Temporal Variation in the Microbiome of Acropora Coral Species Does Not Reflect Seasonality.

Neal E. Cantin,Veronique J. L. Mocellin,Madeleine J. H. van Oppen,Hillary A. Smith,Gergely Torda,Hannah E. Epstein

doi:10.3389/fmicb.2019.01775

Abstract

The coral microbiome is known to fluctuate in response to environmental variation and has been suggested to vary seasonally. However, most studies to date, particularly studies on bacterial communities, have examined temporal variation over a time frame of less than 1 year, which is insufficient to establish if microbiome variations are indeed seasonal in nature. The present study focused on expanding our understanding of long-term variability in microbial community composition using two common coral species, Acropora hyacinthus, and Acropora spathulata, at two mid-shelf reefs on the Great Barrier Reef. By sampling over a 2-year time period, this study aimed to determine whether temporal variations reflect seasonal cycles. Community composition of both bacteria and Symbiodiniaceae was characterized through 16S rRNA gene and ITS2 rDNA metabarcoding. We observed significant variations in community composition of both bacteria and Symbiodiniaceae among time points for A. hyacinthus and A. spathulata. However, there was no evidence to suggest that temporal variations were cyclical in nature and represented seasonal variation. Clear evidence for differences in the microbial communities found between reefs suggests that reef location and coral species play a larger role than season in driving microbial community composition in corals. In order to identify the basis of temporal patterns in coral microbial community composition, future studies should employ longer time series of sampling at sufficient temporal resolution to identify the environmental correlates of microbiome variation.

Highlights

Scleractinian corals are complex holobionts that host a high diversity and abundance of microbial symbionts that make up the coral microbiome (Blackall et al, 2015), some of which are essential to holobiont health, and function
It has been proposed that the coral bacterial community can be partitioned into a stable core component, a site-specific component, and a dynamic and variable component highly influenced by changes in abiotic and biotic factors (Hernandez-Agreda et al, 2016; Leite et al, 2018)
A total of 5,112,489 sequences from 216 samples corresponding to 14,083 unique amplicon sequence variants (ASVs) were recovered to characterize the bacterial communities of A. hyacinthus and A. spathulata at the two mid-shelf reefs through time

Summary

Introduction

Scleractinian corals are complex holobionts that host a high diversity and abundance of microbial symbionts that make up the coral microbiome (Blackall et al, 2015), some of which are essential to holobiont health, and function. The coral microbiome is rarely static and its members can fluctuate as a result of changes in environmental conditions, or possibly due to host regulatory mechanisms (reviewed in Bourne et al, 2016). Symbiodiniaceae communities may fluctuate according to season (e.g., Chen et al, 2005; Ulstrup et al, 2008), but can remain stable through time in some coral species (e.g., Thornhill et al, 2006a,b). It has been proposed that the coral bacterial community can be partitioned into a stable core component, a site-specific component, and a dynamic and variable component highly influenced by changes in abiotic and biotic factors (Hernandez-Agreda et al, 2016; Leite et al, 2018)

Objectives

Methods

Results

Discussion

Conclusion