Product Citations and Abstracts

Digestive tubules from intertidal and subtidal oysters, Crassostrea virginica, were histologically examined to gain a better understanding of their normal morphology during high and low tides and while being held out of water for up to 72 h. Intertidal and subtidal oysters from Bayou Texar, Pensacola, Florida, were collected from adjacent sites and processed for histological examination. A digestive tubule ratio for each oyster was determined by measuring the inside to outside tubule thickness from 20 tubules per animal. Digestive tubules with high tubule ratios (approaching 1.0) had low cuboidal epithelia, whereas tubules with low ratios (approaching 0.0) had columnar epithelia. In tidal studies, intertidal oyster sampled 13-15 h after emersion at low tides had no crystalline styles and high tubule ratios, whereas subtidal oysters collected at the same time exhibited crystalline styles and low tubule ratios. Intertidal oysters sampled 6-14 h after submersion at high tides had crystalline styles present and low tubule ratios, whereas subtidal oysters also possessed crystalline styles and low tubule ratios. These data indicate that intertidal C. virginica respond to tidal cycles with changes in tubule morphology, whereas subtidal oysters do not. In holding experiments, digestive tubule ratios in intertidal and most subtidal oysters held out of water did not significantly change over time, which may be a consequence of collection stress (quiescence and/or anaerobic metabolism).

Winstead, James T. and Lee A. Courtney. 2003. Ovacystis-like Condition in the Eastern Oyster Crassostrea virginica from the Northeastern Gulf of Mexico. EPA/600/J-03/147. Dis. Aquat. Org. 53(1):89-90. (ERL,GB 1167).

Histological examination of the eastern oyster, Crassostrea virginica, from a study in Pensacola Bay, Florida, revealed 2 cases of abnormally large, basophilic ova that resembled cells characteristic of ovacystis disease previously reported in oysters from Maine and Long Island. The hypertrophied gametes measured up to 250 µm in diameter, had scant cytoplasm and contained granular nuclear-masses of Feulgen-positive material. Electron microscopy of reclaimed tissue revealed these masses to consist of virus-like particles (average 46 nm) similar to those reported in cases of ovacystis.

Winstead, James T., Aswani K. Volety and S. Gregory Tolly. 2004. Parasitic and Symbiotic Fauna in Oysters (Crassostrea virginica) Collected from the Caloosahatchee River and Estuary in Florida. J. Shellfish Res. 23(3):831-840. (ERL,GB 1206).

Studies of oysters, Crassostrea virginica, collected from 10 sites in the Caloosahatchee River and Estuary, Florida, revealed a varied parasite and symbiotic faunae that have never been reported from this area. Organisms observed included ovacystis virus infecting gametes at four sites (prevalence <1%), ciliate protozoans Ancistrocoma sp. in the gut of a stressed oyster at one site and Sphenophrya sp. infecting the gills of animals at three sites (prevalence <1%). The gregarine protozoan Nematopsis was found at all 10 sites (prevalence 24% to 90%) and oysters at some sites had concurrent infections of Nematopsis prytherchi and Nematopsis ostrearum in connective tissue near stomach, mantle and gills. Light to moderate infestations of hydrozoan polyps of a species in the genus Eutima were observed in the gills of oysters at all sites (prevalence 1% to 22%). Helminths included an unidentified turbellarian (prevalence 1% to 4%) observed at three sites and the digenetic trematodes Echinostoma sp., Proctoeces maculatus and Bucephalus sp. in oysters at five (prevalence 1% to 93%), three (prevalence >1%) and six (prevalence 1 to 3%) sites respectively. The first two trematodes were found infesting the gonoducts of their hosts while sporocysts of Bucephalus sp. infected connective tissues and gonads. Metacestodes of a species in the genus Tylocephalus were found in vesicular connective tissues near the gut, mantle, and in the gills of animals at all sites (prevalence 7% to 58%). Many sites had oysters with multiple infestations/infections of the above organisms indicating a rich biotic diversity, especially at those sites least impacted by human activity.

