Bull kelp grows and thrives in rough-and-tumble coastal waters. It's aided by its rootlike holdfast, which has many fingerlike projections (haptera) that hold the plant tight to rocks. From the holdfast, a flexible stem (stipe) extends 30 to 60 feet (10-20 m), gradually enlarging to form a single, round float. As many as 30 to 64 long, narrow blades grow from the float and form a golden brown canopy on the water's surface.
Bull kelp is an annual seaweed—meaning it grows from a spore to maturity within a single year. It grows quickly, sometimes 10 inches (25 cm) in one day. Bull kelp reproduces by spores in spore patches (sori), which are heavy enough to fall to the ocean floor. This ensures that spores settle close to parent plants and on suitable substrate. Winter storms wash spent bull kelp onto beaches where the plants dry and turn brown. They have the appearance of bull whips, giving this kelp its common name.
Kelp is harvested to make a variety of commercial products, but the harvest must be carefully regulated to avoid harming the kelp forest ecosystem.
Bull kelp forests offer protective shelter for young fishes and many invertebrates, such as sea urchins, sea stars, snails and crabs. Sea otters thrive in kelp forests too. They can find their favorite foods on the forest floor, then take an after-lunch nap in the forest's golden canopy—often wrapped in a flexible stem or two to keep from drifting away.
The gas in bull kelp floats is up to 10 percent carbon monoxide.
Nereocystis, this plant's genus, is the Greek word for "mermaid's bladder."