Best management practices for the control of blister worm on oyster farms
Blister worm is a polychaete worm that burrows into the shells of oysters; infestations create visible pockets or blisters of mud and fecal waste on the inside surface of the oyster shell. These blisters mar the oyster’s appearance when served on the half-shell and breakage of the blisters can result in off-flavors; both may seriously undermine the market value of oysters from an impacted farm.
Our research and education program targets the onset of pest infestation to eliminate the need for costly and ineffective treatment of infested oysters. We have worked with three Maine oyster farms testing methods that reduce the initial colonization of oysters by blister worm. When we tested our preventative methods in previous years, the number of settling blister worms was relatively low; during the current reporting period we repeated our treatments at one farm where blister worm settlement was over an order of magnitude higher than in previous years. This additional deployment is facilitating an analysis of the efficacy of our methods as a function of seasonal and annual levels of pest pressure.
We have continued with our efforts to develop approaches to help farmers ascertain when blister worm larvae are present and ready to settle. This work has been hampered by the presence of the larvae of closely related species of polychaete that makes visual identification extremely difficult. During the reporting period, we successfully distributed a survey on blister worm and impacts to shellfish growers from Maine to Virginia. The survey returns were modest and we are currently compiling and analyzing the responses we received. We presented the results of our field research at the annual meeting of the National Shellfisheries Association in Las Vegas in February 2016; as part of this presentation we networked with researchers investigating blister worm in other regions of the U.S. and worldwide, which will allow us to better incorporate their experiences with this pest in our education efforts.
Twenty northeastern oyster farms with annual aggregate sales of about $4 million will each implement a comprehensive polychaete pest management plan. This will reduce pest prevalence and improve crop quality compared to prior years, avoiding an estimated $4 million aggregate loss in annual sales.
- 1000 members of the East Coast Shellfish Growers Association receive updated online survey on the impact, prevalence and distribution of blister worm and invitation to participate in blister worm education program. COMPLETED: Our survey was distributed in August/September 2016; implementation was delayed while we addressed concerns expressed by reviewers of our initial drafts of the survey and received IRB clearance.
- 100 oyster growers return survey (10% return rate), and 80 express interesting in joining education program. NEARING COMPLETION: We received 54 completed surveys as of late October 2016. Analysis and full reporting of survey responses will be completed by April 2017.
- Research component of project testing preventative treatments for blister worm established at two oyster farms in Maine. Workers at these farms receive training in monitoring for blister worm larval abundance (plankton sampling), settlement, and reproduction. COMPLETED: We conducted field research on preventative treatments at three Maine farms between May and November 2015.
- Participants in blister worm education program receive regular email/blog updates on project progress and efficacy of preventative treatments. IN PROGRESS: given the delay in implementation of our survey, we did not compile our education program participant list until October 2016. The vast majority of participants indicated interest in receiving email updates. We will be communicating current research results to survey participants by direct email in January 2017, then posting quarterly reports thereafter.
- 40 farmers attend first workshop at the Milford Aquaculture Seminar on blister worm biology, reproduction and settlement, receive update of project goals and progress and begin development of best management plans for blister worm prevention. IN PROGRESS: (The Milford Aquaculture Seminar has been combined with the Northeastern Aquaculture Conference and Exposition [NACE]). We will be presenting results of our field research and our online survey on blister worm at the upcoming NACE meeting in January 2017. Given survey responses, however, it appears that farmers are more likely to attend and participate in workshops held in conjunction with local or regional growers meetings than at scientific meetings such as NACE. Thus we plan to shift the focus of our education program from workshops at NACE and farm visits to workshops held as part of regular growers meetings.
- Second year of activities testing preventative treatments for blister worm established at two oyster farms in Maine. IN PROGRESS: We initiated a second year of testing at one farm in Maine in May 2016. Our e 2016 work was conducted at only one of the three farms because one of the three original farms adopted the preventative treatments while the third could not obtain unaffected oysters for an additional trial. We reported on our 2015 results in February 2016 and expect to complete analyses and distribute a full report on our field work by March 2017.
- Fact Sheet on blister worm biology, reproduction, and population dynamics, and preventative treatments for blister worm distributed to 1000 members of the East Coast Shellfish Growers Association. COMPLETED: Fact Sheet posted September 2015.
- 60 farmers attend site visit at either of our two grower-participant farms to receive hands on training in blister worm prevention. MODIFIED: See #5 above. We will still expect to reach 60-80 growers but will use local and regional growers meetings to present information on blister worm and potential treatments in the late spring of 2017.
- Additional 40 farmers attend second workshop at the Northeastern Aquaculture Conference and Exposition on blister worm biology, reproduction and settlement, receive update of project goals and progress and begin development of best management plans for blister worm prevention. MODIFIED: We plan to conduct a second round of discussion at local and regional growers meeting in the fall of 2017 to being the development of best management plans.
- Twenty farmers utilize educational opportunities, outreach materials or site visits to develop, adapt and adopt best management protocols resulting in reduction of blister worm impacts on market viability of oysters. PLANNED: We will review and work with farmers to share BMPs by late November 2017.
Impacts and Contributions/Outcomes
The research portion of our project was originally targeted for two oyster farms in Maine that have been impacted repeatedly by blister worm. In 2015, we had the opportunity to expand to a third farm, with each farm located on a different estuary/river, providing us with increased replication and the ability to assess whether the same types of treatments work well in different waters. We found that the efficacy of preventative treatments was highly dependent on when the treatments were applied relative to weather patterns. We also noted that worm settlement and overall levels of infestation were low in our initial deployment. Thus, we repeated the treatments in 2016. However, one the three farms adopted the preventative treatments while the third could not obtain unaffected oysters for an additional trial and so our work in 2016 was conducted at only one farm. We reported on our 2015 results in February 2016 and expect to complete analyses and distribute full project results by March 2017.
We also saw significant progress on the education portion of our project. In addition to the FACT SHEET on blister worm that we developed and posted in 2015, we distributed a survey on blister worm to growers from Maine to Virginia. Distribution of the survey was delayed for several reasons, but the response was enthusiastic. Over 50% of the respondents were oyster farmers in Maine or Massachusetts. We expanded our coverage area to include Maryland and Virginia at the request of growers in those two states, although returns from those states were light. All respondents expressed interest in continued education on blister worm. We have used the responses to build our education program participant list and will soon distribute our first of several blister worm education emails. The vast majority of respondents indicated that email distribution of written updates would be an effective mode of communication. Approximately 50% of respondents indicated that discussions and training programs presented at regional growers meetings would also be an effective means of education. Over 80% of respondents are eager to hear more about effective treatments and over 50% would like to learn more about the biology of the pest. Given these responses we are modifying our education program; it appears that our education program participants are more likely to attend and participate in workshops held in conjunction with local or regional growers meetings than at scientific meetings. We are also concerned about the logistics associated with travel to individual oyster farms for farm visits. Thus, we plan to shift the focus of our education program from workshops at NACE and farm visits to workshops held as part of regular growers meetings. We have also been invited to communicate our survey results through the National Shellfisheries Association Quarterly Newsletter and have teamed up with researchers from other regions of the U.S. and worldwide to share information and so we may better incorporate their experiences with this pest in our education efforts. We fully expect to reach at least 60-80 farms, as farms outside of our education program will also attend regional growers meetings. We are still on track to work with growers to develop preventative treatments and best management plans for blister worm by the end of 2017.
Sea Grant Extension Officer
Maine Sea Grant Program
Darling Marine Center
193 Clarks Cove Rd
Walpole, ME 04573
Office Phone: 2075638386
University of Maine
5751 Murray Hall
Orono, ME 04469-5751
Office Phone: 2075814326