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Good Green vs. Bad Green

If you have ever tried to pick the right shade of green to paint your bedroom, you know there are soothing greens and greens you would never want to wake up to. The same holds true in the ocean.

Algae is one of those “greens” that can be a sign of a healthy ecosystem; but large areas of mudflats may become covered in a nightmarish bright green when algal growth is fueled by too much nitrogen in the water.

In 2019, as the water warmed from spring through fall, volunteers in our Water Reporter observing network tracked algal blooms that appeared in 18 different locations around Casco Bay. The photos they took on their smartphones documented changes throughout the summer, as the algal blooms expanded to worrisome levels in many coves from Cape Elizabeth to Harpswell and West Bath.

In 2017, we tracked algal growth at five sites. We do not have enough historical data to know whether nuisance algal blooms are expanding or simply that we are getting better at tracking more sites, thanks to our growing network of Water Reporters.

In any case, nuisance and harmful algal blooms are an increasing concern. Water Reporters are already discovering and tracking sightings in 2020!

Community Engagement Coordinator Sarah Lyman oversees our Water Reporter program. This year, Sarah hopes to recruit additional volunteers to our band of intrepid Water Reporters who track algal blooms. “Each volunteer will adopt a specific Bay location to observe weekly. Images of algae from the ‘good’ amounts to ‘concerning’ amounts are helpful because we can’t predict where and when a small patch of algae may become a nuisance algal bloom.”

Currently, there are 205 volunteers in our Water Reporter network. Together, they have recorded 991 observations about Casco Bay. If you are interested, learn more at cascobay.org/water-reporter.

Our Water Reporters tracked algal blooms at 18 locations around the Bay in 2019.

Nitrogen fertilizes the ocean, too

Nitrogen encourages the growth of plants on land and in the ocean, where it stimulates the growth of algae, from microscopic phytoplankton to sinuous seaweeds, the base of the ocean food web.

Excess nitrogen can stimulate algal growth beyond what marine life can absorb. Nuisance algal blooms can cover tidal flats with a thick carpet of “green slime,” smothering animals below the mat and preventing juvenile clams from settling into the mud. Large phytoplankton blooms can reduce water clarity. When these blooms die, decomposition sucks life-giving oxygen out of the seawater and releases carbon dioxide, creating acidic conditions that make it harder for clams and mussels to build and maintain their shells.