Oyster monitoring in the northern estuaries on the. Southeast coast of Florida

Transcription

1 Oyster monitoring in the northern estuaries on the Southeast coast of Florida 28 Annual Report Melanie L. Parker Stephen P. Geiger Florida Fish and Wildlife Research Institute Eighth Avenue SE St. Petersburg, Florida 3371 June 25, 29 Contract Number: 4684 File Code: F A1

2 TABLE OF CONTENTS Executive Summary Introduction Methods....8 Results St. Lucie Estuary...12 SLE Figures Loxahatchee River...32 LOX Figures. 35 Lake Worth Lagoon...5 LWL Figures Discussion...6 References

3 Executive Summary In this report we present the 28 observations by the Molluscan Fisheries research group at the Florida Fish and Wildlife Research Institute (FWRI) on oysters in southeast Florida. The main objective of this project is to continue a long-term monitoring program intended to document the response of oysters, Crassostrea virginica, in south Florida to CERP activities. FWRI monitored changes in oyster ecology at six sites in three estuaries in southeast Florida: the St. Lucie estuary (3 sites), the Loxahatchee River (2 sites) and Lake Worth Lagoon (1 site). Four aspects of oyster ecology were monitored: spatial and size distribution patterns of adult oysters, distribution and frequency patterns of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX), reproduction and recruitment, and juvenile oyster growth. Water quality parameters including salinity, temperature and chlorophyll a concentrations were also monitored at each study site. Salinities in the St. Lucie estuary (SLE) were near the optimal range (15-2 ppt) for oyster survival and recruitment success during the first six months of the year, decreased rapidly in July leading to the subsequent oyster die-off at all sites in the fall and recovered quickly enough to to allow successful settlement of the last recruits of the year. Salinities in the Loxahatchee River (LOX) were near the optimal range (15-2 ppt) for oyster survival and recruitment success in early months of the year, but throughout the rest of the year salinities were erratic and often either too high (increased predation and disease) or too low. Salinity was highly variable in the Lake Worth Lagoon (LWL), but was generally higher than salinities recorded in the other estuaries. Oysters were abundant at all nine stations in SLE during the spring 28 survey but declined dramatically by the fall survey and were limited to only a scattering of live oysters in central estuarine reefs. Oyster densities at both the LOX and LW sites were high and increased from spring to fall 28. Dermo infection was consistently present in oysters from the LOX and LWL study sites. Oysters from the St. Lucie-Central study site also had a consistent presence of the parasite until salinities substantially declined in late summer. However, infection intensity levels were low throughout the year in oysters sampled from all sites. Reproductive development increased steadily through spring in the SLE and LOX study sites Both estuaries exhibited a spring and fall peak in recruitment. In contrast, gametogenesis was delayed and increased more rapidly in the LWL study site. Recruitment in LWL was much higher and had 3

4 a single peak which lasted for several months. Juvenile growth rates were high in both the SLE and the LOX. Observed juvenile growth rate was low in Lake Worth, but may have been biased by the continual recruitment of small oysters to the population. 4

5 Introduction The Comprehensive Everglades Restoration Program (CERP) has been implemented as a means of reinitiating, to the greatest degree possible, natural freshwater flow to coastal waters on both coasts of south Florida. The Monitoring and Assessment Program (MAP) component of CERP is designed to provide a diverse approach to documenting and describing the impacts of changed freshwater flow to the flora and fauna inhabiting inland landscapes and coastal waters. Because of their wide distribution, historical context, and essential habitat value, the eastern oyster (Crassostrea virginica) is included as a target species for monitoring. Oyster beds provide important habitat for numerous organisms and are indicators of a healthy estuary. Changes in the spatial extent and health of oyster beds in southeast Florida estuaries are key performance measures that will help assess the success of CERP. The eastern oyster occupies estuarine and nearshore habitats throughout the eastern and Gulf of Mexico coasts of the United States. This animal supported a subsistence fishery even before European colonization of the United States (MacKenzie et al., 1997), and throughout recent history has provided an important economic and cultural resource to coastal inhabitants. In addition to its direct economic benefits, the oyster also provides essential habitat for many other estuarine inhabitants (Bahr and Lanier, 1981). The eastern oyster is one of the most culturally, economically, and ecologically important residents of U.S. coastal waters. In Florida, oysters occur along both the Atlantic and Gulf of Mexico coasts in almost all estuarine and nearshore waters. Along the Atlantic coast, oysters are generally confined within bays and lagoons such as Lake Worth Lagoon or the Indian River. These areas are expected to experience changes in water quality, quantities and timing due to the implementation of the C-44 and Indian River Lagoon South CERP components. Those waters, and other coastal waters on the southeast coast of the state, have experienced altered patterns of water delivery and quality as a result of water management practices related to the St. John s River and Kissimmee River basins, Lake Okeechobee, and the Everglades. In particular, the redirection of freshwater out of those inland basins and into the coastal waters mentioned above has altered both the timing and the range of salinity variation in those coastal waters. Alterations in freshwater flow have reduced or eliminated many oyster reef areas and have impacted both the timing and extent of oyster reproduction (Berrigan et al., 1991). The diverse community associated with the oyster reefs has 5

