From Land to Sea: The Cascading Impacts of Wildfires on California’s Kelp ForestsResistance, Resilience and Phase Shifts

Lori Berberian¹, Kyle Cavanaugh¹, Erin Hestir¹, Christine Lee², Amanda Lopez¹, Michelle Gierach², Carmen Blackwood²

¹University of California, USA - ²California Institute of Technology, USA

Wildfires evoke significant concern for their terrestrial impacts, including burned landscapes, destroyed structures, and loss of life. However, their effects can also dramatically alter the marine environment through the deposition of debris, sediment, and ash transported via riverine and atmospheric pathways. Sunlit coastal waters, home to foundational marine species like bull kelp (Nereocystis luetkeana) and giant kelp (Macrocystis pyrifera), confer significant ecological and economic value through their support of biodiversity and contributions to aquaculture. Although wildfire intensity and frequency are rising, little is known about how these events affect water quality and clarity, both critical to the health and distribution of kelp forests. For example, wildfire runoff into kelp habitats deposits sediment onto hard substrates, potentially impeding kelp recruitment and growth through reduced benthic habitat availability and light limitation. In this study, we evaluate nine years (2016–2025) of wildfire-driven sediment contributions to coastal waters using remotely sensed total suspended matter data from the European Space Agency’s Sentinel-3 Ocean and Land Color Instrument. Additionally, we use a satellite based time series of kelp canopy area to assess the impacts of post-fire sediment input on kelp abundance. A Before-After Control-Impact (BACI) analysis compares surface sediment concentrations and kelp canopy dynamics before and after wildfires at both impacted and control sites to assess wildfire effects. This study enhances understanding of how wildfire-driven disturbances interact with natural variability in coastal ecosystems, emphasizing the interconnectedness of terrestrial and marine systems and the cascading effects of wildfires on biodiversity and ecosystem function.