurean, Southeast Environmental Research Program and Department of Biological Sciences, Florida International University; George V.N. Powell, RARE, Inc.;W. Judson Kenworthy, Beaufort Laboratory, NMFS; Joseph C. Zieman, University of Virginia.

As part of an experiment investigating the long-term response of Florida Bay seagrass beds to increased nutrient availability, we have been monitoring species composition and abundance of 5 seagrass beds on Cross Bank in Florida Bay. Long term (11y) continuous fertilization (via application of bird feces) of established seagrass beds in Florida Bay caused a change in the dominant seagrass species. Prior to fertilization, the seagrass beds were a Thalassia testudinum monoculture; after 11 y of fertilization the seagrass Halodule wrightii made up 97% of the aboveground biomass. Fertilization had a positive effect on the standing crop of T. testudinum for the first two years of the experiment. The initial response of T. testudinum to increased nutrient supply was an increase in the leaf biomass per short shoot. Increased leafiness is a well-known plant response to shading, and there is some evidence that T. testudinum may respond to decreased light availability by increasing shoot size. In our experiments, however, T. testudinum shoot size decreased after 1984 , as light availability continued to decrease concomitantly with increases in H. wrightii biomass. This suggests that the initial increase in T. testudinum shoot size was a response to increased nutrient availability, not decreased light availability.

The transition from T. testudinum-dominated to H. wrightii -dominated was dependent on the timing of colonization of the sites by H. wrightii; the decrease in T. testudinum standing crop and density at the fertilized sites occurred only after the colonization of the sites by H. wrightii. There were no trends in the standing crop or density of T. testudinum at control sites, and none of the control sites were colonized by H. wrightii.

Nutrient availability has been correlated with epiphyte loads on seagrass leaves, and shading of seagrasses by epiphytes has been implicated as one of the most deleterious effects of eutrophication of seagrass habitats. Since leaf turn-over is faster for H. wrightii than T. testudinum, it is conceivable that fouling of the longer-lived T. testudinum leaves could cause the loss of T. testudinum from areas of nutrient enrichment, but this mechanism was probably not operative in these experiments. While the epiphyte loads of the seagrasses at fertilized and control sites were not quantified, there were no visual differences in macrophytic or microscopic epiphyte loads at control or fertilzed sites.

The effects of fertilization on these seagrass beds persisted at least 11 y after the cessation of nutrient addition. In 1994, the species composition of seagrass beds that had fertilization discontinued in 1983 were still markedly different than control beds. Halodule wrightii was common at these sites where nutrient addition was stopped. These results suggest that seagrass beds in Florida Bay efficiently retain and recycle acquired nutrients.

Results of these experiments suggest that Halodule wrightii, the normal early-succesional seagrass during secondary succession in Caribbean seagrass communities, has a higher nutrient demand than Thalassia testudinum, the normal late successional species, and that the replacement of H. wrightii by T. testudinum during secondary successsion is due to the ability of T. testudinum to draw nutrient availability below the requirements of H. wrightii.

In the fertilization experiments presented here, Halodule wrightii was clearly favored by fertilization. Fertilized sites eventually converged on similar, H. wrightii-dominated seagrass beds, but the trajectories of the individual sites was dependent on the colonization of the sites by H. wrightii. In the absence of H. wrightii, Thalassia testudinum biomass stayed elevated over control areas, but following the eventual colonization of the sites by H. wrightii, T. testudinum declined. The stochastic event of H. wrightii colonization therefore controlled the response of Florida Bay seagrass beds to manipulations in resource supply rates.

Interpretation of the results of this experiment was dependent on the duration of the fertilization of the seagrass beds. Increased nutrient availability caused a doubling of the Thalassia testudinum leaf biomass over controls for the first two years of this experiment; and were it to have ended at that time we would have concluded that increased nutrient supply to Florida Bay seagrasses would cause an increase in the biomass of the late successional seagrass T.testudinum. The true outcome of such a change in nutrient supply rates was dependent on the colonization of these fertilized, and therefore newly-suitable, areas by the early successional seagrass Halodule wrightii. This time-dependent result underscores the importance of designing field experiments of the proper duration to capture the dynamics of the system being studied.

Seagrass Cover-Abundance and Distribution in Northeast Florida Bay Downstream From the C-111 Canal and Taylor Slough

Lee Hefty, Metropolitan Dade County Department of Environmental Resources Management.

In October 1993, six monitoring stations were established in northeast Florida Bay to document water quality and biological characteristics (seagrass) in the near shore habitats downstream from the C-111\Taylor Slough watershed. A series of water quality parameters and seagrass shoot and blade density data were collected monthly at each station. A cursory review of the data revealed seagrass distribution and species composition appear to be related to overall mean annual salinity. Thalassia testudinum was the dominant seagrass at four out of six stations. T. testudinum was found at four stations which exhibited highest annual mean salinity and narrowest salinity range. These stations were located in basins which were less geographically isolated and more likely to experience water exchange with neighboring basins (i.e. Long Sound, Trout Cove, and Little Madeira Bay). Halodule beaudettei (formerly H. wrightii) and Ruppia maritima were found together as dominant components of the benthic community at two stations located in Highway Creek and Joe Bay . These basins are somewhat geographically isolated and are therefore more likely to be influenced by upland runoff than by direct exchange with neighboring basins. These stations exhibited a wider annual salinity range and overall lower annual mean salinity. T. testudinum mean shoot density ranged from 205 to 376 shoots/m2. H. beaudettei mean shoot density ranged from 0 to140 shoots /m2 when growing heterogeneously with T. testudinum, and from 80 to 860 shoots/m2 when found growing heterogeneously with R. maritima. R. maritima was consistently found with H. beaudettei and exhibited mean shoot densities of 170 -1200 shoots /m2.


