A Team Approach

Project Overview

Bull kelp mapping and monitoring have shown a greater than 96% loss of canopy habitat throughout the Mendocino and Sonoma coasts (hereafter ‘North Coast’) over the past decade due to a convergence of multiple stressors leading to ecosystem imbalance. The sea star wasting disease killed off billions of sunflower sea stars, a primary predator of native purple urchin, and an ocean heat wave, known as “The Blob,” plus an El Niño event raised the surface temperatures by as much as 2.5 degrees Celsius. The warm water inhibited kelp from growing and reproducing, thus leading to a steep decline in detrital material for kelp grazers such as abalone, and red and purple urchin which typically passively feed on these subsidies while protected in cracks and crevices. As a result of this kelp loss and a predator to keep them in check, purple urchin changed behavior in search of food and moved into the nearshore kelp forest environment, increasing their populations by over 3,000%, according to Reef Check data.

Part of the 4% remaining kelp refugia on the North Coast was, for many years, at the mouth of the Big River right off the Headland cliffs at the town of Mendocino. This was a critical habitat of incredible value to protect and defend, given regional losses and its status as a kelp refugia. But in 2022, urchin encroached into the Portuguese Beach area of Big River and began grazing the refugia at an alarming rate with declines continuing into the following year. In less than two years, over 80% loss of critical kelp canopy refugia at Portuguese Beach was observed, threatening the productivity of this Big River site. The Nature Conservancy led an interdisciplinary team in a successful bid for State funding to bring together the research and experts doing experimental restoration and community building for this project to recover five acres of recently lost bull kelp forest at the Big River site. The project team will implement a strategic sequence of grazer suppression and kelp outplanting techniques to optimize kelp restoration success at Big River, expanding best practices in both kelp recovery and community engagement to scale and accelerate bull kelp forest recovery. Pilot restoration work (purple urchin harvest and small scale kelp enhancement) at nearby Albion Cove led by the same project team is continuing and this knowledge is being leveraged at Big River.

Implementation

Spring 2024: TNC is awarded funding by the State (California Sea Grant/Ocean Protection Council). Project Team developed spatial design and approach to kelp recovery to scale and accelerate restoration of kelp in this recently deforested location at Big River. California Sea Urchin Commission Sonoma State, Moss Landing, Reef Check and TNC conducted reconnaissance dives to identify target areas to harvest urchin and ecological surveys prior to restoration to get a baseline understanding of the ecosystem prior to beginning work.

The first North Coast KelpFest! helped launch the Big River project in May/June of 2024 with a series of art, science, food and film events hosted in Mendocino and Fort Bragg, educating the community about kelp forests, elevating multiple perspectives for stewarding kelp forests and introducing them to this project. Summer dive and restoration training internships began with Reef Check and TNC, welcoming a restoration workforce training and experience for local and young scientists.

Grazer suppression by commercial urchin divers starts via hand harvest of native purple sea urchin. Kelp cultivation from sori collected at Albion in winter 2024 allowed for the growth of baby sporophytes at Moss Landing Marine Labs and initial pilot outplanting efforts at Albion with novel ARKEV (Accelerating Recovery of Kelp Ecosystem Vegetation) modules. The ARKEV modules were designed by project team to be low-cost and highly scalable leveraging best practices from previous years of testing kelp enhancement in an open coast system; in short, they are independent units that hold tied in juvenile bull kelp off the bottom to minimize urchin grazing and leverage lessons learned from previous years of exploration.

Summer 2024: Targeted purple urchin harvest by commercial divers at Big River continued, with over 30,000 lbs harvested within the first 6 weeks of project start. Project team navigated small (<5mm) purple urchin recruitment at restoration site, increasing effort to reduce densities to targeted thresholds (<2/m^2). ARKEV units at Albion continued to grow and reach the surface within 2 months of deployment with 40% survival. All surviving plants become reproductive and begin releasing spores back into the restoration site. The ARKEV units are scaled and deployed at Big River. Above/Below begins to catalog biodiversity of algae at Big River restoration site by collecting and scanning seaweed specimens to include in project communications.

Key Findings

Initial findings will be reported in October 2024 at the California Seaweed Festival in Humboldt and an interim project report will be published in January 2026.