Bull kelp

WHILE THIS BULL KELP thrives inside of the Monterey Bay Aquarium Kelp Forest Exhibit, the bull kelp on the Sonoma County coast has been reduced by about 93% due to a combination of environmental stress factors.

A devastating cascade of catastrophes turns vibrant kelp beds into underwater deserts

While there are flashier species out there, the plight of kelp, the giant tree-like algae that have been a dominant feature of the California coastline, is the one that demonstrates the local oceans dire situation.

Once, the great kelp forests flourished, providing habitat and food sources for myriad native aquatic species, but altered ocean conditions driven by climate change — and one badly timed sea star plague — have left barren oceanic deserts in place of once lush underwater jungles.

“Kelp is really the foundation of an ecosystem, so the whole ecosystem is really upended. When you take that out it can cause traumatic changes,” said Andre Boustany, principal fisheries investigator at the Monterey Bay Aquarium.

Boustany said it can affect all the animals in the ecosystem since it is where countless species — from otters to rockfishes and abalone to sea stars — forage and live.

“It would be like taking all of the redwoods out of the redwood forest,” he said.

Kelp cover map

THE KELP FOREST off the Sonoma County coast has slowly been deteriorating due to several environmental stress factors such as an explosion in the sea urchin population and increased water temperatures.

The primary species of concern is the bull kelp (Nereocytis luetkeana), according to the California Department of Fish and Wildlife (CDFW), which for centuries has created “a rich subtidal home for the many fishes and invertebrates that lived and thrived in this region of the state. Today, bull kelp forests should be the foundation of our nearshore coastal ecosystem. The floating canopy of this brown algae gives shelter to young fish and sea stars, and the kelp itself provides food for valuable species, such as red abalone and red sea urchin.”

Most scientists agree the problem started in 2013, when a wasting disease began to plague sea stars along the coastline.

According the University of California at Santa Cruz, “Sea stars along much of the North American Pacific coast experienced a massive die-off in 2013-14 due to a mysterious wasting syndrome. The disease, called ‘sea star wasting syndrome’ (SSWS) has persisted at low levels in most areas, and continues to kill sea stars. Similar die-offs occurred in the 1970s, ’80s, and ’90s, but never before at this magnitude and over such a wide geographic area. (At least 21) species of sea stars have been affected by the current SSWS event.”

Their death is an unpleasant one, as the disease decimates the bodies, leaving dismembered potions of limbs drifting in the tide whilst the main section of the body collapses into jelly.

While the disease does seem to progress through a given ecosystem in a particular order (the sunflower sea star is usually the first species affected) it is not clear to researchers at UCSC whether it does actually move from one species to another in a specific pattern or if some species are simply able to fight off the effects longer than others.

The significant impact on the sunflower sea star population was the first domino in the kelp forest disaster, because they are the predator of the purple sea urchin (Strongylocentrotus purpuratus) a voracious and invasive species that ingests massive amounts of kelp when left undisturbed.

Sea urchins

PURPLE SEA URCHINS have dramatically risen in population and devoured much of the kelp forests off the Sonoma Coast.

According to a study by the CDFW and published in Wildlife Research, in 2014, a large patch of warm water developed in the Pacific, stressing the existing kelp, slowing both growth and reproduction and damaging fronds and stem tissue, leaving them even more vulnerable to purple urchins.

The CDFW has found that the purple urchin population is currently 60 times higher than normal, and that in the past five years California’s kelp forests have declined by 93%. The “urchin barrens” have left behind a rash of dead and starving red abalone, once a prized commercial and recreational catch. As the abalone population plummeted, the fishery for abalone was closed through 2021, though some fear the closure may be permanent.

“The warm water conditions were associated with disruptions of coastal ecosystems along the Sonoma Coast, including harmful algal blooms, mortality of sea birds and marine mammals, and declines in kelp beds along our coast. The decline of kelp has led to the starvation of red abalone (that feed on kelp), leading to population declines in red abalone and the closure of the recreational fishery for red abalone in Northern California,” explained Eric Sanford, a professor in the Department of Evolution and Ecology at the University of California, Davis, and a researcher at the Bodega Marine Lab.

Sea otters once played a pivotal roll in containing urchin populations, but their near-extinction has left one less predator on the prowl for the urchins. The thriving otter population along the central coast has provided some protection for the kelp forests there, the northern population was largely wiped out by fur traders in 19th century.

While repairing the climate damage that leaves the kelp vulnerable will take time, local scientists, researchers, fisherman and grassroots organizations have come together to try to help local populations by holding urchin gathering days, where purple sea urchins are removed from the environment.

Unfortunately, unlike their red cousins, purple urchins are not in demand as an edible, commercial commodity.

However, studies abroad show that these efforts may be the equivalent of putting a finger in a dyke.

Tasmania lost most of their kelp in the early 2000s and studies there have shown that on extensively barren grounds, even significantly knocking back the urchin population (by introducing a species of lobster that is their main predator there) doesn’t mean a return of the kelp.

Similarly, an urchin barren in Hokkaido, Japan, is still bare after almost 80 years.

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