In an effort to address concerns regarding the flow of freshwater to the east Everglades and Florida Bay, regional water managers began to increase water delivery to Taylor Slough in June 1993. As a requirement of the Monitoring and Operating Plan for the C-111 Interim Construction Project, and as recommended by the Taylor Slough Demonstration Project, a water quality and biological monitoring project was undertaken to monitor the downstream effects of this change in water delivery. The South Florida Water Management District (SFWMD) contracted with the Metropolitan Dade County Department of Environmental Resources Management (DERM) to perform water quality and biological monitoring in northeast Florida Bay. In October 1993, DERM established six monitoring stations in northeast Florida Bay. Site locations were determined by SFWMD staff members and were based on proximity to existing water quality stations in basins believed to be influenced by the changes in water management practices. The six stations were oriented to form three north-south transects in the area from Little Madeira Bay eastward to US Highway 1. Each station is sampled monthly for a series of physical water quality parameters and biological characteristics.

The objectives of the study are; 1) To provide baseline data and document changes in the benthic communities of northeast Florida Bay downstream from the C-111\Taylor Slough watershed; 2) To provide baseline data on existing water quality conditions, and document changes in water quality in the surface waters associated with these benthic communities.

Project Methodology

Station Locations

Station Lat\Long Station Lat\Long

Highway Creek 25.2549 \ 80.4451 Long Sound 25.2349 \ 80.4586

Joe Bay 25.2296 \ 80.5263 Trout Cove 25.2169 \ 80.5187

Taylor River 25.1907 \ 80.6355 Little Madeira Bay 25.1741 \ 80.6328

Surface Water Quality Monitoring

In situ physical water quality measurements are collected monthly at each station. A calibrated Hydrolab Surveyor II multi-parameter analyzer is used to collect temperature, pH, dissolved oxygen, conductivity, oxidation/reduction potential, salinity, and depth at each site. A Licor LI 1000 integrating photometer with two 4 pi sensors are used to measure photosynthetically active radiation (PAR). PAR data is used to derive the extinction coefficient KdPAR for the water column at each site. All parameters (except PAR) are collected at the surface, at one meter (where depths allow) and the bottom.

Biological Monitoring (Seagrass)

Each station consists of a 50 meter transect with three randomly located fixed one meter square sampling areas. Transect locations are marked with submerged buoys, and sampling grid locations are marked with cut rebar. A 1m x 1m portable grid is placed in each sampling area and shoots and blades are counted for each species of seagrass present within five randomly chosen 20 cm x 20 cm subunits (Only shoots are counted for Halodule beaudettei and Ruppia maritima). A modified line-intercept method is used to assess seagrass cover and the presence of other macrophytes along the transect. Standing crop biomass is collected quarterly from three 20 cm x 20 cm plots adjacent to the transect at each station. A representative aliquot of ten blades is selected for determining epiphyte loading. Epiphytes are removed by scraping and each fraction is dried in an oven at 60 degrees C and then weighed.


Review of the data and sampling methodology revealed limitations in the statistical integrity of data interpretation. This fact coupled with the efforts of the Interagency Work Group on Florida Bay to standardize sampling methodology have lead to modification of the sampling methods previously used for this project. Modified sampling methods have been derived using guidelines from other studies currently being conducted in Florida Bay and in the Florida Keys National Marine Sanctuary. The modified methods will be implemented in November 1995. The design is comprised of two main elements. The first is a high frequency scattered random sampling that provides status and spatial data on water quality and benthic communities on a basin-wide scale. The second is a lower frequency, repeated sampling of fixed locations in several basins.

Scattered Random Sampling

A study region will be identified within each basin. Each study region will follow basin contours excluding edge effects created by shorelines and islands. Each large study region will be divided into 12 approximately equal subregions (i.e., Long Sound, Little Blackwater Sound, Joe Bay, and Little Madeira Bay), and each small study region (i.e., Highway Creek, Blackwater Sound, Alligator Bay, Devils Cove, Trout Cove, and south of Little Madeira Bay) will be divided into four equal subregions. Each subregion will be further divided into nine sections. A section from each subregion will be randomly selected on a monthly basis and sampled. Sample locations are defined as the approximate center of each section. The sample site location [latitude and longitude] will be derived using geographic information systems (GIS) based software. Navigation to each site will be accomplished using a global positioning system (GPS).

