# Microbes Under Climate Refugia: Equable Subcommunity Rank Dynamics in Large‐River Deltaic Estuaries

## TL;DR

This study explores how microbial communities in large-river deltaic estuaries maintain stable structures despite environmental changes, similar to macroorganisms in climate refugia.

## Contribution

The study introduces a novel approach using topic modeling to identify microbial subcommunities and analyze their rank dynamics in climate refugia.

## Key findings

- LDEs host distinct microbial community structures resilient to environmental changes.
- Subcommunity rank abundance curves show frequent evenness fluctuations.
- Rank-order shifts have strong carryover effects on future dynamics.

## Abstract

Microorganisms, similar to macroorganisms, can be sheltered by climate refugia—a property overlooked due to their speciose nature. Using the latent Dirichlet allocation model to categorize microbial communities into ecologically distinct subcommunities, we conducted a 2‐year survey of large‐river deltaic estuaries (LDEs), recognized as refugial hotspots, and established rank hierarchies with the continuous time dynamic model to monitor temporal changes. We found that, consistent with macroecology, LDEs harbor distinct microbial community structures, with the abundance distribution of subcommunities exhibiting resilience against environmental perturbations, persisting on an annual cycle. Specifically, subcommunity rank abundance curves show frequent evenness fluctuations, whereas rank‐order shifts—though less dynamic—exert stronger carryover effects on subsequent rank dynamics when occurring. Our results suggest that the microbial subcommunity rank structure in LDEs is persistent, aligning with classic patterns of species abundance distributions. This study emphasizes that, despite differences in their roles, the stable functioning of microbial rank systems is also fundamental to the refugial capacity of ecosystems and should be given equal importance.

We identified hotspots for microbial climatic refugia and conducted monthly surveys of microbial temporal dynamics over the course of 1 year at three large‐river deltaic estuaries (LDEs) with high refugial capacity, as well as at two additional sites within large‐river watersheds. Utilizing topic modeling from natural language processing, we distinguished unique microbial subcommunities within the LDEs.