Grantee Research Project Results
2002 Progress Report: Biopollution by the Green Mussel, Perna viridis, in the Southeastern United States
EPA Grant Number: R828898Title: Biopollution by the Green Mussel, Perna viridis, in the Southeastern United States
Investigators: Baker, Shirley M. , Benson, Amy , Phlips, Edward , Williams, James , Nunez, Jose , Baker, Patrick
Institution: University of Florida , United States Geological Survey
EPA Project Officer: Packard, Benjamin H
Project Period: June 1, 2001 through May 31, 2004 (Extended to September 30, 2004)
Project Period Covered by this Report: June 1, 2002 through May 31, 2003
Project Amount: $447,602
RFA: Exploratory Research to Anticipate Future Environmental Issues (2000) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Aquatic Ecosystems
Objective:
The objectives of this research project are to: (1) assess the potential for the future dispersal of a new biological pollutant, the green mussel Perna viridis, within and from Tampa Bay, FL; (2) assess and predict environmental impacts by green mussels on fouling communities, including artificial substrata, and upon native species at risk of displacement; and (3) assess and predict environmental impacts by green mussels on phytoplankton communities.
Six projects will be conducted as follows:
A. Environmental tolerances of green mussels will be quantified in the laboratory, to determine potential U.S. range limits.
B. Life history parameters (reproduction, recruitment, growth, mortality) will be quantified and compared with native species to predict population growth.
C. Habitats and industrial structures used by green mussels will be surveyed.
D. Impacts of green mussels on epifaunal communities will be experimentally inferred.
E. Phytoplankton potentially affected by large populations of green mussels will be surveyed, monitored, and cultured for the following project.
F. Feeding upon native phytoplankton by green mussels will be quantified and compared to native species.
Progress Summary:
Expected Results
As the first study of green mussels as a biopollutant in the United States, this effort will identify areas of concern and future research needs regarding Perma viridis and similar species. Specific predictions will be made concerning the spread and severity of green mussel infestations, and environmental impacts upon epifaunal and planktonic ecosystems, in a form usable to resource and industry managers.
Status of the Project
The project was divided into six tasks (see project summary). Original proposed timelines were altered for reasons discussed in the prior annual report.
Task A. Environmental Tolerances of Green Mussels: Laboratory Work Complete, Write-up in Progress. Trials were conducted at Mote Marine Laboratory in Sarasota, FL, and the University of Florida Tropical Aquaculture Laboratory in Ruskin, FL. Both facilities are adjacent to marine habitat (Sarasota Bay and Tampa Bay, respectively) occupied by pre-study invasions of green mussels, so no additional quality controls were required to prevent the accidental spread of the invasive species.
Goodness-of-fit experimental design was found to be most cost-effective for quantifying physiological impacts on green mussels. In this design, the survival or mortality of each green mussel was a datum. Thermal tolerance experiments were refined to include both gradual (natural) temperature changes and abrupt thermal changes simulating anthropogenic introduction, which can produce heat-shock proteins in the mussels that enhance their tolerance to thermal stress. Salinity trials also included gradual and abrupt changes.
Data collected during the experiments indicate that green mussels either produce unusual quantities of nitrogenous waste products (nitrates and nitrites), or are unusually susceptible to such wastes. This trait has made it difficult for other researchers (at Mote Marine Laboratory, Texas A&M University) to maintain them in captivity. We have found that the experimental containment system (a recirculating seawater system) must be allowed to run for 10 days prior to introducing green mussels to permit a complete denitrifying bacterial flora to develop on all surfaces, and seawater must be exchanged daily. This protocol, or a refinement of it, will be worked into any future quality assurance protocols, and this information has been transferred to the research groups mentioned above.