6 been impacted to an equivalent or greater degree. Monitoring in the St. Lucie estuary, the Loxahatchee River, and Lake Worth Lagoon began in 23 to establish pre-restoration conditions to assess and evaluate any changes related to the implementation of the previously mentioned restoration components. The main objective of this project is to continue a long-term monitoring program intended to document the response of oysters, Crassostrea virginica, in south Florida to CERP activities. The Molluscan Fisheries research group at the Florida Fish and Wildlife Research Institute (FWRI) in conjunction with Dr. Aswani Volety at Florida Gulf Coast University (FGCU) monitored changes in oyster distribution and abundance at a variety of sites on the Atlantic and Gulf of Mexico coasts of south Florida. Six sites in three estuaries in southeast Florida were monitored by FWRI (Figure 1): the St. Lucie estuary (3 sites), the Loxahatchee River (2 sites) and Lake Worth Lagoon (1 site). The Caloosahatchee River and nearby Ten Thousand Islands were monitored by FGCU. The data collected by FWRI and FGCU use methods that, to the greatest degree possible, ensure the resultant data from these contemporaneous projects are statistically and conceptually comparable. Four aspects of oyster ecology are monitored: spatial and size distribution patterns of adult oysters, distribution and frequency patterns of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX), reproduction and recruitment, and juvenile oyster growth. In this report we present the 28 observations by FWRI on oysters in southeast Florida. 6

7 Figure 1. CERP oyster monitoring study sites and stations on the east coast of Florida. 7

8 Methods Study Sites Oyster sampling occurred on oyster reefs within three estuarine ecosystems on the southeast coast of Florida that included the St. Lucie estuary, the Loxahatchee River, and Lake Worth Lagoon. Within the St. Lucie estuary, we considered the north fork, the south fork, and the central estuary to be separate sites and we sampled three oyster reefs (= stations), or three potential oyster reef locations if no oysters were present, within each of those sites. Similarly, in the Loxahatchee River, we considered the south fork and the northwest fork to be separate sites and we sampled three oyster reefs within each of those sites. Three oyster reefs were also selected as study sites within Lake Worth Lagoon. This strategy resulted in a total of six separate study sites (St. Lucie-North, St. Lucie-Central, St. Lucie-South, Loxahatchee-North, Loxahatchee-South, and Lake Worth) each with three stations (i.e., oyster reefs) that were monitored. Station locations can be seen in Figure 1, and coordinates for each sampling reef are provided in Table 1. Table 1. Station locations for CERP oyster monitoring sites in southeast Florida. Site Station Latitude o N Longitude o W St. Lucie North Fork St. Lucie North Fork St. Lucie North Fork St. Lucie Central Estuary St. Lucie Central Estuary St. Lucie Central Estuary St. Lucie South Fork St. Lucie South Fork St. Lucie South Fork Loxahatchee NW Fork Loxahatchee NW Fork Loxahatchee NW Fork Loxahatchee SW Fork Loxahatchee SW Fork Loxahatchee SW Fork Lake Worth Lagoon Lake Worth Lagoon Lake Worth Lagoon Adult Sampling Adult sampling was conducted in the late spring and fall of 28. On each sampled reef, we haphazardly deployed fifteen replicate 1/4-m 2 quadrats and harvested all oysters within each quadrat for 8

9 determination of the number of live and dead oysters with articulated shells. A maximum of live oyster shell heights (SH = maximum linear distance from the umbo to the ventral shell margin) were also measured from each quadrat. Reproductive and Disease Monitoring Oysters were collected for analysis of physiological condition, gonadal development state, and for the prevalence and intensity of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX) on a monthly basis. A sample of ten oysters from each of the three reefs within a study site (total N = ten oysters x three reefs x six sites = 18 per month if live oysters were available at all stations) were transported, live and chilled, to the FWRI laboratory for processing. Each individual oyster was measured (SH mm), shucked, and the tissues processed for reproductive stage, disease status and physiological condition according to the methods described below. For condition analysis, five of the oysters collected from each station within a site were processed by thoroughly cleaning each individual, measuring the shell height, weighing the whole animal, then shucking each oyster and obtaining the tissue wet weight. The shells and tissues were dried for 48 hours and then the shell and tissue dry weights were recorded. Oyster condition index was calculated as the ratio of tissue dry weight to shell dry weight. The remaining five animals collected from each station were processed for reproductive and disease analysis. For Perkinsus marinus (dermo) disease analysis, prevalence and intensity was diagnosed with Ray s fluid thioglycollate method (RFTM) as described by Bushek et al. (1994). Small (1 cm 2 ) pieces of gill and mantle tissue were incubated in RFTM media with antibiotics for seven days in the dark at 25 o C. Tissue pieces were then placed onto glass microscope slides, macerated with razor blades, stained with Lugol s, and examined at 4x for the presence of hypnospores. Parasite density (infection intensity) was ranked using the Mackin scale, which ranges from to 5 (Table 2). Average parasite densities were calculated for each sample. For reproductive and MSX disease analyses, the remaining oyster tissue was preserved in Dietrich s fixative solution (Barber, 1996). Following 2 hours of fixation, the oyster tissues were 9

