Understanding the Resilience of Kelp Forests Amidst Marine Heat Waves: A Comprehensive Study

The ocean, a vast and mysterious body of water, is home to a myriad of life forms, from microscopic organisms to the largest creatures on Earth. Among these are the kelp forests, a unique and vital ecosystem that plays a significant role in the health and balance of the marine environment. However, these forests have been facing unprecedented challenges in recent years, primarily due to marine heat waves. In this article, we delve into a comprehensive study led by Monterey Bay Aquarium and the University of California, Santa Cruz, which sheds light on the resilience of kelp forests during marine heat waves and the consequences of their decline on the broader ecosystem.

The study was published in Proceedings of the Royal Society B and is based on a 14-year dataset. It comes after a multi-year marine heat wave, the product of a 2014 ‘blob’ of warm water prolonged by a 2015-2016 El Niño event, which bathed the North American west coast with sweltering sea temperatures. This event led to pronounced declines in kelp abundance on California’s central coast, with an average decline of 51% in kelp forest density between 2017-2020 and 2007-2013. By 2020, the decline had increased to 72%.

Despite these declines, the study found that larger stands of giant kelp prevented shifts in sea urchin foraging behavior and were better at withstanding multiple stressors. These persistent forests were located in areas that are typically less productive, with a gradual reef slope and protection from wave exposure, enabling them to become densely packed with kelp prior to the marine heat wave.

The importance of habitat features in driving forest persistence was identified in this study. However, predators also play a crucial role in preventing kelp declines. Another recent Monterey Bay Aquarium study reinforced the role of sea otters in preventing kelp declines by eating up sea urchins. In areas where kelp patches were more exposed and less dense, the sudden rise of sea urchins in 2014 led many kelp forests to become ‘barrens’- areas scoured by hungry sea urchins along the rocky reef.

The study examined changes in species composition across the mosaic of barrens and persistent forests to untangle how kelp loss impacts the broader ecosystem. While some kelp forests have endured, the structure of the ecological communities in the barren areas has yet to return to their pre-2013 state. Across the region, the number of species did not decline, but changes in their relative abundances led to an overall decline in species diversity, most notably for marine algae and kelp-associated invertebrates. With less kelp and other macroalgae around, the study noted a disproportionate increase in animals that eat plankton, such as barnacles, scallops, tube snails, and planktivorous fishes.

The study offers important insights to help inform strategies for protecting areas where kelp can persist on its own and siting for kelp restoration efforts, not only in California but around the world. With over half of the ocean surface experiencing extreme marine heat every year since 2014, warming ocean temperatures present a serious threat to cold-water species like kelp. As kelp forests and other marine ecosystems around the world face increasing threats associated with climate change, conservation of ecosystems, like kelp forests, and predators, like sea otters, can mitigate the impacts of extreme events.

In conclusion, the study provides valuable information on the resilience of kelp forests amidst marine heat waves and the consequences of their decline on the broader ecosystem. It highlights the importance of habitat features and predators in driving forest persistence and the need for conservation efforts to protect and restore kelp forests. As the ocean continues to face unprecedented challenges, understanding the mechanisms behind the resilience and decline of kelp forests is crucial for the health and balance of the marine environment.

References:

Joshua G. Smith et al. Consequences of kelp forest ecosystem shifts and predictors of persistence through multiple stressors. Proceedings of the Royal Society B: Biological Sciences, 2024. DOI: 10.1098/rspb.2023.2749

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Monterey Bay Aquarium. (n.d.). Kelp Forests and Climate Change: Research Partners. Retrieved February 10, 2024, from https://www.montereybayaquarium.org/explore/research/kelp-forests/kelp-forests-and-climate-change-research-partners/

Monterey Bay Aquarium. (n.d.). Kelp Forests and Climate Change: Research Publications. Retrieved February 10, 2024, from https://www.montereybayaquarium.org/explore/research/kelp-forests/kelp-forests-and-climate-change-research-publications/