Methods to control bio-fouling of cultured eastern oysters, Crassostrea virginica, by the tube-building polychaete worm, Polydora cornuta

Methods to control bio-fouling of cultured eastern oysters, Crassostrea virginica, by the tube-building polychaete worm, Polydora cornuta

Summary

Oyster farms in the northeastern US are plagued by biofouling caused by marine polychaetes belonging to the genus Polydora. Generally referred to as mud-worms, these ubiquitous polydorid worms can kill oysters, reduce oyster growth, fragment the oyster’s shells making them difficult to shuck, and cause internal shell blisters that decrease product appeal and marketability. Oyster farmers invest an extensive amount of time and resources to control infestations, significantly reducing farm profits. The purpose of this project was to develop efficient and effective methods for control of Polydora infestation in eastern oysters. Two control methods, hypersaline dips and lime dips, which have been used with success to control similar infestations in Pacific oysters grown in Mexico and Australia, were used and evaluated for efficacy in controlling Polydora infestations at an oyster farm in Delaware Bay, NJ. The lime dip was discontinued after several weeks and replaced with a freshwater dip.
Life history aspects of the worm, including seasonal planktonic abundance and settlement patterns, were be investigated to establish treatment regimes that target the worm at the onset of infestation.

Objectives/Performance Targets

1. To evaluate the effectiveness of time targeted hypersaline and lime dip treatments as a control for P. cornuta. Freshwater dips replaced the lime dip to test for better efficacy of cleaning oysters as the lime dip showed no effect within the first weeks of treatment.
2. Conduct plankton and settlement surveys to determine temporal variability in abundances of Polydora cornuta larvae and peak settlement periods to inform and improve the efficacy of treatment timing and options.

Accomplishments/Milestones

None of the treatments tested performed better than the standard method of cleaning oysters. The standard, which is currently used by oyster farmers in Delaware Bay, is pumping bay water over the oyster bags to wash off the accumulated Polydora mud packs. We sampled the wash water coming off the oyster bags and determined that no polydora were killed by the pressure wash but were swimming intact and presumably would resettle easliy and promptly.
The natural history portion of this project is showing some interesting results and may lead to better efforts at treatment in the future. Plankton surverys showed spikes in larval Polydora every four weeks coinciding with full moon. Early season plankton peaks were quite high which suggests that overwintering populations and eggs are significant. Treatment during the winter or very early sping might be most effective at reducing Polydora populations. This effect could possibly slow the onset of heavy summer fouling.

• larvae graph
• Treatment Comparison

Impacts and Contributions/Outcomes

The early peaks in polydora larvae indicate that overwintering popluations may be fecund. Treatment which targets this overwintering population during cold months (when farmers are generally not as busy) could be effective at reducing the Polydora population. This could possibly slow the onset of heavy summer fouling.
We are submitting an abstract tomorrow to the National Shellfisheries Assoc. to present a paper in Jacksonville, FL in March, 2014. We may also be subitting a poster for the  Milford Aquaculture Seminar  (CT) in February, 2014.

Collaborators: