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Spring starts early in Casco Bay!

Our Continuous Monitoring Station chronicles the rise and fall of microscopic blooms in Casco Bay. This graph of chlorophyll fluorescence tells us that the spring bloom of phytoplankton beneath the ocean happens well before plants on land emerge from beneath the snow.


It may be hard to believe if you have spent any time outside this chilly winter, but spring likely has sprung in the waters of Casco Bay.

By January, the lengthening daylight has jumpstarted the growth of phytoplankton, the single-celled plants that are the foundation of the ocean food web. Like plants on land, they respond to increasing sunlight by bursting into bloom. By mid-February, daylight has increased by over an hour since December 21st, and the phytoplankton are flourishing.

Last January, 2017, there was an early bloom of phytoplankton in Casco Bay. How do we know? Friends of Casco Bay maintains an underwater sentinel that collects information about the water of the Bay every hour, 24 hours a day, 365 days a year. It is our Continuous Monitoring Station.

We will soon be crunching the January-February 2018 data, looking for confirmation of this year’s phytoplankton bloom.

A modified lobster trap houses a carbon dioxide sensor and a data sonde, electronic devices that continually take the pulse of the Bay. Together, they provide evidence of how our coastal waters may be changing over time. This long-term monitoring station, fondly known as “the Cage of Science,” is anchored just above the sea floor off Cousins Island in Yarmouth.

We now have over a year of hourly data on oxygen levels, carbon dioxide, pH (the level of acidity of the water), salinity, temperature, water clarity, water depth, and chlorophyll fluorescence, a measure that provides an estimate of phytoplankton abundance. Chlorophyll is the green pigment in plants that traps the energy of the sun for photosynthesis.

Phytoplankton provide food for the smallest zooplankton. These tiny floating animals are eaten by larger zooplankton, such as copepods, shrimplike creatures. Both phytoplankton and zooplankton are at the mercy of the currents, winds, and tides.

The data from the Continuous Monitoring Station documents the changes in the water’s chemistry as a result of these blooms. The net positive effect in Casco Bay over the course of the spring season is more oxygen and less acidic water, thanks to those early-blooming phytoplankton.

Beyond Casco Bay, in the Gulf of Maine, a circular current called a gyre distributes marine life around the Gulf. The gyre transports phytoplankton to where zooplankton are hatching, just in time to feed emerging copepods, which in turn feed baby fish, clams, and other sea creatures.

Success in the ocean food web, like in much of life, depends on being in the right place at the right time.

Our Continuous Monitoring Station has been in place for about a year and a half, too soon perhaps to provide data that might indicate whether or not Casco Bay’s food web is changing. Still, every hour and every day, our cage of science is building a more complete picture of the seasons beneath the Bay, giving us insight into how climate change may alter the food web of our coastal water in years to come.

Thank you to funders of this project, including Casco Bay Estuary Partnership, Davis Conservation Foundation, Horizon Foundation, Schwartz Family Fund of the New Hampshire Charitable Foundation, and WEX. We also thank our Members and the many donors, local businesses, and foundations that give us operational support to do our work each year.