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Abstract Increased ocean temperatures have led to large‐scale declines in many ecologically important species, including kelp forests. Spatial heterogeneity across seascapes could protect kelp individuals and small populations from thermal stress and nutrient limitation. Habitat features within upwelling regions may facilitate the transport of deep, cold water into shallow systems, but little is known about the spatiotemporal occurrence or stability of these climate refugia. Kelp in climate refugia may, however, also experience other stressors, such as overgrazing by kelp herbivores, reducing their effectiveness.Here, we use high‐resolution kelp canopy maps generated from CubeSat constellation data to characterize kelp persistence in northern California following a dramatic decline in kelp abundance due to increased temperature and nutrient limitation during a severe marine heatwave and continued intense grazing pressure by purple sea urchins.Kelp persistence was associated with local areas of relatively cool water temperature and seascape features such as shallow depths and low‐complexity bathymetry, which may have provided refuge from overgrazing. However, a very small percentage of kelp forests in the region exhibited high persistence, with many forests present in only one or two of the 9 years studied. Most kelp patches were not spatially stable over time. Initially, kelp presence aligned with climate refugia, but as overgrazing emerged as the dominant driver of kelp distributions post‐2019, kelp shifted to areas that offered protection from grazing pressure.Synthesis. Cooler areas with localized upwelling acted as climate refugia during the increased ocean temperatures from the 2014–2016 marine heatwave, supporting nutrient‐rich environments and mitigating heat stress for kelp forests. However, these temperature refugia often did not spatially overlap with areas providing protection from grazing pressure, leaving kelp forests vulnerable to future warming even within temperature refugia if grazing pressure remains high.
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Southward decrease in the protection of persistent giant kelp forests in the northeast Pacific
Abstract Kelp forests are globally important and highly productive ecosystems, yet their persistence and protection in the face of climate change and human activity are poorly known. Here, we present a 35-year time series of high-resolution satellite imagery that maps the distribution and persistence of giant kelp (Macrocystis pyrifera) forests along ten degrees of latitude in the Northeast Pacific Ocean. We find that although 7.7% of giant kelp is protected by marine reserves, when accounting for persistence only 4% of kelp is present and protected. Protection of giant kelp decreases southerly from 20.9% in Central California, USA, to less than 1% in Baja California, Mexico, which likely exacerbates kelp vulnerability to marine heatwaves in Baja California. We suggest that a two-fold increase in the area of kelp protected by marine reserves is needed to fully protect persistent kelp forests and that conservation of climate-refugia in Baja California should be a priority.
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- PAR ID:
- 10248727
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 2
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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