Monterey Bay Aquarium researchers strengthen the link between sea otters and long-term health of California kelp forests in a new study released today. The paper, published in the journal PLOS Climate, finds that sea otter population growth during the last century enhanced kelp forest resilience in the state. This finding reinforces the importance of conservation and recovery of the threatened southern sea otter and highlights a potential nature-based solution for restoring kelp forests along the California coast, and perhaps beyond.

The study revealed dramatic regional kelp canopy changes over a 100-year period, from 1910 to 2016. During this time there was a significant increase in kelp forest canopy along the central coast, the only region of California where southern sea otters survived after being hunted nearly to extinction for their fur in the 1800s. At the century scale, the species' favorable impact on kelp forests along the central coast nearly compensated for kelp losses along both northern and southern California resulting in a slight overall decline statewide during this period.

Aquarium scientists used historical surveys of kelp forests dating back to the early 1900s to perform detailed estimates of canopy extent, biomass, and carbon storage -- while correcting for annual variation and differences in survey methods. This allowed the scientists to examine California's kelp forest trends over a longer time period, going back more than 60 years before available data from modern surveys based on aerial or satellite imagery. The team then compared the corrected and conservative historical estimates to contemporary datasets and used a machine learning framework to assess the dominant drivers of change over the last century.