Restoring Underwater Arch Cove


If you have found yourself walking along Palos Verdes bluffs in the past year, chances are that you have seen the Waterkeeper boat either anchored in a cove or slowly moving along the coastline. In 2014, over 100 trips were completed with teams of dedicated volunteers that have worked on the Kelp Project and MPA Watch. We have been busy out there and we plan on continuing full steam ahead on our restoration and monitoring as we move into 2015.

Last year our volunteer divers accomplished 524 dives totaling 513 hours underwater! This effort combined with that of the commercial urchin divers and the biologists from the Santa Monica Bay Foundation has contributed to the restoration of over 20 acres of reef in Palos Verdes. Our method of restoration focuses on reducing the densities of purple sea urchins (Stronglyocentrotus purpuratus) to densities found in healthy kelp forest ecosystems. Once we finish working in an area, the post restoration monitoring has shown that the average density of S. purpuratus averages 1-3 per square meter. With newly available space on the reef, the Giant Kelp (Macrocystis pyrifera) has been able to recruit to the substrate and flourish. M. pyrifera can grow quite fast, and in just about 3 months’ time, we have seen the complete transition from bare reef to a rich and productive kelp forest. It seemed like every day we were out on the water we could see more and more kelp reach the surface while expanding to areas that had been recently cleared.

Witnessing this transition has been an equally interesting and exciting experience. When we first visit a site, we are faced with an expanse of reef that is completely dominated by purple sea urchins. Surveys often find that average densities exceed 30 urchins per square meter. At Underwater Arch Cove, where most of our efforts were focused in 2014, extensive surveys mapped out 13 acres of reef completely dominated by urchin barrens. With so much work to be done, we focused our efforts in quarter-acre plots that we could re-visit and systematically clear. Underwater, we always work along a baseline transect line that is laid between two sub-surface marker buoy’s we call “smiley’s” for obvious reasons (see picture). This baseline ensures that we are working in the exact same spot and are able to track and monitor our progress. Within days after clearing purple urchins, a film of algae begins to grow on the reef and about a week later, small kelp plants begin to establish themselves. A month later the reef really begins to transform as the newly established kelp start to take off and begin growing towards the surface. Just over three months later, the reef is completely unrecognizable as M. pyrifera creates a thick and lush canopy that reaches the surface. Diving through this newly “re-built” kelp forest is truly rewarding, especially knowing that you have contributed to its restoration in a hands on way. A great video from The Bay Foundation that shows this process through time can be found here

Currently, we have moved down the coast to Hawthorne cove and we have already begun clearing patches of reef dominated by urchins. In 2015, our goal is to restore 25 more acres of reef along Palos Verdes. The progress that was made in 2014 could not be accomplished if it weren’t for our incredible team of volunteer divers. The time and effort they have spent underwater has directly facilitated the restoration of the kelp and aided in putting this vital near-shore ecosystem back into balance. To get involved and be a part of our team, visit our volunteer page to find out how you can help!

-Ian Jacobson, Kelp Project Coordinator

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