Climate change taking a toll on underwater forests
By Andrew Beahrs
In August of 2014, my family spent a week off the coast of Southern California on Catalina Island. We spent most of our waking hours in the water, kayaking and snorkeling above and through the kelp forests that were easily the most lush and vibrant part of the drought-dried island.
Giant kelp can grow up to a foot every day, and the fifty-foot stipes and broad blades of the Catalina kelp sheltered an underwater menagerie. I’d breathhold dive through schools of blacksmiths, kelp bass, and inquisitive sheepshead, sometimes startled by the sudden appearance of a harbor seal who would soon disappear back into the forest. Pink and green abalone lived in cracks beside lobster and octopuses; the rocks were covered with gorgonians, crustose coralline algae the color of bubblegum, and clutching kelp holdfasts.
Two months ago I returned to Catalina with Reef Check; a volunteer organization tasked with monitoring the life on California’s rocky reefs, and soon realized that my family had visited the island at a moment of profound change. This time, I met people who began working at the Catalina Island Marine Institute in December of 2014—only four months after my first trip—who have never seen kelp growing.
The rocks where the forests once rose are now covered in tangled, mossy fields of Sargassum horneri (shown left), an invasive seaweed from Japan that first appeared in Long Beach Harbor back in 2003. For eleven years it slowly spread, thick and encompassing, but dying off in summer as though deferring to the giant kelp that has long defined Catalina’s undersea habitats.
Then, in autumn of 2014, warm waters began stressing and finally killing the kelp. This had happened before. But this time, the sargassum was lurking; it spread and spread until it had displaced off what little kelp had survived the warmth.
Now, garibaldi and kelp bass swim over an almost undifferentiated, weedy mass. Most of the invertebrates—the gorgonians, the sea cucumbers—are gone. When the sargassum dies back in summer (as an annual, it always does), it’s clear that the coralline algae beneath is pale and dying, and no kelp returns to cover the bare rock. And there are workers at the Catalina Island Marine Institute, who have never seen the undersea forests the island was known for—forests preserved in the institute’s stained glass windows, which were once tributes and now feel more like memorials.
It’s hard to know just how much of this ecological phase shift can be attributed to climate change. The kelp has died before. The sargassum has been threatening to spread for years. This is an El Niño year, with exceptionally warm waters, perfect for damping down the kelp and promoting a sargassum boom. Maybe this is just bad luck, timed as though designed to kill off the kelp forests.
But the “warm water event” that first stressed the kelp, leaving it vulnerable if not dead, came a full year before El Niño’s exceptionally warm currents arrived. And the sargassum has been present for over a decade; it wasn’t until the waters warmed that it truly exploded, seizing every patch of bare rock until not even the wildly-prolific kelp could take hold. If climate change is not the lone culprit, surely it’s at least contributed to the severity and totality of the change. With the warming of the oceans, it’s virtually certain that we’ll continue to see more such once-anomalous seasons, which will weaken temperature-sensitive species until they’re unable to compete with new invaders.
Wanting to protect a place for its economic value is perfectly valid—but so is wanting to protect it for its spiritual worth. My first visit to Catalina left me inspired; my second left me determined.