The mussel bed at Dillon Beach in Northern California is as rich in health and biodiversity as it was around 80 years ago, just before World War II when two students conducted a survey there.
For years, their unpublished typewritten manuscript rested in the library of UC Davis’s Bodega Marine Laboratory until scientists from UC Davis discovered it. They set out to revisit the exact mussel bed using the old manuscript’s detailed photos and maps as guides.
The results, published in the journal Scientific Reports, reveal a flourishing mussel bed community that nevertheless bears the effects of climate change. The researchers identified 90 different invertebrate species residing within the mussel bed—a slight increase from the 1941 survey. Among these were warmer-climate species usually found in southern regions, like the California horsemussel Modiolus carpenteri and the chiton Mopalia lionota.
“We had expected to see significant declines in species,” noted lead author Emily Longman, a UC Davis graduate student who later became a postdoctoral fellow at the University of Vermont. “We assumed biodiversity would have dropped sharply, but surprisingly, that wasn’t the case. If anything, the number of species was higher. This mussel bed community is flourishing.”
Continuing the Legacy
The researchers were particularly thrilled to discover that one of the original manuscript’s authors, Milton Hildebrand, was alive at age 101 and living nearby in Davis as a retired zoology professor. Longman and Sanford had the opportunity to meet the World War II veteran in 2019, a year before his passing.
“Sharing scientific insights across generations is not just about numbers and statistics; it’s a fundamentally human project,” said senior author Eric Sanford, a Bodega Marine Laboratory professor in the UC Davis Department of Evolution and Ecology. “It was a wonderful experience to see Emily Longman, a graduate student, connect with this 101-year-old scientist who had started this research project eight decades ago.”
The other co-author, Harvey I. Fisher, passed away in 1994 after a notable zoological career. Hildebrand and Fisher had been UC Berkeley graduate students when they conducted their initial survey, which took place before the establishment of the Bodega Marine Laboratory.
“Milton found our results to be fascinating,” Longman remarked. “He was quite charming.”
Foundation of the Ecosystem
Habitat-forming species like mussels, kelp, and coral are essential to marine ecosystems as they offer vital “shelter” for other organisms. The authors meticulously counted and recorded every invertebrate species found in the Dillon Beach mussel bed.
“I liken them to Motel 6 for rocky shores,” Sanford said. “Various species like crabs, snails, worms, limpets, and sea cucumbers all find residence within these three-dimensional structures.”
Earlier studies had noted almost a 60% decline in species diversity in Southern California’s mussel beds. However, little information was available regarding the status of mussel beds in Northern California. While a single mussel bed cannot represent the entire Northern California coast, the Dillon Beach study offers a hopeful perspective amid otherwise troubling oceanic reports.
“Having worked at the Bodega Marine Laboratory for over 20 years, I’ve noticed that the mussel beds at Dillon Beach resemble those found in Sonoma and Mendocino counties,” Sanford stated. “Overall, they seem to be quite robust.”
The recent survey indicated no decline in biodiversity compared to the observations made by Hildebrand and Fisher in 1941, though it did highlight an aspect of climate change: changes in the abundance of various species.
Species adapted to cooler climates, typically found from California to British Columbia and Alaska, have seen a decrease. Conversely, species suited to warmer conditions, usually found down to Baja California, Mexico, have become more prevalent. The study’s authors noted that this shift aligns with the rise in ocean temperatures measured in Bodega Bay since the 1950s.
Remembrance and Recognition
Longman and Sanford emphasized the importance of using what might be seen as “nontraditional” science resources, like old unpublished manuscripts by students from a field course.
“Such untraditional resources—historical maps, Indigenous knowledge, and vintage photographs—are invaluable,” said Longman. “They provide a unique glimpse into the past for many locations.”
This research received funding from the Bilinski Educational Foundation, the Rafe Sagarin Fund for Innovative Ecology, and the National Science Foundation. The researchers also expressed gratitude to Molly Engelbrecht, Bodega Marine Laboratory’s librarian, for her dedication to preserving and digitizing student papers as future historical resources.
The authors acknowledged Hildebrand and Fisher, who expressed in their 1941 report: “We hope our paper may serve as a basis for further ecological studies of the area by ourselves or others in the future.”
