Mud worms. Not the most appetizing name for a critter, and it turns out they are a real problem for the new ‘off-bottom’ oyster farmers in the Gulf of Mexico. Luckily for oyster lovers, mud worms live on the outside of the shell, so they aren’t a problem when eating oysters. Instead, these worms burrow into the shells of the oysters to make a home, leaving dark ‘blisters’ on the shells, weakening the shells and, possibly, making the oyster spend energy walling off these intruders instead of getting fat and plump.
Off-bottom oyster farming, focused on the premium, half shell market, is relatively new on the Gulf Coast, where oyster farmers raise small oysters (‘seed’) in baskets or bags up off the seafloor bottom, where they can feed on the microscopic plants in the water, safe(r) from predators and burial. They are, however, still vulnerable to being overgrown by barnacles, mussels, and mud worms, among other things.
In a research project funded by Mississippi-Alabama Sea Grant Consortium, I am working with colleagues from the Dauphin Island Sea Lab, Dr. Kelly Dorgan and Sarah Cole, to study different means of managing mud worms on oyster farms. To complement this ongoing work, Charlotte Shade, an undergraduate at the University of Dayton and a National Science Foundation Research Experience for Undergraduates participant, conducted a test of two common farming techniques to see how they affected mud worm infestation.
At a commercial oyster farm in Grand Bay, Alabama, she put out baskets of two varieties of oysters, the typical oyster and a variety selected for fast growth, at two tidal heights, either submerged constantly or exposed daily by tidal changes. Each week for six weeks she monitored the oysters to see if they acquired mud worms. She found that while there was no difference between the two oyster varieties, there was a very large difference between the two tidal heights, where the oysters kept at the intertidal height had relatively few worms, while oysters held submerged had tens to hundreds of mud worms burrowing into their shells after just two weeks.
In addition, Charlotte also tried something different to get at the question of how long it takes for oysters to recover from mud worm infestations. The burrows are in the shell and not visible to the naked eye; that’s where Urgent Care by the Bay in Daphne, Alabama, helped out, letting us use their X-ray machine to examine oyster shells over time. This let us measure damage to the shell, compared to what was visible, to get a measure of shell repair over time. While these results were not conclusive, we will certainly be putting that method to use again as we move forward with this work next year.
As these studies move forward, we will continue to share the results with oyster farmers, hopefully allowing them to make better informed decisions about their farm so that they can keep getting those wonderful oysters to market.