At each sample site, four 0.25m2 quadrats will be randomly placed off the boat. Each quadrat will then be assessed using the Braun-Blanquet cover-abundance scale (BBCA). A BBCA rating will be recorded for each species of seagrass and major macroalgal groups present within the quadrat. The BBCA scale will be defined as follows ( 5 = >75%; 4 = <75,>50%; 3 = <50,>25%; 2 = <25,>5%; 1 = <5% numerous; 0.5 = <5% sparse; 0.1 = <5% solitary).When possible, seagrass shoot and blade densities will be recorded in a 0.0625m2 subsection of the quadrat.

Fixed Repeated Sampling

Sample sites will be the existing six stations established in October 1993 with one additional station in Blackwater Sound.

Sampling techniques will consist of a modified version of the techniques used at these stations over the last two years. Each station will consist of a 50 meter transect with three randomly located fixed one meter square sampling areas. A 1m x 1m portable grid will be placed in each sampling area and shoots and blades counted for each species of seagrass present within five randomly chosen 20 cm x 20 cm subunits. Each quadrat will then be assessed using the Braun-Blanquet cover-abundance scale (BBCA). A BBCA rating will be recorded for each species of seagrass and major macroalgal groups present within the quadrat.

Biomass samples will be collected semiannually in the early spring and late fall. Five 8" diameter core samples will be collected adjacent to each station. The sample will be rinsed in the field to remove sediment and kept frozen in freezer bags until processed in the laboratory. In the laboratory the sample will be thawed then rinsed to remove remaining sediment and sorted into groups of seagrass by species, and macroalgae. The number of short shoots, leaf number, leaf length and width measurements will be made on intact Thalassia testudinum shoots. Each seagrass group will then be divided into fractions representing live rhizomes and roots, dead rhizomes and roots, dead shoots, live shoot stems, leaf sheaths, green blades, and brown blades. Epiphytes will be removed by scraping. All fractions will be rinsed in 10% HCl then dried in an oven at 60 degrees C and weighed. Macroalgae will be rinsed then sorted into major groups and dried in an oven at 60 degrees C and then weighed.

Surface Water Quality Monitoring

In situ physical water quality measurements will be collected monthly at each selected scattered random site, and semiannually at each fixed repeated site.

Resource Health Issues in Florida Bay: Linking Disease and Mortalities

Jan H. Landsberg, Barbara A. Blakesley, Florida Department of Environmental Protection, Florida Marine Research Institute, 100 Eighth Ave S.E., St. Petersburg, FL. 33701.

Since 1987, studies in Florida Bay have documented sea grass die offs, mangrove and sponge mortalities, fish kills, and tumors in turtles. Overall evaluation of these disease and mortality events indicates that they are signals of an ecosystem in distress. In addition to impacting the macro-biota, changes in environmental factors such as wide fluctuations in salinity, temperature, light, turbidity, sediment suspension, and nutrient distribution have contributed to increases in phytoplankton blooms, in particular those of the cyanophyte (Synechococcus elongatus). In such a highly dynamic ecosystem, the partitioning of the effects of each of the various stressors is often not possible because of an increased susceptibility of organisms to disease and mortality. The underlying key to understanding health issues in Florida Bay is the systematic evaluation of the basic role and subsequent interactions of potential stressors. A holistic, epizootiological approach is being developed that incorporates the impacts of "a dysfunctional system" on specific aquatic organisms and attempts to determine the interactions between natural and anthropogenic stress, biotoxins, contaminants, and disease.

The role of the slimemold Labyrinthula sp. in the seagrass die-off beginning in 1987 was considered to be that of a secondary pathogen that infected stressed, weakened Thalassia (Robblee al., 1991). In April 1995, we investigated the distribution of Labyrinthula sp. in Thalassia testudinum and began a study to evaluate its role in disease and associated mortality in this seagrass. Labyrinthula sp. was found in lesions that were characterized by thin, brown, longitudinal streaks along the leaf blade. In fresh squash leaf preparations Labyrinthula sp. was typically present at the leading edge of the lesion. We investigated prevalence levels of Labyrinthula sp., adapted some field techniques to rapidly screen for Labyrinthula sp., and evaluated the presence and distribution of leaf lesions. We are also refining histological techniques and staining methodologies to study the pathology of Labyrinthula sp. in Thalassia leaves and scanning electron microscopy techniques to examine the morphology and the surface leaf distribution of Labyrinthula sp. on leaf blades. Baseline microbiology screens are being performed on Thalassia and techniques for axenic culture of Labyrinthula sp. are being developed. In addition, a full health profile of Thalassia will be developed through investigation of other potential pathogens, such as viruses, bacteria, and fungi (Florida Bay Science Plan [1994], Question 1 in "Seagrass, Mangrove and Hardbottom Habitats", Task vi).

