Bull kelp

Natural history

Bull kelp is an annual seaweed—meaning it grows from a spore to maturity within a single year. It grows quickly, sometimes 10 inches (25.4 cm) in one day. Bull kelp have reproductive patches (sori) of spores, which, upon maturity, are heavy enough to drop to the ocean floor. This ensures that spores settle close to the parent alga and on a suitable substrate. Winter storms wash spent bull kelp onto beaches where the kelp dries and turns brown. It has the appearance of bull whips, giving this kelp its common name.

In Monterey Bay

This seaweed thrives in the high-energy wave environment found along the Big Sur coast and in the rougher waters outside protective bays and inlets. Unlike giant kelp, which has blades growing all along the stipe, this seaweed’s canopy is focused at the top.

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.

Conservation

Kelp is harvested for use in aquaculture and can be found in many food products. Commercial harvesting in California is highly regulated to protect our kelp forests from improper or over harvesting. In addition to possessing a license, harvesters must trim kelp from the top, may not go more than four feet (1.2 m) below the surface of the water and may only collect in designated areas.

Protecting sea otters, a keystone species, is crucial to the health of California’s kelp forests. Without a healthy presence of sea otters to prey upon the kelp-consuming urchins, urchin populations can get so large that they destroy entire kelp forests.

Factors such as climate change, pollution, habitat degradation and boating can also affect the health of a kelp forest.

Cool facts

• Kelp forests help protect coastlines from extreme wave action.
• The gas in a bull kelp’s buoyant pneumatocyst is up to 10 percent carbon monoxide—a byproduct of photosynthesis.
• Bull kelp is sometimes called “mermaid’s bladder,” a loose translation of this alga's genus, Nereocystis.