Metacommunity ecology of Symbiodiniaceae hosted by the coral Galaxea fascicularis

Abstract

Coral−algae symbiosis represents the trophic and structural basis of coral reef ecosystems. However, despite global threats to coral reefs and the dependence of coral health and stress resistance upon such mutualisms, little is known about the community ecology of endosymbiotic Symbiodiniaceae. Concepts and methods from metacommunity ecology may be used to help us understand the assembly and stability of symbiont communities and the mutualisms they comprise. In this study, we sampled colonies of the symbiont-generalist coral Galaxea fascicularis in southwestern Japan and assessed the effects of environmental and host factors on Symbiodiniaceae community composition, while simultaneously exploring residual correlations among symbiont types that may reflect non-random assembly processes such as species interactions. We metabarcoded the Symbiodiniaceae ribosomal internal transcribed spacer 2 (ITS2) region and characterized the endosymbiotic community using 2 different OTU identity cutoffs , and analyzed them with generalized dissimilarity modeling and joint species distribution modeling. We found that Symbiodiniaceae form discrete communities characterized by the dominance of ITS2 types C1, C21a, or D1, that are each associated with a different suite of co-occurring background types and tend to exclude each other in an endosymbiotic community. The communities showed modest responses to temperature, water depth, host genotype, polyp size, and bleaching status, and there was local sequence variation within the ITS2 types. After accounting for the effects of those variables, residual correlations remained in community composition, pointing to the possibility that Symbiodiniaceae community assembly in corals may be structured by interspecific competitive or facilitating interactions rather than only exogenous variables.

Biogeochemical niches and trophic plasticity of shallow and mesophotic corals recovering from mass bleaching

“…This study builds on previous research in the Maldives that used coral δ 13 C to show differential trophic strategies in three morphologically diverse species across shallow to mesophotic reefs: massive/encrusting Galaxea fascicularis , flexible trophic strategy with heterotrophic capacity; plating Pachyseris speciosa , physiologically plastic low‐light specialist, relatively more autotrophic; branching Pocillopora verrucosa , effective mixotroph (Supporting Information Table S2) (Radice et al 2019 a ). Although the interaction of symbiont type and light has variable effects on carbon fixation and translocation (Leal et al 2015; Ezzat et al 2017; Ros et al 2021) that may impact coral holobiont δ 13 C (Wall et al 2020), both P. verrucosa and P. speciosa associate with one symbiont genus regardless of depth (Cooper et al 2011; Ziegler et al 2015 a , b ; Bongaerts et al 2021) and while G. fascicularis can host two symbiont genera, host lineage and location primarily affect symbiont composition (LaJeunesse et al 2004; Wepfer et al 2020).…”

Monoclonal Culture and Characterization of Symbiodiniaceae C1 Strain From the Scleractinian Coral Galaxea fascicularis

“…The symbiotic phylotypes associated with G. fascicularis were mainly dominated by Symbiodiniaceae ITS2-C1, D1, and C21a, along with numerous of other background clade C phylotypes ( Xu, 2019 ; Wepfer et al, 2020 ). Even identified as clade C phylotype by n18S-rDNA and Taq I-generated RFLPs ( Santos et al, 2002 ), the symbiotic biota in G. fascicularis could also possess multiple composition of both dominant and background symbionts when probed with ITS2 sequence tagging.…”

“…When cultured in vitro , GF19C1 cells show morphological changes, preparation for the recovery of sexual reproduction, rapid adaptation to light intensity, and rapid evolution of growth rate. Symbiodiniaceae C1 are the most widespread algal symbiont in reef-building corals ( Stat et al, 2008 ), their distribution ranged from high latitude region e.g., Korea-Jeju Island and Japan, to tropical region e.g., South China Sea ( Reimer et al, 2006 ; Ng and Ang, 2016 ; Chen et al, 2019 , 2020 ; Wepfer et al, 2020 ), thus they have experienced large sea surface temperature variations and high turbidity ( Ng and Ang, 2016 ; Wepfer et al, 2020 ). Therefore, in future study it is necessary to further explore the adaptive potential of GF10C1 to multiple environmental factors and high gradient changes.…”

“…It is also the dominant species on the fringing reefs of Hainan Island ( Chen et al, 2013 ; Wang et al, 2013 ). G. fascicularis species includes two morphologically and genetically differentiated lineages characterized by the microbasic p-mastigophores (MpM) types of tentacular nematocyst ( Hidaka, 1992 ) and mitochondrial genotypes ( Watanabe et al, 2005 ) around Hainan Island ( Wu, 2018 ; Wepfer et al, 2020 ). These two lineages demonstrate significant differences in heat resistance ( Xu, 2019 ), indicating the potential of G. fascicularis as an ideal model for exploring the genetic basis of heat resistance differentiation of corals.…”

Help Me, Symbionts, You’re My Only Hope: Approaches to Accelerate Our Understanding of Coral Holobiont Interactions

“…In fact, G. fascicularis has been successfully bleached and then reinoculated with presumed heterologous strains of Symbiodiniaceae (Puntin et al 2022), providing a promising system to cross different host genotypes with algal strains as proposed above (Figure 2). This ability to control and modify symbiosis in combination with previous mechanistic (e.g., ion transport for calcification (Al-Horani et al 2003, 2005) and microbiome (Tang et al 2020;Wepfer et al 2020) research make it an ideal candidate to explore partner interactions.…”