How Heatwaves Push Different Kelps to Their Limits

Jim Crocker
11th March, 2024

How Heatwaves Push Different Kelps to Their Limits

Image Source: Natural Science News, 2024

Key Findings

  • In the southwest UK, kelp species suffer more under longer and hotter marine heatwaves
  • Extreme heatwaves cause kelp to grow poorly, perform less photosynthesis, and bleach
  • Surprisingly, kelp expanding its range is also highly vulnerable to prolonged heat
Marine ecosystems are under threat from a phenomenon known as marine heatwaves (MHWs)—periods of unusually high sea temperatures. These events have been increasing in frequency and intensity, posing risks to marine life, particularly to foundational species like kelp that form the backbone of their ecosystems. The Marine Biological Association of the UK has conducted a study[1] to better understand the effects of MHWs on kelp species, which are vital for biodiversity and carbon storage. Kelps are large brown seaweeds that create underwater forests, offering habitat and food for marine life. They are also significant players in carbon sequestration, drawing down carbon dioxide from the atmosphere. Previous research has shown that kelps' growth and health are closely tied to climate conditions, with their net primary production peaking in temperate regions and contributing substantially to coastal ocean productivity[2]. The study focused on two kelp species, Laminaria digitata and Laminaria ochroleuca, in the southwest UK. L. digitata is retreating from the region, while L. ochroleuca is expanding its range. Researchers simulated MHWs of varying intensities and durations to observe the kelps' responses. They found that moderate MHWs induced stress in both species, with longer events causing greater harm. Extreme MHWs led to severe growth declines, reduced photosynthetic performance, and increased bleaching, with longer durations exacerbating these effects. Notably, L. ochroleuca suffered almost complete tissue death during prolonged MHWs, despite assumptions that species expanding their range would have greater thermal tolerance. These findings are crucial as they indicate that even kelp at the edge of their expanding range, which might be presumed more resilient, are vulnerable to extended high temperatures. This vulnerability could have implications for marine biodiversity and ecosystem services, including the carbon cycle, as kelps are integral to both[2]. The study's results also tie back to earlier research[3], which highlighted that kelp species could cope with summer MHWs under high-light conditions but struggled when light availability decreased. This suggests that environmental quality, such as water clarity, could play a role in kelp resilience to temperature stress. Moreover, the study[4] emphasized the need for a deeper understanding of MHW impacts on marine life to improve predictions and management strategies in the face of climate change. The Marine Biological Association's research adds to this body of knowledge by demonstrating the nuanced ways in which MHW intensity and duration can affect kelp, irrespective of their thermal niches or geographic distribution. This insight is vital for predicting how these foundational species might fare as our oceans continue to warm, and for developing conservation strategies that might help mitigate the impacts of future MHWs. In summary, the study sheds light on the significant threat posed by MHWs to kelp forests, which are essential to the health of marine ecosystems and the broader oceanic carbon cycle. It underscores the importance of understanding specific stressor impacts on marine life to inform conservation efforts and ensure the resilience of these ecosystems in a changing climate.

EcologyMarine Biology

References

Main Study

1) Marine heatwave duration and intensity interact to reduce physiological tipping points of kelp species with contrasting thermal affinities.

Published 8th March, 2024

https://doi.org/10.1093/aob/mcad172

Related Studies

2) Global seaweed productivity.

https://doi.org/10.1126/sciadv.abn2465

3) Marine heatwaves and decreased light availability interact to erode the ecophysiological performance of habitat-forming kelp species.

https://doi.org/10.1111/jpy.13332

4) Biological Impacts of Marine Heatwaves.

https://doi.org/10.1146/annurev-marine-032122-121437


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