Marine heatwaves are projected to become more frequent and severe by the end of the century, especially in areas favored by giant kelp. Giant kelp forests play a crucial role in absorbing carbon dioxide and providing food and shelter for many marine species. However, these vital ecosystems have recently experienced significant declines due to marine heatwaves and the proliferation of sea urchins that feed on kelp.
Research conducted by scientists at Stanford University indicates that restricting fishing in kelp habitats can help these forests recover and increase their resilience to marine heatwaves. One study published in Global Change Biology documented a decline in kelp forest cover off the southern and central California coast during a marine heatwave from 2014 to 2016. The recovery of these forests was significantly higher in marine protected areas where fishing has been prohibited since 2012. In regions with minimal fishing, the recovery rates were only marginally better compared to unprotected areas.
The absence of fishing in protected areas has allowed predator species, such as California sheephead and spiny lobster, which control the sea urchin population, to thrive. “Urchins eat kelp, so preserving their predators indirectly promotes kelp growth,” stated lead study author Joy Kumagai, a biology PhD student at Stanford.
The research also highlights the importance of “trophic cascades,” the indirect impacts of predator presence, in aiding the kelp forests’ ability to survive marine heatwaves. During one of the worst marine heatwaves on record, the study showed evidence supporting that protecting marine predators contributes to the recovery of marine forests despite extended heatwaves.
The findings are critical at a time when 190 countries are striving to protect 30% of Earth’s land and ocean by 2030. Co-senior author Fiorenza Micheli emphasized that “preserving intact food webs matters, but effects take time and require large-scale protection, as well as extensive long-term monitoring to detect ecological benefits.”
A second study, led by Nur Arafeh-Dalmau and published in Nature Communications, projects that the intensity of marine heatwaves in kelp forest habitats could double by 2040, regardless of carbon dioxide emissions reductions. The research analyzed global climate models and satellite data to understand future scenarios. It suggests that regions like Patagonia could serve as “climate refugia,” providing critical havens for kelp forests amidst global warming.
Globally, only 13.7% of kelp forest habitats are under effective marine protection, mainly around remote islands. In contrast, California’s stretch from the San Francisco Bay Area south to the U.S.-Mexico border has enacted fishing bans for at least 10% of kelp habitats, presenting a model for marine biodiversity conservation.
These studies received support from various international institutions, including NASA, the National Science Foundation, and the Lenfest Ocean Program.
For further information, the main contacts are Joy Kumagai at Stanford School of Humanities and Sciences, Nur Arafeh-Dalmau, and Fiorenza Micheli at Stanford Doerr School of Sustainability.
