# Seasonal Fluctuations of the Seagrass Holobiont under Contrasting Environmental Conditions

## TL;DR

This study examines how microbial communities in seagrass biofilms change with environmental factors, offering insights into seagrass health and restoration.

## Contribution

The study identifies specific microbial indicators of seagrass health and potential beneficial bacteria for restoration in the Coorong.

## Key findings

- Turbidity was the main driver of microbiota fluctuations in the Ruppia community.
- Water and sediment microbial communities correlated with the presence or absence of seagrasses.
- Beneficial bacteria were identified that could aid seagrass restoration and inhibit algal blooms.

## Abstract

Microbial communities are widely recognised as indicative of ecosystem health. Changes in the microbial community composition of seagrasses and their environment could act as an important bio‐indicator for stress factors affecting the submerged aquatic plants that make up the Ruppia community in the Coorong. Here, we explored prokaryotes associated with surface biofilms of the leaves and roots of the seagrasses to determine the microbiota composition of the Ruppia community, and their link to the surrounding sediment and water. Ruppia was recorded growing at 55% of the sites surveyed, and all collected samples showed a high diversity of prokaryotes. Turbidity was the main driver of the fluctuations in microbiota composition of the Ruppia community. Water and sediment microbial communities were correlated with the presence/absence of the seagrasses. Seagrass health indicators were assessed, allowing for a clear distinction between the various states of the Ruppia community identified in this study. This study provides key baseline insights into the composition and possible functions of these biofilm microbiota, as well as identifying potential health bio‐indicators for the Ruppia community. Furthermore, it identifies specific beneficial bacteria that could be selected to enhance seagrass restoration efforts as well as inhibit detrimental algal blooms in the Coorong.

(A) The inharmonious state of the Coorong and the different sample types collect with throughout this study. (B, C) Biofilm, including the presence of diatoms and bacteria, attached on the leaves of Ruppia.