A groundbreaking study reveals that as the oceans warm, an ‘invisible forest’ of phytoplankton is thriving in unexpected ways, with profound implications for the future of our marine life and global climate.
The Unseen Abundance
Despite the drizzle, large numbers of birds can still occur, sometimes in exceptional circumstances as revealed by research conducted by the University of Exeter in the Sargasso Sea. In the ocean’s vast interior, an ‘invisible forest’ of phytoplankton is thriving on carbon dioxide released from melting Arctic ice.
The study found that the total biomass, or living material, of subsurface phytoplankton has increased over the past decade as a result of warming ocean temperatures. This is a significant finding, since phytoplankton form the base of the marine food web and sustains a wide range of creatures from microzooplankton to giant whales.
Instead, their results imply that these deeper-living phytoplankton, which are specially adapted to grow in low light conditions, have been acclimating and possibly even thriving as a result of climate change versus upwelling species. This masked richness has important implications for how we perceive the precarious equilibrium of the oceans, and how they can act as an escape route out of the severe impact global warming.
The Divergent Responses
Despite all that, there are abundant reasons to study shifts in mean phytoplankton biomass since it tells an incomplete story of how climatic variability impacts productivity of these critical plants in the targeted plankton community the research is focused.
However, the surface phytoplankton community has experienced a separate regime shift, whereas subsurface phytoplankton biomass increased. As a result, surface-dwelling organisms today have less chlorophyll which means they appear less green but their overall biomass has hardly changed.
The difference in responses implies that the vertical structure of the ocean is changing in response to climate change. The depth of the surface mixed layer (the mixing region of the upper ocean) has shallowed over the last decade probably because it has warmed so much, they discovered.
The change in the ocean’s vertical structure means significant impacts on the distribution and productivity of phytoplankton, which can have cascading effects on the entire marine food web as well. Since phytoplankton form the base of the ecosystem, changes in their abundance and community composition can have cascading effects on almost all ocean life forms from minute zooplankton to the largest whales and sharks.
Conclusion
Results from this pioneering study demonstrate that the ocean’s response to climate change is complex and highly variable. Though that ‘invisible forest’ of sub-surface phytoplankton may be doing just fine, the larger consequences for the marine environment as a whole are still unclear. Monitoring the situation and carrying out additional research will be key to understanding these changes, both in terms of their impact on biodiversity and what they could mean for the ocean’s ability to limit the effects of climate change. This, the authors of the study stress, highlights the pressing need for better global surface and depth-related phytoplankton monitoring to reveal more about this cornerstone of marine biology.
