Around 1,000 adult scallops died after washing up in Madaket Harbor over the weekend, all with the non-native macroalgae codium attached to their shells. A strong north wind caused the scallops to wash ashore, which was exacerbated by the buoyancy of the codium.
According to the Nantucket Land and Water Council, the large amount of codium that washed up indicates an algal bloom occurring in Madaket Harbor. Although the codium doesn’t produce toxins, which is the case for many of the harmful algal blooms happening in island ponds, it still caused harm to the ecosystem with this stranding.
In a video posted on the Nantucket Land and Water Council’s Instagram on Monday, the organization’s eelgrass restoration manager Noah Singer described the event as “a large-scale scallop stranding,” with thousands of scallops covering the beach at Warren’s Landing. Singer further explained that “codium grows so it becomes buoyant and starts floating, and then inevitably washed up on beaches,” this time bringing many scallops with it.
Tara Riley, Shellfish and Aquatic Resources Manager for the Natural Resources Department visited the site on Sunday, where she only recorded about 300 stranded scallops. She believes that more scallops could have washed up on Sunday night, contributing to the 1,000 counted by Singer on Monday. However, according to Riley, this stranding was not catastrophic.
“It's pretty minimal because you can have around 300 scallops in a bushel,” Reilly said. “So really, it's like three, four or five bushels and that's considered…very minor.”
Having witnessed many large-scale scallop strandings over the winters on Nantucket, which can have thousands of bushels of scallops wash up, Riley said she wasn’t too worried about this event.
Although Riley recognizes that a stranding, however minimal, may be alarming to people, she explains that there wasn’t much to do to save the scallops in this case.
“Looking at the scallops on Sunday…[their eyes] were receding, so that told me that they had been up for more than 24 hours on the shore,” she explained. “A lot of heat and sunlight exposure dries them out pretty quickly.” With the scallops already being mostly dried out, even if they were to be rescued, they most likely wouldn’t have survived the transfer back into the water.
The stranding has reinforced the fact that there probably isn’t a lot of eelgrass in the area, due to the large amounts of codium found on shore attached to the scallops.
“Eelgrass is important to protect from strandings because…it has a holding power to hold the shellfish in the harbor,” Riley added.
Due to the loss of eelgrass in harbors around the island, there has been an increased number of strandings over the past 10 years. However, the Natural Resources Department pinpoints areas of scallop seed, which are more vulnerable to large stranding events, to move them to safer areas to prevent large strandings. Riley is confident that there’s plenty of seed in both harbors right now, which will reproduce and continue the scallop fishery.
Riley sees the stranding over the weekend as a unique event due to the large amounts of codium that washed up.
“I don’t know that I’ve personally seen…that much codium with scallops attached wash up in an event,” she said. “Usually it’s a mixed bag.”
The higher levels of codium can likely be attributed to septic system loads in the Madaket Harbor watershed, Riley added, along with nutrient loading from fertilizer coupled with thermal stress and warming waters.
The Nantucket Land and Water Council explained the stranding similarly in its Instagram post, stating that this event was a direct result of excess nutrients in Nantucket’s water bodies.
To preserve the island’s scallop population and the health of the harbors, they stated, “This loss, and future similar losses, can be stopped with a greater effort to decrease the pollutants added to our harbors, ponds, and streams.”