Florida Estuary Research Articles

Habitat Use Patterns of Juvenile Ladyfish (<em>Elops saurus</em>) in Florida (USA) Estuaries

Natural Resource management is evolving toward ensuring sustainable ecosystems rather than sustainable yields. Understanding how a species interacts with its environment is fundamental for sound ecosystem management. If we are progressing toward an ecosystem management approach, then we must first understand how a species interacts with its environment and how the environment affects a species population dynamics. Ladyfish ( Elops saurus ) are a valuable commercial and recreational species; however, limited information is available describing the importance of their habitat. To date, only a few studies have noted the environmental conditions during ladyfish field-collections, and only one study has investigated ladyfish nursery habitats in any detail. Given the economic importance of ladyfish in Florida (USA), the objective of this investigation was to define, for the first time, juvenile ladyfish relative abundance in association to environmental conditions and habitat use at multiple Florida estuaries. In addition, this investigation re-examined some of the scientific findings and conclusions of previous ladyfish studies; incorporated additional data sets; and evaluated available ladyfish data at a finer scale of phenomena. Overall, juvenile ladyfish were collected in waters with wide-ranging environmental conditions having a sandy bottom, but preferred specific locations with particular dissolved oxygen, pH, water temperature, and salinity levels according to their size.

Abiotic affinities and spatiotemporal distribution of the endangered smalltooth sawfish, Pristis pectinata, in a south-western Florida nursery

Understanding how endangered marine species rely on coastal habitats is vital for population recovery planning. The smalltooth sawfish (Pristis pectinata) is one of several critically endangered sawfishes worldwide known to use estuaries and rivers during their early life history. In a Florida estuary designated as critical habitat by the USA government, juveniles were monitored to characterise seasonality, recruitment, and habitat use. Stretched total length ranged from 671 to 2172 mm (n = 137, mean = 1248 mm). Sawfish were captured year round. Captures of neonates with embryonic rostral sheaths allowed refinement of the size at birth (671–812 mm) and confirmed a protracted timing of parturition (November–July), which peaked between April and May. Although sampling occurred throughout the estuary, five locations had the greatest catch rates. Most juvenile sawfish had an affinity for water <1 m deep, water >30°C, dissolved oxygen >6 mg L–1, and salinity between 18 and 30. Greater catch rates for sawfish >1 year old were associated with shoreline habitats with overhanging vegetation such as mangroves. These results detail habitat use within a recognised nursery that can be used for conservation of the first endangered marine fish species in the USA.

Nutrient discharges to Biscayne Bay, Florida: Trends, loads, and a pollutant index

Changes in land use, management practices, and environmental conditions may all lead to detectable differences in nutrients transported to aquatic systems. Biscayne Bay, an oligotrophic estuary in southeastern Florida, requires minimal phosphorus and nitrogen inputs and here we quantified the effects of continued watershed development. Nutrient (nitrate/nitrite–nitrogen [NO X–N], total ammonia nitrogen [NH 3–N], and total phosphorus [TP]) water quality data (1992–2006) from six monitoring sites were evaluated using trend analysis, load estimation, and a new Pollutant Empower Density (PED) index. The PED index assesses the effect of discharged pollutants relative to the background productivity of aquatic environments. NO X–N, NH 3–N, and TP concentrations declined or exhibited no change at most sites, with only six instances of significantly (p < 0.1) increasing trends. Load estimates revealed higher NO X–N loads in the southern, agricultural section of the watershed and higher NH 3–N and TP loads in the urbanized northern and central areas. NO X–N loads from site MW04 (south) were the highest for all sites while site LR06 (north) had the highest NH 3–N and TP loads. Of the evaluated canal discharges, PED index values also suggested that canal discharges from these two sites (MW04 and LR06) had the greatest potential for impact in the bay. Overall, water quality is generally improving but canal discharges are coupled with land use activities in adjacent drainage areas. Trend analysis, load estimation, and the PED index can be used together to provide a more holistic interpretation of water quality, which is necessary for optimizing resources to meet watershed management goals.

