Two centuries ago, the waters off the California coast were home to a vibrant ecosystem of plants and animals. Vast forests of kelp provided habitat for thousands of species of fish and invertebrates. Some of these kelp forests were so dense that light hardly penetrated to the seafloor. But now, along much of the coastline, the kelp is all but gone.

The tragedy here goes far beyond species loss and a troubling decline in overall biodiversity in our coastal waters. Kelp are also great at taking up carbon dioxide from the atmosphere and they help reduce acidification of the oceans, essentially cleaning the water and bringing balance to the entire ecosystem.

But now, that balance is has been disrupted. A recent study says that California’s bull kelp (Nereocytis luetkeana) forests (one of several species that are endemic here) have declined by 93% in just the last five years.

It’s difficult to fathom the scale of this loss, and we are only beginning to understand what it will mean for the overall health of our coastal waters. When the kelp disappears, the entire complex web of organisms that rely on it for habitat and food is disturbed. That is to say, large swaths of the near-shore California coastal ecosystem depend upon kelp.

So, what is happening? Well, first a little history.

A healthy kelp forest in Channel Islands National Park (NPS)

Two centuries ago, when kelp forests along the coast were so abundant they stretched for hundreds of miles with thick canopies that could be seen at the surface. At the time, urchins existed, but their populations were held in check by sea otters, which have been known to eat 1/4 of their body weight in urchins in a day. But unrestrained hunting by trappers (often Russian and British) in the early 1800s and into the mid-century brought sea otter populations down so low, at one point they were considered extinct in the wild. With the otters gone, urchins flourished and along certain stretches of coast, the kelp disappeared. Remember, this was 200 years ago, long before California was even a state.

Otters have come back to certain stretches of the California coast, especially near Monterey, and in some cases, the kelp has come back. And, in fact, even now, some places around the state, things aren’t nearly so bad. One-third of southern California’s kelp forests are found within Channel Islands National Park and Channel Islands National Marine Sanctuary, where no-take marine reserves prohibit all take of living, geological, or cultural resources. In the reserve, California sheephead, spiny lobsters, and sunflower stars eat sea urchins and keep their population from exploding.

Bust most other regions are not so lucky. And things have gotten even worse. And this is where it gets more complicated.

An intense ocean warming period between 2014 and 2017 is the likely culprit in causing a mass die-off of starfish. Starfish prey on native purple urchins, keeping their numbers in check. With mass numbers of sea stars dead, the urchins proliferated, eating their way through the kelp forests. The result: disaster.

“What we’re seeing now are millions and millions of purple sea urchins, and they’re eating absolutely everything,” said Laura Rogers-Bennett, an environmental scientist with UC Davis Karen C. Drayer Wildlife Health Center and California Department of Fish and Wildlife operating out of the UC Davis Bodega Marine Laboratory. “They can eat through all the anemones, the sponge, all the kelp, the fleshy red algae. They’re even eating through calcified alga and sand.”

The loss of kelp forests in California should be immediately recognized as a major ecological problem to solve, and while some projects are underway to do just that, much more needs to be done.

Several organizations, most of them California-based, are trying to reduce the number of urchins in Southern California. For example, UC Davis researchers are working with Bay Area shellfish company Urchinomics to explore “ranching urchins, removing them from the seafloor and fattening them up to be sold as sushi. Urchins are highly valued by Japanese consumers and are even sold in some California sushi restaurants. One problem is that purple urchins tend to be too small to harvest for human consumption, hence the need to increase their size via aquaculture. But will this be enough to stop the urchin’s march towards environmental saturation? Probably not.

The Bay Foundation in Santa Monica launched a program to restore kelp beds around 150 acres of urchin barrens along the rocky reefs off Palos Verdes. Scientists, recreational divers, and fishermen go down and smash the urchins with small hammers. The effort has shown promise, with kelp growing back in 46 acres of restored reef. Again, this is not nearly enough.

Other strategies are outlined in the Sonoma-Mendocino Bull Kelp Recovery Plan, released last June by the Greater Farallones Association and California Department of Fish and Wildlife. It includes measures such as creating a kelp oasis to preserve seed stock and repopulate bull kelp when conditions are conducive to restoration.

This may all be too little too late. But we believe state, local and federal agencies should redouble their efforts now to mitigate the loss of kelp in California waters. The implications for further, perhaps total, loss of California’s once-flourishing kelp forests are just too dire and action is required now. As the authors of the report write “it may take decades before the complex biological communities, associates, and the ecosystem services provided by macroalgal [seaweed] forests rebound.”

