Undergraduate Research Hub

Pyropia spp. (i.e., nori) is an economically, ecologically, and culturally significant red seaweed worldwide. Herbarium records were analyzed to inform our understanding of its distribution along California’s coast. We investigated the relationship between sea surface temperature (SST) and the occurrence of Pyropia spp., and how this relationship has changed temporally in association with ocean warming. Herbaria data was collected from the University of California, Berkeley Herbarium and the Macroalgae Herbarium Consortium (1875-2024), and SST data from the UCSD Shore Stations Program (1919-2024). Additionally, a literature review of the biogeographic regions, life cycle, optimal temperature ranges, and speciation was compiled. We found that relative abundance using herbaria pressings is consistent with past research. There is also a greater amount of Pyropia spp. north of Point Conception, but pressings can only complement in situ data, and not used as a 1-1 replacement. There was not a clear decline in pressings over time by county, although there are limitations due to convenience sampling and lack of available specimens. Preliminary results seem to suggest a possible relationship between SST and the occurrence of Pyropia spp., which may change with warming. Future studies should include visits to various field sites and conduct seasonal sampling to achieve a better understanding of the change in distribution over time. By doing so, we can gain insight into whether herbaria data is a useful indicator of Pyropia spp. occurrence and how SST warming impacts the distribution.