Protracted Recruitment in the Bay ScallopArgopecten irradiansin a West Florida Estuary

Many studies have indicated that annual spawning of bay scallops (Argopecten irradians) peaks during discrete and limited periods each year. Spawning in most Florida bay scallop subpopulations has been shown to occur in fall, whereas more northerly U.S. populations typically spawn in late spring or summer. In this article we describe our efforts to expand our understanding of the seasonality of bay scallop recruitment dynamics in Florida. Visual surveys were conducted by divers each spring from 1994 to 2009 to estimate adult scallop abundance. Adult abundance was low (6.1 scallops/600 m2) during the first 3 y of the study (1994 to 1996), prompting a 7-y restoration effort intended to enhance the number of spawning adults and thereby enhance the local production of larval scallops. Adult abundances increased to an average of 21.9 scallops/600 m2 in 1997 to 2006, and then rose dramatically to an average density of 154.8 scallops/600 m2 in the most recent years (2007 to 2009). Artificial recruit collectors (n = 12) were deployed monthly near the Anclote River estuary beginning in 1997 and were allowed to soak for 2 mo at a time. Each collector's deployment period overlapped with the preceding and following trap's deployment period by 1 mo. The project is ongoing, but only data collected through December 2009 is included here (bay scallops recruited to the collectors during 163 of the 185 deployment periods). For the entire study period, the average recruitment rate was 0.3 scallops/collector/day, the maximum average for a single deployment period was 5.5 scallops/collector/day during November 2001 to January 2002, and the highest rate for a single collector was 19.6 scallops/collector/day during November 2001 to January 2002. In most years, the collectors retrieved in late fall and early winter had the highest settlement rate; a secondary recruitment peak was observed in the spring. A period of protracted recruitment (December 2005 to December 2009) occurred, during which scallops recruited to at least 1 of the 12 deployed collectors deployed during 53 consecutive deployment periods. The average recruitment rate for this protracted period was 0.4 scallops/collector/day; the maximum recruitment rate for a single deployment period (3.5 scallops/collector/day) and individual collector (17.7 scallops/day) occurred during December 2008 to February 2009. Early in our study, scallops were detected in a majority of our recruit collectors, and a protracted period of recruitment (October 2001 to February 2004) coincided with the multiyear restoration effort. However, the recent high adult densities and protracted period of recruitment occurred in the absence of any active restoration in this subpopulation, suggesting that, at least within the Anclote River estuary, the population has stabilized for the short term.

Salinity Tolerance of the African Jewelfish Hemichromis letourneuxi, a Non-native Cichlid in South Florida (USA)

The African Jewelfish (Cichlidae: Hemichromis letourneuxi) is a predatory, non-native fish that has recently (since 2000) begun to expand its geographic range across south Florida. The salinity tolerance of H. letourneuxi was unknown, and thus it was unclear whether the species could use estuarine or coastal environments. The response of H. letourneuxi to chronic change in salinity was evaluated here by exposing fish to progressively increasing salinities (0–80 ppt). Fish were held at target salinities for a minimum of 30 days. The species showed excellent survival from 0–50 ppt. At 60 ppt, only 25% of the fish survived, and mean estimated survival time was 12 days. Above 60 ppt, mortality was 100%. Fish grew equally well from 0–50 ppt. In another experiment, fish were transferred directly from freshwater to various salinities from 5–35 ppt (seawater) and held for seven days, after which survivors were returned to freshwater. All fish transferred directly from freshwater to salinities up to 20 ppt survived; only 56% survived when transferred from freshwater to 25 ppt, and none survived transfer above 25 ppt. Experimental results indicated that H. letourneuxi can persist easily in salinities prevalent in coastal environments, even during periods of hypersalinity common in south Florida estuaries. Salinity will not restrict its dispersal by coastal pathways.

Increase in Bay Scallop (Argopecten irradians) Populations Following Releases of Competent Larvae in Two West Florida Estuaries

We propose the release of ready-to-set pediveliger larvae as a restoration strategy for bivalve shellfish. In this study, bay scallop (Argopecten irradians) larvae were released within two West Florida estuaries (Pine Island Sound and Boca Cicga Bay) currently closed to scallop harvest and where local scallop populations arc severely depleted relative to historical abundances. Populations in both estuaries appear to have limited larval supply and show no tendency toward natural recovery after decades of decline. Larvae were either released into enclosures or free released on four separate dates in each estuary. On a given day we used 1, 2, 3, or 4 enclosures per site; multiple release sites; and multiple releases within a year. Assessments were made via several methods, including larval recruitment to collectors, juvenile quadrat surveys, adult timed surveys, and adult transect surveys. In Pine Island Sound, following the initial larval releases in 2003, an isolated recovery in adult scallops was observed at the release site in 2004 followed by a massive resurgence in the local population in 2005. This population declined dramatically in 2006, however, and had completely collapsed by 2007. In Boca Ciega Bay, the series of larval releases did not immediately produce any detectable scallop patches, but the combined releases did immediately precede a population resurgence to levels greater than had been observed in the past three decades. Scallop abundance increased 10-fold at 10 stations in Boca Ciega Bay from 2007 to 2008. In both Pine Island Sound and Boca Ciega Bay, the increases in scallop populations were probably the result of successful survival, growth, and reproduction of the released larvae, followed by successful recruitment and growth of the subsequent generation.

