Coral reef holobiont community and ocean acidification

A new study has focused on a really interesting perspective on the relationship between coral reefs and ocean acidification

by Lorenzo Ciotti
Coral reef holobiont community and ocean acidification
© Sean Gallup / Staff Getty Images

Due to ocean acidification, marine wildlife is put in serious danger. The lowering of marine pH creates the phenomenon of coral bleaching; the calcium carbonate that makes up shells, molluscs, crustaceans and even coral decreases in relation to the increase in acidity, thus losing the algae that live on the surface of the organism, leading to its death.

The study Decline of a distinct coral reef holobiont community under ocean acidification, published in the Microbiome, made an interesting retrospective on the topic.

The researchers explain: "Microbes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges.

Ocean acidification
Ocean acidification© Sean Gallup / Staff Getty Images

Declining seawater pH, an important global coral reef stressor, can cause ecosystem-level change on coral reefs, providing an opportunity to study the role. of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome.

We test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO2 seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonized by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation.

We demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem changed. Video Abstract."