Coral reefs worldwide confront escalating threats, characterized by heightened sedimentation and diminished light penetration due to extensive land reclamation and coastal development. This critical issue is exemplified by the drastic reduction in underwater visibility, notably in Singapore, where levels have dwindled from over 10 meters in the 1960s to approximately 2 meters today. This study endeavours to explore the repercussions of intermittent light and complete darkness on the transcriptome of the common tropical coral Pachyseris speciosa.

The research implemented a 4-week experiment involving three distinct light treatments: control, representing normal light conditions; intermittent light, with 5 days of normal light conditions and 2 days of total darkness (non-consecutive); dark, maintaining constant total darkness. Coral samples collected at the beginning and conclusion of the experiment underwent RNA sequencing via Illumina for whole transcriptomic analysis, enhancing the depth of understanding regarding molecular responses. Additionally, comprehensive photo-physiological data were recorded at the experiment's onset and conclusion.

Post-experiment analysis revealed the resilience of all P. speciosa colonies, albeit with notable disparities in the transcriptome status. Coral’s transcriptome under intermittent light showcased differential expression of genes involved in pathways like inflammation and immune system, suggesting a possible adaptation to these adverse conditions. On the other hand, the dark treatment transcriptomics responses highlighted a remarkable stressful state, with enhanced KEGG pathways involved in tissue damage and apoptosis. Notably, no corals resulted dead at the end of the experiment, underlying the resilience of this coral species.

Overall, our findings suggest that P. speciosa may possess the molecular and photo-physiology capacity to adapt to intermittent light stress, positioning it as a promising candidate for use in restoration projects in low light environments affected by reduced light penetration.