Inhabitants of the Bull Kelp Forest

The bull kelp forests of the North Pacific are some of the most productive and biodiverse habitats on earth. Bull kelp is the brown algae that holds it all together, creating habitat for countless other organisms and forming the base of the vast ocean food web.

Sea otters are the smallest marine mammal and native to the North Pacific Ocean’s edge from Northern Japan through the Aleutians, south to Mexico. Its range intersects completely with the bull kelp forests. Nearly driven to extinction because of their luxuriant fur, sea otters play an outsize role keeping urchin populations in check so that kelp forests can thrive. 

Known as the wolves of the sea, these large, twenty-armed sea stars can move fast and eat small to mid-sized urchin. Their populations were decimated in 2014–2016 by a sea star wasting disease.

Sea urchins populate all the world oceans, living on algal detritus that drifts down to them. If the kelp forest balance is upset, urchin populations can grow too large and overgraze the kelp, leaving what is known as an urchin barren.

Abalone are sea snails with a large fleshy foot that grows inside a nacred shell. The shells of abalone have been important to indigeous communities for centuries as decorative elements in regalia as well as a trading item. Bits of abalone shell are a tidepooling treasure to find.

The North Pacific has the highest diversity of rockfish in the world. They thrive in the rocky habitat of the bull kelp forest, some living to over 200 years old. Their colors can range from orange to yellow to black.

Humans populated the Pacific Coast of North America during the last ice age by following ‘the kelp highway’ along the coastlines, a region of abundance. Human brains developed and societies evolved because homo sapiens could access the vast protein sources of oyster, fish, and seaweed as well as the minerals of the ocean such as iodine and potassium. From continuous Indigenous relationships to bull kelp to 20th century fisheries management, to 21st century kelp restoration projects, humans have been part of the kelp forest since their arrival.

Known for its beauty and prodigious growth, giant kelp mingles with bull kelp in some regions, but is the signature species that creates the great kelp forests of Southern California, Peru, Chile, and Argentina and can be found in New Zealand, Southern Australia, and South Africa.

Pterygophora californica (walking kelp) and other lower growing kelps thrive under the canopy of bull kelp. These less recognized kelps are vitally important in supporting the rich diversity of life in the kelp forest. Pterygophora is the oldest growing of North Pacific seaweeds and has the toughest, most upright stipe.

Bull kelp wrack is the piles of bull kelp found on beaches or washed up in coves. All kelp and other seaweeds wash up onshore as wrack, but bull kelp wrack is particularly astounding in its shear biomass. Bull kelp grows into a massive mature alga in only a few months, the stipes often entangled with each other. As an annual, it reproduces and then the whole entanglement of kelps dislodges from the ocean bottom. In healthy years of cold water, strong winter storms and abundant kelp growth, there should be piles of bull kelp wrack on the shore.