A Changing Climate in Our Mud Flats: Ribbon Worms

The Maine Coast Fishermen’s Association was started by commercial fishermen who targeted groundfish out on the icy waters of the Gulf of Maine. Before long, our organization had expanded to work with all Maine fishermen who agree that building healthy ecosystems is the first necessary step to ensure the long-term sustainability of all marine species. Today, MCFA works with scallop, shrimp, lobster, herring, and tuna fishermen who embrace resource stewardship as the path to a future with diverse and robust fisheries for the next generation. And while the iconic Maine fisherman may be imagined firmly rooted behind a ship’s wheel, we can’t forget about the fishermen that work closest to shore with boots that are covered in mud rather than planted on the deck of a boat.

Climate change on the clam flats

At last winter’s Maine Fishermen’s Forum, we heard fishermen from around the world speak about the impact warming waters are having on their catch. But the impact of global climate change isn’t only felt in the warming waters of our oceans. In fact, some of the effects of our changing ecosystems are easiest to see right where the land meets the water.

MCFA’s Monique Coombs began exploring the shellfish flats in her hometown of Harpswell after hearing from commercial shellfish fishermen about the issues that they, and the mudflats they rely on, face. A warming climate can cause a slew of changes in our marine environment, many of which are seriously hazardous to shellfish health. However, the issue currently occupying the shellfish community is the plague of ribbon worms (more formally called “nemerteans”) that have lately descended upon Maine’s mudflats.

The fight to save Maine’s shellfish

While the persistent nuisance of shellfish-eating green crabs has gotten most of the public’s attention, they can be trapped and removed using relatively low-tech methods. There are have even been recent attempts to commercialize green crabs, which would create further incentives to remove this species from our intertidal waters. The same cannot be said of ribbon worms: diggers are still trying to figure out the best way to gather and remove ribbon worms, to limited success. And the sooner the better: ribbon worms prey upon adult and juvenile clams at alarmingly high rates, leaving the clam flats ravaged in their wake Maybe even more distressingly, the worms may even poison the flats themselves due to their toxic secretions.

While some might argue that shellfish overharvesting has caused the increase in ribbon worms, many others (including most shellfish diggers) instead argue that changing water temperatures and ocean acidification are causing the nemerteans to become so prolific. While clams are finding it more difficult to thrive in the flats due to inability to seed, changing temperatures, ocean acidification, and increasing predation, hardier species like ribbon worms are finding optimal living conditions.

Going after the worms

Not surprisingly, commercial shellfish harvesters have seen an increased presence of nemerteans in the muddy flats that line many of Maine’s coastal areas. Some marine resource committees, such as those in Brunswick and Harpswell, are starting to investigate how to better manage and/or eradicate the species. However, many other town committees are still trying to understand what is happening to their dwindling clam populations. The Brunswick and Harpswell Marine Resource Committees have dedicated significant time and effort to the manual removal of ribbon worms from their flats, but it has yet to be determined whether or not this will be an effective tool for decreasing the worms’ presence

On September 24 and 25, 2016, Harpswell shellfish harvesters took to the flats not to dig clams, but to try and put a dent in the ribbon worm population. Monique took the opportunity to join them.

Ribbon worm fun facts