# Impacts of Nearby Algae on Recruitment Success and Early Microbiome Development of the Coral Acropora cytherea

## TL;DR

This study shows that while certain algae help coral survival, the coral's early microbiome is shaped more by the coral's development than by the surrounding algae.

## Contribution

The study reveals that coral microbiome development in early life is driven by host ontogeny, not by specific nearby algae.

## Key findings

- Crustose coralline algae enhance coral recruit survival and growth.
- Coral recruit microbiomes are colonized by bacteria common to all benthic substrates, not unique to specific algae.
- Larval and recruit microbiomes differ, indicating microbiome changes during coral development.

## Abstract

The persistence of coral reefs is dependent on the arrival and settlement of coral larvae followed by their post‐settlement growth and survival. Despite evidence showing that benthic algae have variable effects on corals, it is still unclear how benthic communities of the coral nursery habitat impact the early development of the coral microbiome and if these impacts relate to the survival and growth of newly settled corals. Here, we tested whether the survival and growth of
Acropora cytherea
recruits are impacted by surrounding algae, and whether specific algae influence their associated bacterial and Symbiodiniaceae communities. A 6‐month survey of coral larvae experimentally settled near different algae showed that crustose coralline algae enhanced recruit survival. However, despite variation in their microbiome, the presence of different algae did not impact the coral microbial community composition. The recruit microbiome was colonised by bacteria shared among all benthic substrates rather than bacteria unique to specific algae. Furthermore, the microbiome of coral larvae was different from that of the recruits. We conclude that the microbiome of corals in their early life stages is structured by host ontogeny rather than by their surrounding benthos, but that the surrounding benthos contributes to the transfer of opportunistic bacteria.

Crustose coralline algae promote the survival and growth of coral recruits. However, these positive effects are not linked with the dynamics of the coral microbiome. Results reveal a transfer of opportunistic bacteria shared with all surrounding benthos, rather than a transfer of bacteria from specific algae to corals.