In this project we have worked with three Maine oyster farms testing methods that reduce the initial colonization of oysters by blister worm. More intensive research has continued at one farm where blister worm has been particularly problematic; this additional work is supporting a more detailed 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 on-going work has been hampered by the presence of the larvae of closely related species of polychaete that makes visual identification extremely difficult.
We have also made progress on the education goals in our project. We collected responses to our survey on blister worm presence and impacts through December 2016 and presented an initial report on the results at two conferences, regularly attended by industry members, in early 2017. Based on feedback received we have modified our analysis of the survey data, drafted a full report on the survey data, and are awaiting reviews on the draft. As soon as the reviews are received we will distribute the results to the industry, at-large. As part of this survey we have learned that participants are most interested in either email communication of information on blister worm and pest management solutions or regional workshops/growers’ meetings where there is an opportunity to thoroughly discuss blister worm biology and best management plans. Thus, to date most of our farmer learning and adoption outcomes stem from individual email conversations or individual farm visits. However, given participant input we are organizing regional workshops on blister worm and BMP development for late winter/early spring 2018 in advance of the next growing season.
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.
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.
Blister worm burrows will be substantially reduced in oysters that receive preventative treatments compared to oysters grown in standard surface cages without preventative treatments.
Blister worm burrows will be substantially reduced in oysters that receive preventative treatments once a week compared to those that receive treatments less frequently.
Blister worm burrows will be substantially reduced in oysters receive combined air-drying and pressure washing treatments compared to those that receive only single treatments.
Oysters without infesting blister worm have been deployed in cages at standard culture densities (1000 per cage) at oyster farms in Maine. In 2014 we worked with a single farm and in 2015 we had the opportunity to expand to two additional farms, each located on a different estuary/river. At each site, we included five treatment combinations; control – no preventative treatment in which oysters were deployed in surface bags and continually submerged; air-drying for 6h (or till surface of oysters dry) once every week, air-drying for 6h once every other week, air-drying and pressure washing every week, and air-drying and pressure washing every other week. Our three grower-participants were responsible for regular application of treatments and we visited the sites every other week to collect 5 oysters from replicate bags within each treatment type. The oysters were returned to the University of Maine where they were shucked and the internal and external shell surfaces of each oyster will be examined for the presence of settled worms and burrows.To assess impact on the oysters themselves, we have monitored average shell dimensions for each replicate sample. In a follow-up experiment we deployed a cohort of oysters in each treatment at a single farm on the central coast of Maine and tracked blister worm settlement over a two-year period and survival of blister worm as a function of overwintering treatment. For the latter, oysters were either overwintered on the bottom of the river or held in cold-dry storage (on land).
During the 2014 and 2015 seasons, we used plankton nets to determine the seasonal variation in abundance of larval blister worms at each site each time we visited to collect oysters for the work described, above. The plankton samples were preserved in 70% ethanol and returned to the University of Maine for processing. We sampled polydorid larvae from these tows based on morphological descriptions available in the scientific literature and employed a polymerase chain reaction-based assay to confirm or species identifications.
As part of our work, we received information from oyster growers of burrowing polychaetes that did not fit the typical description of our target species, Polydora websteri. We conducted both morphological and molecular analyses to identify these worms. For the latter, we extracted DNA from these atypical worms (provided by the growers) and amplified and sequenced a portion of the nuclear 18S rRNA and mitochondrial COX1 genes using PCR-based approaches and compared the resulting sequences to polydorid sequences on public databases.
The application of air-drying and air-drying with washing treatments had a significant impact on the appearance of new blister worm burrows. This effect was particularly strong and consistent over multiple growing seasons at one farm in our research program. At this farm, treated oysters had, on average, 1-2 few blister worm burrows per oyster while control oysters had an order of magnitude higher level of infestation. Blister worm settlement at this farm was highly seasonal with most new burrows appearing in late July and August. However, we found that the level of pest reduction and the efficacy of preventative treatments was both farm specific and highly dependent on when the treatments were applied relative to weather patterns. Analysis of the final two year deployment testing for overwintering effects is on-going. Preliminary analysis suggests that oysters placed on the bottom of the river in winter (to avoid ice) end up with higher levels of blister worm infestation at the completion of a two year grow-out cycle.
Despite our observation that the appearance of new blister worm burrows occurs over a fairly consistent time frame we found no correlation of the appearance of burrows with changes in the abundance of larvae. Early and late stage polydorid larvae were highly abundant in plankton tows from May through late June. However, over 95% of these larvae belonged to a congener, P. cornuta, which will form surface tubes on oysters but does not burrow into the shell. Larval abundance declined as the season progressed and we found almost no late stage polydorid larvae in tows taken in late July and August when new burrows typically appear. This result was unexpected given reports from other parts of the world on the timing of reproduction and settlement in various blister worm species. These results suggest that monitoring for larval abundance in order to predict when settlement prevention treatments are needed is not straightforward and farmers will likely have to apply preventative treatments throughout the growing season.
