Phototrophic and Sulfate-reducing Growth in a Hycean Ecosystem Model

Abstract

Cooke et al. recently adapted a light-dependent population model to possible Hycean ocean ecosystems. Their simulations combine a green sulfur bacterium with five psychrophilic sulfate-reducing strains, while local light availability multiplies both active-cell growth and reactivation. That dependence has a clear physiological basis for the phototroph. Sulfate reducers, by contrast, obtain energy from redox reactions involving electron donors and sulfate or related acceptors. Setting the light factor to zero therefore removes growth from organisms that can remain metabolically active in darkness when chemical substrates are available. This distinction affects the multispecies simulations in which attenuation or removal of a surface population regulates the persistence of deeper sulfate reducers. Such outcomes describe competition for light among phototrophs, but not direct light limitation of sulfate-reducing populations.