Seagrass samples were obtained from field surveys being conducted by Durako et al. (this meeting), and shipped daily to FMRI in St. Petersburg. Leaf blades were examined for % lesion cover and presence or absence of Labyrinthula sp. A total of 10,516 Thalassia leaves were examined from 306 sites in 10 Florida Bay basins. A range of 27 to 35 sites were examined from each basin. Whenever possible, at least 10 individual shoots were examined from each site. Prevalence of infected seagrass (n) ranged from 0.0% at Eagle Key (n = 33), 2.9% at Crane Key (n = 35), 3.45% at Madeira Bay (n = 29), 3.7% at Whipray (n = 27), 6.7% at Calusa Key (n = 30), 7.1% at Blackwater Sound (n = 28), 10.3% at Rankin Lake (n = 29), 23.53% at Rabbit Key (n = 34), 25.81% at Twin Keys (n = 31) and 33.3% at Johnson Key (n = 30). A significant difference (t-test, n = 304, P < 0.0001) was noted between the mean % lesion cover of infected (2.35%) and uninfected (0.245%) shoots at all sites. The number of lesioned leaves per shoot varied by site. Typically, older shoots with a higher leaf number had more lesions, and outer leaf blades were more heavily infected than new leaves. The mean total % of leaves (n) with lesions varied by site from 4.2% at Eagle Key, 3.53% at Crane Key, 6.23% at Madeira Bay, 11.2% at Whipray, 9.22% at Calusa Key, 12.9% at Blackwater Sound, 12.6% at Rankin Lake, 30.4% at Rabbit Key, 9.0% at Twin Keys and 36.3% at Johnson Key. Evaluations for Labyrinthula sp. in fresh squash preparations of lesioned leaves were conservative in that not every lesioned plant was found to be infected. Heaviest infections by Labyrinthula sp. were noted in the central portion of Florida Bay at Twin Keys, Rabbit Key, and Johnson Key. The question remains as to whether heavily infected seagrass beds are in areas that were not decimated by the earlier die off such as was described in Rankin Lake (Robblee et al. 1991) and therefore are still susceptible to disease. Initial indications suggest that Labyrinthula sp. may be more significant in seagrass die off than is currently recognized. Spatial and temporal trends in the distribution of Labyrinthula sp., % leaf lesion cover, and overall seagrass health will be determined twice yearly for 3 years (in conjunction with the study of Durako et al. this meeting). Studies on the life history and transmission of Labyrinthula sp. are in progress. Additional lesioned Thalassia was obtained from areas near the Florida Keys island chain (N. Diersing, FMRI, pers.comm.), examined, and Labyrinthula sp. was identified. Labyrinthula sp. has also been found in Halodule wrightii leaves exhibiting characteristic lesions. This Labyrinthula sp. will be identified and compared to the Labyrinthula sp. from Thalassia.

The presence of persistent blooms of the cyanophyte Synechococcus elongatus has been associated with sponge mortalities in Florida Bay. Other negative impacts of this cyanophyte upon aquatic organisms have not been well documented. We have recently obtained mussels Brachidontes exustus from heavily populated areas in Florida Bay (W. Lyons, this meeting), acclimated them to laboratory conditions at 30 ppt, and have maintained them on a subsistence diet of Cyclotella sp. and Isochrysis sp. (K. Steidinger & W. Richardson, FMRI, unpublished). Cultures of Synechococcus elongatus have been maintained in the microalgal culture collection at FMRI. We will use feeding studies to investigate the effects of different densities of Synechococcus on these mollusks. Health evaluations will determine potential effects on growth, feeding, and susceptibility to disease (Florida Bay Science Plan [1994], Question 1 in "Living Resources", Task i - health and condition of organisms). Health evaluations of B. exustus obtained from the molluscan mapping study will also be carried out.

In addition, we plan to experimentally examine the potential effects of Synechococcus on the health of resident fish species such as the rainwater killifish (Lucania parva) or the goldspotted killifish (Floridichthys carpio). Fish will be exposed to different densities of Synechococcus in the laboratory and studied for behavioral changes, susceptibility to disease, and presence of histopathology. Health evaluations will determine changes in parasite densities, and determine pathology in target organs such as gills, spleen, liver, kidney, and intestine. This study will be part of an overall field health assessment of fish, decapod, and seagrass samples that will be obtained from the faunal community study of seagrass beds at the eight different locations in the Bay described by Matheson et al. (this meeting). Seagrass samples will be studied using the same techniques as described above. The rationale will be to determine if areas with unhealthy, lesioned seagrass are a signal of a generally unhealthy habitat and whether the health of fish and decapod residents becomes similarly compromised. Our health assessment is designed to measure sensitive changes in fish and decapod health and comprises a combination of disease, parasite, and pathology studies. By studying the parasite assemblages of target organisms together with changes in fish or decapod morphometrics, organosomatic indices, and pathology of selected tissues, an overall comparative health index will be developed. Common parasite species that may be good indicators of changing environmental conditions may also be selected for study. For example, the dinoflagellate Crepidoodinium cyprinodontum is a unique photosynthetic parasite that lives on the gills of some killifish. This parasite is likely to be influenced by ambient light levels and its presence may signal optimal light regimes, or conversely its absence may signal turbid conditions (Florida Bay Science Plan [1994], Question 1 in "Living Resources", Task i - health and condition of organisms).

