Marine heatwaves are driving ecosystem change and altering the distribution of foundation species globally. However, our understanding of the recovery of marine ecosystems from these events is limited.  Here we use twenty years of satellite time series and scuba surveys to evaluate the state and recovery of giant kelp forests to the 2014-2016 unprecedented marine heatwaves in Baja California, Mexico, across 800km of latitude. For the post-marine heatwave period (2017-2022), we found an 85% recovery in the south and a 45% recovery of giant kelp forests in the north of Baja California, when compared to the pre-heatwave period (2004-2013). Since 2015, we found 100 kilometers of range contraction in the south (loss of ~ 99.9%), and in the north, 100 kilometers with 99% loss since 2021. Despite the range contraction, the rest of giant kelp in the south recovered better than in the north, with some places exceeding pre-heatwave coverage. Scuba surveys in 2022 revealed that competition with Eisenia arborea (palm kelp) drives giant kelp range contraction in the south. In contrast, sea urchin barrens and trophic cascades explain the loss in the north. In this highly human-populated region, the densities of sea urchin predators were very low (sheepheads and lobsters), and both giant and palm kelp were absent. Our results indicate that the recovery of foundational species may be localized and driven by various factors (e.g., human activities, species competition, environment), suggesting that alternative management strategies are needed, depending on the local status of ecosystems. 

Primary Presenter: Nur Arafeh Dalmau, University of California, Los Angeles and Stanford University (n.arafehdalmau@uq.net.au)

Authors:

Fiorenza Micheli, Stanford University  (micheli@stanford.edu)

Gabriela Montaño Moctezuma, Universidada Autónoma de Baja California  (gmontano@uabc.edu.mx)

Kyle Cavanaugh, University of California, Los Angeles  (kcavanaugh@geog.ucla.edu)