How did we calculate?
APPROACH
To assess kelp, scientists and resource managers monitor the canopy which forms at the ocean’s surface. Historical satellite and aerial imagery programs date back more than 40 years. Since kelp forests naturally fluctuate from year to year, this historical perspective is necessary to generate a robust expectation of kelp performance in any individual year. For the Indicator, the status is based on the current year of kelp canopy extent.
The extent of kelp within a coastal segment is standardized relative to a fixed historical baseline and expressed as a percentile. Such an approach gives equal weighting to all coastal segments with kelp. The status for the entire U.S. West Coast is synthesized as the median of the percentile coverage from all of the segments. The median value is assessed as either Far Below, Below, Meeting, Above, or Far Above Expectation. The Expectation categories are defined from the historical distribution of median coast-wide coverage.
Trends are assessed based on the full historical period for which data is available, as well as the time period since 2017. This latter time period is to assess trends in kelp since the 2014-15 marine heatwave, ‘the blob,’ which resulted in significant temporary kelp losses along many parts of the West Coast. Based on the significance and magnitude of these two trends, kelp-containing coastal segments are categorized as Degrading, Slightly Degrading, Staying the Same, Improving, and Slightly Improving.