10 Table 2. Mackin scale showing different stages of Perkinsus marinus (dermo) infection intensity. Stage Category Cell Number Notes Uninfected No cells detected.5 Very light < cells in entire preparation 1 Light 11- cells in entire preparation Cells scattered or in localized clusters of -15 cells 2 Light-moderate Cells distributed in local concentrations of 24-5 cells; or uniformly distributed so that 2-3 cells occur in each field at X 3 Moderate 3 cells in all fields at X Masses of 5 cells may occur 4 Moderate heavy Cells present in high numbers in Less than half of tissue appears blueblack macroscopically all tissues 5 Heavy Cells in enormous numbers Most tissue appears blue-black macroscopically thoroughly rinsed in tap water and preserved in 7% ethanol for subsequent histological preparation. Histological preparation consisted of dehydrating each oyster in 95% ethanol for a minimum of three hours, then embedding the tissue in paraffin. Depending upon the size of the individual oyster, a minimum of one to a maximum of six 3.5 micrometer sections were cut from each embedded sample using a microtome mounted with a glass knife, maintaining a minimum separation of 6 micrometers (the approximate maximum diameter of an oocyte) between sections. The sections were stained with hematoxylin and eosin, and then mounted onto pre-labeled glass slides for analysis. Resultant slides were examined at 2-4x on a compound microscope and each sample was assigned to a reproductive stage following the classification scheme (Table 3) modified from the work of Fisher et al. (1996). Finished slides were also examined at x for the presence of MSX parasites. Spat Recruitment Juvenile oyster recruitment was monitored at each of the reefs within each study site. Three replicate spat monitoring arrays were deployed and retrieved at each station on a monthly schedule. Each array consisted of 12 axenic adult oyster shells (5 - cm SH) strung onto two separate lengths of galvanized wire. The shells were oriented with their inner surface facing downward when suspended off the bottom, and spat recruitment was estimated by counting the number of settled spat on the underside of the strung shells.

11 Table 3. Qualitative reproductive staging criteria for oysters collected from Florida waters. Value Observations Neuter or resting stage with no visible signs of gametes 1 Gametogenesis has begun with no mature gametes 2 First appearance of mature gametes to approximately one-third mature gametes in follicles 3 Follicles have approximately equal proportions of mature and developing gametes 4 Gametogenesis progressing, but follicles dominated by mature gametes 5 Follicles distended and filled with ripe gametes, limited gametogenesis, ova compacted into polygonal configurations, and sperm have visible tails 6 Active emission (spawning) occurring; general reduction in sperm density or morphological rounding of ova 7 Follicles one-half depleted of mature gametes 8 Gonadal area is reduced, follicles two-thirds depleted of mature gametes 9 Only residual gametes remain, some cytolysis evident Gonads completely devoid of gametes, and cytolysis is ongoing Juvenile Growth Monitoring Juvenile growth monitoring was initiated at each study site in March 28. Growth arrays were constructed of 12.7-mm-mesh plastic-coated wire mesh with dimensions of approximately.6-m L x.6-m W. On each of these growth arrays, 25 adult, axenic oyster shells were attached by fishing line to serve as substrate for wild juvenile oysters. Cage sampling involved measuring the shell heights of 3 haphazardly selected live oysters (or all live oysters if <3). This monitoring was conducted in concurrence with the monthly recruitment sampling at all sites. Monitoring of juvenile oyster growth continued until February 29 at all sites. Water Quality Monitoring ly water quality sampling was conducted in conjunction with field sampling at all stations within each study site. Recorded parameters included water depth, temperature, salinity, turbidity, ph, dissolved oxygen concentration and chlorophyll a concentration. Water depth was determined with a sounding line and turbidity was obtained using a standard Secchi disk. All other parameters were measured with a YSI 682 multi-parameter data logger. 11

12 Results St. Lucie Estuary Adult Sampling During the spring oyster survey in May 28, mean live oyster densities exceeded m -2 at all sampled stations in the north fork, the central estuary and at one station in the south fork (Figure 2). These live densities were among the highest recorded in the St. Lucie estuary since the start of our oyster monitoring program in early 25. Mean shell heights of these oysters ranged from approximately 5 to 8 mm (Figure 3) suggesting that oysters were surviving many months and thus achieving larger sizes. Unfortunately, storm activity coupled with water releases into the estuary caused salinities to fall below 5 ppt at all stations in September and October. As a result, during the fall survey in October 28, we found that oyster populations were completely decimated in the north and south forks and reduced by approximately 99% in the central estuary. Numbers of dead oysters greatly increased and almost mirrored the live densities that were present during the previous spring survey (Figure 2). Because only dead oysters with articulated shells are counted during our surveys, some recently dead oysters may not have been accounted for in the north fork. Oysters in this study site are present in clumps rather than in a more traditional benthic reef structure. When oysters in these areas die-off, the shells become disarticulated much more rapidly than would typically occur at a reef site. As previously mentioned, not all oysters were lost in the central study site. However, mean shell heights at these three stations only ranged from approximately 5 to 14 mm (Figure 3). The small size of these oysters suggests that they were actually new recruits that were able to settle onto the reefs before the end of the spawning season. Disease Monitoring When present, live adult oysters were collected monthly from each station in the St. Lucie estuary for determination of the prevalence and intensity of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX). However, at in the St. Lucie-South study site, oysters were not collected during the months of January through March 28. This was due to an oyster die-off that occurred at that station in November 27. This die-off can be attributed to decreased salinities resulting from increased freshwater flow into the area from the nearby canal. Oysters were also not collected for 12

