Grantee Research Project Results
2007 Progress Report: Potential Transport of Harmful Algae through Relocation of Bivalve Molluscs
EPA Grant Number: R831704Title: Potential Transport of Harmful Algae through Relocation of Bivalve Molluscs
Investigators: Shumway, Sandra E. , Wikfors, Gary H. , Burkholder, Joann M.
Current Investigators: Shumway, Sandra E. , Joann, Burkholder , Gary H, Wikfors
Institution: University of Connecticut , National Oceanic and Atmospheric Administration , North Carolina State University
Current Institution: University of Connecticut , NOAA-NMFS , North Carolina State University
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2003 through September 1, 2007 (Extended to December 31, 2008)
Project Period Covered by this Report: January 1, 2007 through December 31,2007
Project Amount: $477,526
RFA: Ecology and Oceanography of Harmful Algal Blooms (2004) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water
Objective:
Our primary objectives are to:
- Determine which algal species (harmful and potentially harmful) pass intact and viable through the digestive tract of commercially-important bivalve molluscs.
We have completed screening of many interactions between species of bivalve mollusc/ HAB that potentially can occur in the natural environment. Our results show that cells of most HABs are able to pass intact through the digestive tract of most of the bivalve species studied, with the exception of Mya arenaria, for which no intact cells of the HABs tested was present in biodeposits.
- Determine the extent to which washing and purging shellfish intended for transfer can slow or eradicate the potential transfer of a suite of HAB species.
In this study we demonstrated the risk of transfer of harmful algae associated withi movement of bivalve molluscs. We also showed that a “depuration” period of 24 h in filtered seawater (FSW) mitigates the risk of transplanting an HAB into new areas. This study further shows that a 24-hour period holding the shellfish out of the water, for species that can survive this treatment (mussels, oysters, hard clams), or 6 hours depuration time in the water for bay scallops, are also ways to mitigate the risk of transfer of HAB from within the shells of bivalves into new areas.
- Determine when bivalves are safe to transport following exposure to specific HAB species by measuring rates of uptake, gut residence time, and elimination of HAB species fed to the molluscs, i.e. establish the time period for which particular shellfish/algal interactions remain capable of inoculating new areas.
As noted in the last report, softshell clams Mya arenaria do not seem to present a risk of serving as vectors transporting HABs into new areas, as no intact HAB cells were found in their biodeposits.
The other interactions present a higher risk of transfer. Indeed, in the first 24h of “depuration” in seawater, the risk of transferring harmful algae is high; however, after more than 24h in seawater, the risk is highly limited, but still present. Additional studies assessed the possibility that a period of time holding the shellfish out of the water could be a way to limit the risk as well. Results indicate that holding mussels, hard clams and oysters out of water, after exposure to Prorocentrum minimum and Heterosigma akashiwo, essentially eliminates the risk of introduction of these harmful algae into a new environment upon re-immersion of the shellfish. Moreover, for scallops, which cannot be held out of the water for a long period of time, a “depuration” period of 6h in seawater also seems to mitigate the risk of transport of harmful algae into new environments.
- Sample target shellfish species during an ongoing bloom event(s) (if the opportunity presents itself) and assess viability of cells after gut passage.
As with our lab studies, results suggest that the harmful algae are not able to recover from the biodeposits after the animals, exposed to natural HAB, have been shipped overnight and transferred back into seawater. Opportunities were presented with several species of bivalve molluscs and the harmful algae Alexandrium spp, Karenia brevis, and Prorocentrum minimum. The bivalves shipped overnight and transferred back into seawater did not release apparently-viable HAB cells. These results are now confirmed by the findings of this year’s laboratory experiments demonstrating that 24h out of the water is a good way to mitigate the risk of introduction of new harmful algae into new environment.
- Provide information to the user groups through presentations, management agencies, trade publications, pamphlets, and WEB pages
See below
Absence or changes of key personnel involved in the project
The project was completed on time.