Winstead, James T. and John A. Couch. 1981. Proctoeces Sp. (Trematoda: Digenea) in the American Oyster, Crassostrea virginica. EPA-600/J-81-042. Trans. Am. Micros. Soc. 100(3):296-305. (ERL,GB 278). (Avail. from NTIS, Springfield, VA: PB82-205816)

Histological examination of over 6,600 individuals of the American oyster, Crassostrea virginica, inhabiting northern Gulf Coast estuaries revealed unencysted juvenile and possible adult stages of digenetic trematode, Proctoeces sp., infecting the gonadal ducts of the mollusc. Infection is the highest in oysters from Mississippi Sound near Pascagoula, Mississippi with prevalence peaking in later summer and early winter. The worm did not provoke a significant hemocytic response from the oyster. Oyster hemocytes were observed inside the digestive caeca of worms but there was no evidence of significant germinal feeding or gonadal impairment to the oyster. The hooked mussel, Brachidontes recurvus, found attached to shells of oysters may serve as first intermediate host and thus be significant in supplying cercariae for worms' opportunistic exploitation of C. virginica as surrogate intermediate host or final host.

Winstead, James T. and John A. Couch. 1988. Enhancement of Protozoan Pathogen Perkinsus marinus Infections in American Oysters Crassostrea virginica Exposed to the Chemical Carcinogen N-nitrosodiethylamine (DENA). EPA/600/J-88/352. Dis. Aquat. Org. 5(3):205-213. (ERL,GB 645). (Avail. from NTIS, Springfield, VA: PB89-237184)

American oysters Crassostrea virginica exposed to high concentrations (600 mgl-1) of n-nitrosodiethylamine (DENA) during winter (February to May) showed significant enhancement of an epizootic apicomplexan parasite, Perkinsus marinus. The parasite reproduced and caused atypical lesions in exposed oysters in water temperatures at its lower range (20°C). The reasons for this enhancement are not clear but may reflect damage to the oysters' nonspecific, cellular defense mechanisms by the DENA without concomitant negative effects on the parasite.

Winstead, James T., Douglas P. Middaugh and Lee A. Courtney. 1991. Ovarian Mycosis in the Topsmelt, Atherinops affinis (Ayres). EPA/600/J-91/332. Dis. Aquat. Org. 10:221-223. (ERL,GB 702). (Avail. from NTIS, Springfield, VA: PB92-129691)

An ovarian mycosis in a topsmelt, Atherinops affinis (Ayres) collected from Elkhorn Slough, Monterey County, California, is reported. The fungus caused a considerable host response resulting in numerous granulomas, fibrosis and egg compression. Based on morphologic characteristics and the elimination of other fungal pathogens, the fungus is probably a member of the class Oomycetes. This is the first report of an invasive ovarian mycosis in a marine fish.

Winstead, James T. 1995. Digestive Tubule Atrophy in Eastern Oysters, Crassostrea virginica (Gmelin 1791), Exposed to Salinity and Starvation Stress. EPA/600/J-95/435. J. Shellfish Res. 14(1):105-111. (ERL,GB 900).

Oysters sampled in February, 1992, from a low salinity site (3 ppt) in Apalachicola Bay, Florida, showed digestive tubule atrophy when compared with oysters from a higher salinity site (18 ppt) 16 kilometers away. Experiments designed to induce tubule atrophy in the laboratory consisted of two starvation and two salinity stress tests. To quantify tubule condition for each oyster, inside to outside diameter tubule ratios were calculated from 20 tubules per animal using an ocular micrometer. Higher tubule ratios indicated greater tubule atrophy. The experiments showed poor nutrition, perhaps due to low salinity, may have played a significant role in the tubule atrophy of Apalachicola Bay oysters.