Vulnerability and resilience of seagrasses to hurricane and runoff impacts along Florida’s west coast

Many climate change models predict increasing frequency and severity of tropical cyclones (hurricanes) in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. To assess this potential threat to seagrass communities in Florida’s Big Bend region, we performed a habitat change analysis based on aerial seagrass surveys performed prior to, and after, the extremely active Atlantic cyclone seasons of 2004 and 2005. To provide a regional context for changes in the Big Bend region, we also compared impacts there with changes in three other West Florida estuaries. Our analysis showed that storm impacts on seagrasses varied along Florida’s west coast. Physical disturbance caused minor losses in parts of Charlotte Harbor and the Big Bend region. However, heavy rainfall in Florida and Georgia associated with Frances and Jeanne combined with winter rains to cause complete loss of 1,500 ha of seagrasses and thinning of another 1,700 ha in the vicinity of the Suwannee River mouth. In Tampa Bay, Sarasota Bay, and Charlotte Harbor, despite localized losses, total seagrass area actually increased between 2004 and 2006. On the other hand, Tampa Bay, Sarasota Bay, and Charlotte Harbor all showed significant, and more pronounced, declines in seagrass cover as the result of another major rainfall and runoff event: the 1997–1998 El Nino event. Our results indicate that light stress, likely caused by suspended sediments, phytoplankton blooms, and dissolved organic matter, resulted in seagrass losses extending up to 40 km from the mouth of the Suwannee River. We conclude that water quality impacts, especially if they are persistent, can be more damaging than physical impacts of moderate (Category 1–3) tropical cyclones. We also conclude that runoff-related impacts on seagrasses vary depending on the timing, volume, and persistence of storm runoff in relation to normal seasonal runoff patterns and seagrass growth in each estuary.

Significant lateral inputs of fresh groundwater into a stratified tropical estuary: Evidence from radon and radium isotopes

River discharges are usually gauged at sites farther upstream than estuarine tidal reaches. As a result, global estimates of river water and nutrient fluxes to the ocean are likely underestimated as they often neglect groundwater discharge occurring in estuaries downstream of river gauging stations. We used radon and radium isotopes as tracers of groundwater discharge into the Sebastian River Estuary, a gaining stream in Florida, USA. We developed a spatially-distributed mass balance model that accounts for radon sources and sinks in waters above and below the estuarine pycnocline. Radium isotopes ( 224Ra, 223Ra, and 226Ra) were not enriched in groundwater relative to surface water and thus had limited usefulness as tracers at this specific site. The detection of fresh groundwater just beneath the sediment:water interface overlain by brackish bottom water implies that fresh groundwater dominates over saline groundwater in this salt wedge estuary. Lateral groundwater inputs from sandy banks into waters above the estuarine pycnocline were about 6-fold higher than inputs into waters below the pycnocline. Groundwater discharge rates into the surface layer of the estuary estimated from a radon mass balance ranged from 5 to 18 m 3/s (or 18 to 62 cm/day if uniformly distributed throughout the entire estuary area). The fluxes into the bottom layer ranged from 0.8 to 1.1 m 3/s (or 2.8 to 3.9 cm/day). These groundwater inputs augmented river discharges gauged upstream of the estuary tidal reaches by about 260% during the dry period and 135% during the wet period. As nutrient and other dissolved species are often highly enriched in groundwaters, groundwater probably controls surface water quality in this and other Florida estuaries.