Approach:
We will address these questions using standard laboratory techniques and well-established experimental protocols to determine rates of uptake, retention, and elimination of toxic cells/cysts, as well as excystment and release from fecal strands and the subsequent culture of viable cells. In collaboration with industry we will design, apply, and evaluate management strategies and BMPs.
Progress Summary:
Discussion of the expenditures to date along with a comparison of the percentage of the project completed to the project schedule
The project was completed on time. We have completed screening of many of the interactions between bivalve molluscs and HAB species that occur in the natural environment. Samples of target shellfish species have also been collected during ongoing bloom events and analysed for intact cells in the biodeposits, and for their ability to recover after gut passage. We have also assessed the ability of harmful algae to recover from biodeposits of bivalves after the animals were held in or out of the water for several periods of time and determined some ways to mitigate the risk of introduction of harmful algae into new environments. Finally, as bivalve seed (juveniles) were produced, we tested the ability of the harmful algal cells to recover from the biodeposits of the seeds, to be able to assess the potential risk of transfer of harmful algae into new environment following shipment of seed.
Statement addressing how the quality assurance requirements and agreement are being met
Data generated by this study are mainly not environmental measurements, per se, but rather measurements and observations from laboratory experiments. Data files are acquired either directly from instruments (flow-cytometer), or recorded manually, on paper, before entry into spreadsheet or text files (qualitative microscope observations). Microscope observations are documented with digital-image files generated by a PC-based photomicrograph acquisition and analysis system. All original, digital files (data and images) are archived on a NOAA LAN (Milford Laboratory) that is backed up to digital tape daily. Hand-written observations and notes are recorded in a laboratory notebook maintained by the graduate student specifically for the grant and kept in a secure location (US Government facility with card-access and 24-hour video surveillance). Hand-written observations and documentation of procedures are entered into spreadsheet or text files and maintained on the LAN. The daily LAN back-up achieves archive redundancy, in that at least three copies of the network contents exist at any given time. Short-term redundancy (should the LAN fail with the current day’s updates) is achieved by maintaining copies of data files on individual PC hard drives until at least one LAN back up. Access to files archived on the LAN server is password-protected, and all individuals with network privileges are required to pass an annual network-security exam.
Results to date, emphasizing findings, their significance to the field, their relationship to general goals of the award, their relevance to the Agency’s mission, and their potential practical applications
Laboratory experiments - Experimental Bivalves and Algae and Experimental design: Presence of intact cells in the biodeposits of bivalves and recovery of harmful algal cells after gut passage
Six microalgal taxa were tested thus far; these are common components of the phytoplankton community in shellfish-growing waters: Prorocentrum minimum, Heterosigma akashiwo, Karenia mikmotoi and Aureococcus anophagefferens are known to be ichthyotoxic (Landsberg 2002), and Alexandrium fundyense and Alexandrium monilatum have been shown to affect the physiology of bivalves that accumulate paralytic shellfish toxins from ingesting it (Shumway and co-workers; Pate 2006). Species of bivalves tested are all fished and cultured or ecologically important on the east coast of the USA: eastern oysters Crassostrea virginica; northern quahogs (= hard clams) Mercenaria mercenaria, softshell clams Mya arenaria, blue mussels Mytilus edulis, green mussels Perna viridis and northern bay scallops Argopecten irradians irradians. Also included in this study is the HAB species, Karenia mikimotoi, which is a common phytoplankter of the coast of Brittany, France; it can bloom in locations where the clam Ruditapes philippinarum or mussel Mytilus edulis are harvested. Thus, interactions between the selected shellfish and microalgal species are very likely to occur and have been observed in the past. Moreover, all the shellfish species from the US east coast or the French coast that we studied are regularly moved from one body of water to another as part of routine management.