Winstead, James T. 1979. Simple Method to Obtain Serum from Small Fish. U.S. Fish Wildl. Serv. Fish. Bull. 77(2):509-511. (ERL,GB X136).

This note describes a simple method to obtain pooled serum samples, without anticoagulants, from fish less than 60 mm when heparinized tubes are not practical.

Oysters from 16 sites in Tampa Bay, Florida, were collected during a 6-week period in winter 1993 and analyzed for both biological characteristics and tissue chemical concentrations. Using previous sediment contamination and toxicity data, oyster tissues from the selected sites were expected to exhibit a wide range in both quantity and type of chemicals. Chemical analysis showed tissue concentrations at some of these sites to be greater than national averages, as reported by the National Status and Trends Mussel Watch Program, for total PAH, total PCB, total chlordanes, DDT, Cu, Pb and Zn. Measures of oyster internal defense characteristics, including hemocyte density, rate of locomotion and superoxide generation, varied significantly among sites and were generally higher at sites with higher tissue concentrations of xenobiotic chemicals. Potential associations between oyster defense characteristics and accumulated chemical contaminants, either singly or in chemical classes, were explored using correlation analysis and a composited ranking procedure. Positive relationships were found for hemocyte characteristics with certain trace metal (Cu, Sn and Zn) and PAH analytes, whereas negative relationships were found with certain PCB and pesticide analytes. Heightened defenses in contaminated conditions may reflect a hemocyte process for sequestration and detoxification of environmental contaminants. Oysters from four of the 16 sites were additionally collected in June and September 1993 and site-related differences did not closely parallel those obtained in winter. Seasonal environmental factors may have altered contaminant-related differences among sites.

Oliver, Leah M., William S. Fisher, James T. Winstead, Becky L. Hemmer and Edward R. Long. 2001. Relationships Between Tissue Contaminants and Defense-Related Characteristics of Oysters (Crassostrea virginica) from Five Florida Bays. Aquat. Toxicol. 55(3-4):203-222. (ERL,GB 1106).

Evidence linking bivalve defense responses with pollutant exposure is increasing. Contaminant effects on immune or defense responses could influence the ability of an organism to resist infectious disease. This study explored relationships between xenobiotic chemicals accumulated in oyster (Crassostrea virginica) tissue and various measures of putative oyster internal defense activities and physiological condition. Defense-related and physiological measurements were made on individual oysters collected from 22 sites at five Florida bays and pooled oyster tissue from each site was analyzed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), metals and certain pesticides. Chemical concentrations, physiological condition, and hemocyte and hemolymph characteristics varied across bays and among sites within a bay. Within-bay comparisons showed that sites with high oyster defense-related activities often had accompanying high tissue concentrations of one or more classes of xenobiotic chemicals. Correlation analysis performed across bays demonstrated significant positive relationships between most defense-related characteristics and at least one contaminant, including various PAH, PCB and trace metal analytes. In combination with other recent studies, these results strengthen the hypothesis that certain xenobiotic chemicals may be associated with elevated oyster hemocyte activities, even though the ultimate influence on disease resistance reamins unknown.

Fisher, William S., Leah M. Oliver, James T. Winstead and Aswani K. Volety. 2003. Stimulation of Defense Factors for Oysters Deployed to Contaminated Sites in Pensacola Bay, Florida. EPA/600/J-03/405. Aquat. Toxicol. 64(4):375-391. (ERL,GB 1161).