Task B. Life History Parameters: Field Collections Complete, Data Analysis Underway. Samples of green mussels and native scorched mussels are complete, and have been fixed and placed in cassettes in preparation for mounting and staining. The latter has been contracted to the University of South Florida. Slides will be ready for analysis by late November 2003. Dr. Bruce Barber (see last annual report), now at Eckerd College, St. Petersburg, FL, will provide use of his image analysis software and will analyze histology data in early 2004. This will be done at no additional cost to the grant.
Three study stations (hereafter designated TB1, TB2, and TB3) were established for these and portions of other tasks. TB1 is a high-salinity site near the mouth of the bay, TB2 is about mid-bay near the original peak density of green mussels, and TB3 is near the head of the bay near the low-salinity limits for populations of green mussels.
Protocols for settlement surveys have been refined by increasing the frequency with which settlement substrata are replaced during peak settlement seasons, and dividing each study site into tidal strata, each with separate settlement plates. No other quality control improvements yet have been made, but recent work by other researchers has caused us to consider two alternative models for the actual settlement plates. Some researchers prefer horizontal plates, whereas others prefer vertical. Our experiments used both methods. Upper, middle, and lower vertical intertidal plates were replaced on a weekly basis during peak settlement periods. Adjacent sets of vertical plates were left in place for 5 months to study recruitment. Horizontal plate arrays were suspended one, two, and three meters from the bottom and checked weekly for settlement. This experiment was designed to examine depth selection by settling larvae.
Task C. Habitats and Industrial Structures Used by Green Mussels: Field Study Complete, Final Writeup in Progress. Field surveys are complete, although additional surveys may be conducted if time permits. Coastal surveys were extended to include all of peninsular Florida. Based upon preliminary results, we have improved survey methodologies to include a new quantitative survey for Tampa Bay. This survey will use either a stratified random sampling design, based on geographic information system mapping coordinates for quality assurance, or cross-bay transects, using transect lines based on prior Tampa Bay benthological studies for quality control. Either design will provide slightly higher data resolution than previously planned.
Task D. Impacts of Green Mussels on Epifaunal Communities: 20 Percent Complete. This task is scheduled for 2004. The required data from other tasks, particularly portions of Task B (estimated growth) and Task C (habitats) have been collected.
A separate study, "Oyster Reef Assessment in the Suwannee River Estuary," was conducted by these researchers and Dr. Derk Bergquist of the University of Florida, funded by the Suwannee River Water Management District, a Florida state agency. As a side benefit of this project, oyster reefs impacted by green mussels in Tampa Bay, near site TB3 (see Task B) were surveyed for the same parameters (living and dead oysters of various size classes and other bivalves) using the same methods. This was not part of the original U.S. Environmental Protection Agency (U.S. EPA) project proposal, but relates directly to the topic of Task E. No additional costs to the U.S. EPA grant were incurred for the oyster reef study.
Task E. Survey of Phytoplankton Potentially Affected by Green Mussels: Field Collections Complete, Analysis in Progress. Permanent study stations TB1, TB2, and TB3 (see Task B) were used as sample sites. Weekly samples were collected beginning April 5, 2002. All samples collected for plankton analyses have been preserved, and handled/stored according to project quality assurance protocols. Microscopic analyses of phytoplankton and zooplankton samples are underway. Percent organic carbon analyses also are underway. Color and turbidity information is complete through the last sampling.
Task F. Feeding Upon Native Phytoplankton by Green Mussels: 20 Percent Completed. This project is scheduled for early 2004. The required data from other tasks, particularly portions of Task A (physiological requirements of green mussels) and Task E (phytoplankton species) have been collected. There have been no expenditures specifically related to this task to date.
Several of the original objectives are completed except for final analysis and write-up, and progress has been made since the last annual report on the remaining tasks. We have used both surveys and laboratory experiments to assess the potential for dispersal of the green mussel within and from Tampa Bay, Florida. We have an excellent qualitative understanding of the habitats in Tampa Bay that are used by green mussels, and those which are avoided, although we cannot determine, within the scope of the project as it was originally designed, why habitat selectivity exists. We also have a healthy understanding of the modal salinity and thermal tolerances of green mussels, based on field and laboratory data. These data are essential for predicting estuarine and latitudinal distribution of green mussels in the United States. Preliminary results are summarized below.
