On Wednesday, August 15th, our intern Andrew Staley and our watershed ecologist Sara Grady went snorkeling to gather information about the past mussel enhancements made by the NSRWA near the banks of the North River in Marshfield. The mussel enhancements were made in 2015 by the watershed to boost the population of mussels, a key part of the river ecosystem, along the North River. Andrew and Sara studied the mussels along 150 feet of the riverbed, using transect tapes to mark off the section of riverbed where the mussels had been placed and taking samples every 15 feet. Three mussels were measured every 15 feet so that the watershed could determine if the individuals were growing and if the population was healthy.
There was a range of mussel sizes, although most fell in the 68-74 millimeter range (including both live and dead mussels). Along the riverbed, it was evident that the mussel colonies that were more successful had created a ledge along the riverbed as they began to increase in size and number. In addition, the mussel colonies that seemed to be healthiest in size and number of individuals were the colonies that had been dropped on the parts of the riverbed with a more solid bottom or on rocks. Mussels that had been dropped in the river in the mud had trouble surviving; many of them were dead with only shells remaining.
The healthier colonies, by clinging onto the harder stretches of riverbed, changed the landscape of the river bottom and shifted the once-gradual sloping bed into a more distinct shelf. The mussels are vital to the North River ecosystem because they act as natural biofilters and add complexity to the bottom. Keeping the mussel population healthy is important to a healthy watershed.