Ecological modelling of hycean worlds

TL;DR

This study applies ecological Lotka-Volterra models to hycean exoplanets, revealing diverse microbial ecosystems, competitive interactions, and the impact of viruses, advancing understanding of potential extraterrestrial biospheres.

Contribution

First application of Lotka-Volterra equations to model microbial ecology on hycean worlds, exploring ecological diversity and viral effects in exoplanetary water environments.

Findings

Microbial diversity can be extensive under hycean conditions.

Phototrophic bacteria dominate upper water layers, similar to Earth.

Viruses can cause ecosystem collapse or enhance diversity depending on timing.

Abstract

New observations are opening the possibility of characterising habitable environments in exoplanetary systems, with the recent example of the candidate hycean world K2-18 b. This motivates an exploration of the possible ecological conditions on such planets to better interpret biosignatures as well as understand the nature of potential life. On Earth, the Lotka-Volterra equations have been used to model numerous coupled populations within ecosystems, from interactions between large vertebrates, to systems with multiple microbial species. In this work, we apply the Lotka-Volterra equations to the ecology of habitable exoplanets for the first time, focusing on hycean worlds. We simulate scenarios in a vertical water column with between 1-5 bacterial species that thrive in anoxic environments on Earth, i.e. similar to predicted hycean conditions. We find that a wide range of ecological diversity is possible for microbial populations under hycean conditions. We demonstrate that dominating phototrophic bacteria at the top of a water column out-compete deeper dwelling phototrophic bacteria, analogous to bacterial blooms on Earth. Incorporating microbial viruses (bacteriophages) within our models can cause ecosystem collapse depending on the time of their introduction, and such phage inclusion can be beneficial to ecological diversity. Finally, our work shows that bacterial populations inhabiting tidally locked exoplanets may be more stable due to constant illumination of the ocean, but can have lower peak population densities in such cases when compared to seasonal scenarios. Our work provides an initial step towards understanding the possible ecological diversity on habitable worlds beyond Earth.