New monitoring shows the Palos Verdes Reef restoration project has increased fish biomass by over 150 percent just 4 years after construction
From NOAA Fisheries:
If you’ve stood on the bluffs of the Palos Verdes Peninsula and gazed out at the Pacific, you might never guess at the transformation happening beneath the waves. In 2020, as part of an effort to restore an area impacted by historical chemical pollution, divers and scientists lowered more than 70,000 tons of rock onto the ocean floor in carefully engineered mounds. Their goal: restore the rocky reef habitat that fish, kelp, and countless marine creatures need to survive, in an area long-contaminated with DDT and other toxins, and buried by sediment.
Today, that effort is paying off in ways that even the scientists didn’t fully expect.
Why Habitat Matters
Healthy reefs are critical for the survival of many species. From small forage fish to larger predators, rocky reefs support species that feed seabirds, harbor seals, and humans. Hard surfaces give kelp and algae a place to anchor, which in turn creates shelter and food for fish and invertebrates. Off the Palos Verdes coast in particular, species like kelp bass, barred sand bass, sheephead, and California spiny lobster are important for commercial and recreational fishing.
But in the mid-20th century, sewage outfalls and landslides stripped the eastern side of the Palos Verdes shelf of much of its kelp forest. By the 1960s, giant kelp—once so abundant it created a canopy visible from shore—had all but disappeared.
Restoration efforts slowly brought kelp back in some areas, but many natural reefs remained smothered under shifting sediment. They were also heavily impacted by the lingering effects of DDT and PCB contamination. In 2001, NOAA and other federal and state agencies reached a settlement with the responsible parties. As a result, the Montrose Settlements Restoration Program was established to restore the natural resources harmed by the chemicals, including fishing and fish habitat.
Building a Rocky Reef from Scratch
The Palos Verdes Reef was designed after years of study and community input, funded through the program. The project is the last in a series of almost 20 restoration efforts resulting from the settlement.
From May to September 2020, construction crews deposited quarry rock in 18 modules across more than 30 acres of seafloor. The design was a collaboration between the Vantuna Research Group and the Southern California Marine Science Institute. It mimicked the natural structure of successful reefs nearby, with a mix of heights, gaps, and channels to create hiding places and keep sediment moving. The new reefs were also built high enough to avoid being re-buried by future landslides and keep fish away from the polluted sediment below.
The project had four goals to ensure the reef functioned as a true habitat:
- Increase the cover of marine life on the reef surface
- Boost the biomass of fish on the new reef
- Improve fish biomass across the broader 62-acre reef complex
- Prevent invasive species from taking over
Revival of a Reef
A recent report on monitoring efforts in 2024, 4 years after the reef was established, shows striking results.
Fish Are Thriving
Biomass—the total weight of living organisms—has jumped by 1,178 percent as compared to pre-construction levels. Across the entire reef complex, fish biomass in particular is up 166 percent, adding nearly 4 metric tons of living fish to the ecosystem.
Habitat Is Expanding
Not only are fish using the new structures, but sediment has also shifted to reveal an acre of long-buried natural reef nearby, effectively increasing the habitat footprint.
A Healthy Native Community
Despite fears that invasive algae or invertebrates might colonize the new structures, none were detected. Instead, native kelp, coralline algae, and invertebrates are making use of the reef.
Benefits Go Beyond the Reef
Fish biomass more than doubled in the 30 meters that surround the reef—called “halo zones”—as compared to pre-construction numbers.
The thousands of fish darting around the Palos Verdes Reef, invertebrates hiding in its crevices, and marine mammals foraging through the flowing kelp forests were unthinkable sights just a few short years ago. This transformation, from a barren sea floor to a habitat teeming with life, isn’t just a local success story. It’s a demonstration of how habitat restoration can bring marine ecosystems back to life.