Relative Abundance and Distribution of Common Snook along Shoreline Habitats of Florida Estuaries

AbstractQuantitative estimates of relative abundance, spatial and temporal distribution, and habitat preference of common snook Centropomus undecimalis along shoreline habitats in four Florida estuarine areas were determined. Significant differences in the relative abundance of common snook among the estuarine areas suggested marked variation in common snook population abundance and densities on a regional scale. The highest adjusted mean relative abundance of common snook occurred in the southern Indian River Lagoon (4.68 fish/haul; SE = 0.08), followed by Tampa Bay (3.36 fish/haul; SE = 0.11), Charlotte Harbor (2.13 fish/haul; SE = 0.10), and the northern Indian River Lagoon (0.76 fish/haul; SE = 0.21). Several common factors (e.g., mangrove and seagrass habitat, salinity, and water temperature) among the estuarine areas were linked with common snook relative abundance and distributions, allowing us to better understand how these fish interact with their environment in different regions of Florida.

General empirical models for estimating nutrient load limits for Florida's estuaries and inland waters

We developed empirical models that can predict maximum allowable, nutrient loading rates or load limits (LM) for maintenance of mesotrophy in Florida’s fresh and estuarine waters. Water residence time (tw) explains most of the variation in LM previously set by the U.S. Environmental Protection Agency and Florida’s environmental agencies for total phosphorus (TP) and for total nitrogen (TN). We found that a single model for TP and for TN fit data from both estuarine and freshwater systems. Further, we show that the models are consistent with or analogous to the critical loading model of the Organization of Economic Cooperation and Development (OECD 1982): Lc = [TP or TN]c x z/Τw(1 + Τw0.5). The LM ‐ Τw model for TP is sufficiently similar to the OECD model as to indicate that either model could provide a reasonable fit to mesotrophy in both temperate and subtropical systems. The models can facilitate the development of total maximum daily loads for estuaries and inland waters of Florida and may have broader regional utility. They may also aid the development of nutrient concentration criteria.

Determining Spatial and Temporal Inputs of Freshwater, Including Submarine Groundwater Discharge, to a Subtropical Estuary Using Geochemical Tracers, Biscayne Bay, South Florida

Geochemical mixing models were used to deci- pher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr 2+ /Ca 2+ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ 18 O=�2.66‰, δD �7.60‰) similar to rainfall (δ 18 O= �2.86‰, δD=�4.78‰). Canal water had a heavy isotopic signature (δ 18 O=�0.46‰, δD=�2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr 2+ /Ca 2+ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr 2+ /Ca 2+ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/ groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1-2% of the total fresh and saline water input.

Application of microbial source tracking methods in a Gulf of Mexico field setting

Microbial water quality and possible human sources of faecal pollution were assessed in a Florida estuary that serves shellfishing and recreational activities. Indicator organisms (IO), including faecal coliforms, Escherichia coli and enterococci, were quantified from marine and river waters, sediments and oysters. Florida recreational water standards were infrequently exceeded (6-10% of samples); however, shellfishing standards were more frequently exceeded (28%). IO concentrations in oysters and overlaying waters were significantly correlated, but oyster and sediment IO concentrations were uncorrelated. The human-associated esp gene of Enterococcus faecium was detected in marine and fresh waters at sites with suspected human sewage contamination. Lagrangian drifters, used to determine the pathways of bacterial transport and deposition, suggested that sediment deposition from the Ochlockonee River contributes to frequent detection of esp at a Gulf of Mexico beach. These data indicate that human faecal pollution affects water quality in Wakulla County and that local topography and hydrology play a role in bacterial transport and deposition. A combination of IO enumeration, microbial source tracking methods and regional hydrological study can reliably inform regulatory agencies of IO sources, improving risk assessment and pollution mitigation in impaired waters.

Cohort-specific Winter Growth Rates of YOY Bluefish,Pomatomus saltatrix, in Northeast Florida Estuaries: Implications for Recruitment

Age and growth were determined from otoliths for 181 juvenile bluefish (Pomatomus saltatrix ), collected using a variety of gear in northeast Florida during 2003 and 2005. Three distinct cohorts were identified recruiting to the near shore waters during spring, summer and autumn. Growth rates were high regardless of cohort or season. To compare pre- and post-recruitment growth rates, models were fit to individual growth trajectories using change point analysis. Post-estuarine growth rates were generally higher. Growth rates and hatching times were within the range of those obtained in other bluefish studies conducted at higher latitudes. As this is the only area where winter recruitment of bluefish has been observed, coastal Florida habitats may be essential for the bluefish stock and will need to be carefully monitored in future studies.

