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

Abstract

Tropical corals construct the three-dimensional framework for one of the most diverse ecosystems on the planet, providing habitat to a plethora of species across taxa. However, these ecosystem engineers are facing unprecedented challenges, such as increasing disease prevalence and marine heatwaves associated with anthropogenic global change. As a result, major declines in coral cover and health are being observed across the world's oceans, often due to the breakdown of coral-associated symbioses. Here, we review the interactions between the major symbiotic partners of the coral holobiont – the cnidarian host, algae in the family Symbiodiniaceae, and the microbiome – that influence trait variation, including the molecular mechanisms that underlie symbiosis and the resulting physiological benefits of different microbial partnerships. In doing so, we highlight the current framework for the formation and maintenance of cnidarian-Symbiodiniaceae symbiosis, and the role that immunity pathways play in this relationship. We emphasize that understanding these complex interactions is challenging when you consider the vast genetic variation of the cnidarian host and algal symbiont, as well as their highly diverse microbiome, which is also an important player in coral holobiont health. Given the complex interactions between and among symbiotic partners, we propose several research directions and approaches focused on symbiosis model systems and emerging technologies that will broaden our understanding of how these partner interactions may facilitate the prediction of coral holobiont phenotype, especially under rapid environmental change.

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

“…This demonstrated how targeted inoculation can successfully shift Symbiodiniaceae community composition toward a higher proportion of heat tolerant strains without thermal treatment (Silverstein et al 2015). Although the longevity of these partnerships is still unclear, these are promising results for future development of in hospite studies on the role of temperature on inter-partner symbiosis dynamics and symbiont recognition mechanisms (Bove et al 2022). The success and potential insights from such experimental approaches will rely on future efforts to establish a variety of coral host-specific Symbiodiniaceae cultures (including the establishment of specific cultures from G. fascicularis) for further study.…”

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

“…This demonstrated how targeted inoculation can successfully shift Symbiodiniaceae community composition towards a higher proportion of heat tolerant strains without thermal treatment (Silverstein et al 2015). Although the longevity of these partnerships is still unclear, these are promising results for future development of in hospite studies on the role of temperature on inter-partner symbiosis dynamics and symbiont recognition mechanisms (Bove et al 2022). The success and potential insights from such experimental approaches will rely on future efforts to establish a variety of coral host-specific Symbiodiniaceae cultures (including the establishment of specific cultures from G. fascicularis ) for further study.…”

Impact of Marine Chemical Ecology Research on the Discovery and Development of New Pharmaceuticals

“…Evidence of marine microbiome changes due to environmental stressors is provided by metagenomic studies, which have revealed the alteration of core microbial communities in certain sponge species, including Rhopaloeides odorabile , Xestospongia muta , Halichondria bowerbanki and Haliclona cymaeoformis [ 191 , 192 , 193 , 194 ]. Such shifts in the host microbiome in response to environmental stresses can result in the loss of metabolic potentials and dysbiosis, leading to sponge disease and mortality [ 70 , 195 ]. There are currently gaps in our understanding of the effects of environmental perturbance on the production of secondary metabolites by microbial symbionts.…”