A positive association between chemical contaminants and defense factors has been established for eastern oysters (Crassostrea virginica) from Florida, but it is unknown whether such factors can be stimulated through short-term exposure to contaminants in the field. Hatchery oysters were deployed at two contaminated and one reference site near Pensacola, Florida, during spring and summer 1998. Putative defense measurements, notably hemocyte count and bactericidal activity, were significantly elevated after 12-week deployment during summer at the most contaminated site. This site exhibited a dramatic increase in chemical concentrations in oyster tissue relative to both the initial concentrations in hatchery oysters and to oysters deployed at the reference site. Hemocyte activity was not stimulated after 16-week deployment of hatchery oysters in spring, despite similar increases in tissue chemical concentrations, so defense activation by short-term exposure may covary with other unmeasured environmental or physiological parameters. Using the converse approach, Pensacola Bay oysters were collected from two contaminated sites and deployed at the reference site for 16 week during spring. Results from this converse deployment were ambiguous; serum lysozyme concentrations were reduced for oysters transplanted from both sites, but hemocyte activities were not significantly changed. The principal outcome from this study was the demonstration of enhanced defense activities for oysters upon short-term summer deployment at a contaminated site.

Couch, John A., James T. Winstead and Larry R. Goodman. 1977. Kepone-Induced Scoliosis and Its Histological Consequences in Fish. EPA-600/J-77-077. Science. 197(4303):585-587. (ERL,GB 327). (Avail. from NTIS, Springfield, VA: PB-277 182)

Scoliosis in fish is caused by several diverse agents that possibly act on the central nervous system, neuromuscular junctions, or ionic metabolism. The organochlorine pesticide Kepone induces scoliosis in the sheepshead minnow. Some effects associated with Kepone-induced scoliosis in these fish are disruption of myotomal patterns, inter- and intramuscular hemorrhage, fractured centra of vertebrae, and death. The histological syndrome of Kepone poisoning in fish and the clinical syndrome in humans suggest that the nervous system is a primary target for Kepone and that scoliosis is a secondary effect of Kepone poisoning in fish.

Couch, John A., Lee A. Courtney, James T. Winstead and Steven S. Foss. 1979. American Oyster (Crassostrea virginica) as an Indicator of Carcinogens in the Aquatic Environment. In: Animals as Monitors of Environmental Pollutants. EPA-600/J-79-080. National Academy of Sciences, Washington, DC. Pp. 65-84. (ERL,GB 338). (Avail. from NTIS, Springfield, VA: PB80-18524)

The American oyster (C. virginica) was used as the experimental animal for chronic exposure to 3-methylcholanthrene (3-MC) and benzo[a]pyrene (BP) in an exposure system in which the carcinogens can be continuously injected into free flowing water at fixed rates ranging from 1 to 5 µg/l. Experiments designed to determine uptake and distribution of H3MC and H3BP showed that these are concentrated in oyster tissues in direct proportion to the dosage of carcinogen injected into the system. Residual concentrations as high as 84.4 µg/kg of MC and 36.4 µg/kg of BP were present in oysters as long as 6 months following exposure. Autoradiography showed intense localization of H3BP in distal portions of the tubules of the digestive gland and to a lesser extent in the gonadal tissues. Aryl hydrocarbon hydroxylase (AHH) activity was present in homogenates of hepatopancreas after 5.5 months of exposure to the carcinogens, in contrast to control animals in which AHH activity was quite low. In eight oysters exposed to MC, an infiltration of cells believed to be of hematopoietic origin was encountered in the mantle. Some appear to be identical in type to those which constitute sarcoma-like lesions encountered in feral oyster populations. However, it would be premature at this stage to assign any etiological significance to the experimental findings.

Couch, John A. and James T. Winstead. 1979. Concurrent Neoplastic and Protistan Disorders in the American Oyster (Crassostrea virginica). EPA-600/J-79-099. Haliotis. 8(2):249-253. (ERL,GB 353). (Avail. from NTIS, Springfield, VA: PB80-199706)

One of 373 oysters examined as part of a histological survey of oysters from Apalachicola Bay, Florida, USA, had a concurrent blood cell proliferative disorder and a protistan infection. The neoplastic blood cells (leukocytes) were found throughout the vesicular connective tissues and blood spaces in sections of the oyster. These proliferating cells resembled the neoplastic cells described by Couch and Farley from other specimens of Crassostrea virginica from Chesapeake Bay, Maryland, USA. Mitotic figures were abundant in foci of the neoplastic tissue. Epithelial tissues of the gut of this oyster were infected by spore and schizogonic stages of Dermocystidium marinum, a presumed pathogenic protist of oysters. Spores of this protist and other proliferative stages were observed in connective tissues and blood spaces. There was no morphological evidence that the neoplastic blood cells were related to the protist life cycle stages.