13 analyses from all stations in all three study sites during the months of September through December 28. This is the die-off mentioned in the previous section that resulted from a combination of local storm events and freshwater releases. Those few live oysters that survived and were present in the central estuary during the fall were too young to exhibit any degree of disease infection or prevalence and as such were not collected for these analyses. Dermo infection was almost absent from oysters collected from the north and south fork study sites but was present in low to moderate levels in oysters from the St. Lucie-Central study site (Figures 4 and 5). Even these infection levels were relatively low with mean intensities remaining below 1, indicating that sampled oysters were only lightly infected with the parasite. The prevalence of dermo reached moderate levels in oysters collected from the central estuary, especially at where 6% of the oysters collected during the months of March through July were infected with dermo. Infection levels began declining in August which suggests that the lower salinities associated with the wet season were inhibiting the parasite. At this time we have found no evidence of Haplosporidium nelsoni (MSX) infection in any of the oysters collected from the St. Lucie estuary. Physiological Condition and Reproductive Development When present, live adult oysters were collected monthly from each site in the St. Lucie estuary for determination of physiological condition and reproductive development. As previously mentioned, oyster collections did not occur at in St. Lucie-South from January through March and at all stations in all study sites from September through December. Reproductive tissues were sexed (neuter, male or female) and then assigned a reproductive development stage (Table 3). Analysis of gonadal tissues indicated that most oysters are in various stages of reproductive development including gametogenesis, active spawning and gonadal recycling throughout most of the year (Figures 6, 7, and 8). However, most oysters collected in January and February were found in a resting (i.e., neuter) stage with gonads completely devoid of gametes. In previous years studies, we found that oysters are in this resting state throughout the winter which would also include the month of December. Changes in physiological condition generally reflected these reproductive patterns in that condition index values were typically 13

14 higher in the spring at the beginning of the spawning season and slowly declined throughout the summer as fall approached (Figure 9). Spat Recruitment Juvenile oyster recruitment was monitored at each station in the estuary on a monthly basis. Three replicate spat monitoring arrays were deployed at each station for a period of approximately 28 days and then collected and returned to the lab for processing. Larval recruitment is reported as the mean number of spat counted per shell per month. Peak larval oyster recruitment rates occurred in July followed by a second peak in November at most stations (Figure ). In St. Lucie-Central larval recruitment occurred almost continuously from April through November. The spat recorded at in January are likely recruits from the 27 spawning season. Recruitment occurred over a slightly shorter time frame in both the north and south forks ranging from May or June through November. Overall these recruitment rates are fairly low, rarely exceeding 1 spat/shell/month. This reflects a decrease in mean recruits at most stations when compared with peak recruitment rates in 26 and 27. Juvenile Growth Monitoring The juvenile growth monitoring component of our project was initiated in March 28. At each station within a site, one growth array containing 25 adult, axenic oyster shells attached by fishing line was deployed directly on the reef or monitoring location. Each shell was checked monthly for the presence of wild oyster spat and up to 3 shell height measurements were recorded at each station. Juvenile oysters first appeared in St. Lucie-Central in May, in the south fork in June and in the north fork in July (Figure 11). This closely corresponds to the spat recruitment results in that juvenile oysters were found in each study site exactly one month following the first recruits recorded in each study site. However, survival of these juveniles was short-lived as the wet season progressed and by September juveniles at most stations were dead. Fortunately, salinities recovered quickly and recruits from the last pulse of the spawning season settled onto the growth arrays in each study site. These juveniles exhibited a rapid growth rate adding an average of over 5 mm shell height per month. When the study was completed in February 29, the juvenile oysters had reached a mean size of approximately 3 mm shell height. 14

15 Water Quality Monitoring Several water quality parameters were recorded in conjunction with monthly field sampling at each station. These parameters included water depth, temperature, salinity, turbidity, ph, dissolved oxygen concentration and chlorophyll a concentration. Salinity was highly variable in the estuary ranging from a low of nearly ppt to almost 25 ppt throughout the year. Salinities were near the optimal range (15-2 ppt) for oyster survival and recruitment success during the first six months of the year, but decreased rapidly in July leading to the subsequent oyster die-off at all sites in the fall (Figure 12). In November, the rapid increase in salinities coincided with the last recruitment peak of the year. As a result, it s likely that those spat will survive to grow and spawn in the 29 and allow for some recovery of oyster populations in the estuary. Temperatures recorded at each station in the estuary exhibited a typical seasonal pattern with values ranging from approximately 16 o C to 32 o C over the year (Figure 13). Dissolved oxygen concentrations and ph measurements in the estuary were as expected ranging from approximately 4 mg/l to 11 mg/l and 6.3 to 8.2 respectively (Figures 14 and 15). Chlorophyll a concentrations ranged from a minimum of 6 ug/l to a maximum of 28 ug/l (Figure 16). Turbidity in the water column is presented as a Secchi penetration value which is calculated as the percentage of the water column through which the Secchi disk could be seen. Turbidity was low at most stations from January through August but began increasing in the fall when freshwater inputs into the estuary increased (Figure 17). 15

