A recent study conducted by researchers at the Monterey Bay Aquarium has revealed the crucial role played by sea otters in preventing widespread declines in California’s kelp forests over the past century. The study, published in the journal PLOS Climate, underscores the positive impact of sea otter population growth on the resilience of kelp forests in the state.

According to the findings, the growth of the sea otter population over the last century has significantly enhanced the resilience of kelp forests in California. This has important implications for the conservation and recovery of the threatened southern sea otter and suggests a potential nature-based solution for restoring kelp forests along the California coast and potentially beyond.

The study, which examined changes in regional kelp canopy over a 100-year period from 1910 to 2016, found a notable increase in kelp forest canopy along the central coast, the only region where southern sea otters managed to survive after being hunted to near extinction in the 1800s. The favorable impact of sea otters on kelp forests in this region almost compensated for kelp losses in both northern and southern California, resulting in a slight overall decline in kelp forests statewide during this period.

Lead author Teri Nicholson, Senior Research Biologist with the Monterey Bay Aquarium Sea Otter Program, emphasized the significance of the findings, stating, ‘Our study showed that kelp forests are more extensive and resilient to climate change where sea otters have reoccupied the California coastline during the last century. Where sea otters are absent, kelp forests have declined dramatically. In fact, we found sea otter population density to be the strongest predictor of change in kelp canopy coverage over this hundred-year span.’

The researchers utilized historical surveys of kelp forests dating back to the early 1900s to estimate canopy extent, biomass, and carbon storage, while accounting for annual variation and differences in survey methods. This allowed the team to analyze California’s kelp forest trends over a longer time period, predating modern surveys based on aerial or satellite imagery. The study employed a machine learning framework to assess the primary drivers of change in kelp forests over the last century.