Fisher, William S., Julie D. Gauthier and James T. Winstead. 1992. Infection Intensity of Perkinsus marinus Disease in Crassostrea virginica (Gmelin, 1791) from the Gulf of Mexico Maintained Under Different Laboratory Conditions. EPA/600/J-93/057. J. Shellfish Res. 11(2):363-369. (ERL,GB 769). (Avail. from NTIS, Springfield, VA: PB93-168912)

A protozoan parasite, Perkinsus marinus, has been responsible for infection and mortality of eastern oysters, Crassostrea virginica, since before 1950. Studies on the course of infection intensity in individual animals have been restricted by the need to sacrifice animals for diagnosis, so quantitative association of disease intensity with environmental conditions and individual survival has not been accomplished. A recently developed hemolymph assay provided the means to quantitate infection intensity from live oysters. Application of this technique demonstrated progression of P. marinus intensity in Gulf of Mexico oysters maintained in laboratory aquaria in fed and unfed conditions at different test temperatures (18° - 27°C) and salinities (6 - 36 ppt). In one experiment, the infection intensities over eight weekly samplings increased 100.09 mL-1 hemolymph week-1 for low temperature/low salinity conditions and 100.36 hypnospores mL-1 hemolymph week-1 for high temperature/high salinity conditions. Temperature was more influential than salinity in P. marinus intensity and oyster mortalities. Oysters containing 103 - 104 hypnospores mL-1 hemolymph survived in low temperatures, but not in high. Feeding did not affect the intensity of P. marinus, but may have been a factor in survival of infected oysters.

Fisher, William S., James T. Winstead, Leah M. Oliver, H. Lee Edmiston and George O. Bailey. 1996. Physiologic Variability of Eastern Oysters from Apalachicola Bay, Florida. J. Shellfish Res. 15(3):543-553. (ERL,GB 972).

Eastern oysters, Crassostrea virginica, were collected monthly during a one-year period from two study sites in Apalachicola Bay, Florida, and several measurements were made of their physiological condition. Continuous and intermittent temperature measurements at both sites showed highly coincident ambient temperature regimes. Salinity measurements however, were erratic and varied dramatically between sites. Oyster gonad size and gametogenic condition were highly synchronous at both sites, supporting the concept of temperature-driven reproductive cycles. Other measurements, including condition index, wet:dry tissue weight ratio, digestive tubule condition and vesicular connective tissue condition, showed significant variability due to sampling month, but also differed due to site and/or to interaction between date and site, indicating that local effects influenced oyster physiology. Temperature control over condition index and wet:dry tissue weight seems apparent, but it is not known whether the changes resulted directly from temperature or from temperature-driven reproductive and metabolic cycles. A significant difference between site means at specific dates was observed for digestive tubule condition and may relate to short-term salinity differences. Other physiological variations could not be attributed to any of the physical conditions monitored (temperature, salinity, pH and dissolved oxygen). Variability of oyster physiological measurements inherent at different sites and seasons must be well understood to properly interpret them in the context of biological indicators of environmental condition.

Genthner, Fred J., James T. Winstead, Jeanne E. Gillet, Amy L. Van Fleet, John J. Viel, Erin E. Genevese and Samuel Singer. 1997. Effects of a Molluscicidal Strain of Bacillus alvei on Digestive Tubules of Zebra Mussels, Dreissena polymorpha. J. Invertebr. Pathol. 69(3):289-291. (ERL,GB 981).

