The poet Virgil wrote, “Nihil vilior alga” or, “there is nothing more worthless than seaweed.” Before becoming a diver, I pretty much agreed with him, having never really thought much about the stuff, other than remembering its stringy, smelly strands that washed up on beaches.

The big wide fronds of Southern Kelp. Charles Lagerbom

Once I got into diving, however, I became amazed by the variety, size, colors and shapes of the different species, especially here in New England waters. Seeing them in action, waving long strands in their element and glory, I wanted to learn more.

Sea Colander at the Rockland Breakwater. Charles Lagerbom

So last fall I took an online natural history seminar entitled “Marine Macroalgae: Ecology, Identification, Distribution, and Importance” through the Eagle Hill Institute. It opened up for me the entire world of phycology or “study of algae.” I came away with a new-found respect for these hardy denizens and learned there is quite a bit more to them than just being the weeds of the sea.

Southern Kelp off Marshall Point Lighthouse in Port Clyde. Charles Lagerbom

What we commonly call seaweed are really two kinds of marine algae, macro and micro. With ten thousand different species, macroalgae is one of the most resilient plants on the planet. It survives and thrives in waters from the tropics to the poles, as well as along rugged, crashing surf-filled coastlines. They have evolved little since first appearing in the fossil record nearly 1.7 billion years ago.
Some patches of seaweed are wicked thick. Medieval scholars wrote of sailors’ greatest fears known as mare coagulatum or “curdled sea.” Columbus’ men were frightened when they encountered large patches of seaweed in the mid-Atlantic, what would later become known as the Sargasso Sea.

: Iridescent Blue tips on the Irish Moss found off Ash Point, Owls Head. Charles Lagerbom

Most seaweeds need a hard substrate upon which to grow. Depending on the species, they are located in one of three zones along the shore. The Splash Zone is rarely underwater, the few species there are hardy enough to remain dry for long periods of time. The Tidal Zone is partially underwater depending on the tide, so species there go dry for a set time before waters return. Finally, there is the Sublittoral Zone, species there stay completely submerged even at the lowest of tides.
Macro algae in Maine waters tend to be Brown Seaweeds. They are multi-celled, with complex construction and leaf and stem structures. The largest, fastest growing of them are called kelp. The big, long fronds of Fingered Kelp (Laminaria digitata) as well as the broader-leafed Southern Kelp (Laminaria agardhii) can often be found at Rachel Carson Salt Pond in New Harbor.
They can have up to 30 long blades, slimy to the touch, which can grow up to six feet in length. Also known as Tangle or Oarweed, they are found on rocks and in strong current areas, moving water allows them to wave at you as you pass by. New England kelp tend to be found solo or in small clumps, rather than the thick forests of kelp you read about off the California coast, down around the Falkland Islands or at the Galapagos Islands.

Coral Weed off Penobscot Park in Lincolnville. Charles Lagerbom

Then there is the broad-leafed Sea Colander (Agarum cribrosum), filled with holes like the name implies. Looks like someone took a shotgun to kelp. We tend to see lots of it at the Rockland Breakwater in the low tide to subtidal zone. Sea Colander ranges from the Arctic to Cape Cod.
We come across lots of Irish Moss (Chondrus crispus) and Coral Weed (Corallina officinalis) off Lincolnville, Beauchamp Point in Rockport, and Ash Point, off Owls Head. Irish Moss seems to carpet the rocks in a thick mat, much like turf. At certain times of the year, Irish Moss produces beautiful iridescent blue or purple-tinged tips of their leaves, the young parts of the thallus. Irish Moss gets harvested for an extract called carrageenin, used in ice cream, toothpaste and make-up.
The Coral Weed is fern-like and stands upright in the water due to calcium carbonate produced in its cells, but individual segments are lime-free so can still move. Once the hold-fast breaks free of the substrate, Coral Weed tends to turn white and brittle.
The well-known Knotted Wrack (Ascophyllum nodosum) is profuse at Marshall Point Lighthouse, Rachel Carson Salt Pond, and the Rockland Breakwater; sometimes there are large enough patches that you need to navigate around or power through. Diving through the stuff is pretty tough. It can knock your mask off or rip the regulator out of your mouth.
The thick-walled air bladders are the Knots and there are both male and female plants. They produce fruiting receptacles in the fall and release sperm and eggs in early spring. By end of May, the receptacles are shed. They are found in quiet rocky intertidal waters with minimal wave action and are commercially harvested for food emulsifiers and thickening agents. Knotted Wrack has also been used to pack around lobsters or bait worms.
Spiral Rockweed (Fucus spiralis) can be found in large numbers at Rachel Carson Salt Pond in the higher areas of the intertidal zone. While it does have receptacles, they do not have bladders. Their hold-fast, which keeps them anchored, is disk shaped. They range from the Arctic to North Carolina.

Spiral Rockweed off Duck Trap Harbor. Charles Lagerbom

In Japanese poetry, seaweed is associated with prosperity. They even incorporate it into New Year’s celebrations, freshly cut seaweed is believed to bring good luck in the coming year.
The artist Henri Matisse even used many forms of seaweed he encountered on a trip to Tahiti as his muse when he painted birds, corals, fish and other creatures in his “Matisse’s Oasis.” Inspired by the seaweed, they became colorful shapes and symbols forming his dream-like images.
There is big business in seaweed, known for their iodine, minerals and antioxidants. Dulse (Palmaria palmata) is popular because you can eat it right out of the bag. Many people cook it with vegetables or put it in fish chowders. Dulse flakes and salt blends can be used for seasoning as well. Dulse, Digitata Kelp, and Bladderwrack are all popular seaweed food products packaged and sold. Commercial opportunities and possibilities are rapidly expanding.
Not only can you eat it, but seaweed is thought to have curative powers as well. Algotherapy baths have been offered at spas now for some time, seaweed stimulates blood flow. The Penobscot Indians cooked Dulse in seawater over a fire until it turned to a jelly-like substance, which they would then apply to their chest for heart ailments. When on military campaigns, Passamaquoddy warriors popped pieces of dried Dulse into their mouths to keep themselves from becoming fatigued. Early Maine seafarers learned that Dulse also proved effective against the effects of scurvy.
Bigelow Lab was recently awarded a $900,000 grant to explore kelp aquaculture and climate change. Increased carbon dioxide in seawater can cause acidification and harm mussel beds. Kelp, known to absorb carbon dioxide, might be grown and harvested nearby, thus possibly lowering the acidity of the surrounding seawater and raising oxygen levels.

Knotted Wrack Seaweed grows in thick clumps, tough for divers to navigate through. Charles Lagerbom

Seaweed this, seaweed that…the list goes on and on. There is definitely way more to this stuff than just the smelly strands that wash up on the beach. Something simple yet sturdy, plain but exquisitely intricate, seemingly uncomplicated yet incredibly complex. To Virgil’s original statement regarding seaweed, I would reply “Non solum nulla, sed inferno non!”
Charles Lagerbom teaches AP US History at Belfast Area High School and lives in Northport. He can be contacted at He is author of “Whaling in Maine” available through