To assess the presence of intact harmful algal cells and their recovery from biodeposits of bivalves, 10 individual bivalves were held for 48 h in FSW, to depurate previously-consumed algae and become conditioned to the experimental conditions. Conditioned shellfish then were transferred to an 80-L basin containing a cultured HAB strain at a natural bloom concentration for 48 additional hours. After 2 days in the HAB, the shellfish were transferred to individual, 3-liter containers of FSW for 24 h, followed by an additional transfer to new FSW for 24 h. Parallel experiments have been conducted, where, after 2 days in the HAB, the shellfish were left out of the water for 24 h, before being transferred to individual, 3-liter containers of FSW for an additional 24 h. Feces were collected for microscopic observations, to allow determination of whether or not intact cells were able to pass though the digestive systems of bivalves and be released after the animals had been removed from the bloom for 24 or 48 h, or after 24 h out of the water followed by re-emersion in FSW. To determine the potential for any intact cells in biodeposits to re-establish viable algal populations, 500-μl sub-samples of fecal slurry produced after 24 and 48 h in FSW or 24 h out of the water and re-emersion, were collected from each individual basin, mixed by vortex, and inoculated into test tubes containing 1) 5 ml of FSW or 2) the culture medium in which the harmful alga was grown. The tubes were observed periodically with an inverted, light microscope to assess recovery of motile, vegetative populations from fecal sources.
Intact cells in the biodeposits after 24 and 48 h in FSW or after 24 h out of the water before re-emersion were observed in most of the bivalves, with the exception of softshell clam Mya arenaria (not tested out of the water). Tables 1A and B summarize observations of intact cells in the biodeposits of each bivalve species exposed to each harmful-algal culture after 24 and 48 h of depuration in FSW. Most tubes inoculated with fecal slurry showed growth of the harmful algae from the biodeposits collected during the first 24 h of depuration, but almost never after more than 24 h (Table 2A and 2B). Table 3 summarizes the results of the recovery and growth of the harmful algae from the biodeposits collected after 24 h out of the water and re-emersion.
The results from the laboratory experiments clearly demonstrate that transplanted bivalve molluscs can serve as vectors for introduction of harmful algae. This risk is widespread among the bivalve-HAB combinations tested, though not identical for all combinations. Species specific shellfish/HAB interactions need to be considered in management, restoration, and aquaculture activities for which shellfish are transplanted. A 24-h depuration period in seawater or out of water seems to mitigate the risk of harmful algae introduction via movement of bivalve shellfish.
To assess the presence of intact harmful algal cells and their recovery from biodeposits of small, seed-sized bivalves (1-3mm), 1,000 individual bivalves were held for 48 h in an 80-L basin containing a cultured HAB strain at a natural bloom concentration. After 2 days in the simulated HAB, 4,000 seed were rinsed once with FSW, to simulate the rinsing seed could undergo in hatcheries, and transferred into 4 replicate (1,000 seed per replicate maintained in downwellers), 3-liter containers of FSW for 24 h, followed by an additional transfer to new FSW for an additional 24 h.
To determine the potential for any harmful algal cells to re-establish viable algal populations, 500-μl samples of water were taken every week for 2 months and examined microscopically. Results indicated that no harmful algae grew back in the tanks after transfer of seed into FSW, suggesting that the movement of seed may not carry high risk of introduction of harmful algae into new areas. These results, however, must be interpreted very carefully, as the seeds were rinsed with FSW before being transferred, which may not be the case in every hatchery. Further investigation may be needed to assess best management practices to transport of bivalve seed.
