Allelopathic interactions between the brown algal genus Lobophora (Dictyotales, Phaeophyceae) and scleractinian corals.

Christophe Vieira,Julie Gaubert,Grégory Genta-Jouve,Gérald Culioli,Olivier De Clerck,Olivier P Thomas,Claude E Payri,Fanny Houlbreque

doi:10.1038/srep18637

Abstract

Allelopathy has been recently suggested as a mechanism by which macroalgae may outcompete corals in damaged reefs. Members of the brown algal genus Lobophora are commonly observed in close contact with scleractinian corals and have been considered responsible for negative effects of macroalgae to scleractinian corals. Recent field assays have suggested the potential role of chemical mediators in this interaction. We performed in situ bioassays testing the allelopathy of crude extracts and isolated compounds of several Lobophora species, naturally associated or not with corals, against four corals in New Caledonia. Our results showed that, regardless of their natural association with corals, organic extracts from species of the genus Lobophora are intrinsically capable of bleaching some coral species upon direct contact. Additionally, three new C21 polyunsaturated alcohols named lobophorenols A–C (1–3) were isolated and identified. Significant allelopathic effects against Acropora muricata were identified for these compounds. In situ observations in New Caledonia, however, indicated that while allelopathic interactions are likely to occur at the macroalgal-coral interface, Lobophora spp. rarely bleached their coral hosts. These findings are important toward our understanding of the importance of allelopathy versus other processes such as herbivory in the interaction between macroalgae and corals in reef ecosystems.

Highlights

Allelopathy has been recently suggested as a mechanism by which macroalgae may outcompete corals in damaged reefs
Taking into account that: (1) some Lobophora species are naturally occurring associated with coral species on healthy reefs without apparent signs of competition towards their coral “hosts”, and; (2) that Lobophora organic extracts displayed allelopathy against some coral species in bioassay experiments, we address the following questions: Do Lobophora species naturally found in association with corals present negative allelopathy against the latter; are all Lobophora species, regardless of their association with corals, susceptible to bleach corals; and last, if allelopathic interactions are at play, which compounds mediate these interactions? To tackle these questions, we implemented a multi-level approach of allelopathic bioassays starting from a multi-species and crude extract level to a single species and isolated compounds level
Given the recent progress in understanding species-level diversity in the genus, it is not known whether all or only a subset of Lobophora species compete with corals for space

Summary

Introduction

Allelopathy has been recently suggested as a mechanism by which macroalgae may outcompete corals in damaged reefs. Members of the brown algal genus Lobophora are commonly observed in close contact with scleractinian corals and have been considered responsible for negative effects of macroalgae to scleractinian corals. We performed in situ bioassays testing the allelopathy of crude extracts and isolated compounds of several Lobophora species, naturally associated or not with corals, against four corals in New Caledonia. In situ observations in New Caledonia, indicated that while allelopathic interactions are likely to occur at the macroalgal-coral interface, Lobophora spp. rarely bleached their coral hosts. These findings are important toward our understanding of the importance of allelopathy versus other processes such as herbivory in the interaction between macroalgae and corals in reef ecosystems. L. undulata a percentage of transects where the species were observed in the vicinity of corals. baverage percentage of associations as assessed by the stratified random point count method in transects where the species was present

Methods

Results

Conclusion