Experimental trials on green mussel impacts to benthic ecosystems have not begun, but both qualitative and quantitative data applicable to this question already have been collected. Distributional studies and population parameter data have revealed that impacts occur on some native species, and that whereas some species, such as oysters, appear to be adversely affected (displaced), other species, such as small native mussels and mangroves, are not affected. These findings are discussed in more detail below.
Experimental trials on green mussel impacts on phytoplankton communities have not begun, but the prerequisite data collection on phytoplankton species in Tampa Bay is completed. We have obtained information indicating that the plankton community affects the green mussel (mortality in response to some algal blooms). Although the original project does not include funding to examine this unexpected result, some experiments in this area already have been conducted at Mote Marine Laboratory (Jay Leverone, personal communication) at no additional cost to the grant, and we are seeking additional sponsors (such as the Ecology and Oceanography of Harmful Algal Blooms) to examine the effects of red tide organisms on the survival of the green mussel.
Preliminary Results and Evaluations
Task A. Environmental Tolerances of Green Mussels. Intertidal densities of green mussels within Tampa Bay reached peaks of 4,117·m-2, 3,675·m-2, and 4,033·m-2 at the marine (TB1 Skyway Bridge), introduction epicenter (TB2 Gandy Bridge), and estuarine (TB3 Safety Harbor) sites, respectively (see Figure 1). Mean shell lengths at these densities were 31.3 mm (TB1), 62.0 mm (TB2), and 47.5 mm (TB3). These are not the highest densities observed, which were approximately 9,000-12,000·m-2 on pilings at the mouth of the Little Manatee River in preliminary sampling in 2001. The density difference appears to be the result of the distribution of individuals at the two sites. Samples from the Little Manatee River consisted of several layers of green mussels on cylindrical treated wood pilings, while samples from the three main sampling sites formed single monospecific layers over flat surfaces of concrete pilings.
Figure 1. Densities of Green Mussels at Three Sites in Tampa Bay
There do not appear to be any correlations between green mussel density and temperature or salinity, as peak densities for each site occurred at different times of the year with widely differing temperatures and salinities. Field distributional surveys in Tampa Bay indicate that this species occurs in all major portions of the estuary, but is less abundant in regions of highest salinity (about 30 ppt or above). A buoy sampled outside of Tampa Bay (salinity usually above 30 ppt) had a green mussel density of only 158 m-2 (mean shell length 38.8 mm). By comparison, green mussel density at the same time at site TB1 (salinity usually slightly below 30 ppt) was 3,133 m-2 (mean shell length 46.4 mm). As salinities above 30 ppt are well within the physiological tolerance reported for green mussels in the literature, we suspect that there is an ecological explanation for lower densities. This issue–physiological versus ecological factors setting the high-salinity distributional limit for estuarine invertebrates– never has been properly addressed. Green mussels in west Florida may provide a good model for such studies in the future.
Modal low salinity limits for green mussels appear to be around 16-17 ppt in Tampa Bay, based upon the field distribution. From the co-occurring distribution of other taxa with known salinity ranges (e.g., oysters and native mussels), however, green mussels at least briefly can tolerate significantly lower salinities and appear to have a functional salinity range as great as the eastern oyster, Crassostrea virginica. Various sized green mussels survived 14 days at 10 ppt with less than 10 percent mortality in laboratory studies, which suggests that reduced salinity from coastal estuaries, such as the Suwannee River, probably will not present a biological barrier to the coastal spread of this animal.
