Cockerell's dorid (Limacia cockerelli) nudibranch

A Cockerell’s dorid — a type of sea slug called a nudibranch — creeps over a rock in a tide pool near Half Moon Bay, California.


Stephen Shankland/CNET

I was sloshing around knee-deep in the Pacific Ocean, leaning on my camera tripod to avoid slipping on seaweed, excited to see some nudibranchs — but utterly failing to find any of the tiny, outrageously colorful sea slugs.

I’d soaked my sneakers for some photographic fun. But searching for nudibranchs is part of the job for Alison Young and Rebecca Johnson, two marine biology researchers with the California Academy of Sciences who fortunately were much more adept at finding the gastropods. They’d led me and a few other nature enthusiasts on a “citizen science” excursion to Pillar Point, a beach 15 miles south of San Francisco that’s next to the famed Mavericks big-wave surfing competition near Half Moon Bay, California.

Every two weeks when the tide is particularly low, Johnson and Young wade into the Pillar Point tide pools and stake out one of six plots they’ve been monitoring since 2012. Their purpose is to track populations of the nudibranchs, starfish, chitons, snails, shrimp and other intertidal zone species.

The two don’t work alone, though: They get a lot of help from volunteers. And from technology like iNaturalist, an app anyone can use to log plant and animal sightings with their smartphone. You can also use iNaturalist to see what creatures are in a particular area and get help with identifications.

Johnson and Young’s work is part of a movement called citizen science that’s helped bring discovery out of academia’s ivory tower and into the lives of people who have curiosity and enthusiasm if not an advanced degree.

“I love being able to find an excuse to explore nature. On top of that I love that I’m also able to contribute data to an archive of data,” said Jane Kim, a Half Moon Bay artist and illustrator who was on her fourth trip out to the tide pools. Nature is her passion: She’s just finishing a 12-story butterfly mural in San Francisco, one of a series of 10 across the country located along monarch migration routes. She also painted the smaller but vastly more detailed Wall of Birds at Cornell University.

There were just five citizen scientists on my outing with Young and Johnson. Sometimes they get as many as 20 volunteers, a useful crowd when counting Pacific purple sea urchins that are abundant in one of the Pillar Point plots.

Citizen science in the digital age

Citizen science, in which data gathered by enthusiasts helps the work of professionals, has a long history. For example, the Audubon Society has relied on volunteers to help record bird activity every year since 1900 with its annual Christmas Bird Count. Technology has added new dimensions to the idea.

Digital cameras and recorders have made it easy to share photos and audio recordings. GPS has added precision to location data. The internet helps people organize groups and exchange data. And smartphones combine all that into one package that fits in your pocket or pack.

iNaturalist gives anyone “the opportunity to be a natural history museum naturalist,” Johnson said. “You have that joy of discovery,” Johnson said.

A tiny baby sea star, Dwarf mottled Henricia (Henricia pumila), seems to wave from its perch on my fingertip.

A tiny baby sea star, dwarf mottled Henricia (Henricia pumila), seems to wave from its perch on my fingertip.


Stephen Shankland/CNET

Now there are hundreds of citizen science projects on everything from tracking butterflies and moths to monitoring landslides, from searching for alien communications to transcribing 150-year-old scientific records. Scientists have installed metal perches on wilderness trails to encourage hikers to take photos of a particular spot to be shared with a hashtag. Researchers can then use the photos to record changes to the ecosystem. If you catch a white cabbage butterfly, you can mail its body to scientists studying variations in the insect’s genetics. 

Boosted by iNaturalist

Two big services stand out, though. eBird, managed by the Cornell Lab of Ornithology, now has 737 million bird observations from more than a half million birders around the globe. iNaturalist has more than 20 million identifications from more than 1 million people.  

The Cal Academy researchers keep their own records, with 650 species discovered at Pillar Point, but you’ll see results of their trips on iNaturalist, too. Johnson logged 28 species during our trip.

“Really quickly we started using it as a data collection platform,” Johnson said. “We were really interested in building a community of naturalists,” and they adopted iNaturalist almost immediately as a good way to marshal people’s efforts.

The California Academy of Sciences natural history museum — Cal Academy for short — took over iNaturalist and its employees in 2014, and National Geographic became an official supporter in 2018.

Scientific results

Johnson and Young have seen scientifically interesting phenomena, like the 2014 disappearance of nearly all Pillar Point’s starfish — which scientists generally call sea stars — during an epidemic of sea star wasting disease. All but two species — the sunflower sea star and the short-spined sea star — have since returned. The recovery began with a lot of baby starfish that ordinarily are hard to find since they have to survive on the margins while adults claim the best feeding areas.

The eBird project has marshaled the efforts of thousands of citizen scientists. One result is this map showing warbling vireos’ annual migration. The birds spend winter in Central America.


eBird; GIF by Stephen Shankland/CNET

When others verify your iNaturalist sightings, they can be promoted to “research grade,” which gives them more authority for inclusion in scientific studies. Right now, 390 peer-reviewed research papers logged at the Global Biodiversity Information Facility use iNaturalist data.

The Pillar Point research has also revealed effects of global warming, with southern species becoming more common farther north as waters have warmed. And during the 2015 and 2016 El Niño years, when the weather gets warmer and wetter, the surveys revealed an abundance of Hopkins’ rose nudibranchs that have mostly disappeared since.

“Your observations help us understand how species’ ranges are changing,” Johnson said. The tide pool research feeds into California marine management policy decisions. 

‘Nudibranch people’

Naturalists spend a lot of time dividing plants and animals into different categories. This taxonomic activity applies to the naturalists, too. And one branch of naturalists can find people of another branch peculiar, though there’s still clearly camaraderie.

“The lichen and moss people!” Young exclaimed. “The slime mold people!” Johnson added. Birdwatchers seem downright pedestrian by comparison.

Alison Young photographs a brilliant sunset just after low tide at Pillar Point about 15 miles south of San Francisco. The rocks of Pillar Point just out into the Pacific Ocean toward the left; the Mavericks surfing competition takes place in the waves to

We didn’t come for the sunset, but we got one. Here, Alison Young of the California Academy of Sciences takes a photo at Pillar Point about 15 miles south of San Francisco, site of the Mavericks surfing competition.


Stephen Shankland/CNET

When Young speaks enthusiastically of the day’s nudibranch rarity — a pale yellow hallaxa chani, aka Chan’s Dorid, she adds, “We’re nudibranch people. Seeing one we hardly ever see is really exciting.”

I was glad to have nudibranch people around, because I really wanted to take some photos but couldn’t find a single nudibranch. Young and Johnson spotted one after another even as the sun dipped down to the horizon and the light dimmed. The little slugs were creeping about on rocks, gravel, seaweed and even the back of a hermit crab. They’re grazing carnivores, consuming what they come across, including starfish, sea anemones and even fellow nudibranchs.

After a few hours photographing underwater crustaceans, gastropods and echinoderms, I felt like I’d journeyed to another planet.

“Sometimes you think of adventure as this big unattainable journey to some remote spot,” said Thayer Walker, Kim’s husband, an Outside Magazine correspondent and a fellow citizen scientist on the trip. “The reality in this neck of the world is you can go into your backyard and have a pretty cool journey of discovery.”