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What's behind the loss of the forests of the sea?


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Posted by on June 03, 2006 at 00:20:39:

Scientists now say the main culprit affecting kelp isn't pollution but overfishing.

Giant kelp forests once dominated the Southern California coast, but these important sea-life habitats have dwindled away in the face of a variety of challenges.

While the storms and warm water of El Niņos have denuded their share of kelp forests, a new study shows that, among human influences, it's overfishing -- not polluted runoff -- that does the most damage.

The study by the National Center for Ecological Analysis and Synthesis in Santa Barbara found that the main constituents in the runoff from cities and rural areas do not seem to be the culprit for kelp degradation.

Instead, it's the lack of predators that eat the animals that graze on kelp. Their absence is due to overfishing, scientists say, and allows kelp-eaters to mow down the kelp.

That conclusion jibes with the observations of kelp restorers at Santa Monica BayKeeper, which for years has been working to re-establish kelp growths off Malibu and the Palos Verdes Peninsula. The work starts with removing urchins -- kelp grazers -- by the thousands.

The study shows the importance of careful management of fishing, said lead researcher Benjamin Halpern of the center, which is funded by the National Science Foundation and affiliated with the University of California, Santa Barbara.

It also shows that the marine preserves being proposed along the coast could be very helpful for kelp forests, Halpern said.

'We are doing the right thing'

"What we've found in the study is that we are doing the right thing, the (Marine Life Protection Act) is the right thing," Halpern said. "One of the goals of that is to set aside part of our coast for 'no-take' preserves, and to limit fishing in a bunch of areas."

While he focused on the northern Channel Islands off the Ventura County coast, Halpern said the study is applicable to kelp habitat throughout Southern California.

Halpern and his team looked at data from years of kelp surveys from the northern Channel Islands. Then they looked at counts of 46 species of fish and invertebrates such as snails and urchins, as well as levels of nitrogen and phosphorus in the water.

These are two chemicals that are typically found in urban and farm runoff and are considered "nutrients" that, in overabundance, have been thought to be detrimental to kelp. The study found that not to be the case. (The study did not examine levels of toxic metals that can also be found in urban runoff.)

Halpern said that the study does not suggest any cutback in efforts to control polluted runoff.

In the study, Halpern found that the presence of spiny lobsters and Kellet's whelks, two species in the north Channel Islands that eat the kelp-munching urchins and snails, was important to the abundance of kelp.

California sheephead, a large fish that is a prized catch by anglers and another predator of urchins, was not much of a presence in the study because it doesn't generally dwell in the northern Channel Islands. The sea otter, also not in the study, is a very efficient urchin eater, but wildlife managers keep it north of Point Conception, away from the Channel Islands and the Southern California area.

There's not much people can do about El Niņo, which can hurt kelp with strong storm waves and warm water. But human activity can adversely affect the regrowth periods, when normal climate conditions return and kelp should otherwise be able to spread and grow quickly.

Local efforts paying off

Marine biologist Tom Ford leads Santa Monica BayKeeper's effort to restore kelp off Malibu and Palos Verdes Peninsula's Long Point. Before "replanting" a new site, he and his volunteer divers typically remove thousands of urchins.

Since getting started in November of last year off Long Point, Ford and crew have taken 7,500 urchins. A similar earlier effort has helped restore kelp to a spot off Malibu.

While Ford said the new study by Halpern could have been improved by also looking at areas where sea otters and sheephead play a role, he said its findings concur with his experience.

"The findings in that article agreed with popular opinion in science, and agree with what I observe, and the changes that I see due to our restoration efforts," Ford said.

Locally, lobsters and sheephead eat the urchins, but to become highly proficient at eating urchins, these crustaceans and fish need to be big, and the biggest ones among them are the ones that get fished out, Ford has said.

The Cabrillo Marine Aquarium is holding special events this month to spotlight California kelp forest restoration.

Educator workshop: 8 a.m. to 3:30 p.m. Saturday . K-12 teachers will learn about hands-on activities and other methods for teaching about kelp. Go towww.usc.edu/org/cosee-west/.

Lecture: "Where the Kelp Are We?" 11 a.m. to noon Saturday . Marine biologist Tom Ford -- "Captain Kelp" of the Santa Monica BayKeeper -- talks about the history and future of kelp forests, and the progress of local kelp restoration efforts. Free. Go to www.cabrilloaq.org.

Visiting exhibit opens: Tuesday evening . "Kelp Perception" with artist Dawn Navarro explores the world of kelp through art. Go to www.cabrilloaq.org.



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