# Bacterial Communities Associated With Crustose Coralline Algae Are Host‐Specific

## TL;DR

This study explores the bacterial communities on crustose coralline algae and finds they are specific to the host species and influenced by phylogeny and environment.

## Contribution

The study provides the first comprehensive characterization of bacterial communities across multiple Indo-Pacific crustose coralline algae species.

## Key findings

- Bacterial communities on crustose coralline algae are distinct and primarily differentiate by host species.
- Core bacterial communities correlate with host phylogeny and environmental factors like light and depth.

## Abstract

Crustose coralline algae (CCA) comprise hundreds of different species and are critical to coral reef growth, structural stability and coral recruitment. Despite their integral role in reef functioning, little is known about the diversity and structure of bacterial communities associated with CCA. We address this knowledge gap by characterising the surface microbial communities of 15 Indo‐Pacific CCA species across eight different families from the Great Barrier Reef, using 16S rRNA amplicon sequencing. CCA microbial community composition was distinct and found to primarily differentiate by algal host species. When looking at the core bacterial communities, divergence across CCA microbiomes was additionally correlated to host phylogeny. CCA from similar light environments and depths also had more similar microbial communities, suggesting the potential role of environmental parameters in influencing microbial community organisation. The fundamental descriptions of CCA bacterial communities for a wide range of Indo‐Pacific species presented here provide essential baseline information to further inform CCA microbial symbiosis research.

Fifteen Indo‐Pacific crustose coralline algae (CCA) species surface microbial communities were characterised with 16S rRNA amplicon sequencing and are distinct. The CCA surface microbiome primarily differentiate by algal host species, but core bacterial communities additionally correlated to host phylogeny.