Coral larval settlement preferences linked to crustose coralline algae with distinct chemical and microbial signatures

Hendrikje Jorissen,Bernard Banaigs,Laetitia Hédouin,Pierre E Galand,Anne-Leila Meistertzheim,Isabelle Bonnard,Maggy M Nugues,Claude E Payri,Delphine Raviglione,Sonora Meiling

doi:10.1038/s41598-021-94096-6

Abstract

The resilience of coral reefs is dependent on the ability of corals to settle after disturbances. While crustose coralline algae (CCA) are considered important substrates for coral settlement, it remains unclear whether coral larvae respond to CCA metabolites and microbial cues when selecting sites for attachment and metamorphosis. This study tested the settlement preferences of an abundant coral species (Acropora cytherea) against six different CCA species from three habitats (exposed, subcryptic and cryptic), and compared these preferences with the metabolome and microbiome characterizing the CCA. While all CCA species induced settlement, only one species (Titanoderma prototypum) significantly promoted settlement on the CCA surface, rather than on nearby dead coral or plastic surfaces. This species had a very distinct bacterial community and metabolomic fingerprint. Furthermore, coral settlement rates and the CCA microbiome and metabolome were specific to the CCA preferred habitat, suggesting that microbes and/or chemicals serve as environmental indicators for coral larvae. Several amplicon sequence variants and two lipid classes—glycoglycerolipids and betaine lipids—present in T. prototypum were identified as potential omic cues influencing coral settlement. These results support that the distinct microbiome and metabolome of T. prototypum may promote the settlement and attachment of coral larvae.

Highlights

The resilience of coral reefs is dependent on the ability of corals to settle after disturbances
While these studies have shown that crustose coralline algae (CCA) species harbour highly diverse and distinct bacterial c ommunities[18,19,20], coral settlement has only recently been correlated with the microbiome community composition of CCA1 8,20
Our results show that metabolomic and microbiome profiles of CCA differed significantly between species, but that all CCA species induced high (> 54%) rates of total settlement

Summary

Introduction

The resilience of coral reefs is dependent on the ability of corals to settle after disturbances. Several studies have used culture-independent techniques to examine the bacterial communities associated with CCA While these studies have shown that CCA species harbour highly diverse and distinct bacterial c ommunities[18,19,20], coral settlement has only recently been correlated with the microbiome community composition of CCA1 8,20. Two classes of metabolites found in CCA cell walls (glycoglycerolipids and polysaccharides) have been identified as the main components of the coral settlement-inducing fraction[10] While both compound classes were detected in natural samples, they have not been successfully characterized and may form bioactive conformational units that cannot be purified[10]. Systematic studies on the metabolomic diversity of CCA species are currently lacking, and information on the microbiome and metabolome of CCA has never been combined to explore their ecological functions

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