Home » Is it good green or bad green?

Is it good green or bad green?

Many thanks to our Volunteer Water Reporters for keeping an eye on algal blooms—and other concerns around Casco Bay.

We shared these things to think about as they surveyed conditions around the Bay this summer. We are sharing it here as others may be interested as well.

A little algae is a good thing.

Nitrogen is one of the three most important “food groups” for plants. It is also one of the primary components of fertilizer, along with phosphorus and potassium. In the ocean, nitrogen is generally the critical element needed for plant growth. Algae, ranging in size from microscopic phytoplankton to sinuous seaweeds, form the base of the ocean food web.

Too much algae—when it covers a large area of the flat—is cause for concern.

Excess nitrogen can stimulate algal growth beyond healthy amounts for the ecosystem.

Nuisance algal blooms can cover tidal flats with a thick carpet of “green slime,” smothering animals below the mat and preventing juvenile clams from settling into the mud. Large phytoplankton blooms can reduce water clarity.

When the algal mats die, they release carbon dioxide. The carbon dioxide mixes with sea water to create carbonic acid, in a process known as coastal acidification. Coastal acidification changes water chemistry and can make it harder for shellfish such as oysters, clams, and mussels to build and maintain their shells.

For more information on excess nitrogen and green algae visit cascobay.org/our-work/science/nuisance-algal-bloom-tracking.

Observing and recording observations of an area regularly helps us track algal blooms around the Bay

We want to see images of algae from the small amounts to “concerning” amounts because we can’t predict where and when an outbreak may become a nuisance algal bloom.

To better document and track algal blooms spreading to worrisome levels, we encourage Water Reporters to choose a specific location to observe weekly, ideally an hour before or after low tide. More details at cascobay.org/water-reporter/#WRalgalblooms.

Go back every week—just not at the same time on the same day the next week! The time of low tide differs every week. For example, if it is low tide at 10 a.m. one Wednesday, low tide will be closer to 4 p.m. the following Wednesday. The tidal cycle changes by about 52 minutes each day. Tide charts can help you plan your visit: https://me.usharbors.com/monthly-tides/Maine-Southern%20Coast or use a tide app. You do not need to visit on the same day each week.

Green is really good news when it is eelgrass! 

The presence of eelgrass is a sign of healthy water, so share photos using another hashtag: #eelgrass.

Share your #eelgrass posts in celebration of healthy marine waters! We also want posts of places that used to have eelgrass but don’t now.

Eelgrass (Zostera marina) is one of the few flowering plants found in the ocean. It grows in shallow water on sandy or muddy bottom, and its long blades grow to 30 centimeters (11 inches) or more. Eelgrass needs clean, clear water to grow, so the presence of eelgrass is a visible sign that water quality is healthy in a location.

How do you tell the difference between eelgrass and green algae?

Eelgrass is usually a less bright green than green algae and is usually underwater. You may see it at the water’s edge at low tide, when the tops of the blades may be seen floating on the surface, as seen in the photo above. In contrast, green algae is usually further up the shore and is often exposed at low tide.

The image to the right shows eelgrass that has been washed ashore. From a distance, this can look like a green algal bloom.

Why do we love eelgrass?

  • It provides essential habitat for fish, crabs, and shellfish
  • It produces oxygen
  • Its roots anchor sediments
  • Its long, flowing leaves dampen wave action
  • It improves water quality by tempering the effect of ocean acidification because eelgrass captures and stores carbon dioxide.

Because eelgrass is such important habitat, it is essential to not disturb or trample it!

“A drowned island of shelter and security for many animals” is how Rachel Carson described the sinuous sea meadows that grow just beneath the surface of the Bay. Many commercially-important species, including flounder, striped bass, cod, lobsters, crabs, mussels, and scallops, use eelgrass beds as a nursery area, feeding ground, or refuge from predators. Dead eelgrass decomposes into a “sea soup” that is an essential part of the marine food web.

 

Get close! A close-up photo can help us to identify the green growth. 

Be careful where you step. We don’t want you falling and getting hurt, treading on private property, or damaging growing eelgrass.

 

Thank you to our Water Reporters!