Bull Kelp: The Underwater Tree of Life

April 13, 2020

One of the Earth’s most mysterious forests is growing below sea level. Kelp forests are the foundation of diverse and unique marine ecosystems around the world. Despite their importance, many people don’t have a full understanding of these undersea trees. While there are many types of seaweed around British Columbia, one of the most noticeable is bull kelp (Nereocystis luetkeana).

Credit: Monterey Bay Aquarium

The bull kelp life cycle completes in a single year, yet it can reach lengths of up to 40 metres (130 feet)!

Where does it grow?

Despite its abundance, bull kelp is quite picky about its habitat, and is thought to be easily outcompeted by other kelps like the giant kelp (Macrocystis). It is found in nutrient-rich waters between 5°C and 20°C from Alaska to Northern California. Bull kelp needs a rocky ocean floor and clear enough water for sunlight to penetrate.

When does it grow?

During the summer, bull kelp forests thrive around British Columbia. The water stays cool in BC waters year-round, and sunnier days allow the marine forests to flourish. As autumn rolls around, kelp fronds (the long leaves) release spores onto the ocean floor before it dies in the winter. These spores will get together to make new baby kelp, which will grow to be the majestic forests of the next summer. The bull kelp life cycle completes in a single year, yet it can reach lengths of up to 40 metres (130 feet)! It grows at an average rate of 10 cm (4 inches) a day and can grow up to 18 cm (7 inches) in a day.

Marine mammals such as sea otters hunt for sea urchins in kelp beds and may use the kelp to avoid battling strong currents.

What other species depend on it?

Intact and healthy kelp forests keep other marine species safe and alive from the bottom of the food chain to the top predators. Invertebrates, such as sea urchins, feed on the kelp, while benefitting from the shelter from predators and strong currents. Fish use kelp forests as nursery grounds for their babies. Marine mammals such as sea otters hunt for sea urchins in kelp beds and may use the kelp to avoid battling strong currents. Without kelp, many marine animals would be vulnerable to storms, predators, and starvation.

Historical Use

First Nations have historically made use of many different kelps and sea grasses for food and tools. Bull kelp was specifically useful to make lines for anchors, fishing, and harpoons, and fishing nets. The solid part of the stipe (the stem part) near the bottom was cured with saltwater, freshwater, and dogfish oil, sometimes for up to a year. Even before curing the stipe is exceptionally strong. It withstands months of storms and weathering. These stipes could be knotted to create longer lines. The hollow part of the stipe was used as a hose to add water into steaming pits. It could also be used with the hollow bulb to store seal oil and molasses.

Credit: Schroeder et al. (2019)

One of the biggest threats to bull kelp is climate change.

Modern Use

Bull kelp can technically be eaten raw, though there are ways to prepare it. Some harvesters pickle it by slicing the stipe into thin rings, or the blades can be dried and used as seasoning.

What are the threats?

One of the biggest threats to bull kelp is climate change. It lives in cold, nutrient-rich waters. Even slight raises in ocean temperature will create an environment in which this keystone species will not be able to survive. Commercial harvesting is another potential threat, and more research is needed to manage this natural resource sustainably.

Sources

https://sanctuaries.noaa.gov/visit/ecosystems/kelpdesc.html

http://www.mapping.uvic.ca/section/bull-kelp-0

http://www.alaskafloatsmyboat.com/beachcombing/2013/8/26/harvesting-bullwhip-kelp

https://www.montereybayaquarium.org/animal-guide/plants-and-algae/bull-kelp

Schroeder, S. B., Dupont, C., Boyer, L., Juanes, F. & Costa, M. (2019). Passive remote sensing technology for mapping bull kelp (Nereocystis luetkeana): A review of techniques and regional case study. Global Ecology and Conservation, 19. Victoria, BC.

Springer, Y., Hays, C., Carr, M. & Mackey, M. (2007). Ecology and management of the bull kelp, Nereocystis luetkeana: A synthesis with recommendations for future research. Department of Ecology and Evolutionary Biology at the University of California. Santa Cruz. California.

Turner, N. J. (2001). Coastal people and marine plants on the northwest coast. https://hdl.handle.net/1912/2545

https://oceanservice.noaa.gov/facts/kelplives.html

 

Written By: Lili Wilson