What is Rockweed and why is it important?

The familiar greenish-brown macroalgae that covers the rocky shores of New England and maritime Canada is commonly called rockweed. Most of it is the species Ascophyllum nodosum. Rockweed has been harvested commercially and extracts from it are used for fertilizer or thickeners for food and cosmetics (these thickeners are called alginates). Until recently, there has been little regulation on rockweed harvesting.

In 2000, the Maine Department of Marine Resources implemented a regulation requiring that the bottom 16 inches must remain when harvesting rockweed. Companies harvesting rockweed in Cobscook Bay submit a plan to the DMR that describes what areas they will harvest, how much of the biomass they will take, their methods of harvest (hand raking or cutting, or mechanical), how they will train their harvesters, and how they will manage bycatch.

Rockweed is fast-growing and long-lived, reaching over eight feet in length and living up to 15 years. In fact, you can age rockweed by counting the segments between air bladders similar to counting the rings of a tree. Because of this, rockweed is quite a renewable resource. However, rockweed also plays a crucial role in the intertidal ecosystem.

Smaller algae and some invertebrates grow on the rockweed. Other species, such as snails, eat the things growing on the rockweed. Rockweed also helps provide habitat and protects intertidal species from desiccation and extreme temperatures. Crabs and amphipods (scuds) are frequently found hiding amongst the rockweed fronds.

In addition, rockweed acts similarly as vegetation along streams, capturing sediments and organic matter and preventing erosion, all of which provides food and habitat for very small organisms (mostly types of worms). When the tide comes in, these worms and amphipods are food for animals such as juvenile lobsters and fish.

Submitted by Dr. Aimee Phillippi, Unity College