Kelp — A Deeper Look
What is the recent status of kelp across the US West Coast?
Status
The coast-wide status for the most recent year was assessed as Far Below Expectation. Over 80% of the kelp beds are below historical expectation. The coast-wide median coverage of all kelp segments was 31%.
This figure shows kelp canopy coverage for individual kelp segments along the U.S. West Coast (orange circles; n = 210). Kelp canopy coverage is assessed as the percent of coverage relative to the historical baseline. The historical baseline is defined as the median coverage for all years 1984-2013. The number of kelp segments that exceed the y-axis (> 200%) are indicated.
How does the status of kelp compare among states?
Washington
- Kelp canopy in Washington is on par with historical coverage (105%).
- Very few beds exhibit low canopy.
Oregon
- Kelp canopy in Oregon is below historical coverage (30%).
- Majority of beds exhibit low or no canopy.
California
- Kelp canopy in California is below historical coverage (19%).
- More variability across the coast, but the majority of beds exhibit low or no canopy.
These figures show kelp canopy coverage of individual kelp beds grouped by state. Kelp canopy coverage is assessed as the percent of coverage relative to the historical baseline. The historical baseline is defined as the median coverage for all years 1984-2013. The average coverage within a status is indicated and shown in bold. The total number of kelp beds that had greater than 200% kelp canopy coverage relative to historical are shown at the top of the y-axis.
How does this year compare to others?
2023 was the second to worst year on record for coast-wide kelp coverage. While the median coverage across the coast was just 18%; over 80% of all kelp beds were below the historical median. The only year worse on record was 1998 in response to the 1997-1998 El Niño.
This figure shows the distribution of percent canopy coverage across the coast by year (individual curves). 2023 is shown in red; 2014-2022 is shown in orange; all other years (fixed baseline) are shown in grey.
How is kelp changing across the US West Coast?
Trends
Changes in coast-wide kelp are assessed as having No Trend. The vast majority of beds, three-quarters, have no significant long-term or recent trend.
There are more kelp beds with significant decreasing trends than those that are increasing.
This table shows the percent of kelp beds along the U.S. West Coast that have No Trend, are Increasing, or are Decreasing at the 40-year and 7-year time scale. The 40-year is the full extent of the available dataset. The 7-yr is from all years since the end of the 2014-2015 marine heatwave. Trends are determined based on a linear fit of the annual data.
How do trends in kelp compare among states?
As a percent of segments, the majority of beds in all states are exhibiting no 40-year or post-MHW trend. However, for the 40-year trend, there are both increases and decreases in each state, with more decreasing trends. For the recent post-MHW trend, there have been few increasing trends detected (only two segments in California; there are more segments with decreasing trends even since the MHW; most beds still exhibit no trend at this time scale.
These pie charts show the percent of kelp-containing coastal segments within each state that have kelp canopy coverage with No Trend, Increasing or Decreasing at the 40-year and 7-year time scale. The 40-year is the full extent of the available dataset. The 7-yr is from all years since the end of the 2014-2015 marine heatwave. Trends are determined based on a linear fit of the annual data in the maximum extent of kelp canopy coverage for individual coastal segments.
What is the magnitude of the trends?
While the majority of kelp segments show no long-term (40-year) trends, there are segments in each state exhibiting both increases and decreases. The magnitude of change for those segments that are increasing are between 0.2 – 0.8% per year. The magnitude of change for those segments that are decreasing also falls within the same range (-0.2 to -0.8% per year). However, there are not only more segments undergoing decreases, but also a few segments undergoing losses greater than 1% per year. Of those, they are all within California.
Trends in more recent years, since the marine heatwave of 2014-2015, show a similar pattern. The majority of kelp segments exhibit no significant trend, but there are more beds undergoing decreases than increases and the magnitude of that change is greater for those segments that are decreasing in kelp coverage. There are a handful of beds in each state that exhibit losses greater than a 2% per year rate.
These figures show the slope of the 40-year trend (left panel; % per year) and the recent post-MHW trend (right panel) for all kelp segments along the U.S. West Coast categorized by state (California – blue circles; Oregon – orange circles; Washington – green circles). If the linear fit was nonsignificant (alpha = 0.05), the slope is reported as zero. There are overlapping data points on the no trend, zero line.
Trend Story: Point Loma Kelp Forest
An example from an individual kelp bed with high year-to-year variability
The Point Loma Kelp Forest is one of the West Coast’s largest giant kelp forests. The forest spans along 10 km of coast between San Diego Bay and Mission Bay in San Diego, California. The forest has a rich history of observation. Kelp canopy coverage detected by satellite has been highly variable since the early 1980’s to the present. In 2023, kelp canopy coverage was at less than 1% of the historical median. Very little canopy was detected. The recent low is not part of a long-term trend (loss since 1984). However, since 2017, kelp canopy coverage has (on average) been at 40% of the historical baseline.
This figure shows kelp canopy coverage for the Point Loma Kelp Forest for the historical baseline period. Data is plotted as a percent of the historical median (1984-2013). The percent coverage for the current year is shown. Values above 100% are more kelp canopy relative to the historical baseline; values less than 100% are less kelp canopy relative to the historical baseline.
This map shows the full historical extent of kelp canopy detection (light green) and where kelp canopy was detected (dark green) for the most recent year.