Green mussels do not experience their upper thermal tolerances in most of Tampa Bay, but they may do so in shallow embayments exposed to continuous sun and with low flushing rates. Green mussel survival in the laboratory was no different from the control at 30°C, but was significantly reduced at 35°C, and near 100 percent mortality occurred at 40°C over a period of 2-14 days. In the field, green mussels survived water temperatures of 12°C, but intertidal specimens exposed to air temperatures near freezing for a period of hours did not survive. Green mussels exposed to 10°C for 14 days in laboratory experiments experienced less than 50-percent mortality. Field and laboratory data suggest that Georgia will be the northern limit of the green mussel spread on the east coast of the United States for the near future. Some of these data were presented at the annual meeting of the National Shellfisheries Association in New Orleans, LA, April 2003. Tolerance data will be presented at the World Aquaculture/National Shellfisheries Association triennial meeting in Honolulu, HI, March 2004.
Task B. Life History Parameters. Initial settlement in 2002 occurred in early May; settlement in 2003 began in early April. This implies (based on previously published studies) that spawning occurred in late April and late March, respectively, and gametogenesis probably began more than a month prior to that. Histological samples collected during this time have yet to be analyzed to test these estimates. Summer 2003 settlement and recruitment data currently are being analyzed. Tampa Bay green mussels appear to occur in distinct cohorts, based on size distribution. No small (under 10 mm) juveniles were found in early November 2002, but 5-10 mm mussels were still present in late September samples, indicating that significant spawning activity probably had ceased by mid-September. Preliminary analyses indicate that green mussels reach 75-100 mm by their second year, but can live 1-2 years longer and exceed 150 mm in length. A world record specimen (Hutsell, et al., 2001) measuring 171.5 mm in shell length was found in 6 m of water during this study. Growth during the first 6 months post-settlement occasionally exceeded 4 mm per week. Several aging techniques commonly used on bivalve shells have been used for green mussels collected from Tampa Bay. Data from this study may have relevance to other mytilid species.
Task D. Impacts of Green Mussels on Epifaunal Communities. This task is scheduled for 2004, but preliminary findings can be inferred from work completed for other tasks. Green mussels of all sizes are abundant at all depths, and into the lower intertidal on bridge piers and other artificial structures away from the shoreline from the mouth of the bay to around 17 ppt in upper portions of the bay. Densities of large juveniles (greater than 10 mm) and adults can exceed 10,000 m-2, but densities of 1,500-3,000 m-2 are more typical. At or beyond the mouth of the bay, however, distribution of green mussels is more patchy. Green mussels still are almost entirely absent from mangroves, but gradually are becoming more abundant on piers and pilings near shore, relative to initial surveys.
Where they occur, green mussels appear to displace native oysters. Native oysters have a greater tidal range and still occur above green mussels on bridge pilings, but within the zones occupied by green mussels, oysters are rare or occur only as dead shells. Of greater concern are native oyster reefs. At first glance, the reefs appear structurally intact, but a closer look reveals that most of the oysters recently have died (shells still attached to each other), and the living biomass mainly consists of barnacles and green mussels. One-hundred percent of adult oysters in the mid-intertidal were dead, and juvenile densities were significantly reduced compared to a similar reef outside of the green mussel range. Impacts were similar, but less severe, at mean low water. A summary of these results was presented at the 3rd International Marine Bioinvasions Conference in La Jolla, CA, in February 2003.
Task E. Survey of Phytoplankton Potentially Affected by Green Mussels. Phytoplankton abundance in Tampa Bay is spatially and temporally variable. The three sites selected for this study provide a general view of variations of abundance from the mouth of the estuary (TB1) to the inner reaches of Old Tampa Bay (Safety Harbor, TB3). Seasonal mean chlorophyll a concentrations at Site TB3 always exceeded levels at the other two sites by more than twofold (Table 1). Chlorophyll a concentrations at Site TB3 were as high as 54 µg·L-1. Mean chlorophyll levels at Site TB2, in the center of the bay, exceeded levels at Site TB1, but the disparity was not as dramatic as with Site 3. From a temporal perspective, peak phytoplankton standing crops generally were observed in the summer and fall (see Table 1).
