Kelp: California's Coastal Forests

Kelp: California's Coastal Forests

Kelp: California's Coastal Forests

Written by Jane Park

Using science to inform the restoration of California’s underwater forests

Kelp forests are underwater forests that support some of the world’s most productive fisheries and unique ecosystems.  Kelp forests occur throughout the world.  California’s kelp forests are particularly unique, as our “redwood forests of the sea” are among the tallest and most productive of the world: Northern California’s “bull kelp” grow an average of 4 in./day and can reach heights over 100 ft. 

Bull Kelp Diagram showing parts of the plant

Kelp Forests in Decline

In 2019, Coastal and Marine Sciences Institute researchers documented interacting environmental stressors that led to the precipitous decline in bull kelp: a harmful algal bloom in 2011, a sea star wasting disease in 2013, a marine heatwave from 2014 to 2015, and the ensuing proliferation of purple urchins starting in 2014. Warmer waters both stress kelp and benefit the urchins that eat kelp. Urchins further benefited from the disease outbreak that decimated their main predator, the sunflower sea stars, now locally extinct on the California north coast. The purple urchin population off California’s north coast has increased 60-fold, and kelp in the north coast declined dramatically, by 86-97%. As a result, a barren landscape, similar to the aftermath of clear-cutting trees, has replaced the once abundant kelp forests.  

The purple urchins also suppress kelp recovery. As the amount of kelp decreases, the urchins go dormant without food, where they are essentially empty and lack any nutritional value for predators or for fisheries. Dormant urchins do still graze on food if it becomes available, so the persistence of dormant urchins slows down the regrowth of kelp. In contrast to the urchins that can live for over 50 years, bull kelp on the north coast are “annuals” that live one year, and kelp forests re-grow from microscopic spores each year. Therefore, the eventual recovery of kelp forests relies on near-term protection and restoration. 

The Importance of Kelp Forests

Kelp forests support California coastal communities in a number of ways. They contribute to ecotourism and support both commercial and recreational fisheries. For instance, the recreational fishing industry for red abalone, which eat kelp, is valued at  $44 million. Because of the lack of food, the abalone are starving. Consequently, the industry experienced a reduction in fishing in 2017 and complete closure in 2018. The commercial fishery for red urchins, a distinct species from the purple urchin that also feeds on kelp, was declared a federal fishing disaster in 2019. In addition, these underwater forests are biodiversity hotspots, associated with a far greater number of species than urchin-dominated barrens. 

A small purple urchin on a hand
Photo by David Slipher

Discovering the Road to Recovery

The first step of any effort to restore kelp forests is reducing the purple urchin populations. Government agencies, fishery alliances, non-profits, and citizen groups are organizing to harvest urchins. This faces inevitable funding limitations because dormant, empty urchins do not have the “uni” for sushi and purple urchins, unlike the larger red urchins, have no commercial fishery to date. In addition, even if kelp forests thrive again, the sea life communities that depend on them will likely need some help to bounce back. While urchin harvest is underway based on the best available science, scientists and managers face a number of unknowns: given limited resources, what is the optimal urchin harvest strategy in terms of location, intensity, and timing? Can kelp re-seeding, sea star reintroduction, and red abalone reintroduction be successful and improve restoration outcomes? How do different government actions and regulations affect restoration success not just for kelp forests, but also for the people that rely on them?  What restoration actions might most improve resiliency to future marine heatwaves? 

CMSI researchers are playing a critical role in developing the science that informs kelp forest restoration, with projects including: 

  • Using genomics to measure movement of kelp forest species: UC Davis and partners are currently working through the California Conservation project to conduct a ‘community genomics’ assessment of connectivity and climate tolerance in multiple kelp forest species, including giant kelp and purple urchins. Connectivity is a measure of how frequently organisms move between patches of habitat. This could aid in choosing restoration sites that maximize connections between patches and protect climate change tolerant populations.
  • Understanding sea urchin population dynamics in a changing ocean: Temperature may affect the quality of sea urchin eggs and the quantity and behavior of their larvae as they are transported along ocean currents to their final settling places. UC Davis researchers and partners are using climate-controlled experiments mimicking ocean warming coupled with oceanographic transport models to predict how purple urchin populations will respond to different circulation patterns and warmer conditions in California’s future ocean. 
  • Developing the science of abalone restoration: Bodega Marine Laboratory (BML) is a member of The White Abalone Recovery Consortium, a team of state, federal, university and private partners improving our understanding of how to raise white abalone in captivity and release them into the ocean. The lessons they are learning about white abalone will inform the restoration of red abalone. 
  • Scaling up kelp cultivation: The low density of kelp is making it difficult for kelp to regenerate and recover, even in areas with urchin removal. To accelerate recovery of Bull Kelp, UC Davis researchers are developing replanting strategies for kelp at the Bodega Marine Laboratory to support large-scale offshore kelp forest restoration efforts.
  • Expanding the restoration toolkit: UC Davis received seed funding from California Sea Grant and the Ocean Protection Council to lead a multi-university effort to develop the science behind novel restoration approaches, such as more efficient urchin removal techniques, ensuring that remnant kelp patches remain connected within a broader network, introducing heat-tolerant strains of kelp, and reintroducing sea stars. This effort includes UCD-led models to predict optimal restoration approaches to maximize long-term benefits. 
  • Considering the human dimensions of restoration: UC Davis is currently seeking funding to lead a multi-university effort to create a “socio-ecological systems” framework for engaging in proactive restoration that incorporates the human, ecological, and physical components of the system. A key goal of this effort is to identify policy changes that might allow for efficient restoration and a more nimble response to future marine heatwaves.

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