Like many of the ocean’s most vital processes, the offshore kelp forests change in constant cycles. It’s for this reason that marine scientists are not troubled by a recent study that found San Diego’s kelp forests have diminished by 90 percent.
The study conducted by Costa Mesa-based MBC Applied Environmental Sciences was done by examining the kelp from the air. It’s for that reason that Scripps Institution of Oceanography marine scientist Ed Parnell believes 90 percent may be a little high.
“A lot of the kelp in northern La Jolla, the shallowest it gets is 25 feet from the surface,” Parnell said. “So, you’re not going to see that from the air.”
Parnell said that the kelp forest off the coast of La Jolla, which is one of the largest in Southern California and stretches from La Jolla Shores to Pacific Beach, has actually depleted by a smaller amount. He estimates that the kelp forest has diminished by about 75 percent from peak levels in the northern portion of the forest and by about 50 percent in the southern area. Scripps monitors the kelp forests using sonar testing, rather than airborne observation.
Kelp is a habitat for marine life and an important part of the ocean’s ecosystem, but even if the forest was down 90 percent from peak levels, it wouldn’t be cause for alarm, Parnell said.
“Kelp is highly dynamic,” he said. “It is very capable of a quick recovery.”
Parnell said that the best example of the wild fluctuation of kelp forests came in 1988, when a huge storm ripped out virtually all kelp off the coast of San Diego.
“The bottom looked like it had been sandblasted,” Parnell said. “By the next year, it was approaching all-time historic highs.”
Kelp can grow at a rate of two feet per day. The current down cycle in kelp has been caused mostly by high water temperatures, Parnell said. Water temperatures got an early boost with the July heat wave that struck San Diego, and surface water temperatures reached 75 degrees. Warmer water has fewer nutrients that kelp needs to survive than does cold water.
Another factor that could have caused the kelp to diminish even more dramatically is red tide. Red tides, which are algal blooms that give the ocean water a reddish tint, block the sunlight that kelp needs to flourish. San Diego didn’t experience any significant red tides this summer.
“If it had,” Parnell said, “there would be even less kelp than there is now.”
Parnell is convinced it will all grow back. “What might delay it coming back is more warm water again next year, or red tides.”
The warm water has also led to an abundance of bryzoans, a bacteria that lives on the kelp and breaks it down. Parnell said that Scripps scientists first started noticing an increase in the presence of bryzoans in the kelp forests off North County San Diego, which has much smaller kelp forests than those off La Jolla because there is very little hard bottom in North County. Kelp does not grow well over sand.
The current decrease in kelp may create the exact conditions necessary for the forests to rebound to peak levels that were last reached in 2002, Parnell said. With less kelp growing to the surface now, more sunlight is able to reach the ocean bottom and feed the root system, which is called holdfast.
Holdfast lives for between four and eight years and goes through a high turnover of stipes, the bladed fronds that are a common sight on our local beaches. Stipes typically survive for about six months.
“How much the kelp comes back will be a function of how clear the water is and how much light gets to the bottom, and a function of how cool the water is,” Parnell said.
In the meantime, kelp is currently down and what’s left is harder to see. Large kelp forests have the ability to stall ocean currents, but with the plants currently relatively scarce, the currents are running strong and pushing kelp further toward the ocean bottom.
Local fisherman who work the perimeters of kelp beds in search of yellowtail and mackerel are finding they have a little less area to work with. Kelco, a company that harvested kelp and extracted the algin that is used in many pharmaceutical and food products, moved its base of operations last year from San Diego to Scotland, but it wasn’t because of the decrease in kelp. The company simply had lower costs of operation overseas.