A CRY FOR KELP: Dead seaweed masses concern La Jollans

A dramatic increase in dead seaweed floating in the ocean and depositing on the beaches around San Diego has La Jollans concerned that underwater kelp forests are being decimated by global warming.

So are they?

With ocean temperature nearing 80 degrees by Scripps Pier for the first time in recorded history, this does not seem like an unreasonable conclusion to draw, and social media has been atwitter with freak-outs.

“I’m seeing giant swaths of unhinged kelp all over the place,” La Jolla surfer Pierce Kavanagh posted on Facebook, to which his followers replied with “Kelp is getting thrashed!” and “It dies at 70 degrees!”

The kelp is so unusually thick this summer that a huge, decaying mass is believed to have slid down an underwater canyon off La Jolla Shores on Aug. 1, releasing a cloud of hydrogen sulfide so smelly that facilities workers at Scripps and Birch Aquarium reportedly searched for a gas leak.

“Not to worry,” says seaweed expert Ed Parnell of the Scripps Institution of Oceanography (SIO). The great kelp wash-up is not due to the oceans hitting 80 degrees, since that’s only on the surface, not where kelp grow.

“The surface temperature is not what’s important when they germinate as juvenile life stages,” the associate researcher in SIO’s Integrative Oceanography Division wrote in an e-mail to the Light. “It is the bottom that is important.”Below 30 feet, the temperature is still in the mid 50s, perfect for kelp plants, which live up to 10 years each and continually shed the fronds we sea at the surface.

“The recent wash-up is due to the summer swell we’ve been having,” Parnell wrote, explaining that a small portion of the kelp forests were ripped out by strong hurricane swells but that giant kelp is “still doing fine, much better than last year.”

However, what Parnell really meant was not to worry yet. In the long term, local kelp forests are still very much endangered by global warming. For instance, a separate series of warming events that began in 2013 — often referred to as “the blob” — was followed by an El Nino and, according to Parnell, “devastated” the kelp forests.

“This pattern of disturbance is happening more frequently, and with continued warming, the giant kelp forests in SoCal will become smaller and smaller,” he wrote.