Back to the Future of Sea Urchins: Using Long-term Datasets to Generate Proxies of Climate Change Impacts on California’s Purple Urchin Populations

This project examines how California’s purple urchin (Strongylocentrotus purpuratus) populations have responded over the last two decades to increasing ocean acidification (OA) and extreme climate anomalies that may serve as proxies for future climatic impacts. Our work focuses upon calcification in juvenile urchins as OA may greatly impair the CaCO₃ biomineralization process necessary to create and maintain urchin body structures. We hypothesize that juvenile urchins have high vulnerability to OA because the CaCO₃ mineralogy of this life cycle stage (dominated by high-Mg calcite) is particularly susceptible to dissolution, thereby engendering potential bottleneck conditions in the populations. Our aim is to study controls on juvenile urchin calcification to learn about the impacts of OA on urchin biomineralization as well as population fitness, a crucial metric for evaluating local ecological and economic health.

We analyze the CaCO₃ content of purple urchin juveniles sourced from four California coastline sites: Fort Bragg/Mendocino, Gaviota Pier, Anacapa Island, and Scripps Pier over twenty years. These sites span a significant range of California coast, and as such represent points along a spectrum of strong to weak upwelling regimes (i.e., low to high pH), thus enabling our results to be potentially applicable across large gradients of environmental change. Samples have been sourced from a twenty-year sampling archive of the Santa Barbara Coastal Long Term Ecological Research project. Our results are discussed in the context of past climatic events, such as the extreme El Niño periods of 1996-1997/2015-2016 and the La Niña period of 1998-1999, which may act as analogs for future climatic scenarios characterized by increased seawater acidification and other perturbed environmental metrics.