Heterogeneity leads to increased marine plankton blooms, model shows

• The study, published in Nature Communications, shows that dilution and mixing of water patches with different properties can significantly increase plankton biomass growth in response to local nutrient injections.
• The approach used allows a deeper and more precise understanding of biophysical mechanisms in drifting marine ecosystems, providing a solid basis for improving the understanding of these ecosystems by using observations and models synergistically.

A new study presents a model for drifting ecosystems that reveals an increase in marine plankton blooms when marine plankton are under spatial variability of available resources. The study, published in the prestigious journal Nature Communications, shows that the response of plankton biomass to a perturbation of available resources can vary significantly, depending solely on the physical processes to which the region of water in which it is found is subjected. 

The team of scientists behind the paper, including IFISC (UIB-CSIC) researcher Enrico Ser-Giacomi, used the Lagrangian perspective in the model. This is based on tracking over time a patch or patch of water that hosts a drifting ecosystem, along with its physical, environmental and biochemical characteristics. The response of the plankton biomass within the patch of water to a resource perturbation can vary in size by up to six times depending solely on the physical processes to which the area is subjected, say the researchers. The study also shows that water dilution and mixing, driven by deformation mechanisms and diffusion, are responsible for the initial generation of heterogeneity in planktonic Lagrangian ecosystems, and that such heterogeneity can significantly enhance plankton growth, highlighting the existence of optimal dilution rates that maximise patch-integrated biomass. 

The researchers used data collected during the SOIREE experiment to test the model. SOIREE was a large-scale iron fertilisation experiment conducted in the Southern Ocean in 1999. The researchers compared the temporal evolution of model variables, such as patch width and length or spatial means of iron and biomass, with measured values for the corresponding variables from in situ sampling or remote sensing. The study shows that the proposed model captures the biophysical dynamics of the iron bloom during the SOIREE experiment. 

The findings of the work have important implications for the understanding of marine ecosystems. The study provides a theoretical framework that incorporates all aspects of drifting ecosystems, including physical, environmental and biochemical characteristics, and demonstrates that these processes must be taken into account when interpreting and modelling marine ecosystems. This information could inform policies for the protection of marine ecosystems by providing a better understanding of their functioning and response to disturbance, and could be applied to the assessment of other ecological aspects, such as species diversity.

 Photo: Image taken by MERIS (Medium Resolution Imaging Spectrometer) on 6/11/2007. The red line indicates the water patch where the bloom is occurring. The coupled biophysical processes result in a marked spatial deformation within the region.

Ser-Giacomi, E., Martinez-Garcia, R., Dutkiewicz, S. et al. A Lagrangian model for drifting ecosystems reveals heterogeneity-driven enhancement of marine plankton blooms. Nat Commun 14, 6092 (2023). https://doi.org/10.1038/s41467-023-41469-2