Movement patterns and water quality preferences of juvenile bull sharks (Carcharhinus leucas) in a Florida estuary

Acoustic telemetry was used to examine the size of daily activity space, small-scale movement patterns, and water quality preferences of juvenile bull sharks in the Caloosahatchee River, Florida. Movement pattern analysis included rate of movement, swimming depth, linearity, direction, tidal influence, diel pattern, and correlation with environmental variables. Manual tacking occurred before and after a large freshwater influx which divided the sharks into two groups based on movement patterns. The first group displayed increased rate of movement, distance traveled, and space utilization at night, and movements correlated with salinity, temperature, and dissolved oxygen. The second group had an increased rate of movement, distance traveled, and space utilization during the day, and movements correlated with temperature, dissolved oxygen, turbidity and pH. These juvenile bull sharks displayed distinct diel movement patterns that were influenced by physical factors, which may account for the distribution of this top-level predator in the Caloosahatchee River.

Phytoplankton bloom status: Chlorophyll a biomass as an indicator of water quality condition in the southern estuaries of Florida, USA

Altered freshwater inflows have affected circulation, salinity, and water quality patterns of Florida Bay, in turn altering the structure and function of this estuary. Changes in water quality and salinity and associated loss of dense turtle grass and other submerged aquatic vegetation (SAV) in Florida Bay have created a condition in the bay where sediments and nutrients have been regularly disturbed, frequently causing large and dense phytoplankton blooms. These algal and cyanobacterial blooms in turn often cause further loss of more recently established SAV, exacerbating the conditions causing the blooms. Chlorophyll a (CHLA) was selected as an indicator of water quality because it is an indicator of phytoplankton biomass, with concentrations reflecting the integrated effect of many of the water quality factors that may be altered by restoration activities. Overall, we assessed the CHLA indicator as being (1) relevant and reflecting the state of the Florida Bay ecosystem, (2) sensitive to ecosystemdrivers (stressors,especially nutrient loading), (3)feasible to monitor, and (4) scientifically defensible. Distinct zones within the bay were defined according to statistical and consensual information. Threshold levelsof CHLA for each zonewere defined using historical data and scientific consensus. A presentation template of condition of the bay using these thresholds is shown as an example of an outreach product.

Pink shrimp as an indicator for restoration of everglades ecosystems

Abstract The pink shrimp, Farfantepenaeus duorarum, familiar to most Floridians as either food or bait shrimp, is ubiquitous in South Florida coastal and offshore waters and is proposed as an indicator for assessing restoration of South Florida's southern estuaries: Florida Bay, Biscayne Bay, and the mangrove estuaries of the lower southwest coast. Relationships between pink shrimp and salinity have been determined in both field and laboratory studies. Salinity is directly relevant to restoration because the salinity regimes of South Florida estuaries, critical nursery habitat for the pink shrimp, will be altered by changes in the quantity, timing, and distribution of freshwater inflow planned as part of the Comprehensive Everglades Restoration Project (CERP). Here we suggest performance measures based on pink shrimp density (number per square meter) in the estuaries and propose a restoration assessment and scoring scheme using these performance measures that can readily be communicated to managers, policy makers, and the interested public. The pink shrimp is an appropriate restoration indicator because of its ecological as well as its economic importance and also because scientific interest in pink shrimp in South Florida has produced a wealth of information about the species and relatively long time series of data on both juveniles in estuarine nursery habitats and adults on the fishing grounds. We suggest research needs for improving the pink shrimp performance measure.

Movements of bonnetheads, Sphyrna tiburo, as a response to salinity change in a Florida estuary

The movement of bonnetheads, Sphyrna tiburo, within an estuarine system on the Gulf of Mexico coast of Florida was examined to define response to salinity change. Shark presence and movements were evaluated by acoustic monitoring and gillnet sampling. Acoustic monitoring data were used to investigate active selection of different zones within the estuary based on differences in salinity among zones. Sharks were monitored for 187 days in 2003 and 217 days in 2004 in salinities ranging from 11.0 to 31.0 ppt in 2003 and 15.8 to 34.6 ppt in 2004. Monitoring data supported the hypothesis that salinity played a role in the distribution and movement of S. tiburo. Catch per unit effort (CPUE) data obtained from gillnet sampling from 1995 to 2004 were examined to determine affinity or avoidance of specific salinities within the study site as calculated using an electivity index. Electivity analysis showed almost no affinity or avoidance for specific salinity values. The difference in results between the CPUE and acoustic monitoring in relation to the potential effects of salinity likely relate to the nature of the data, with acoustic monitoring providing continuous data and CPUE providing snapshot location data. The results of this study suggest that although S. tiburo are collected within a wide range of salinity levels, salinity may affect movement and distribution. Salinity effects may be more pronounced during periods of prolonged and/or large changes in salinity as detected by long-term monitoring.

