“Thin” Algae in Competitive Environments, Is It Bad News for the Planet? | Ocean

Microalgae have a “secret” to success in competitive environments: they are able to “adjust” their size and metabolism to the circumstances in which they live. These evolutionary characteristics of species Dunaliella tertiolectawhich are part of the ocean’s phytoplankton, have been identified in a study led by Giulia Ghedini, senior researcher at the Gulbenkian Institute of Science, Oeiras.

The discovery, published in an article in the scientific journal Current Biology Review, provides clues to understand the behavior of these organisms in an increasingly warm ocean. With the climate crisis and the increase in the average temperature on Earth, environmental changes are occurring that modify the competition for the resources of the aquatic environment. And it can impact marine ecosystems, causing imbalances in both the food chain and oxygen production.

“We know that temperature normally makes species smaller and increases competition. We believe that the results of our study would be further exacerbated in a warmer ocean: cells would become smaller and metabolism would change to rapidly utilize available resources. If we find that other species of phytoplankton react in the same way, it means that oxygen production may drop – which is concerningGiulia Ghedini told PÚBLICO.

It is estimated that microalgae are responsible for the production of at least 50% of the oxygen present in the atmosphere, as they absorb carbon dioxide carbon and release oxygen during photosynthesis. The study conducted by the IGC researcher indicates that in denser environments, the metabolism of green microalgae can be 15% slower – which has implications for productivity during photosynthesis.

These single-celled beings are part of marine phytoplankton, a group of microscopic organisms that float in the ocean. It’s a fine example of collective power: once brought together, creatures invisible to the naked eye can even be observed from space. And together they form the base of the aquatic food chain.

compete for food

“The main question we are trying to answer in this study is: how do living things manage competition for food? This is a crucial question because it concerns all species. In ecology, there are different forms of interaction and you can never predict exactly what will happen,” explains Giulia Ghedini. The IGC researcher designed the study in collaboration with Dustin Marshall, a professor at Monash University in Australia.

The objective of the duo of scientists was to test the hypotheses of the metabolic theory, which predicts that competition conditions the evolution of the size and metabolism of living beings. Until today, the IGC statement states, this conjecture had not yet been “widely tested, especially in communities where organisms have to compete with several species”.

To test the hypothesis, the pair of scientists assessed what are the physiological characteristics of green microalgae that evolve when this species (Dunaliella tertiolecta) faces competition from others for food.

The study followed the evolution of this organism over ten weeks (which is equivalent to about 70 generations, since green microalgae “evolve rapidly”). During this period, it was observed Dunaliella tertiolecta in three different contexts: 1) the green microalga alone (therefore without competition), 2) cohabiting with a population of the same species and 3) with a community composed of three other species of phytoplankton.

“What we have found is that these organisms expend different amounts of energy depending on the competition that exists. It is this metabolic plasticity that evolves in microalgae. This is important because it means the species can thrive in different conditions. When food is plentiful, the metabolism is very fast. However, when resources are scarce, the metabolic system tends to slow down, compared to species that were not in competition,” explains the scientist in a call video.

flexible metabolism

Scientists have evaluated the long-term effects of this flexible metabolism and found it to be a good thing. “This metabolic plasticity gives these cells the ability to grow rapidly when population densities are low. […] and be effective when populations are dense […]. The best of both worlds! Smart cells! wrote co-writer Dustin Marshall on Twitter.

In part, the study’s conclusion helps to understand how single-celled species survive and grow rapidly even under adverse conditions. However, this metabolic plasticity has a price: what green microalgae gain in efficiency they lose in cell size.

“What we have identified as less positive is that there have been changes in the size of the organism, which tends to become smaller. From our perspective, this reduction in body mass n isn’t fantastic. Phytoplankton is at the base of the food chain: if there is less biomass, there is less food for fish, for example. And this also means a reduction in productivity, given the role of phytoplankton in oxygen production,” explains Giulia Ghedini.

The scientist points out that the study was conducted with a single species and therefore this conclusion cannot be extrapolated to other species of phytoplankton. “This knowledge is important because it gives us a framework to test how this metabolic response occurs in other species”, observes the researcher, who now aims to deepen this work and analyze the behavior of other aquatic organisms that make up marine phytoplankton.

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