How to (Re)Build a Kelp Forest

At first, the dive day seems like any other. We meet a small bunch of enthusiastic divers on the dock, load our gear onto the boat and jealously check out each other’s equipment. We jokingly express concern about the marine forecast, which has accurately predicted near-perfect conditions. Once we exit Los Angeles harbor and start motoring north, however, the atmosphere becomes all business. Clipboards emerge, foreheads furrow, and the other passengers begin to discuss the day’s goals in earnest.

Given the pedigree of these divers and the problem at hand, we should have expected as much. Our group consists of scientists representing The Bay Foundation, Los Angeles Waterkeeper and the National Oceanic and Atmospheric Administration (NOAA) — along with two photographers who quickly decide that their wisest move is to keep quiet and try to learn something. Tom Ford, the director of marine programs for The Bay Foundation and one of the leaders of the reforestation effort since 1998, completes his dive briefing and turns to us.

Healthy, green kelp forest
A healthy kelp forest can harbor all manner of marine life.

“See that kelp bed over there?” he asks, pointing toward the telltale gas bladders on the surface near the shoreline. “We restored that one in 2006 and the ones adjacent to it in 2007 and 2008. That one around the corner was done in 2009.”

Looking at the large swath of affected coastline (nearly 4 linear miles), we are stunned. This is bigger than we could have imagined.

Although it’s pretty well known that the beauty of kelp forests can match that of the most exotic warm-water destinations, underneath the superlatives is a less well-known similarity: These temperate ecosystems are in just as much peril as coral reefs. The nearshore kelp forests in some parts of southern California have experienced up to 75-percent declines in the last century, a multifactorial crisis brought about by storms, the El Niño phenomenon, pollution, urban water runoff in populous areas and predation.

Key among kelp predators is the purple sea urchin (Strongylocentrotus purpuratus). While larger urchins such as the red sea urchin (Strongylocentrotus franciscanus) are valuable to commercial fishermen because of their large gonads (the edible portion of the urchin), the far smaller purple sea urchins have miniscule gonads and are not harvested commercially. This combined with the hunting- and fishing-related declines of natural urchin predators such as sea otters, spiny lobsters and California sheepheads set the stage for disaster. Purple sea urchins, which number approximately two per square meter in healthy kelp ecosystems, have overpopulated the kelp forests in some areas, devouring the kelp holdfasts and creating bleak urchin barrens in their wake.

The terminology is absolutely accurate: Urchin barrens can hold as many as 70 purple urchins per square meter — and little else. Red sea urchins in such areas are much smaller than those in healthier marine environments, producing gonads that are approximately one-fifth the normal size. The barrens are valuable to no one: Divers don’t have kelp forests, fishermen can’t find robust urchins to harvest, and the other marine life that normally populates kelp ecosystems is pushed out. Even in places where water quality has improved, the barrens remain, which indicates that once purple urchins overpopulate an area, the kelp is doomed.

Purple urchins devour a kelp holdfast.
Purple urchins devour a kelp holdfast.

Academic researchers and conservation organizations have been grappling with this issue for decades. Urchin removal and relocation showed promise in small areas, demonstrating that the kelp could replenish rapidly if the purple urchin numbers were diminished. However, the process was laborious and dangerous for divers, and the weight limits of the boats restricted daily yields. Leaders ultimately decided to cull rather than remove the purple urchins in badly affected areas. The culling method is unsophisticated, using simple geologists’ picks to crush the urchins’ endoskeletons, but the results are undeniable. In recent years the effort has forged unlikely close partnerships among conservation organizations, divers and commercial fishermen, all united toward the goal of rebuilding the kelp forests. Ultimately, The Bay Foundation hopes to restore 150 acres, an area the size of a small college campus.

As we pull up to the dive site, we count four boats nearby, all owned by commercial fishermen working to help cull the purple urchins. Ford waves to the fishermen and talks to us about some of the recent successes. “For a long time people thought that smashing urchins would induce a spawning event, but research has never supported the theory — it’s just a myth. And do you see that?” he asks, gesturing to some kelp at the surface. “We just cleared that area of purple urchins four months ago, and the kelp is already starting to come back. It’s incredible to see. It grows so fast that in a few areas the fishermen have even been able to harvest red urchins again.”

He explains to us the goals for today, which include evaluating the perimeter of the new kelp growth and counting the urchins in the barrens. On the bottom, we slowly examine the edge of the kelp forest, noting clusters of large red urchins and sea stars on the rocks. Delicate strands of new kelp have taken hold on the sea floor, and garibaldi and surfperch weave lazily through the leaves.

Only 40 feet away kelp is absent, and the pale rocks are covered with purple urchins. The difference is frightening. We watch in gratified awe as the divers begin moving in an automated and perfectly tuned fashion. They set a central marker line, then each diver runs a 100-foot-long perpendicular transect line. Once the lines are set the divers begin counting the purple sea urchins in their area, then they pull up their line and run a new transect. When we have reached our agreed-upon bottom time, we ascend, and Ford collects the divers’ urchin survey numbers so they can determine which areas are most appropriate for culling.

Our work for the day complete, the captain starts the motor, and we head back to the harbor, examining the nearshore water for areas that appear to lack kelp growth. There are many, but the mood is optimistic as the divers excitedly compare the marine life they saw in the areas of newly reestablished kelp. As we pull up to the dock, Ford turns to us and says, “I have seen some incredible life come back to these areas: giant black sea bass, harbor seals and even a school of baby molas once; an excellent reforestation effort, I think.”

© Alert Diver — Q2 Spring 2014