Exploring how deep the mussel decline goes in Casco Bay

By Ramona du Houx

Blue mussels have been noticeably less abundant in Casco Bay during recent years.

Mussels are like vacuum cleaners of the ocean, cleaning up unwanted pollutants but not passing them on to consumers who partake in the pleasures of eating them. They play an important role in the ocean's eco-system.

Warming waters, invasive species such as green crabs, and other challenges have been recognized as contributing factors to the decline in shallow waters. Mussels typically do well below the tide line, thanks to stable temperatures and less predation from green crabs — but deep water can make mussel research more challenging. Hence, the scientific community knows relatively little about subtidal populations, deeper water populations, compared to those in the intertidal.

Scientists at the Gulf of Maine Institute needed to find out what was happening in deeper water. So, after four years of studying the shallows, they’ve began exploring the subtidal region to assess whether mussel population losses observed above the tide line are universal.

"It’s critical to develop effective survey methods at the beginning of a project like this,” said Dr. Lisa Kerr, who leads the study. “That’s the first step toward reliably tracking changes to this resource over time.”

Researchers spent this first field season assessing which techniques and locations will work best. They explored new camera technologies, built custom hardware, and covered a lot of ground exploring the best potential research sites in Casco Bay. This approach should help produce cost-effective sampling methods to support long-term monitoring. 

Fieldwork will continue next spring, and researchers hope the data gathered will help them ask and answer questions about blue mussel presence, population density, and habitat. 

If blue mussels are declining overall, the consequences to the environment would be significant.

A lot of factors point to climate change due to human activities, warming the oceans. Evidence shows this to be true. The Gulf of Maine is warming 99 percent faster than the rest of the oceans because it is in a unique position feeding from southern currents and northern currents. As ice melts in the north it warms the ice waters so that when they combine with the southerly currents the waters in the Gulf of Maine get warmer too.

This video expalins it further.