Fish kills have been frequently reported in Florida Bay. There is a pressing urgency to establish protocols to determine the nature of these fish kills and obtain samples rapidly for diagnosis. We need to develop methods for recovery and shipment of organisms for timely examination. We wish to examine water samples for natural algal blooms that could be toxic to fish, for physico-chemical factors such as low dissolved oxygen, or for pesticides introduced into the Florida Bay ecosystem. Sediment, water, and biotic samples should also be examined to obtain baseline contaminant information. Plans are being developed in conjunction with the FDEP chemistry laboratory in Tallahassee (B. Coppenger & T. Fitzpatrick), and FDEP, FMRI laboratory in Marathon (J. Hunt) to complement existing contaminant studies (Scott et. al.; Summers et al.; this meeting) in Florida Bay. Muscle, gonad, and liver samples from selected fish species will be examined for contaminants in parallel with a fish health evaluation similar to that described above (Florida Bay Science Plan [1994], Question 1 in "Living Resources", Task i - health and condition of organisms, and Question 4 in "Water quality and nutrient cycling", task vii).

Fish kill events should be interpreted with caution and we need to ensure that a full analysis of all possible samples is completed. This is a critical process to ensure that kills are not immediately "blamed" on anthropogenic inputs or the current "dysfunctionality" of Florida Bay. These fish kills need to be evaluated in the full context of natural and anthropogenic phenomena. Contaminants can and should be examined but only together with a full suite of other diagnostic procedures. It is hoped that efforts for coordination will be discussed by the National Park Service, the Department of Environmental Protection, and other cooperating agencies to maximize data collection efforts and facilitate coordination in the interpretation of results. The occurrence of fish kills should be entered into a Florida Bay database that also includes other mortality and disease events. A holistic approach to such events will aid in the identification of "hot spots" and temporal and spatial trends that may not otherwise be apparent.

The Influence of Salinity Fluctuation on Submersed Vegetation at the Land Margin of Northern Florida Bay

Clay L. Montague , Associate Professor, Department of Environmental Engineering Sciences, University of Florida.

Field monitoring of biota and water quality at 12 stations in northeastern Florida Bay south of C-111 canal 11 times during 1986 and 1987 revealed very low densities of submersed vegetation and associated fauna. The best correlate with total station biomass was the standard deviation of the 11 salinity spot checks made at each station. This led to the hypothesis that salinity fluctuation -- possibly assisted by high temperatures and low nutrients -- prevented the sustained development of healthy communities of submersed vegetation at the land margin of northern Florida Bay (see Montague and Ley 1993, Estuaries 16(4): 703-717). If this hypothesis is true, then gaining control over salinity fluctuation in northern Florida Bay means gaining control over the biomass of submersed vegetation. Control may be within the power of society if management decisions for the C-111 canal influence salinity fluctuations in northern Florida Bay. Hence, it is important to test the salinity fluctuation hypothesis.

Six testable predictions can be made based on this hypothesis: 1) experimental exposure of submersed vegetation to salinity fluctuation should elicit a negative physiological response in the plants; 2) shifts in submersed plant biomass and community composition should follow changes in salinity; 3) submersed plant biomass should be higher both upstream and downstream of the zone of maximum salinity fluctuation; 4) plants transplanted out of areas of high salinity fluctuation should flourish, while reciprocally transplanted plants should grow poorly; 5) total plant biomass should negatively correlate to the degree of salinity fluctuation among areas of similar mean salinity; and 6) a computer simulation model of the plant response to salinity fluctuation should predict the distribution of submersed vegetation near the land margin of northern Florida Bay. Funding has just been made available to the University of Florida by the South Florida Water Management District to test these predictions, no data are yet available.

Benthic Macrophyte and Invertebrate Distribution and Seasonality in the Florida Bay - Everglades Ecotone: Influence of Salinity Variation

Douglas Morrison, Everglades System Restoration Office, National Audubon Society, Miami.

This project will investigate the influence of salinity fluctuation on the seasonal abundance and distribution of benthic macrophytes and invertebrates in the Everglades - Florida Bay ecotone. This study will provide baseline data to assess the ecological effectiveness of management actions to restore more natural freshwater inflow patterns. The study will also provide information to identify and evaluate potential biological indicators of freshwater inflow patterns. This project is designed to complement and integrate with other ongoing and proposed macrophyte studies in the ecotone and Florida Bay. Field sampling will begin in October 1995 and continue for one year.

The geographic focus of the study is the lakes and embayments along the mainland shore of north Florida Bay from Seven Palms Lake west to Lake Ingraham. Specific study sites will include Seven Palms Lake, Monroe Lake, Terrapin Bay, West Lake, Long Lake, The Lungs, Garfield Bight, Cuthbert Lake, Coot Bay, Bear Lake, and the unnamed water body between West Lake and Lake Ingraham. Two sets of study sites will be oriented along the salinity gradient from inland to the Bay. These are: Seven Palms Lake to Terrapin Bay and West Lake to Garfield Bight. These will complement existing FDEP seagrass monitoring sites seaward in Florida Bay.

Two sampling regimes will be used for submerged macrophytes. All study waterbodies will be surveyed twice-yearly, in October (end of wet season) and April-May (end of dry season) to assess species distribution and abundances on a waterbody-wide scale. Ten randomly located 50m transects will be surveyed for macrophyte percent cover in each study waterbody. These transects will be marked so that the same transect can be sampled in both periods. GPS coordinates will be recorded for all study sites and transects. Five to ten 0.25m2 quadrats at random locations off each transect will be sampled for macrophyte percent cover using a modified Braun-Blanquet cover-abundance scale (same as FDEP). This sampling regime will provide information on macrophyte composition, distribution, and abundance in wet and dry seasons on a relatively large spatial scale.