16 Mean Live Oysters per m St. Lucie-North 25 Mean Dead Oysters per m Spring 28 Fall 28 Mean Live Oysters per m St. Lucie-Central Mean Dead Oysters per m Spring 28 Fall 28 Mean Live Oysters per m St. Lucie-South 25 Mean Dead Oysters per m Spring 28 Fall 28 Figure 2. Mean number (+ S.D.) of live and dead oysters present at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites during the spring and fall 28 surveys. Filled bars represent the number of live oysters and the hollow bars represent the number of dead oysters with articulated shells. Please note the differences in the y-axis range among the different study sites. 16

17 Mean Shell Height (mm) St. Lucie-North * * * Spring 28 Fall St. Lucie-Central Mean Shell Height (mm) Spring 28 Fall St. Lucie-South Mean Shell Height (mm) * * * Spring 28 Fall 28 Figure 3. Mean shell height (+ S.D.) of live oysters present at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites during the spring and fall 28 surveys. Asterisks denote stations where no live oysters were present for measurement. 17

18 Mean Dermo Infection Intensity Mean Dermo Infection Intensity St. Lucie-North *** *** *** *** St. Lucie-Central *** *** *** *** Mean Dermo Infection Intensity St. Lucie-South * * * *** *** *** *** Figure 4. ly mean infection intensity (+ S.D.) of oysters infected with Perkinsus marinus at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Asterisks denote stations where no live oysters were present for collection and disease analyses. 18

19 Mean Dermo Infection Prevalence Mean Dermo Infection Prevalence Mean Dermo Infection Prevalence St. Lucie-North St. Lucie-Central St. Lucie-South * * * *** *** *** *** *** *** *** *** *** *** *** *** Figure 5. ly mean prevalence (%) of oysters infected with Perkinsus marinus at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Asterisks denote stations where no live oysters were present for collection and disease analyses. 19

20 8 6 4 Stage 1 - Early gametogenesis Female Male Neuter Stage - Gonads completely devoid of gametes Stage 2 - Up to 1/3 mature gametes 8 Stage 9 - Only residual gametes remain % Frequency Stage 3 - Equal numbers of mature and immature gametes Stage 8 - Follicles 2/3 depleted of mature gametes 8 Stage 4 - Follicles dominated by mature gametes 8 Stage 7 - Follicles 1/2 depleted of mature gametes Stage 5 - Follicles distended and filled with ripe gametes 8 Stage 6 - Active spawning occuring Figure 6. Reproductive development of oysters collected from the St. Lucie-North study site in 28. The gray shaded areas represent the time period when live oysters were not available for collection from any of the three stations. 2

21 8 6 4 Stage 1 - Early gametogenesis Female Male Neuter Stage - Gonads completely devoid of gametes Stage 2 - Up to 1/3 mature gametes 8 Stage 9 - Only residual gametes remain % Frequency Stage 3 - Equal numbers of mature and immature gametes Stage 8 - Follicles 2/3 depleted of mature gametes 8 Stage 4 - Follicles dominated by mature gametes 8 Stage 7 - Follicles 1/2 depleted of mature gametes Stage 5 - Follicles distended and filled with ripe gametes 8 Stage 6 - Active spawning occuring Figure 7. Reproductive development of oysters collected from the St. Lucie-Central study site in 28. The gray shaded areas represent the time period when live oysters were not available for collection from any of the three stations. 21

22 8 6 4 Stage 1 - Early gametogenesis Female Male Neuter Stage - Gonads completely devoid of gametes Stage 2 - Up to 1/3 mature gametes 8 Stage 9 - Only residual gametes remain % Frequency Stage 3 - Equal numbers of mature and immature gametes Stage 8 - Follicles 2/3 depleted of mature gametes 8 Stage 4 - Follicles dominated by mature gametes 8 Stage 7 - Follicles 1/2 depleted of mature gametes Stage 5 - Follicles distended and filled with ripe gametes 8 Stage 6 - Active spawning occuring Figure 8. Reproductive development of oysters collected from the St. Lucie-South study site in 28. The gray shaded areas represent the time period when live oysters were not available for collection from any of the three stations. 22

23 Mean Condition Index St. Lucie-North 8 *** *** *** *** St. Lucie-Central Mean Condition Index St. Lucie-South *** *** *** *** Mean Condition Index * * * *** *** *** *** Figure 9. ly mean condition index (+ S.D.) of oysters collected from stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Asterisks denote stations where no live oysters were present for collection and physiological condition analysis. 23

24 Mean Spat/Shell/ St. Lucie-North 4 St. Lucie-Central Mean Spat/Shell/ St. Lucie-South Mean Spat/Shell/ Figure. Mean number (+ S.D.) of oyster recruits collected per shell each month from stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. 24

25 Mean Shell Height (mm) St. Lucie-North 8 St. Lucie-Central Mean Shell Height (mm) St. Lucie-South Mean Shell Height (mm) Mar 28 Apr 28 May 28 Jun 28 Jul 28 Aug 28 Sep 28 Oct 28 Nov 28 Dec 28 Jan 29 Feb 29 Mar 29 Figure 11. ly mean shell height (+ S.D.) of wild juvenile oysters settled onto growth arrays at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Growth arrays were planted in March 28. s with no data indicate months when no juvenile oysters were present on the growth arrays. 25

