Sofia Urgoiti Crespo1,2, Jennifer Caselle1, Peter Carlson1, Avrey Parsons-Field1, Robert Miller1, Adrian Stier1
1University of California Santa Barbara, France - 2Fulbright Spain, Spain
Marine heatwaves are becoming increasingly prevalent and pose significant threats to kelp forest ecosystems worldwide. Community responses to these disturbances are context-dependent and influenced by a myriad of local factors. This study analyzed a 20-year subtidal kelp forest time series to assess the long-term impact of the 2013-2016 North Pacific marine heatwave (MHW) on macroalgal and benthic invertebrate communities in a biogeographic transition zone (Santa Barbara Channel, California, USA). Using canonical analysis of principal coordinates (CAP) and generalized linear mixed models (GLMMs), we explored pathways and rates of community change along a strong environmental gradient over a small geographic area. We also examined how marine protection in marine protected areas (MPAs) influenced community responses to the MHW. Results showed contrasting regional trajectories: warmer regions exhibited kelp increases and declines in urchin grazers (Strongylocentrotus purpuratus and Mesocentrotus franciscanus), while the colder region showed the opposite trend. The extent to which echinoderm disease may have contributed to these regional patterns is not well quantified. Contrary to expectations, MPAs did not uniformly buffer community change, though protection had region-specific benefits, including increased diversity and abundance of targeted species. Additionally, marine heatwave-driven increases in grazers like the gastropod Megastraea undosa were observed, though long-term implications of this trend remain uncertain. These findings highlight the unpredictable ecological responses of kelp forests to marine heatwaves, challenging the prevailing notion that warming consistently leads to kelp loss and ecosystem degradation. This research reveals a spectrum of post-disturbance pathways within a relatively small geographical area, influenced by the interplay of biogeographical gradients, marine protection, and disease dynamics.
Biography
Sofía Urgoiti Crespo is a third-year Master’s student at the University of California, Santa Barbara, where she began her graduate studies in September 2022. Her research, supported by Fulbright Spain, is conducted under the supervision of Dr. Jennifer Caselle and focuses on understanding the impacts of climate change (marine heatwaves) on kelp forest macroalgal and invertebrate communities in a biogeographic transition zone.