More detailed and frequent sampling to evaluate macrophyte seasonality and the influence of salinity fluctuation will be conducted in a subset of study waterbodies. At this time, these waterbodies include Seven Palms Lake, Terrapin Bay, West Lake, and Garfield Bight. One or two additional waterbodies will likely be added after further exploratory surveys. Macrophyte species composition and abundance will be surveyed every two months at one site in each of the selected waterbodies. Macrophyte biomass will be harvested from 10 randomly located 0.25m2 quadrats at each site during each sampling period.

All study waterbodies will be surveyed twice-yearly, in October (end of wet season) and April-May (end of dry season), for benthic infauna. At least 10 randomly located 15 cm diameter sediment cores will be collected in each study waterbody for each sampling event. Infauna will be separated from sediment using a 0.5mm sieve. Invertebrate species and number of individuals will be recorded.

The following physicochemical parameters will be sampled at least once each month in each study waterbody: salinity/conductivity, temperature, irradiance and extinction coefficient, dissolved oxygen, pH, and turbidity. Nutrients (total phosphorus, ammonium, nitrate/nitrite) will be sampled every month at sites with detailed (every two months) macrophyte monitoring.

Benthic Macrophyte Seasonal and Longer-Term Patterns in Florida Bay Along the Key Largo Shoreline

Douglas Morrison , Everglades System Restoration Office, National Audubon Society, Miami, FL.

In 1979 and 1980, I investigated seasonality in macrophyte communities dominated by Batophora oerstedi in Florida Bay along the upper Keys shoreline. This study assessed seasonal patterns in macrophyte assemblages and Batophora seasonality in photosynthesis, respiration, abundance, and reproduction. Seasonal differences were observed in species richness, species diversity, total vegetational abundance, and the abundances of individual species. Ten species varied seasonally in abundance, including the dominants: Batophora, Laurencia spp., and Acetabularia crenulata. Some species (e.g., Batophora) were more abundant in summer; other species (Laurencia, Acetabularia) were more abundant in winter. Macrophyte associations can be subdivided into summer and winter dominated communities. Batophora photosynthesis, respiration, and reproduction also varied seasonally. Temperature is the major abiotic causal factor of macrophyte seasonality here.

In 1994 and 1995, I resurveyed two of these sites to evaluate any long-term (14 years) changes in these macrophyte communities. These sites are a natural bay flat and a finger canal near Hammer Point on Key Largo. Macrophyte species composition and abundance (percent cover) were surveyed in March 1994 (winter), September 1994 (summer), and March 1995 using a point intercept method in randomly located 0.25m2 quadrats (25 points per quadrat). At least 20 quadrats were sampled at each site during each sampling event.

I also collected biomass samples for Batophora, Laurencia spp., and Acetabularia in March, June, September, and December 1994 (10 0.2m2 quadrats each site, each period).

Macrophyte community composition and seasonal patterns in 1994 at these sites were similar to those observed in 1979-80. Batophora abundance was greatest in summer; it was the dominant species in summer on the bay flat and canal wall. Laurencia abundance peaked in winter; it was the dominant species in winter on the canal wall. Acetabularia abundance was greatest in winter.

Rainfall in the 1994 wet season was well above average resulting in considerable freshwater flow into Florida Bay. This inflow lowered salinity substantially in much of Florida Bay for several months. At my sites salinity was 22-24 ppt from mid-October 1994 to mid-March 1995. Previously (1979-80, 1994 through August), I had never recorded salinity below 32 ppt. However, this extended period of lower salinity had little or no effect on these macrophyte assemblages. The macrophyte community in March 1995 was similar to that in March 1994 and March 1980.

Habitat Inventory and Change in Seagrass and Other Aquatic Beds in Florida Bay

Frank J. Sargent, Florida Department of Environmental Protection, Division of Marine Resources, Florida Marine Research Institute, 100 Eighth Avenue S.E., St. Petersburg, Florida 33701; Randolph L. Ferguson , Ford A Cross, NOAA/NMFS, Southeast Fisheries Science Center, Beaufort Laboratory, 101 Pivers Island Road, Beaufort, North Carolina 28516.

This research, cooperatively funded by NOAA's Coastal Change Analysis Program (C-CAP) and Florida Department of Environmental Protection (DEP), is generating geospatial data of benthic habitats in central and eastern Florida Bay from NOAA NOS tide coordinated metric quality aerial photographs. Source photographs are both contemporary (1991-1995) and historical (1950-1990). Analysis includes comprehensive contemporary habitat inventory and spatially limited recent and historical change detection. The work is being conducted in cooperation with NOAA, National Ocean Service (NOS) and the National Park Service, Everglades National Park. The work is a companion effort to the Florida Keys National Marine Sanctuary (FKNMS) Benthic Habitat Mapping Program. The Florida Bay research will provide information essential to assess recent and historical change and to guide efforts to manage and restore shallow water benthic habitats in Florida Bay. The project is scheduled for completion in FY97.

