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As Bay Warms, Harmful Algae Bloom WHOI researcher Jennie Rheuban (top left) led a study showing that warmer water temperatures are fueling an increase in algae growth in Buzzards Bay, Mass. The study used data compiled over twenty years by Buzzards Bay Coalition volunteers (bottom left) who monitor water quality at sites around the bay (below). (Courtesy of Buzzards Bay Coalition)

As Bay Warms, Harmful Algae Bloom

Volunteer network provides crucial data

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Warming coastal waters off southern Massachusetts are worsening the effects of pollution from septic systems, wastewater treatment plants, and fertilizer runoff—­and causing a rise in harmful algal blooms.

Researchers at Woods Hole Oceanographic Institution (WHOI) and the Marine Biological Laboratory in Woods Hole analyzed water samples and temperature data collected along the coast of Buzzards Bay from 1992 to 2013 by a network of trained citizen scientists called Baywatchers. These volunteers, working with the Buzzards Bay Coalition, head out to their local beaches and docks in a program established by the Buzzards Bay National Estuary Program to help monitor the health of the bay. The researchers found that climate change has caused average summertime water temperatures to warm by almost 2° Celsius, or more than 3.5° Fahrenheit.

“That is a rapid temperature increase for marine life,” said WHOI research associate Jennie Rheuban. “For some species, a single degree-Fahrenheit change can mean the difference between a comfortable environment and one where they can no longer thrive.”

In this case, Rheuban said, the warmer water temperatures are fueling an increase in the growth of algae. These microscopic plants form the base of the marine food web and are vital to a healthy coastal ecosystem. But too much algae can turn clear water murky, reducing sunlight and oxygen levels in the water and ultimately harming marine life.

Why would warmer temperatures mean more algae? Rheuban’s analysis suggests that higher temperatures are changing the way algae use nitrogen, a nutrient in the water that algae need to grow.

Some coastal watersheds off Cape Cod and other parts of southeastern Massachusetts are already suffering from too much nitrogen pollution, and it’s no surprise that nitrogen boosts algal growth. But the long-term data show “that the same levels of nitrogen in the system result in much more algae growth than they did two decades ago,” Rheuban said.

The result is more algae—and poorer water quality—for the same amount of nitrogen pollution. That finding could have big implications for policymakers and watershed managers trying to improve water quality in Buzzards Bay and other coastal waters. 

This research was funded by the John D. and Catherine T. MacArthur Foundation. Research findings were published January 2016 in Biogeosciences by Jennie Rheuban, Shanna Williamson, David Glover, Dan McCorkle, and Scott Doney (WHOI); Joe Costa (Buzzards Bay National Estuary Program); Tony Williams and Rachel Jakuba (Buzzards Bay Coalition); and Christopher Neill (Marine Biological Laboratory).