Never underestimate bull kelp.

At this point in the year, you may see bull kelp in the intertidal zone looking more like organic sludge than the epic growing algae of the Pacific. What is witnessed in the winter washed up on beaches, its stalk wound round itself in lifeless knots, is the life’s end of bull kelp. However, the life of the Pacific bull kelp (Nereocystis luetkeana) is the life of the type-A of seaweeds.

Bull kelp, one of the largest seaweeds in the North Pacific, begins life as a spore and then grows a root-like holdfast and a long hollow cylindrical stalk called a stipe. As the stipe grows toward the water’s surface, its diameter increases until it is topped with a hollow floating bulb. To that bulb are attached leaf-like blades. This seaweed has been humorously described as “a large gothic brown onion of extraterrestrial origin.”

Let’s talk numbers now.

  • The stipe can grow to 118 feet (36 metres) long.
  • The showy brown-green blades grow up to 13 feet (4 metres) long.
  • Bull kelp grows seven inches a day; some of the real over-achievers grow up to a foot a day. It grows faster than a 14-year-old boy, and most bamboo.
  • Bull kelp achieves its impressive size in one growing season, with the most growth in just six months, from March to September.

Not impressed? Consider the carbon. When you think of carbon offsets you might consider tree planting. Instead, consider kelp. An aquatic forest of kelp can grow faster in relation to land forests, giving it the ability to capture carbon at a faster rate. This high growth rate means increased photosynthesis – requiring sunlight, water and carbon dioxide. A lot of carbon is absorbed into the kelp during growth and some of it can be found in the bull kelp float. The onion-shaped bulb captures and contains carbon monoxide as a buoyancy gas. The bulb contains up to three litres of air, of which about 12 per cent is carbon monoxide, so, in case you were wondering, inhaling from an intact bull kelp bulb is a bad idea. The annual growth of bull kelp adds important energy from the sun into nearshore food webs. It is hard to measure what percentage of the carbon stored by bull kelp makes its way deep into the ocean for long-term storage, but many climate and marine scientists have suggested canopy forming kelps such as bull kelp contribute in a significant and largely unrecognized way to sequestering atmospheric carbon.

A kelp forest alongside St. John Point, 2023

Globally, kelp forests are estimated to capture 4.5 million tonnes of carbon dioxide every year. The portion of this carbon that makes its way into long-term storage in the deep ocean is unknown, but if we hope to limit the devastating impacts of climate change, we need to protect all sources of carbon storage, especially ones such as bull kelp that create important habitat and food for so many other creatures.

Which is why it’s so important to monitor the health of the local kelp forests. The Conservancy has been monitoring the extent of kelp beds around Mayne Island since 2010, and in 2019, expanded the monitoring program into what is now known as the Southern Gulf Islands Bull Kelp Monitoring Collaboration. Read more about this kelp monitoring work here, and look for an update in the coming months with results from the 2023 monitoring data.

Conservancy staff and volunteers mapping kelp at Conconi Reef, 2023.

By winter, brought in by winter storms, bull kelp are all washed up. But, oh what a life they’ve lived.


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