Why Rockweed is Cool (Really): Christine Walder’s Biodiversity Project

The Intertidal Zone on Kent Island

The Intertidal Zone on Kent Island

When Christine assured me that Rockweed, the seaweed that dominates the intertidal zone on Kent Island, is extremely exciting and cool, I had my doubts. Seaweed is slimy, smelly when it dries, and makes walking around the Island at low tide like trying to climb mountains of banana peels. Christine began to change my mind when she told me, “You expect seaweed to be goopy and fast-growing, but Rockweed is slow-growing and fragile, and its hold-fasts are up to 400 years old. Some of the Rockweed beds here are ancient.” Rockweed only grows 4-6 cm annually, and while most strands are covered in air bladders for flotation at high tide, they grow one bladder per year, which scientists count to age the strands. Before coming to Kent Island, I never would have considered a type of seaweed to be what Christine described as “the old growth forest of the ocean.”

Not only is Rockweed fascinating as an organism, but it also supports the diverse life in intertidal ecosystems. Christine’s project, which she started last summer and is continuing for a few weeks this summer, looks at the effects of Rockweed harvesting on intertidal biodiversity. Ascophyllum nodosum, commonly called Rockweed, covers tide pools like a blanket, blocking the drying effects of the sun and diffusing the force of the currents that rip through the Bay of Fundy. The intertidal zone is a very high-stress environment for organisms: for six hours a day they are totally submerged in cold water, while for another six they are high and dry in the sun. Rockweed helps to regulate the extremes of daytime heat and strong currents, providing a more stable habitat for *macroinvertebrates such as crabs and periwinkles.

This morning, I ventured out to the intertidal zone on West Beach with Christine to experience the wonders of the intertidal for myself. Last summer, she marked 15, 1-meter square plots of Rockweed that she surveyed for macroinvertebrates, and cut the seaweed out of half of the plots to measure the difference in species diversity between harvested and unharvested plots. Today, we prepared four new plots to increase her sample size, improving the accuracy of her experiment. The weather was foggy and wet, and we hiked across the seemingly endless hills and valleys of Rockweed, decked out in our rain pants, boots, jackets and hats. Christine knows her Rockweed plots well enough by now to find them by sight, though we marked new plots with orange painted rocks and ribbons of neon tape. Sorting through the Rockweed was a full body experience. First, we picked snails off of the surface of the seaweed, and then the real fun began. We dug through the tangles of Rockweed with our hands, combing for small crabs, amphipods (bug-like crustaceans), anemones, and a host of other small organisms that Christine identified on sight.

Looking at a pile of Rockweed, I never would have expected to find anything as spectacular as the buried nudibranch that we discovered, with its swirling tentacles and its amazing ability to incorporate stinging cells from anemones and photosynthetic cells from algae into its body. It soon started to rain, but I became so absorbed digging through and measuring sometimes two-meter strands of Rockweed that I forgot that I was wet and covered in its sticky, reproductive slime.

Christine surveying a Rockweed plot

Christine surveying a Rockweed plot

Helping Christine for only a few hours this morning taught me about the incredible amount of biodiversity present in even a small area of the intertidal, and gave me a taste of the hard work in sometimes unpleasant conditions that is the foundation of field research. Her project is especially relevant because Rockweed is being harvested in Canada and the U.S. for use in fertilizers and food additives, but large quantities must be cut to make a profit. Her work will help to determine the ecological effects of harvesting, which may create greater environmental problems on a commercial scale.


J.A. Percy, “The Seaweed Forest, Rockweed Harvesting in the Bay of Fundy.” The Bay of Fundy Ecosystem Project. Issue 4: 1996.http://www.bofep.org/rockweed.htm


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