Tunicate Trouble

Every other day, I hose down the one-year-old clams and their mesh-bottom buckets with salt water. As I was rinsing and washing these buckets, I saw an increasing number of unfamiliar organisms attached to the one-year-old clams. After discussing these organisms with the Downeast Institute (DEI) as well as the Department of Marine Resources (DMR), we concluded that they were all different species of tunicates. Tunicates are marine invertebrates that attach themselves to solid surfaces. Like soft-shell clams, tunicates are filter feeders and they mostly feed on plankton and other nutrients in the water. Seeing an increasing number of tunicates attached to our clams was not good news. These tunicates were competing for the same resources as our clams. Most of the tunicates we identified were colonial tunicates. Colonial tunicates have the ability to split off from the original tunicate and spread to new clams, eventually creating a colony. 

We knew that we had tunicates growing on our clams and we knew that they could increase competition, leading to clam mortality, but what we didn’t know was the best way to get rid of them. We were advised by both DEI and the DMR to just throw out any clams that had tunicates growing on them. Another suggestion was to rinse the clams with fresh water. I started to sift through each bucket looking for clams with tunicates, but I knew it would be almost impossible to get every single one and if I left one in the bucket, it could potentially start a new colony. Instead of throwing away all of our tunicate-covered clams, we decided to run a small experiment. We put a bunch of tunicate-covered clams in a separate mesh-bottom bucket and added three periwinkles to that bucket. We hoped that the periwinkles would eat the tunicates on our clams and do the removing for us without having to throw away the entire clam. As soon as I placed the periwinkles in the bucket they began munching on the tunicates. However, after two days with the periwinkles in the bucket, it looked like they didn’t even make a dent. We hope to add more periwinkles to the bucket to see if that will speed up the process. If this experiment works, we might consider placing periwinkles in every bucket to control the tunicate population.