Inventory and change detection of seagrasses and other benthic habitats is combining the photogrammetric and benthic habitat expertise in NOAA and Florida. NOAA staff and cooperators include Greg Fromm, Coast and Geodetic Survey, Photogrammetry Branch, and Peter L. Grose, Chief, Data Management and Geographic Information Systems, Strategic Environmental Assessments Division, Office of Ocean Resources Conservation and Assessment. The goal of this research includes addition of the data to the C-CAP national resource spatial data base and the transfer of data conversion and thematic data processing technology to the State of Florida.

An aerial photographic mission for benthic habitats and shoreline delineation was conducted in the winter of 1991/92. The mission was limited by recurrent turbidity. To complete coverage of the study area and to allow for analysis of recent change for part of the study area, additional photography was acquired in April, 1995. The 1992 and 1995 photography plus historical photography from NOS complete the source data.

C-CAP funded James Fourqurean, Florida International University (FIU), to interpret benthic habitats consistent with the classification schemes developed for the (FKNMS) Benthic Habitat Mapping Program and for C-CAP. The FIU effort to interpret the 1991/92 photographs received logistical support from the Everglades National Park. That interpretation has been completed and is being quality assured by the Florida DEP, Florida Marine Research Institute (FMRI) for cartographic consistency prior to submission to NOS for georegistration and digitization at the end of this calendar year.

The protocol for interpretation, surface level signature verification and the classification system to be followed in the study were developed by C-CAP and FKNMS and have been integrated by FMRI to accomodate regional conditions and to meet both regional and national information needs. Metric quality photography (natural color, 1:48,000) was acquired with standard operating procedures for NOS photographic missions and C-CAP (Coastal Change Analysis Program (C-CAP): Guidance for Regional Implementation, NOAA Technical Report NMFS 123, April, 1995). Digital shoreline data critical to the proposed study are being generated by NOS.

The retrospective change analysis will be based on selected metric quality historical photography from 1950 through 1990. All interpretations of the historical photography are supported by contemporary aerial photographs and extensive surface level verification of contemporary aquatic bed signatures as described in the C-CAP guidance document. Interpretations of habitat polygons will be geopositioned by NOS in an analytical plotter, converted to ARC/INFO files using Standard Digital Data Exchange Format, and processed to a thematic inventory and change database. The horizontal accuracy for geopositioning (excludes habitat polygon interpretation error) is 3 meters.

Products will include photographs of central and eastern Florida Bay (1992 and 1995), digital geospatial data and hard copy maps of aquatic bed occurrence and change. The metric quality aerial photographs will be deposited in the NOAA photographic archive.

Spatial data files will be available through the NOAA National Oceanographic Data Center and FMRI.

Spatial and Temporal Variations in Seagrass Biomass and Productivity Across Florida Bay

J.C. Zieman , Department of Environmental Sciences, University of Virginia, Clark Hall, Charlottesville VA 22903; James Fourqurean , Thomas Frankovich , SERP, Florida International University, Miami FL 33199.

The bay bottoms and banks of Florida Bay constitute one of the largest seagrass resources in north America. As such it has served as a major nursery and feeding ground for numerous organisms that are important commercially or are in the trophic web of important sportfish. The system has historically been dominated by turtle grass, Thalassia testudinum, which has high habitat values. Among the most important of these are its high productivity in areas with sufficient light, and the strong sediment stabilization offered by its dense rhizome and root mat, and by its dense canopy of leaves. Syringodium filiforme, Halodule wrightii, and Ruppia maritima also occur, but in less abundance than Thalassia, and moreconfined areas throughout the bay.

Since the fall of 1987, Florida Bay has experienced a major dieoff of Thalassia over large portions of Florida Bay. Initially the effects were confined to the immediate basins containing the originial dieoff patches, but by 1992 these effects had spread to hundreds of square miles outside of the ENP boundary. The primary downstream effects of the dieoff are large plumes of turbid and pigmented water, varying in density, size, and duration.

The recent distribution and abundance of seagrass in Florida Bay was mapped in the early 1980's (Zieman et al, 1989). The dominant pattern one of sparse seagrass in the northeastern bay increasing in density to the south and west. The highest densities and productivities were in the basins and on the banks of the western bay, roughly from Rabbit Key Basin westward.

Following the initial episodes of dieoff studies of plant and nutrient dynamics were done in the summer and fall of 1988. In 1989 a number of stations were established to determine the current and future state of Thalassia. Among the parameters measured are standing crop, biomass, areal productivity, turnover rate, shoot density and growth rate, leaf growth rate, and LAI. Initially stations were established in Rankin Lake, Rabbit Key Basin, Johnson Key Basin, Sunset Cove, and at Duck Key. Later stations were added at Sprigger Bank, Whipray Basin, and on the seaside off Tavernier Key. Monitoring rates have been from five to two times per year, depending on funding.

Analyses in progress relate the plant parameters described above to temperature, salinity, and seasonal factors. The pattern and response of Thalassia turnover rate (or specific productivity) is of primary importance, as it is normalized for plant biomass. This allows more direct comparison of the plant responses across the nearly 50 km gradient across Florida Bay. Standing crop routinely is 8-10 times greater at Spigger Bank and Rabbit Key Basin in the west than at Duck Key in the northeast, and can reach a 20x difference.

Primary Productivity and Standing Stock Estimates of Benthic, Epiphytic, Plankton, and Seagrass Communities of Florida Bay

Paul V. Zimba, Department of Fisheries and Aquatic Sciences, University of Florida .

As part of FMRI sponsored research on discoloration events in Florida Bay, field assessment of seagrass and microalgal standing stock has occurred on a bimonthly basis for over 15 months. This work is nearing completion, with interim reports due in November 1995, and a project summary report due in June 1996. Sites studied in this work include Rankin Bight (dominated by Thalassia testudinum and Halodule wrightii), Captain Key (monotypic Thalassia), and Sprigger Bank (dominant seagrass Syringodium, with Thalassia). Each site was analyzed for water column nutrient content (alkalinity, N, P, and Si), chlorophyll a, and physico-chemical conditions (salinity, temperature, pH, dissolved oxygen, and light penetrance). Standing stock was estimated using fixed point-transect methodology to collect seagrass biomass, partition epiphytes (as dry weight and chlorophyll a), and estimate benthic chlorophyll levels. For reference water column planktonic chlorophyll samples were also collected. Primary productivity was determined in situ using plexiglass chambers and a two hour incubation period (14C methodology). All productivity components were measured in the chambers simultaneously. Supporting data includes PAR measures made at least once during each incubation, HYDROLAB data (salinity, temperature, pH, and dissolved oxygen), as well as water column nutrient data (N,P, and Si) including alkalinity. Microalgal samples have been collected for cell identifications and enumerations, this data will not be presented comprehensively herein.

Primary productivity results for two representative sites ("pristine" - Captain Key and "impacted" - Rankin Bight) are presented in Figure 1. Significant correlations were observed between bottom irradiance (4 p spherical sensor) and rates of carbon uptake. Wind speeds greater than ca. 15 mph at Rankin Bight resuspend sediments and benthic microalgae (primarily pennate diatoms), causing a shift in bottom light to orange-yellow wavelengths. Increased turbidity at Captain Key (since Spring 1995) has reduced seagrass biomass, bare areas have been colonized by drift and benthic microalgal red and green species. Analysis of suspended particulate by x-ray diffraction methodology confirmed calcite as the dominant mineral present. Increased sediment productivity at Rankin Bight (up to 32 fold higher than initial conditions) has coincided with periods of increased light transmittance to sediments, lowered water column productivity, and declines in seagrass biomass. Seagrass productivity at Captain Key has declined from February 1995 to present.

Standing stock estimates of seagrass, benthic microalgae, plankton, and epiphytes were measured simultaneously to the productivity experiments. For comparative purposes, dry weight equivalents for each productivity component will be calculated using standard conversion factors. Preliminary data analyses suggest epiphytic biomass in terms of chlorophyll a exceeds 75 g/seagrass shoot in Florida Bay, mean epiphytic biomass in the Indian River Lagoon by contrast is around 50 g/shoot. This work will be completed as part of the November interim report.

Analysis of water column, epiphytic, and benthic microalgal samples for species composition and abundance are also required in this contract. Taxonomic composition of water column samples reveal at least two distinct plankton communities. The central interior Bay (Captain Key and Rankin Bight) have a mixed diatom/ cyanobacterial composition, whereas the more open water stations have algal assemblages more typical of continental shelf waters/Gulf waters. Typical species in Rankin Bight samples include the centric diatoms Cyclotella choctawhatcheena Prasad and unicellular Chaetoceros spp., along with epiphytic and benthic pennate diatoms from the genera Cocconeis, Mastogloia, and Amphora, as well as cyanobacteria from the genera Oscillatoria, Synechococcus, and Microcystis. On a biovolumetric basis, Rankin Bight is typically dominated by diatoms. The two western stations (Sprigger Bank and Sandy Key) are strongly influenced by offshore waters. Continental water intrusions entrain centric diatoms from the genera Rhizosolenia (e.g. R. calcar-avis, R. alata v. indica) and Chaetoceros spp. into Florida Bay, higher nutrient waters found within the Bay relative to shelf waters increase cell densities relative to offshore waters. Sediments are dominated by pennate diatoms from the genera Nitzschia, Pleurosigma, Amphora, Mastogloia, and Cocconeis. Epiphytic samples contain many of these same genera, with at least four other genera well represented. Potential results from these counts include canonical correspondence analyses using cell counts correlated with environmental conditions to develop a Florida Bay specific gradient model employing environmental measures made in the field. This model should then be tested by canonical discriminant analyses to identify similar patterns in the species and environmental data.

Mesocosm experiments currently underway include examination of altered light quality on seagrass photosynthetic efficiency, pigment composition, as well as spectral influences on the epiphytic microalgae. This work will be completed in late Fall, and would not be possible without support from Keys Marine Laboratory or FMRI personnel in Marathon, FL.

Last updated: 07/16/98
by: Monika Gurnée