Field experiments: Presence of intact cells in the biodeposits of bivalves naturally exposed to harmful algae during an natural bloom and recovery of harmful algal cells after gut passage
Some experiments simulating holding and shipping were also carried out. Bivalve molluscs that had been exposed to harmful algal blooms were sent to the Milford laboratory by FedEx overnight to simulate regular shipping practices, and were transferred into individual basins containing FSW for 24 and 48 h. Similarly to the laboratory exposure, biodeposits were microscopically observed and cultured in test tubes. Between May and June 05, we received bivalves, including oysters, blue mussels, razor clams, northern quahogs and softshell clams, which had been exposed to an exceptionally large Alexandrium spp. bloom, which occurred northeast coast of the US, from Maine to Massachusetts. Similarly, we received green mussels, Perna viridis, from Florida, exposed to a bloom of Karenia brevis, andoysters Crassostrea virginica and Crassostrea ariakensis exposed to a bloom of Prorocentrum minimum in Maryland. Intact cells were present in the biodeposits of most of the bivalves received by FedEx and naturally exposed to a HAB. Alexandrium sp. and Prorocentrum minimum cells were able to pass intact through the guts of bivalve shellfish. However, the cells did not appear to recover in the test tubes. Thus, after a shipment period of 24h, harmful algal cells, even though they were still present and intact in the biodeposits, did not reform blooms in the tubes. These findings confirm that a period of 24h if the bivalves are held out of the water mitigates the risk for bivalve shellfish from being vectors of transport of harmful algae from one body of water to another.
Conclusion:
The results of this study show that the majority of the bivalve shellfish species tested clear their guts or otherwise kill consumed microalgal cells within 24 h in or out of the water and do not thereafter readily serve as vectors transporting ingested harmful algae. Mitigation of the risk of transport of harmful algal blooms into new areas by keeping the shellfish out of the water for 24 h represents a very important fact, as most of the shellfish are shipped or transported overnight via mail or FedEx and, therefore, are held out of the water for a long period of time. This indicates that the risk of introducing new harmful algal blooms is often reduced in common practice. In contrast, relay and local transplant operations, or local sales of freshly-harvested shellfish to consumers with shoreline homes, wherein harvest and re-release may be accomplished in one day still present a risk. Fortunately, this risk can be mitigated by delaying re-planting for one day.
Information was provided to the user groups through presentations at scientific and professional meetings and at management agencies, which have been emphasized. Scientific articles and pamphlets have already been accepted or published; additional products will arise from this grant, to enhance education and provide information to user groups.
Expected Results:
This research will be valuable to aquaculturists, watermen, processors, and managers for public health, and will assist in both habitat management and preservation of habitat integrity. Understanding the vectors for transfer of HAB species is critical to responsible environmental stewardship. This study specifically addresses special emphasis areas 1 and 4(b)–prevention and mitigation strategies, and the sources, fates, and consequences of HABs in food webs and fisheries. Results from this study will ensure that the user groups are provided the most current information available, in a useable format, to control and mitigate impacts of HABs on public health, shellfish aquaculture, and the environment.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 41 publications | 8 publications in selected types | All 8 journal articles |
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Hegaret H, Wikfors GH, Shumway SE. Diverse feeding responses of five species of bivalve mollusc when exposed to three species of harmful algae. Journal of Shellfish Research 2007;26(2):549-559. |
R831704 (2007) R831704 (Final) |
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Hegaret H, Wikfors GH, Soudant P, Lambert C, Shumway SE, Berard JB, Lassus P. Toxic dinoflagellates (Alexandrium fundyense and A. catenella) have minimal apparent effects on oyster hemocytes. Marine Biology 2007;152(2):441-447. |
R831704 (2007) R831704 (Final) |
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Hegaret H, da Silva PM, Wikfors GH, Lambert C, De Bettignies T, Shumway SE, Soudant P. Hemocyte responses of Manila clams, Ruditapes philippinarum, with varying parasite, Perkinsus olseni, severity to toxic-algal exposures. Aquatic Toxicology 2007;84(4):469-479. |
R831704 (2007) R831704 (Final) |
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Supplemental Keywords:
RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Health Risk Assessment, Oceanography, algal blooms, Environmental Monitoring, Ecological Risk Assessment, marine ecosystem, shellfish transport, bloom dynamics, algal bloom detectionProgress 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.