LB 5-40 - Increase in microbial diversity with depth emerges from a simple but general marine ecosystem model

Marine heterotrophic microorganisms are key players in organic matter decomposition. Evidence has increasingly shown that microbial biodiversity increases with depth in the ocean. While several hypotheses have been proposed to explain this vertical diversity pattern, a mechanistic/theoretical understanding is still lacking. Here, we construct a mechanistic, trait-based model to describe the fundamental ecological interactions between functional groups in a food web. An analytic relationship between biomass and the net growth rate is derived to demonstrate how apparent competition and resource limitation drive microbial diversity patterns. Embedding the model in a 1-dimensional oceanic water column model, we observe a successional emergence of slow-growing micro heterotrophic functional types with depth. This pattern is consistent with observations of microbial diversity and with estimates of community-averaged maximum growth rate derived from genomes. The analytic formula well captures the vertical distribution of biodiversity, thus providing a mechanistic explanation for the observed vertical biodiversity pattern of microorganisms in the ocean.