Above image: Bull kelp habitat off the coast of California taken April 10, 2023. © 2023, Planet Labs PBC. All Rights Reserved.
Ecosystems are full of complex and interacting elements, both biotic and abiotic. But when several of these elements begin to change at the same time, scientists have witnessed a dramatic decline in certain species populations, such as the northern California bull kelp. From 2014-2016, a marine heatwave in the Pacific ocean coincided with the mass die-off of sea star populations in northern California. This was followed by a population boost in purple sea urchins, a natural prey of the sea star and a natural consumer of bull kelp. Increases in temperature anomalies as well as sharp spikes in predation led to the near-total collapse of bull kelp in the region. However, small, remnant populations survived, and in order to protect and restore these populations, scientists have used PlanetScope data to monitor these kelp communities from space. Research led by the University of California, Los Angeles leveraged Landsat data to create long-term time series of kelp communities, however, due to the sparse nature of these small refuge kelp communities, the research team decided to turn to PlanetScope’s 3 meter resolution data, enabling them to identify the small kelp communities along the coast. Their study developed a method for mapping the bull kelp canopy, accounting for managing surface reflectance corrections. The team of researchers also leveraged the high temporal frequency of the PlanetScope data to support the automation of classifying kelp in satellite imagery. “These areas may be critical to the success of kelp forest re-establishment in northern California, which increases their importance for ongoing monitoring, conservation, and restoration efforts,” said the authors.
The full study can be found in Remote Sensing of the Environment.