Parental bleaching susceptibility leads to differences in larval fluorescence and dispersal potential in Pocillopora acuta corals

Metabolic signatures of two scleractinian corals from the northern South China sea in response to extreme high temperature events

Coral bleaching events are becoming increasingly common worldwide, causing widespread coral mortality. However, not all colonies within the same coral taxa show sensitivity to bleaching events, and the current understanding of the metabolic mechanisms underlying thermal bleaching in corals remains limited. We used untargeted metabolomics to analyze the biochemical processes involved in the survival of two bleaching phenotypes of the common corals Pavona decussata and Acropora pruinosa, during a severe bleaching event in the northern South China Sea in 2020. During thermal bleaching, P. decussata and A. pruinosa significantly accumulated energy products such as succinate and EPA, antioxidants and inflammatory markers, and reduced energy storage substances like glutamate and thymidine. KEGG analysis revealed enrichment of energy production pathways such as ABC transporters, nucleotide metabolism and lipid metabolism, suggesting the occurrence of oxidative stress and energy metabolism disorders in bleached corals. Notably, heat stress exerted distinct effects on metabolic pathways in the two coral species, e.g., P. decussata activating carbohydrate metabolism pathways like glycolysis and the TCA cycle, along with amino acid metabolism pathways, whereas A. pruinosa significantly altered the content of multiple small peptides affected amino acid metabolism. Furthermore, the osmoregulatory potential of corals correlates with their ability to survive in heat-stress environments in the wild. This study provides valuable insights into the metabolic mechanisms linked to thermal tolerance in reef-building corals, contributes to the understanding of corals' adaptive potential to heat stress induced by global warming and lays the foundation for developing targeted conservation strategies in the future.

Photodegradation of a bacterial pigment and resulting hydrogen peroxide release enable coral settlement

The global degradation of coral reefs is steadily increasing with ongoing climate change. Yet coral larvae settlement, a key mechanism of coral population rejuvenation and recovery, is largely understudied. Here, we show how the lipophilic, settlement-inducing bacterial pigment cycloprodigiosin (CYPRO) is actively harvested and subsequently enriched along the ectoderm of larvae of the scleractinian coral Leptastrea purpura. A light-dependent reaction transforms the CYPRO molecules through photolytic decomposition and provides a constant supply of hydrogen peroxide (H₂O₂), leading to attachment on the substrate and metamorphosis into a coral recruit. Micromolar concentrations of H₂O₂ in seawater also resulted in rapid metamorphosis, but without prior larval attachment. We propose that the morphogen CYPRO is responsible for initiating attachment while simultaneously acting as a molecular generator for the comprehensive metamorphosis of pelagic larvae. Ultimately, our approach opens a novel mechanistic dimension to the study of chemical signaling in coral settlement and provides unprecedented insights into the role of infochemicals in cross-kingdom interactions.

Telomere dysfunction is associated with dark-induced bleaching in the reef coral Stylophora pistillata

Telomere DNA length is a complex trait controlled by both multiple loci and environmental factors. A growing number of studies are focusing on the impact of stress and stress accumulation on telomere length and the link with survival and fitness in ecological contexts. Here, we investigated the telomere changes occurring in a symbiotic coral, Stylophora pistillata, that has experienced continuous darkness over 6 months. This stress condition led to the loss of its symbionts in a similar manner to that observed during large-scale bleaching events due to climate changes and anthropogenic activities, threatening reef ecosystems worldwide. We found that continuous darkness was associated with telomere length shortening. This result, together with a phylogenetic analysis of the telomere coral proteins and a transcriptome survey of the continuous darkness condition, paves the way for future studies on the role of telomeres in the coral stress response and the importance of environmentally induced telomere shortening in endangered coral species.