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Climate Change

A bad kelp review: trouble in times of warming

Wernberg T, Bennett S, Babcock RC, de Bettignies T, Cure K, Depczynski M, Dufois F, Fromont J, Fulton CJ, Hovey RK, Harvey ES, Holmes TH, Kendrick GS, Radford B, Santana-Garcon J, Saunders BJ, Smale DA, Thomsen MS, Tuckett CA, Tuya F, Vanderklift MS, and Wilson S. Climate-driven regime shift of a temperate marine ecosystem. Science 353 (6295), 169-172. 7 July 2016. doi: 10.1126/science.aad8745.

(Panels courtesy Wernberg et al., Science)

(Panels courtesy Wernberg et al., Science 2016)

Foundational species form the basis for communities, providing resources and structures that are essential to the very existence of an ecological community. One such species is kelp, fast growing macroalgae that take root in the shallow ocean to form vast underwater forests. These kelp forests are home to an enormous diversity of sessile (immobile) and motile invertebrates that cling to the algae’s stipes (stalks) and blades, as well as fish and mammals that seek food and refuge within the algal sanctuaries. The delicate balance between kelp grazers and their predators helps sustain kelp forest ecosystems.  Beyond their ecological importance, kelp forests provide valuable “ecosystem services” for millions of people, from supplying nutrition to sustaining livelihoods.

Ecosystems are anything but fragile, as attested by their resilience to seasonal changes. Yet, when faced with unusual stressors like record temperatures due to global climate change, ecologists wonder how ecosystems such as kelp forests will fare. Kelp forests are only as resilient as the kelp that forms their structures. If kelp were to disappear so would the associated flora and fauna. So, how resilient are the kelp themselves to stresses like increasing ocean temperature due to climate change? When is hot too hot, and when do communities cease to exist as we have known them?

A recent study published in Science by a team of Australian and Kiwi researchers suggests that kelp forests are in dire straits as a result of record warming in the Indian Ocean. The study is a culmination of a fifteen-year survey of kelp forest communities off the western coast of Australia. In 2011—one decade into the survey—a dramatic collapse in kelp forests was witnessed coinciding with record temperatures. This collapse lead to the replacement of native kelp communities with flora and fauna from warmer tropical and subtropical latitudes. More disturbingly, these kelp forests showed no sign of recovery in the subsequent years, suggesting that the change in ecosystem was essentially irreversible. The authors cited an increased grazing rate by invading tropical and subtropical fish species, which could prevent a young kelp forest from taking root. Moreover, they point out that projected increases in the frequency of extreme warming events will further exacerbate recovery of kelp forests.

Sadly, the tale of the kelp forests of western Australia seems to fulfill the greatest fears of ecologists in the light of climate change. While ecosystems are resilient, there appears to be a tipping point of no return that threatens to change the face of our planet. Record temperatures due to human-driven climate change have lead to the blurring of lines between tropical and temperate ecosystems. The short-term implications for these kelp communities are clear, but the long-term effects of ecosystem flipping remain uncertain, as does the potential for recovery. Scientists should continue to monitor these ecosystems for years to come, while society should continue to work to reverse the detrimental effects of climate change.

Abrahim El Gamal
Abrahim is a PhD student at Scripps Institution of Oceanography in San Diego where he studies marine chemical biology.

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