Phytoplankton composition of Tampa Bay was dominated by cyanobacteria, diatoms, and dinoflagellates. Picoplanktonic cyanobacteria generally were the most abundant taxa from a numerical perspective (cells/mL). Concentrations of the picoplankton cells were particularly high at Sites TB3 and TB2, particularly in the months of July and September when densities exceeded 1 million cells mL-1. Although picoplankton generally was dominant on a numerical basis, diatoms and dinoflagellates more often were dominant on a biomass basis because of their larger size. Within Safety Harbor, the diatom Skeletonema costatum often was a prominent feature of the phytoplankton community. Small, delicate Pseudonitzschia sp. from the Nitzschia delicatssima complex also widely were observed and may warrant closer examination because of their potential toxicity. Another potentially toxic species, Pyrodinium bahamense var bahamense, was observed at very high concentrations in the summer at Site TB3, but was absent at Site TB1. The phytoplankton community at Site TB1 near the mouth of the bay was characterized by a larger presence of true marine species. Larger diatoms, such as Dactyliosolen fragilissimus and Guinardia striata, often dominated the community from a biomass perspective. The toxic dinoflagellate Karenia (Gymnodynium) brevis was present at TB1, but no bloom was reported during our sampling period.
Season/Year | TB1 | TB2 | TB3 |
Spring '02 | 2.0 (0.8) | 3.8 (1.5) | 8.7 (2.7) |
Summer '02 | 4.6 (1.7) | 5.0 (3.2) | 14.9 (9.1) |
Fall '02 | 5.3 (2.8) | 6.9 (1.8) | 19.0 (15.5) |
Winter '02-'03 | 3.9 (2.1) | 5.6 (1.8) | 6.3 (2.8) |
Spring '03 | 2.4 (1.2) | 5.9 (2.4) | 11.0 (2.1) |
Task F. Feeding Upon Native Phytoplankton by Green Mussels. This project is scheduled for 2004.
Other: Green Mussels on Navigation Buoys. It is the preliminary finding of the U.S. Coast Guard (USCG) (Wayne Danzik, USCG Headquarters, Washington, DC) that green mussels are correlated with an unusual incidence of navigation buoy failure in Tampa Bay. We have conducted preliminary surveys of green mussel density on buoys in cooperation with the USCG, but results are inconclusive pending further research. The USCG has indicated an interest in pursuing the matter, but has not made it a priority. Further research into this matter is on hold pending a USCG decision, because we have allocated no funds from the current project towards this task.
Problems and Issues
Prior issues have been resolved using the steps outlined in the last annual report. Two issues remain: (1) the need for a no-cost extension (Attachment A) because of the unavoidable delays discussed in the prior annual report; and (2) a funding deficit for Task D caused by collaborator losses described in the prior annual report. The cost overruns for Task D are discussed below.
Funding Deficit for Task D. Task D involves the most intensive field efforts of the project because of the requirement for trained scuba divers. In the initial proposal, field research of this nature would be coordinated and conducted by Dr. Marelli, an American Academy of Underwater Sciences (AAUS) certified science diver, then of the Florida Marine Research Institute (FMRI), conveniently located at the project site. Dr. Marelli moved to a different institution, however, and FMRI pulled out of the project (see prior annual report). This left the remainder of the project with two additional costs to absorb: (1) AAUS-certified science divers (salary, training, equipping, and safety costs); and (2) travel (Gainesville to Tampa) and lodging (for up to 16 weeks) for divers and tenders (see Table 2). Savings from other areas of the program were absorbed by the cost of outfitting the primary research vessel for this project (see prior annual report), leaving insufficient funds in the U.S. EPA grant to cover overruns in this area. We have trained University of Florida graduate and undergraduate students as science divers, but student turnover is high because of graduation, and new students must be trained regularly.
