Developing a Status and Trends Assessment for Floating Kelp Canopies across Large Geographic Areas.

Effective kelp forest stewardship and management requires understanding of status and trends, but most kelp monitoring data streams on the U.S. West Coast are focused on subregional scales with outputs targeted toward a scientific audience. Here, we developed an index of kelp status and trend that integrates across thousands of kilometers and is presented as a simple, informative gauge that can be easily communicated to multiple audiences, including high-level policymakers. The indicator has three main features: (1) it is based on floating kelps as they create canopies, and managers indicated their interest in whether the quantity of kelp surface canopy had changed relative to historical levels. (2) Kelp canopy is assessed within segments along the coastline, rather than as a single coast-wide, cumulative amount. This approach retains local-level information allowing the indicator to be calculated at multiple scales, which accommodates the multigovernance landscape of the U.S. West Coast. (3) Status of kelp is expressed as a comparison to a reference period, established using all data prior to a marine heat wave in 2014 that led to substantial kelp losses. When applied to data from recent years, we found that the kelp canopies continue to be below their historical baseline. Since 2014, there has been no coast-wide recovery to reference levels. Still, despite 2023 being among the worst years on record, there was substantial improvement in kelp canopies in 2024 and recent downward trends have stalled. This Kelp Indicator provides a tool to inform resource management, improve policy, and prioritize scientific research, recovery efforts, and monitoring.