What’s all the red seaweed?
Yesterday was a beautiful sunny February day. Nicole Corbett, founder and lead researcher for the Popponesset Water Stewardship Alliance (PWSA) walked Popponesset Beach taking photos of the coastline and collecting water samples for nutrient water quality testing. Like many Mashpee residents, I’ve been following Nicole’s work for a while. (https://www.facebook.com/groups/poppywateralliance)
Yesterday I was fortunate to be able to accompany her on her walk and learn more about the water sampling process and the visual data she and volunteers regularly collect to learn more about water quality and invasive species in our coastal waters. The focus yesterday was on the proliferation of Dasysiphonia japonica (Dasy), a non-native red macroalga.
Dasy Found on Popponesset Beach
Nicole, a secondary science teacher, department head, and an avid swimmer, first noticed the abundance of this red seaweed, several years ago. She reached out to the Massachusetts Office of Coastal Zone Management to report her observations and learned that Dasy had not previously been found in Nantucket Sound. She formed PWSA, a small all-volunteer group, to conduct nutrient water quality testing. The results of this testing indicated that this red seaweed that covered the coastline particularly during colder months is Dasy, an invasive non-native seaweed.
Dasy Thrives in Eutrophic Waters
A study of Dasy in Long Island Sound suggested that eutrophic bays and estuaries provide an environment for increased Dasy growth. Why? Eutrophic waters are characterized by increased levels of CO2 and nutrients (many from wastewater). More so than native algae, Dasy thrives in these conditions. Watch this one-minute video that explains eutrophication in plain language.
Concerns for Popponesset Bay and Mashpee Beaches
Popponesset and Waquoit bays have eutrophic conditions (Howes, Samimy, & Horvet, 2021), which provide favorable growing conditions for Dasy. As Nicole wrote, “If you have taken a boat around Popponesset Island, you can smell the seaweed decomposition. Last summer, this group with the Barnstable Clean Water Coalition had our seaweed sampling nets get stuck in feet of muck about 3 feet down in the bay, all of which was dead seaweed.”
As Dasy continues to grow, it will crowd out other native seaweed species that are integral to the ecosystems of the bays. The proliferation and decay of Dasy will increase CO2 and further deplete Oxygen, which fish and other organisms need to survive. This process is cyclical, resulting in further declining water quality.
The Popponesset Water Stewardship Alliance’s (PWSA) Continuing Work
Nicole continues to collect water samples, which are analyzed by the University of New Hampshire to confirm that the nitrogen present in Dasy samples is from wastewater. During summers the PWSA’s youth volunteers help with this research. Findings from the PWSA’s study will help us understand what we need to do to slow down the growth of Dasy and further degradation of our coastal waters.