Initial estimates put the above funding deficit at about $28,316. Our options are as follows: (1) omit Task D and justify this as the unavoidable consequence of the loss of a key collaborator; (2) apply for a cost extension from the U.S. EPA for Task D, with the same justification as above; and (3) seek external funding to complete Task D. Most granting agencies are unwilling to cover cost overruns of prior projects, so Task D would have to be redesigned as a new project for this purpose.
Future Activities:
Task A. Environmental tolerances of green mussels. Data are being analyzed and prepared for publication and report at the World Aquaculture/National Shellfisheries Association triennial meeting in Honolulu, HI, in March 2004.
Task B. Life history parameters. Histological analysis of preserved specimens will be conducted with the assistance of Dr. Bruce Barber (Eckerd College) in early 2004. A portion of his salary will be paid for by the University of Florida, Department of Fisheries and Aquatic Sciences, in return for his professional expertise in bivalve reproduction and histology related to this project. As mentioned in the last annual report, funds for Dr. Barber are the result of salary-saving negotiations between Dr. Shirley Baker of this project and the University of Florida, and involve no additional costs to this grant. Other aspects of this task are complete.
Task C. Habitats used by green mussels. Data are being analyzed to determine if additional sampling is required. Occasional qualitative surveys to monitor the coastal spread of green mussels still are being performed. Preliminary results were presented at the 3rd International Marine Bioinvasions Conference in La Jolla, CA (February 2003), the National Shellfisheries Association Annual Meeting in New Orleans, LA (April 2003), and the American Malacological Society Annual Conference in Ann Arbor, MI (July 2003).
Task D. Impacts of green mussels on epifaunal communities. Permanent station TB2 has been selected for this study. The primary portion of this study is scheduled for May-September 2004, contingent upon funding (see Problems and Issues, above).
Task E. Survey of phytoplankton potentially affected by green mussels. Sampling is complete and analyses will continue as outlined in the project proposal. This portion of the project is designed to support Task F, and results of these tasks will be combined.
Task F. Feeding upon native phytoplankton by green mussels. This part of the project will use resources purchased for the green mussel environmental tolerance studies (Task A) that have been completed. Feeding studies will begin in early 2004 at Mote Marine Laboratory in Sarasota, FL. Laboratory space has been donated to facilitate completion of these experiments.
The unexpected finding that blooms of the nuisance dinoflagellate Karenia (Gymnodynium) brevis apparently are correlated with high mortalities of green mussels introduces a new component to green mussel ecology in Florida. Our current proposal is not designed to examine this issue, but we are seeking additional collaborators and funding to address this possibility.
Journal Articles:
No journal articles submitted with this report: View all 13 publications for this projectSupplemental Keywords:
marine, estuary, ecological effects, population, stressor, diet, ecology, surveys, Southeast, Florida, FL, ecosystem protection, environmental exposure, risk, geographic area, scientific discipline, biochemistry, chemical mixtures, human health, ecological indicators, ecological risk assessment, ecology and ecosystems, ecosystem, exploratory research, environmental biology, estuaries, biodiversity, biopollution, conservation, ecological dynamics, ecological exposure, ecological pollutants, emerging environmental problems, futures research, green mussel, green mussel infestation, marine ecology, phytoplankton., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Ecological Effects - Environmental Exposure & Risk, Monitoring/Modeling, Biochemistry, Southeast, Ecological Risk Assessment, Exp. Research/future, Futures, emerging environmental problems, ecological effects, ecological exposure, biodiversity, Southeastern Estuaries, stressors, green mussel, marine ecology, biopollution, conservation, phytoplankton, exploratory research, ecological pollutants, green mussel infestation, ecological dynamics, Florida, futures researchRelevant Websites:
http://fishweb.ifas.ufl.edu/ Exit
http://www.floridamarine.org/features/ Exit
http://greenmussel.ifas.ufl.edu/ Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.