Simulating Hydrodynamics in the Upper Charlotte Harbor and its Major Tributaries in Florida

Charlotte Harbor is one of major estuaries in Florida. The upper portion of the estuary receives freshwater inflows mainly from the Peace and Myakka Rivers. To study the hydraulic interactions between the Upper Charlotte Harbor (UCH) and its major tributaries, a multi-block model was used to simulate hydrodynamics and salinity transport processes in a simulation domain that includes the UCH, the Lower Peace River (LPR), the Lower Myakka River (LMR), the Shell Creek, and a portion of the Myakkahatchee Creek. In the modeling study, the simulation domain is split into a 3D simulation block and several 2DV blocks. The 3D block includes the UCH and the most downstream portions of the LPR and LMR, while the 2DV blocks contain the rest of the tributaries. All the blocks are patched together without any overlaps. The coupled model solves 3D RANS equations for the 3D block, but laterally averaged RANS equations for the 2DV blocks that consist of narrow and braided tributaries. Both 3D and 2DV sub-models use an efficient semi-implicit, flux-based finite difference method. The dynamic coupling is facilitated using a free-surface correction method, in which matrixes for the water surface correction in both the 3D and 2DV sub-domains are solved simultaneously after they are merged together. Model simulations demonstrated that the multi-block model is an efficient tool for simulating hydrodynamics in a very complex environment and the model application to the LPR-LMR-UCH system is successful.

Eastern oysters (Crassostrea virginica) as an indicator for restoration of Everglades Ecosystems

The Comprehensive Everglades Restoration Plan (CERP) attempts to restore hydrology in the Northern and Southern Estuaries of Florida. Reefs of the Eastern oyster Crassostrea virginica are a dominant feature of the estuaries along the Southwest Florida coast. Oysters are benthic, sessile, filter-feeding organisms that provide ecosystem services by filtering the water column and providing food, shelter and habitat for associated organisms. As such, the species is an excellent sentinel organism for examining the impacts of restoration on estuarine ecosystems. The implementation of CERP attempts to improve: the hydrology and spatial and structural characteristics of oyster reefs, the recruitment and survivorship of C. virginica, and the reef-associated communities of organisms. This project links biological responses and environmental conditions relative to hydrological changes as a means of assessing positive or negative trends in oyster responses and population trends. Using oyster responses, we have developed a communication tool (i.e., Stoplight Report Card) based on CERP performance measures that can distinguish between responses to restoration and natural patterns. The Stoplight Report Card system is a communication tool that uses Monitoring and Assessment Program (MAP) performance measures to grade an estuary's response to changes brought about by anthropogenic input or restoration activities. The Stoplight Report Card consists of both a suitability index score for each organism metric as well as a trend score (− decreasing trend, +/− no change in trend, and + increasing trend). Based on these two measures, a component score (e.g., living density) is calculated by averaging the suitability index score and the trend score. The final index score is obtained by taking the geometric score of each component, which is then translated into a stoplight color for success (green), caution (yellow), or failure (red). Based on the data available for oyster populations and the responses of oysters in the Caloosahatchee Estuary, the system is currently at stage “caution.” This communication tool instantly conveys the status of the indicator and the suitability, while trend curves provide information on progress towards reaching a target. Furthermore, the tool has the advantage of being able to be applied regionally, by species, and collectively, in concert with other species, system-wide.

Trends and explanatory variables for the major phytoplankton groups of two southwestern Florida estuaries, U.S.A.

Multi-year phytoplankton abundance data from two estuaries in southwest Florida were combined into taxonomic groups, assessed for trend, and compared with water quality data using multivariate techniques. Interannual flow variations were linked to climatic indices and were relatively large. Trends in water quality included declining biomass, N and P signals in Tampa Bay, and declining P and a complex but slightly increasing N in Charlotte Harbor. Trends were superimposed on flow-dominated seasonal and annual variations in nutrient loads. Trends in phytoplankton abundance were both gradual and abrupt, were not always monotonic, and were most noted for cyanobacteria. One species of cyanobacteria, Schizothrix calcicola sensu Drouet could be considered an indicator species. At specific stations, nutrient concentrations and seasonal parameters were significant explanatory variables for variations in community structure. Clustering of community structure by taxonomic groups did not align well with known trends in nutrient loadings or biomass.