The zebra mussel, Dreissena polymorpha, an invading exotic pest, has been a great concern in North America. Control of the zebra mussel through physical or chemical means has numerous drawbacks and has met with limited success (Kovalak et al., 1993). Microbes have been considered as possible alternative means of control (Molly and Griffin, 1992). Genovese and Singer (1994) found several strains of Bacillus sp. of morphological group II that possessed toxic activity toward zebra mussels. In the present study, we conducted bioassays with adult zebra mussels and dilutions of a culture of B. alvei 2771. Histopathological analysis was performed to identify affected tissues. These results suggest exposure of zebra mussels of B. alvei 2771 caused death and that the digestive gland was adversely affected prior to death.

Dantin, Darrin D., William S. Fisher, Stephen J. Jordan and James T. Winstead. 2005. Fishery Resources and Threatened Coastal Habitats in the Gulf of Mexico. EPA/600/R-05/051. U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, Gulf Breeze, FL. 52p.

EXECUTIVE SUMMARY All life is supported by—and limited by—the physical, chemical, and biological properties of its environment. Organisms, populations, species, and biotic communities inhabit complex spaces bounded by multi-dimensional ranges of tolerance. Hutchinson (1959) dubbed these spaces, or niches, “hypervolumes;” we use the simpler, albeit vaguer term, habitat. Habitat has many definitions, none of them fully satisfactory. Peters and Cross (1992), in attempting to define coastal fish habitat, determined that the definition (properly) depended upon the context. In this document, habitat generally means those features of the physical environment without which selected species cannot thrive. Humans, by altering landscapes and seascapes to extend and modify their habitats, alter other species habitats in ways that can shrink their boundaries and weaken their supporting functions. It is sometimes observed, more often inferred, that such alterations reduce the abundance and productivity of affected species or populations. If essential habitats are totally destroyed or their functions thoroughly degraded, it is clear that local or global extinctions (depending upon the scale of destruction) will result. It is much more difficult to determine, in the absence of catastrophe, how population success is related to habitat extent and condition (USEPA 2002). The fisheries of the United States are heavily dependent on estuaries and the unique habitat features they provide; estuarine-dependent species comprise more than 50% of U. S. commercial fisheries landings (Houde and Rutherford 1993). Commercial and recreational fisheries in the northern Gulf of Mexico (western Florida through Texas) have a combined annual economic value of more than $1 billion (NMFS 2003a, 2003b ). These facts have guided the selection of the following species for initial attention by the Gulf Ecology Division’s altered habitat research project: shrimp (three species), blue crabs, eastern oysters, and spotted seatrout (the last representing several species of sciaenid fishes). There is strong evidence that all of these species, at some point in their life cycles, depend on specific types of physical habitats in areas where freshwater and saltwater mix. A review of the life histories and habitat dependencies of these economically important species indicates a few habitat factors of major importance for the species of concern. These include (1) sources of freshwater inflow to coastal waters, (2) tidal marshes, (3) submerged aquatic vegetation, (4) shallow, near-shore soft bottoms, and (5) shell reefs and the associated oyster communities. Our research is focused on physical alterations of these habitat features. Contamination of coastal habitats by nutrients, sediments, and toxic contaminants is being addressed by other research teams (USEPA 2002).

Volety, Aswani K., S.G. Tolley and James T. Winstead. 2002. Utilizing Shellfish Responses to Set Target Water Quality Conditions for the Restoration of Oyster Reefs in the Caloosahatchee Estuary, Florida. Presented at the International Workshop on Restoration of Benthic Invertebrate Populations: Genetics, Diseases & Ecology, 9-12 November 2002, Coquimbo, Chile. 2 p. (ERL,GB R960).