26 St. Lucie-North Salinity St. Lucie-Central 3 Salinity St. Lucie-South 3 Salinity Figure 12. ly salinity recorded at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. 26

27 Temperature ( o C) St. Lucie-North St. Lucie-Central Temperature ( o C) St. Lucie-South Temperature ( o C) Figure 13. ly temperature recorded at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. 27

28 2 15 St. Lucie-North DO (mg/l) 5 2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov St. Lucie-Central 15 DO (mg/l) 5 2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov St. Lucie-South 15 DO (mg/l) 5 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Figure 14. ly dissolved oxygen concentration recorded at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 28

29 9 St. Lucie-North 8 ph St. Lucie-Central 9 8 ph St. Lucie-South 9 8 ph Figure 15. ly ph recorded at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 29

30 5 4 St. Lucie-North Chl a (ug/l) St. Lucie-Central 4 Chl a (ug/l) St. Lucie-South 4 Chl a (ug/l) 3 2 Figure 16. ly chlorophyll a concentration recorded at stations in the St. Lucie-North (top), St. Lucie-Central (middle) and St. Lucie-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 3

31 % Secchi Penetration St. Lucie-North St. Lucie-Central % Secchi Penetration St. Lucie-South % Secchi Penetration Figure 17. ly percent Secchi penetration recorded at stations in the St. Lucie-North (top), St. Lucie- Central (middle) and St. Lucie-South (bottom) study sites. 31

32 Loxahatchee River Adult Sampling Live oyster densities in the Loxahatchee River reached a mean of nearly 3 m -2 at all stations in the northwest fork and over 2 m -2 at two of the three stations in the south fork during the spring oyster survey in May 28 (Figure 18). In the northwest study site, these numbers are comparable to densities seen in previous years but in the south fork these values were slightly higher with approximately 8 to more live oysters m -2 present. Oyster shell heights in the Loxahatchee were similar to those from previous years with a mean size of approximately 4 mm in both study sites (Figure 19). During the fall survey in October 28, live oyster densities more than doubled at all stations in the Loxahatchee-North study site yielding a mean of over 7 live oysters m -2 (Figure 18). Live densities also increased at two of the three stations in the south fork with an average of more than 3 m -2 at a Stations 1 and 3. Mean density at did not decrease but was identical to the mean from the spring survey. In the Loxahatchee, fall mean shell heights are typically lower than those from the spring surveys due the presence of recently settled larval oysters. Fall 28 was no exception with mean shell heights in the northwest fork ranging from 33 mm to 38 mm at each of the stations and in the south fork from 34 mm to 41 mm (Figure 19). Disease Monitoring Live adult oysters were collected monthly from each station in the Loxahatchee River for determination of the prevalence and intensity of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX). Dermo infection was consistently present in oysters collected from both the northwest and south fork study sites. Prevalence of the disease in was moderate to high with anywhere from 7% to 67% of oysters from the northwest fork and 2% to 92% from the south fork infected each month (Figure 21). However, infection intensity was low with levels rarely exceeding a score of 1 (light infection) on the Mackin scale (Figure 2). At this time we have found no evidence of Haplosporidium nelsoni (MSX) infection in any of the oysters collected from the Loxahatchee River. 32

33 Physiological Condition and Reproductive Development Live adult oysters were collected monthly from each site in Loxahatchee River for determination of physiological condition and reproductive development. Reproductive tissues were sexed (neuter, male or female) and then assigned a reproductive development stage (Table 3). Analysis of gonadal tissues indicated that most oysters are in various stages of reproductive development including gametogenesis, active spawning and gonadal recycling throughout most of the year (Figures 22 and 23). However, the majority of oysters collected in January, February, November and December were found in a resting (i.e., neuter) stage with gonads completely devoid of gametes. Changes in physiological condition generally reflected these reproductive patterns in that condition index values were slightly higher during the winter months when oysters are able to devote energy to somatic growth (Figure 24). Spat Recruitment Juvenile oyster recruitment was monitored at all six stations in the Loxahatchee River on a monthly basis. Three replicate spat monitoring arrays were deployed at each station for a period of approximately 28 days and then collected and returned to the lab for processing. Larval recruitment is reported as the mean number of spat counted per shell per month. Recruitment rates peaked twice in both study sites the Loxahatchee River. In the northwest fork, there was a recruitment peak in June and September while in the south fork the peaks occurred in April and September (Figure 25). In both study sites, recruitment occurred continuously from April through December. The spat recorded at 5 of the 6 stations in January are likely recruits from the 27 spawning season. Overall, the peaks and duration of the recruitment season are comparable to rates seen in previous years at the Loxahatchee River study sites. Juvenile Growth Monitoring The juvenile growth monitoring component of our project was initiated in March 28. At each station within a site, one growth array containing 25 adult, axenic oyster shells attached by fishing line was deployed directly on the reef or monitoring location. Each shell was checked monthly for the presence of wild oyster spat and up to 3 shell height measurements were recorded at each station. Juvenile oysters first appeared in Loxahatchee-South in April and in Loxahatchee-North in May (Figure 26). This 33

