The reef-building coralGalaxea fascicularis: a new model system for coral symbiosis research

Abstract

Reef-building corals owe their evolutionary success to their symbiosis with unicellular algae (Symbiodiniaceae). However, increasingly frequent heat waves lead to coral mass-bleaching events and pose a serious threat to the survival of reef ecosystems. Despite significant efforts, a mechanistic understanding of coral-algal symbiosis functioning, what leads to its breakdown and what can prevent it, remains incomplete. The main obstacles are low amenability of corals to experimental handling and, owing to its obligatory nature, the difficulties of manipulating the coral-algal association. Indeed, many studies on the symbiotic partnership are conducted on other cnidarian model organisms and their results may therefore not be fully transferable to tropical reef-building corals. Here, we identify the tropical stony coral species Galaxea fascicularis as a novel candidate coral model system. Individual polyps of this species can be separated, enabling highly replicated genotype studies, and are well suited to experimental investigation of the symbiosis as they can be easily and effectively rid of their algal symbionts (bleached). We show that bleached adult individuals can reestablish symbiosis with homologous and heterologous symbionts. We also report the completion of the gametogenic cycle ex-situ and the successful spawning in aquaria over multiple years. These achievements help overcome several of the major limitations to direct research on corals and highlight the potential of G. fascicularis as an important new model system for investigations of symbiosis functioning and manipulation.

The bacterial microbiome of symbiotic and menthol-bleached polyps of long-term aquarium-rearedGalaxea fascicularis

“…Raw sequencing data submitted to NCBI SRA BioProject PRJNA947274 Representative sequences (ASVs) submitted to NCBI GenBank Accession numbers OQ677536 to OQ677992 Additional data, scripts, and code are available online: https://doi.org/10.5281/zenodo.10551928 (Puntin 2024)…”

“…To include these critical features, research with corals is irreplaceable (Puntin et al 2022b). The reef-building coral Galaxea fascicularis (Linnaeus, 1767) has been proposed as a model species for coral symbiosis research (Puntin et al 2022a). This species is well represented in the literature, featured in studies that characterize the coral gastric cavity (Agostini et al 2012; Zhou et al 2020) and the calcification processes (Al-Horani et al 2003, 2005, 2007), among others (Ferrier-Pagès et al 1998; Niu et al 2016; Miura et al 2019).…”

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

“…This ability to modulate symbiont state is valuable; however, to date, no studies have reported successfully inoculating A. poculata with different (i.e., heterologous) symbiont strains. While other studies have reported acquisition of novel algal symbionts in adult corals (Puntin et al 2022;Scharfenstein et al 2022), inoculation of A. poculata with heterologous algal strains should remain a priority.…”

“…Several other reef building species are emerging as potential models, including Oculina arbuscula (Rivera and Davies 2021) and Galaxea fascicularis (Puntin et al 2022), which can also have their symbiotic states experimentally manipulated. 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).…”

“…Several other reef building species are emerging as potential models, including Oculina arbuscula (Rivera and Davies 2021) and Galaxea fascicularis (Puntin et al 2022), which can also have their symbiotic states experimentally manipulated. 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.…”