The unknown exists. There are plenty of events in the natural world that leave scientists perplexed. The infamous paradox of plankton, which sustains marine biomes around the world, is one of these mysteries. First proposed in 1962 for The American Naturalist, G. E Hutchinson’s problem challenged the notion of competitive exclusion while broadening our understanding of marine diversity.
Competitive Exclusion
The main goal of any sustainable environment is to maintain equilibrium. In consequence, two species cannot survive indefinitely if their niches are identical. Either the location, diet, or interactions with other organisms must differ if they are to live in the same habitat (Reeves et al. 2023). The potential a species has to occupy a location under ideal conditions (its fundamental niche) can be reduced once it yields to the actual conditions of its environment (realized niche) (Allot, 2014). Yet, when different species compete for the same resources, at least one of them must evolve to use a different resource, the same resource in a different way (or at a different time), or outlive the other (Kneitel, 2019).
An example are the two protozoan species in the graphs. Independently, they grow. Together, only P. aurelia can survive.
Figure 1. Lab – grown Paramecium aurelia and Paramecium caudatum. Adapted from Concepts of biology by Flower et al. 2023, Openstax. CC BY 4.0
A study in green
Hutchinson proposed the following problem: how can different species of phytoplankton coexist in the same habitat if they are competing for the same resources? After all, the mode of nutrition is not the only characteristic phytoplankton share; they also exhibit exponential growth in inorganic media (Hutchinson, 1962).
Modern studies have shown that more than a hundred species of eukaryotic phytoplankton can coexist in the same habitat. Each population thrives individually, and the community does so as a whole as well (Malviya, 2016). Not only do these supposedly incompatible phytoplankton species coexist, but they also significantly contribute to marine biodiversity.
Searching for a solution
Possible interrelated explanations for the paradox of plankton include:
One species survives by using the waste material of the other. This way, the resources expand overall.
Once a new species is introduced, it must fill an already occupied niche. Only if it is better than the already-located species at filling this niche, it will take over.
To test this theory, researchers Akshit Goyal and Sergei Maslov developed a mathematical model in which products were recorded and new bacteria was introduced randomly. Their conclusions? Their theoretical explanation could account for equilibrium. However, it might be seen as reductionist since it has limitations due to its account for variables with an artificial nature (Buchanan, 2018).
Real-Life Impact
By being dominant species for their environments, phytoplankton are the base of the food chain. And so, they are also the foundation of biodiversity. Scientists might still be confused as to how these microorganisms blend and expand their niches, but by doing so, phytoplankton could make endangered ecosystems thrive.
Chlorophyll Map Distribution adapted from Chlorophyll by NASA Earth Observatory. 2002.
The Galapagos Islands, for example, are the home of almost 3,000 species, many of them endemic, such as the only marine iguana. Their biodiversity extends from ocean to earth, where birds and cacti prosper too (World Wildlife, 2023). All its biodiversity is greatly impacted by a crucial factor: four ocean currents intersect on the islands. The various nutrients they bring are used by phytoplankton, which now reach over 100 species in the area (Forryan et al. 2021).
Nowadays, the Galapagos are threatened by industrial fishing, marine pollution, and other human activities. The preservation of plankton could ensure that the environment remains healthy. The Emperor Seamount Chain, the Sargasso Sea and Corner Rise, and the Arabian Sea are similar cases (Lohan, 2020). Ultimately, if the reasons for the coexistence of phytoplankton are uncertain, the impact of phytoplankton on biodiversity is undeniable.
Picture by Peter Stuar Mill on Pixabay
Bibliography:
Allot, A. (2014). Biology for the IB Diploma. Oxford University Press.
Forryan, A. Hearn, A. Naviera, A. (2021, February 2). Galápagos: we've found out why the islands are blessed with such nutrient-rich waters. The Conversation. https://theconversation.com/galapagos-weve-found-out-why-the-islands-are-blessed-with-such-nutrient-rich-waters-154020
Hutchinson, A. (1961). The Paradox of the Plankton. The American Naturalist. (Vol 95, No 882), Pp. 137. https://www.journals.uchicago.edu/doi/epdf/10.1086/282171
Kneitel, J. (2019). Gause’s Competitive Exclusion Principle. Encyclopaedia of Ecology (Vol 95). Pp. 110-113
Lohan, T. (2020, May 21). The Top 10 Ocean Biodiversity Hotspots to Protect. The Revelator. https://therevelator.org/ocean-biodiversity-mpa/#:~:text=Key%20areas%20also%20included%20the%20Sargasso%20Sea%2C%20as,Ridge%2C%20an%20undersea%20mountain%20range%20off%20southwestern%20Africa.
Malviya, S. Scalco, E. et al. (2016, May 14). Insights into global diatom distribution and diversity in the world’s ocean. PNAS. https://www.pnas.org/doi/10.1073/pnas.1509523113
NASA Earth Observatory. (2002). Chlorophyll Concentration [Map]. NASA Observatory. https://earthobservatory.nasa.gov/global-maps/MY1DMM_CHLORA
Buchanan, M. (2018). How 1000 Bacterial Species Can Coexist. Advancing Physics. https://physics.aps.org/articles/v11/37
Reeves et al. (2023). Concepts of Biology. Openstax. https://openstax.org/details/books/concepts-biology
World Wildlife. (2023). The Galápagos. WWF. https://www.worldwildlife.org/places/the-galapagos