Climate Desk

Researchers are tracking a large algal bloom spanning 100 miles in the Gulf of Maine

Maine Public | By Murray Carpenter

Published August 23, 2023 at 6:11 PM EDT

Satellite images of the Gulf of Maine compare chlorophyll concentrations from August 2023 to those from 2022. The chlorophyll concentration in the left images shows high concentrations (yellow colors) throughout the region in 2023 (top row). The images of chlorophyll anomalies on the right, show chlorophyll concentrations in 2023 are up to 10 times greater than the long-term July average - indicating that the current concentrations of phytoplankton are unusually high.

An unusually large algae bloom in the Gulf of Maine has researchers trying to understand its cause and possible effects.

At its peak, the algae bloom extended from Penobscot Bay to Martha's Vineyard. The bloom is comprised of a naturally occurring phytoplankton that is not toxic to humans or animals.

A nearshore Gulf of Maine water sample full of Tripos Muelleri collected in May 2023.

University of New Hampshire scientists first noticed the bloom in April when they recorded the lowest carbon dioxide and highest pH levels in their 20 years of monitoring.

Nicole Poulton, of Bigelow Laboratory for Ocean Sciences, says it's hard to know what's causing it, but the rapidly warming waters of the Gulf of Maine could be playing a role.

"We do know that the Gulf is changing quite rapidly. And it could be a variety of things," Poulton says. "Both the increasing temperatures in the Gulf of Maine, as well as increased rainfall into the Gulf as well."

Poulton says a dozen research groups from Maine to Rhode Island are collaborating to understand the event. One concern is the possibility that the algae will deplete oxygen in parts of the Gulf when it dies and decomposes.