At first glance, purple sea urchins might appear harmless enough, scurrying across the ocean floor in their spiky domed shells. And, under normal circumstances, that would be true. But a "perfect storm" of changing oceanic conditions over the last several years combined to set the scene for a population explosion of the creatures, which has devastated the North Coast's ecosystem.

Unfettered by their primary predator — sea stars — the purple urchins are wreaking havoc in the region's reefs, continuing to persist in record numbers with an almost otherworldly ability to survive in the most desolate of environments, even after stripping once thriving bull kelp forests to bare rock.

With the future of one of the most diverse underwater worlds hanging in the balance, a coalition of scientists, government agencies and environmental groups is partnering with commercial and recreational divers to give the waxy canopies that once blanketed the coastline a fighting chance.

That means reducing the number of urchins — the so-called "goats of the sea," which in some areas are packed so tightly they're amassing spine to spine in "urchin barrens" of their own making — down to a very specific level of two per square meter.

Plans are underway for a concerted effort to cull the purple urchins in the water at Caspar Cove in Mendocino County while removing others by hand at two nearby sites — Noyo Harbor and Portuguese Beach. The removal effort will provide scientific testing grounds for what research indicates will be an important tool for preserving the region's remnant bull kelp, which is estimated to be just 10 percent of what it once was and what will be needed to restore areas left devoid of life in the urchins' wake.

The process will be closely monitored and there will be pre-dive and post-dive surveys to gauge the effectiveness and potential for rebuilding the once lush aquatic edens before they vanish forever.

Unable to compete for the remaining kelp, two important North Coast fisheries —the less hardy but coveted red sea urchin and red abalone — have already collapsed, a situation that cannot be rectified without the "eventual recovery of bull kelp forests and the return of sufficient food to support survival and reproduction," according to a California Department of Fish and Wildlife report.

James Ray, a Fish and Wildlife environmental scientist, is helping to coordinate the Mendocino urchin removal effort, which he says comes at a "critical juncture" for saving the bull kelp on which a dizzying array of species rely.

The idea, he says, is to "try to evaluate how effective that method might be," viewing it as a possible first step toward a broader project to preserve and restore kelp forests up and down the state.

"We hope to relieve the pressure of grazing over certain areas in these coves with the hope of getting the recovery of algae, more broadly, and to help ... kelp recovery at these sites," Ray says.

Unlike giant kelp, its southern cousin, bull kelp grows as a single stalk and dies off each year — basically an annual marine plant rather than a perennial — which makes it more vulnerable to hungry urchins that can hinder its ability to establish new growth.

The Mendocino sites are among a patchwork of places with bull kelp left standing on the North Coast — Trinidad Bay is another — which are needed as "seed banks" to store the spores needed to make new stocks in the future.

Scientists hope concentrating on areas with kelp forest remnants will give the preservation and restoration effort a solid start that could then be expanded once oceanic conditions improve. The concept is rooted in a project started down in Southern California in the 1990s that showed success in restoring giant kelp beds.

To facilitate the undertaking, the California Fish and Wildlife Commission — which last year raised the daily recreational purple urchin take limit to 40 gallons in Humboldt, Mendocino and Sonoma counties — recently passed an emergency rule that lifts those limits altogether at Caspar Cove.

Late last month, the Ocean Protection Council approved allocating nearly $500,000 for the one-year project's planning and oversight, as well as to pay commercial divers for the removal effort. Those funds will be combined with $75,000 from CDFW and another $60,000 from the Waterman's Alliance, a nonprofit that is coordinating the recreational divers volunteering to aid in the purple urchin removal effort.

"This project has the potential to significantly improve our understanding of the ecological and economic crisis that has devastated California's North Coast in recent years," the council's staff report states. "In particular, the project will provide a scientific basis for evaluating the efficacy of large-scale purple urchin removal as a kelp restoration tool on California's North Coast, directly informing future management actions as California seeks to protect its iconic underwater forests in the face of changing ocean conditions."

The Ocean Protection Council, which oversees the state's Marine Protection Areas and promotes ocean and coastal resource management with partner agencies, also placed a high priority on protecting and restoring California's kelp habitat in its recently released five-year strategic plan for protecting the state's coast and oceans.

How did things get this bad?

The first signs started emerging in August of 2011, when an outbreak of toxic algae off the Sonoma County coast caused a massive die off of marine life. Two years later, a mysterious sea star wasting disease appeared, wiping out about 80 percent of the purple urchins' main predator and causing local extinctions of the large, 24-armed sunflower sea star.

Cue the ensuing purple sea urchin explosion, which arrived just as a marine heatwave hit the North Coast when the so-called "warm water blob" showed up in 2014. That was trailed a year later by the "Godzilla" El Niño of 2015.

While bull kelp stands can be resilient, they are highly sensitive to rising ocean temperatures and the convergence of environmental circumstances proved too much. Now the race is on, as one sport diver who spoke in favor of the urchin removal project put it, to make sure "Mother Nature has something to work with when she's ready to rebuild."

As it stands now, Ray says most of the remaining pockets of bull kelp "persist in naturally self-defending locations."

In the case of Trinidad, that includes stands that are growing on boulders and rock set amid a large expanse of sand, which has slowed the urchins' spread because they don't like to cross it as much as a continuous reef. But, Ray notes, that doesn't mean those areas aren't vulnerable as well.

"Don't get me wrong," he says. "The urchins will eventually get there."

Kimberly Wear is the assistant editor at the Journal and prefers she/her pronouns. Reach her at 442-1400, extension 317, or [email protected]. Follow her on Twitter @kimberly_wear.