When people imagine studying marine life, they often picture scuba divers swimming alongside schools of fish, or scientists carefully tagging sea lions and sharks. Those methods are important, but today we also have a new, powerful tool to understand ocean ecosystems: analyzing invisible fragments of DNA floating in the water.
This is called environmental DNA, or “eDNA.” Every living thing sheds DNA into its environment — through skin cells, mucus, waste, or reproductive material. In the ocean, these tiny genetic breadcrumbs drift in the water column. By collecting and analyzing just a liter of seawater, we can capture traces of dozens, sometimes hundreds, of species that recently passed through that area.
The Southern California Bight — stretching from Point Conception above Santa Barbara to the Mexican border — represents one of the most unique marine ecoregions in the world. In the Channel Islands, where Oceana and expedition partner Blancpain have been conducting research expeditions to characterize the marine biodiversity of the region, eDNA has become a game-changer. These islands and the waters that surround them are one of California’s biodiversity hotspots, home to kelp forests, rocky reefs, cold water corals, seabird nesting sites, migratory highways for whales and dolphins, and shark nursery grounds.
Traditionally, documenting this abundance of life has meant diving with clipboards or deploying cameras on the seafloor. Those methods are still essential — and we’ve been employing them alongside our eDNA sampling — but they can miss the quieter, cryptic, super small, or rare species that don’t always show up when divers happen to be watching. Environmental DNA gives us a new set of eyes.
Here’s how it works: On a dive or from the deck of a boat, we collect samples of seawater from different sites around the islands. We filter the samples and take them back to the lab, where we extract the DNA and sequence it. Sophisticated computer tools then match those sequences to species in genetic reference databases. Within weeks, we can generate a biodiversity snapshot that tells us which fishes, invertebrates, marine mammals, and even microorganisms were present in these waters.
Kelp sand bass swim among golden gorgonian coral in California’s Channel Islands. © Oceana/Danny Ocampo
One of the most exciting things about eDNA is its sensitivity. We’ve detected rare and elusive species that we might never encounter during a scuba survey. We’ve discovered DNA from certain sharks and rays, like the horn shark and pacific angel shark, that only pass by occasionally or remain well camouflaged along the sandy bottom or rocky reef. We’ve found DNA from microscopic organisms, and picked up signals from highly mobile animals, like cetaceans or pinnipeds, that a diver could easily miss.
These discoveries matter for conservation. By combining eDNA data with traditional scuba surveys, we can better understand how marine areas around the Channel Islands are functioning. We can learn where species are thriving and where they may be declining, gather data on how marine communities vary by season and depth, and better understand how human influences like fishing or climate change might be shifting distributions over time. This helps both fishery managers and conservation advocates make more informed decisions about protecting habitats, wildlife, and our rich marine resources.
Beyond California, scientists are now using eDNA across the globe — from monitoring endangered sawfish in Florida, to tracking invasive species in European rivers, to mapping coral reef biodiversity in the Pacific. As the technology advances, eDNA will allow us to detect not only which species are present, but could also reveal early warning signs of disease outbreak and improve fisheries stock assessments.
To me, eDNA powerfully demonstrates the profound interconnectedness of ocean ecosystems, revealing signals from species that interact in ways we are only starting to understand. Even when we can’t see an animal, its genetic traces are there, carried through the currents. Each drop of seawater holds a story about life beneath the surface — stories we’re only just beginning to read.
Caitlynn Birch
Marine Scientist
Caitlynn Birch holds a Master of Science in Environmental and Ocean Sciences from the University of San Diego, and leads science and policy advocacy and campaign strategy for Oceana’s U.S. team on the West Coast. Birch led Oceana’s environmental DNA work during the organization’s recent expeditions to California’s Channel Islands.