34 corresponds to the spat recruitment results in that the first recruits recorded in each study site were found in April. In the northwest fork, juvenile oysters at stations 1 and 2 exhibited a moderate growth rate adding an average of 3.5 mm shell height per month while juveniles at station 3 achieved a growth rate of only 1.5 mm per month. In the south fork, growth rates were similar to the stations 1 and 2 in the northwest site with rates ranging from 3.4 mm to 4.1 mm per month. When the study was completed in February 29, the juvenile oysters had reached a mean size of approximately 3 mm shell height in the northwest fork and 42 mm shell height in the south fork. Water Quality Monitoring Several water quality parameters were recorded in conjunction with monthly field sampling at each station. These parameters included water depth, temperature, salinity, turbidity, ph, dissolved oxygen concentration and chlorophyll a concentration. Salinity was highly variable in both Loxahatchee study sites ranging from a low of 2 ppt to over 3 ppt throughout the year. Salinities were near the optimal range (15-2 ppt) for oyster survival and recruitment success in early months of the year, but throughout the rest of the year salinities were erratic and often either too high (increased predation and disease) or too low (Figure 27). Temperatures recorded at each station in the estuary exhibited a typical seasonal pattern with values ranging from approximately 17 o C to 33 o C over the year (Figure 28). Dissolved oxygen concentrations and ph measurements in the estuary were as expected ranging from approximately 4 mg/l to 8 mg/l and 7.3 to 8.3 respectively (Figures 29 and 3). Chlorophyll a concentrations ranged from a minimum of approximately 3 ug/l to a maximum of 3 ug/l (Figure 31). Turbidity in the water column is presented as a Secchi penetration value which is calculated as the percentage of the water column through which the Secchi disk could be seen. Secchi penetration was % at all six stations in the Loxahatchee River for almost the entire year (Figure 32). The only exception was in Loxahatchee-South during the months of October and November. Even so, Secchi penetration was still greater than 75% of the water column in both months. 34

35 Mean Live Oysters per m Loxahatchee-North 2 Mean Dead Oysters per m Spring 28 Fall 28 Mean Live Oysters per m Loxahatchee-South Mean Dead Oysters per m Spring 28 Fall 28 Figure 18. Mean number (+ S.D.) of live and dead oysters present at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites during the spring and fall 28 surveys. Filled bars represent the number of live oysters and the hollow bars represent the number of dead oysters with articulated shells. Please note the differences in the y-axis range between the two study sites. 35

36 Mean Shell Height (mm) Loxahatchee-North Spring 28 Fall 28 Mean Shell Height (mm) Loxahatchee-South Spring 28 Fall 28 Figure 19. Mean shell height (+ S.D.) of live oysters present at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites during the spring and fall 28 surveys. 36

37 Mean Dermo Infection Intensity Mean Dermo Infection Intensity Loxahatchee-North Loxahatchee-South Figure 2. ly mean infection intensity (+ S.D.) of oysters infected with Perkinsus marinus at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. 37

38 Mean Dermo Infection Prevalence Loxahatchee-North Mean Dermo Infection Prevalence Loxahatchee-South Figure 21. ly mean prevalence (%) of oysters infected with Perkinsus marinus at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. 38

39 8 6 4 Stage 1 - Early gametogenesis Female Male Neuter Stage - Gonads completely devoid of gametes Stage 2 - Up to 1/3 mature gametes 8 Stage 9 - Only residual gametes remain % Frequency Stage 3 - Equal numbers of mature and immature gametes Stage 8 - Follicles 2/3 depleted of mature gametes 8 Stage 4 - Follicles dominated by mature gametes 8 Stage 7 - Follicles 1/2 depleted of mature gametes Stage 5 - Follicles distended and filled with ripe gametes 8 Stage 6 - Active spawning occuring Figure 22. Reproductive development of oysters collected from the Loxahatchee-North study site in

40 8 6 4 Stage 1 - Early gametogenesis Female Male Neuter Stage - Gonads completely devoid of gametes Stage 2 - Up to 1/3 mature gametes 8 Stage 9 - Only residual gametes remain % Frequency Stage 3 - Equal numbers of mature and immature gametes Stage 8 - Follicles 2/3 depleted of mature gametes 8 Stage 4 - Follicles dominated by mature gametes 8 Stage 7 - Follicles 1/2 depleted of mature gametes Stage 5 - Follicles distended and filled with ripe gametes 8 Stage 6 - Active spawning occuring Figure 23. Reproductive development of oysters collected from the Loxahatchee-South study site in 28. 4

41 Mean Condition Index Loxahatchee-North 8 Loxahatchee-South Mean Condition Index Figure 24. ly mean condition index (+ S.D.) of oysters collected from stations in the Loxahatchee- North (top) and Loxahatchee-South (bottom) study sites. 41

42 Mean Spat/Shell/ Loxahatchee-North Mean Spat/Shell/ Loxahatchee-South Figure 25. Mean number (+ S.D.) of oyster recruits collected per shell each month from stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. 42

