What's Up with Kelp?

Redwoods of the Ocean

Bull Kelp (Nereocystis luetkeana) is the majestic kelp that grows up to sixty feet in one season, to reproduce and be washed away by winter storms each year. It is the signature species making up the vastly productive kelp forests of the Northern Pacific coastline from Central California through Northern California, the Pacific Northwest, British Columbia, Alaska, and halfway through the Aleutian Islands. It is the kelp within which herring school and spawn, rockfish abound, seals seek prey and refuge from sharks, and young salmon adapt to their salty home. It is the canopy under which countless other seaweeds grow including the understory kelps and pink rock-encrusting coralline algae that attract the settling of urchin and abalone and young bull kelp. Under the gestural swaying largess of the bull kelp is a colorful world with sea stars and nudibranchs and sponges. There are also other large kelps in the mix—Macrocystis pyrifera, or giant kelp, which dominates the kelp forests south of Monterey clear to Mexico. But from Central California to Alaska, bull kelp is the major player, massive and hefty, thriving in the nutrient-rich, cold waters of the Northern Pacific. It is the pride of the North Coast of California. Known as cʰanamá by the Pomo, it usually thrives in the dynamic, wave-churned waters, with great heaps of tangled wrack thrown onto the beaches and coves every year when these ocean forests are healthy.

Kelp Abundance Until 2014

The bull kelp forest once supported various dynamic fisheries along the Mendocino and Sonoma coast including the red urchin fishery where divers walk the ocean floor collecting the larger urchin for the uni market. The recreational abalone fishery along the North Coast was legendary, until it was closed in December of 2017. Both urchin and abalone feed on kelp—they are herbivores—typically subsisting on the detritus from kelp as it sinks to the seafloor. The crab, rockfish, and salmon also depend on healthy kelp forests for increased abundance.

And then it went away. Sea star wasting disease was first detected at the end of 2013 and felled all sea stars on the west coast during the years of 2014 and 2015. Millions of sunflower sea stars, before now unassuming in its role as purple urchin predator, vanished from the waters. Research suggests that as many as 5.75 billion animals died from the disease (Gravem et al. 2021, Hamilton et al. 2021).

Simultaneously an ocean heat wave, known as “The Blob,” plus an El Niño event, parked a large mass of warm water offshore raising the surface temperatures by as much as 2.5 degrees Celsius—a huge amount. The third event, surmised to be a result of the previous two, was an explosion in native purple sea urchin abundance. The annual surveys of the Mendocino and Sonoma coast done by Reef Check reported that the purple urchin numbers as measured before and after these ocean events increased by over 3,000%! And these hungry purple urchins (though native to these waters) with no predators, are eating the kelp. Lots of it. Kelp canopy mapping and monitoring have shown a greater than 96% loss in bull kelp canopy throughout the Mendocino and Sonoma coasts. The ramification of this kelp loss goes deep into the community with closed fisheries, loss of legacy dive shops and the loss of an ecosystem highly valued by a coastal community deeply rooted in kelp.