High temperatures and salinities favor P. marinus resulting in high prevalences and intensities of infection in oyster. However, in our study while P. marinus infections are higher, intensities of infections are low. High temperatures and low salinities during summer and low temperatures and high salinities during winter may act antagonistically to keep P. marinus infections in oysters from the Caloosahatchee River at low levels. These results further suggest that well-timed freshwater releases onto Caloosahatchee River may lower P. marinus infections to non-lethal levels in oysters, thereby increasing survival. High freshwater flows during summer through water management practices and/or heavy summer rains flush out oyster larvae and spat from areas with suitable cultch and/or reduce salinities to levels that are unfavorable for spat settlement and survival. Flows between 500 and 2000 CFS will result n optimum salinities for oysters (15 - 25 ppt) and will result in sustaining and enhancing oyster populations in the Caloosahatchee Estuary. Through our studies we identified water quality targets and specific sites that should sustain, enhance and restore oyster reefs and have communicated to water resource managers. This information is currently being used by resource managers in setting minimum and maximum freshwater flows into the Caloosahatchee Estuary. A pilot project focusing community-based restoration of oyster reefs in targeted areas is now underway. When appropriate, restoration efforts should be coordinated with both water management policies and sound science to ensure success.

Volety, Aswani K., S. Gregory Tolley and James T. Winstead. 2003. Effects of Seasonal and Water Quality Parameters on Oysters (Crassostrea virginica) and Associated Fish Populations in the Caloosahatchee River. Florida Gulf Coast University, Fort Myers, FL. 59 p. (ERL,GB X1068).

Under the current freshwater release regime and seasonal rainfall patterns, sampling locations in the Caloosahatchee Estuary are experiencing high temperatures and extended low salinities during summer months and low temperatures and extended high salinities during winter months. These conditions of temperature and salinities are acting antagonistically in keeping P. marinus infection in oysters at low levels. Freshwater releases from Lake Okeechobee during the dry months in year 1 were low (<300 cfs) to absent compared to year 2 when water releases were greater than 300 cfs. Lower salinities at all stations corresponding with freshwater releases, indicate that salinities were influenced by the water releases. While the infection levels in oysters were lower in the dry months of year 2 compared to year 1, overall infection intensities were light. The results suggest that flows <3000 cfs do no cause "significant harm" as measured by P. marinus infections in Caloosahatchee oyster populations. However, given that optimum salinity for oysters ranges from 14-28 ppt, under the prevailing salinity regimes, high flows exceeding 3000 cfs may cause severe mortality and low spat recruitment into the system. Results of juvenile oyster survival in the field as well as the laboratory, and spat recruitment in the peak summer months support the predicted detrimental effects of high freshwater releases during summer months. Complete cessation of freshwater discharges into the Caloosahatchee Estuary during the winter will result in increased salinities in areas normally associated with low salinities and the concomitant migration of marine predators and pests (oyster drills, crown conchs, whelks, boring sponges, mud worms, etc.) that dominate high salinity waters (White and Wilson 1996). It is speculated that oyster spat that is recruited to downstream areas (e.g., Tarpon Bay) will be exposed to high salinities and heavy predation pressure resulting in very little survival. Given the high spat recruitment at intermediate salinities along with good growth rates and low disease prevalence and intensity at upstream locations having intermediate salinities for most of the year, it is very feasible to develop oyster reefs at upstream locations by strategically placing oyster cultch (construction of oyster reefs) at these locations and regulating water flows. Flows between 500 and 2000 cfs would result in salinities of 16-28 ppt at all stations, conditions that are favorable to sustain and enhance oyster populations in the Caloosahatchee Estuary. Under current water management practices, oysters in the Caloosahatchee River are not stressed by low flows (<300 cfs), but are stressed due to high flows exceeding 3000 cfs for extended periods (2-4 weeks). It is recommended that minimum and maximum flows from Lake Okeechobee into the Caloosahatchee Estuary be maintained at 500 and 2000 cfs respectively, for the development of oyster reefs. It is also recommended that when freshwater releases are necessary, repeated pulsed releases of <1 week duration during winter months be made instead of sustained releases of freshwater during summer or winter months. The use of adaptive management approaches involving freshwater releases to sustain and enhance oyster populations is invaluable to the ecology of the Caloosahatchee Estuary.