43 Mean Shell Height (mm) Loxahatchee-North 8 Loxahatchee-South Mean Shell Height (mm) Mar 28 Apr 28 May 28 Jun 28 Jul 28 Aug 28 Sep 28 Oct 28 Nov 28 Dec 28 Jan 29 Feb 29 Mar 29 Figure 26. ly mean shell height (+ S.D.) of wild juvenile oysters settled onto growth arrays at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. Growth arrays were planted in March 28. s with no data indicate months when no juvenile oysters were present on the growth arrays. 43

44 Loxahatchee-North Salinity Loxahatchee-South 3 Salinity Figure 27. ly salinity recorded at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. 44

45 Temperature ( o C) Loxahatchee-North Loxahatchee-South Temperature ( o C) Figure 28. ly temperature recorded at stations in the Loxahatchee-North (top) and Loxahatchee- South (bottom) study sites. 45

46 2 15 Loxahatchee-North DO (mg/l) 5 2 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Loxahatchee-South 15 DO (mg/l) 5 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Figure 29. ly dissolved oxygen concentration recorded at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 46

47 9 Loxahatchee-North 8 ph Loxahatchee-South 9 8 ph Figure 3. ly ph recorded at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 47

48 5 4 Loxahatchee-North Chl a (ug/l) Loxahatchee-South 4 Chl a (ug/l) 3 2 Figure 31. ly chlorophyll a concentration recorded at stations in Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. Missing data is due to our malfunctioning YSI unit. 48

49 % Secchi Penetration Loxahatchee-North Loxahatchee-South % Secchi Penetration Figure 32. ly percent Secchi penetration recorded at stations in the Loxahatchee-North (top) and Loxahatchee-South (bottom) study sites. 49

50 Lake Worth Lagoon Adult Sampling In Lake Worth Lagoon, mean live oyster densities during the spring survey were approximately 25 m -2 at the large reef found at, 5 m -2 at and 2 m -2 at (Figure 33). Spring oyster densities have been steadily decreasing in Lake Worth Lagoon over past few years with densities at almost 5% reduced since spring 26. In stark contrast to the spring survey, fall densities at increased by over 4-fold with a mean density of over 1 m -2, while densities at the other two stations were both greater than 3 m -2 (Figure 33). This substantial increase in live oysters can likely be attributed to the large recruitment event that occurred from the months of April through October. The influence of new recruits can be further demonstrated by comparing the mean shell heights of live oysters from both surveys. Mean shell heights of oysters at all stations in the spring were approximately 34 mm which is comparable to sizes seen in previous years (Figure 34). However, in fall 28 the mean shell height of oysters ranged from approximately 13 mm to 25 mm at the three stations in Lake Worth Lagoon (Figure 34). Disease Monitoring Live adult oysters were collected monthly from each station in Lake Worth Lagoon for determination of the prevalence and intensity of the oyster diseases Perkinsus marinus (dermo) and Haplosporidium nelsoni (MSX). Dermo infection was present almost every month in oysters collected from all three stations in Lake Worth with prevalence ranging from 7% to 8% (Figure 36). Despite the persistent presence of dermo, infection intensity levels were low with scores rarely exceeding a rank of light infection on the Mackin scale (Figure 35). At this time we have found no evidence of Haplosporidium nelsoni (MSX) infection in any of the oysters collected from the Lake Worth Lagoon. Physiological Condition and Reproductive Development Live adult oysters were collected monthly from Lake Worth Lagoon for determination of physiological condition and reproductive development. Reproductive tissues were sexed (neuter, male or female) and then assigned a reproductive development stage (Table 3). Analysis of gonadal tissues 5

51 indicated that most oysters are in various stages of reproductive development including gametogenesis, active spawning and gonadal recycling throughout most of the year (Figure 37). However, the majority of oysters collected in January, February, March, November and December were found in a resting (i.e., neuter) stage with gonads completely devoid of gametes. When compared to oysters from St. Lucie estuary and Loxahatchee River, this appears to be a somewhat protracted period of time for oysters to remain in the resting state. In the other estuaries, condition index values are typically higher in the winter months when oysters are devoting energy to somatic growth. In Lake Worth Lagoon oysters, condition index values exhibited the opposite pattern with peak values occurring in the summer and fall months (Figure 38). The impacts of this gonadal development pattern will be demonstrated in the following section. Spat Recruitment Juvenile oyster recruitment was monitored at all three stations in Lake Worth Lagoon on a monthly basis. Three replicate spat monitoring arrays were deployed at each station for a period of approximately 28 days and then collected and returned to the lab for processing. Larval recruitment is reported as the mean number of spat counted per shell per month. At all three stations in Lake Worth, recruitment occurred from the months of April through November with peak recruitment rates occurring in August (Figure 39). This is in stark contrast to recruitment patterns observed in the other estuaries in that they typically exhibit a bimodal pattern with peaks occurring in the both spring and fall. In previous years, recruitment patterns in Lake Worth also appeared to be bimodal but this pattern was much less pronounced than those seen in the Loxahatchee River. The reduced period of reproductive development described in the previous section is likely responsible for the recruitment pattern observed in Lake Worth in 28. As far as the recruitment season duration and peak recruitment rates, the values recorded in 28 are comparable to previous years in the Lake Worth Lagoon study site. Juvenile Growth Monitoring The juvenile growth monitoring component of our project was initiated in March 28. At each station within a site, one growth array containing 25 adult, axenic oyster shells attached by fishing line was 51