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Our Warmest Time of Year is Getting Warmer

Although temperature averages fluctuate year-to-year, the black lines show a trend of warming water at our sentinel sites over ten years.


According to Research Associate Mike Doan, Casco Bay’s critters are experiencing longer summers and warmer autumns.

For 25 years, Friends of Casco Bay staff scientists monitored water quality every month of the year at three deepwater sentinel sites in the Bay, from surface to sea floor, aboard our research vessel. This data set indicates that the waters of Casco Bay have been getting warmer.

A comparison of the ten most recent years of data collected from August through October (2007-2016), at these sentinel sites, shows there has been a significant jump in water temperatures in late summer and early autumn (see graph).

Concerned about a changing Casco Bay, we launched a Continuous Monitoring Station* in 2016 to help us better understand the chemistry of our coastal waters. The Station consists of electronic monitoring equipment housed in a converted lobster trap. This “Cage of Science” collects an hour-by-hour record of conditions in the Bay, including temperature, carbon dioxide, oxygen, pH, salinity, and chlorophyll.

While we may appreciate being able to swim in the ocean well into the fall, there are significant downsides to warming water. We run the risk of seeing impacts similar to what others are reporting elsewhere in the Gulf of Maine:

More invasive species may move in
A change in the composition of species could affect the ocean food web
More bacterial outbreaks and nuisance and harmful algal blooms may result
The amount of oxygen available for marine life may decrease, especially in the months of August through October
These and other concerns are all the more reason for us to continue to closely monitor the changes happening in Casco Bay.

*Maintenance of our Continuous Monitoring Station is funded, in part, by Casco Bay Estuary Partnership and by generous donors like you.