Our morphological and molecular analyses identified three distinct species of blister worm. In addition to P. websteri we also identified P. haswelli and P. onagawaensis. The latter two have not been reported on farms in the U.S. before, although P. haswelli may be confused with a species described as P. neocaeca. Although the burrows of these three species differ, we do not know whether the preventative treatments we have applied at farms where P. websteri are common will address blister worm infestations at sites where the other species occur.
As part of our educational approach, we have distributed a survey assessing the impact of blister worm on Northeast oyster farms (Maine to Virginia but also adopted by colleagues in Gulf Coast states) that includes an invitation to participate in our workshops and on-site demonstrations of methods developed during research project. The survey was distributed via the list-server of the East Coast Shellfish Growers Association which boasts over 1000 members. We received 56 completed responses and have completed a draft report (sent for independent review); the results encapsulated in this report will be disseminated to industry members via the ECSGA list-server and by other electronic means. Our education program has and will utilize multiple avenues of communication and instruction. We presented results from our research and information from the blister worm survey to growers and members of the scientific community at the Northeastern Aquaculture Conference and Exposition in January 2017 and the National Shellfisheries Association Annual Meeting in March 2017. In 2018, we will convene blister worm workshops at two regional shellfish meetings regularly attended by many of the region’s growers. At these workshops we will discuss what is currently known about blister worm, risks and benefits of treatments, and project results. Participating growers will demonstrate blister worm treatments using video and still images. Our goal in these workshops is to facilitate detailed discussions among growers about blister worm and assist in the production of best management plans. In addition, we have produced a FACT SHEET (2016) on blister worm that was disseminated through the East Coast Shellfish Growers list server and posted on the Maine Sea Grant Shellfish Aquaculture webpage.
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.
Survey was distributed to industry members although implementation was delayed while we addressed concerns expressed by external reviewers of a draft of the survey and completed IRB clearance/certification.
Oyster growers return survey and express interesting in joining education program.
We received 56 completed surveys as of December 31, 2016. All respondents indicated an interest in blister worm education program with 37 expressing a high level of interest.
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.
Together with direct industry participation, 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.
Given the delay in implementation of our survey, we did not compile our education program participant list until December 2016. We had intended to begin regular email communication in 2017 starting with dissemination of the survey results. However, we just completed the draft report of the survey and have just initiated our communication efforts.
Farmers (industry participants) 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.
The Milford Aquaculture Seminar has been combined with the Northeastern Aquaculture Conference and Exposition (NACE). We presented the results of our field research and our online survey on blister worm at the NACE meeting in January 2017. We also presented our work at the Annual Meeting of the National Shellfisheries Association in March 2017.
Second year of activities testing preventative treatments for blister worm established at two oyster farms in Maine.
We initiated an additional experiment at one farm in Maine in May 2016. This 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. This work included overwintering trials and continued monitoring of blister worm through the 2017 growing season at the request of the participating farmer.
Fact Sheet on blister worm biology, reproduction, and population dynamics, and preventative treatments for blister worm distributed to members of the East Coast Shellfish Growers Association.
Fact Sheet posted September 2015. Link to Fact Sheet on Maine Sea Grant Aquaculture webpage accompanied the 2016 report.
Farmers attend site visit at either of our two grower-participant farms to receive hands on training in blister worm prevention.
Based on attendance at the NACE presentation in January 2017, we still expect to reach at least 60 growers in the education component of our project. However, given survey responses we feel that farmers are more likely to attend and participate in workshops held in conjunction with local or regional growers meetings than at scientific meetings. Thus, in 2018 we will hold blister worm workshops at regular regional growers meetings.
Additional farmers will 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.
We will present a second workshop at NACE. However, NACE is only held every other year so we will not be able to conduct this workshop until December 2018 or January 2019, depending on the timing of the conference.
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.
While we have discussed approaches to minimizing blister worm impacts with several (5-6) farmers in person and on-line, including oyster farmers in Hawaii, we will not be able to fully realize this milestone until we conduct the shellfish growers’ workshops described in previous milestones during 2018.
Milestone Activities and Participation Summary
Adoption of best management plans for blister worm: Farmers who have used methods identified in this project as reducing blister worm abundance (i.e., treatments for adult worms) – 4; method – direct contact.
Farmers who have adopted methods for reducing settlement of new blister worm – 1; method – direct contact.
Performance Target Outcomes
Develop, adapt and adopt best management protocols resulting in reduction of blister worm impacts on market viability of oysters
Up to $4 million in aggregate sales could be impacted by lost sales.
Reduction in pest prevalence and incidence will result in improved crop quality.
Farmer began using Oyster-Gro cage systems for regular drying of oysters to reduce impact of not only blister worm but other shell-fouling species.
Cannot be ascertained at present.
Single farmer adopting system to date has reported highly reduced level of blister worm infestation.