The rhythm of the reef — Diel cycles of the coral holobiont

Sun, 30 Jun 2024 00:00:00 +0000

Coral physiology is intimately dependent on diel cycles, as fluctuations in light intensity and spectrum, nutrient availability, and temperature directly change the respiration and energy assimilation capabilities of the coral colony. As complex sessile organisms, corals harbour incredibly diverse microbial assemblages of prokaryotes and microeukaryotes that provide functional roles in the coral ecosphere. Corals and Symbiodiniaceae have co-evolved, resulting in a symbiotic life strategy that benefits the coral host through the intracellular production of organic compounds such as carbon and oxygen. During sunlit hours, photosynthetic efficiency has been observed to increase oxygen levels ~250% of air saturation, stimulating hyperoxic environments. Corals and their aerobic microbial associates consume available oxygen through the night, where levels can become hypoxic. Given this extreme variation in abiotic parameters, it is likely that microbial communities reflect measurable changes through diel cycles, while cellular mechanisms help corals adapt to these extreme abiotic shifts.

This project explored three scleractinian corals — Pseudodiploria strigosa, Orbicella faveolata, and Diploria labyrinthiformis — through three diel cycles to characterise their microbial associates (including surrounding seawater) and the host transcriptional response. Coral samples were collected in triplicate and 1L reference seawater samples were acquired off the leeward side of Curaçao at 6-hour intervals over three days, resulting in a total of 3 replicated diel cycles. DNA was isolated, amplified using the V4 region of the 16S and 18S rRNA genes, and sequenced using Illumina MiSeq 2×250bp; RNA was sequenced using poly-A selection/enrichment.

We hypothesise that microbial taxa follow trends in abundance with respect to anoxic and hyperoxic conditions, and that circadian genes such as cry1, cry2, clock, and cycle show diel oscillations in expression. This work was published in Cell Host & Microbe (Weiler et al. 2026).

Circadian Rhythms | del Campo Lab - Microbial Ecology and Evolution

The rhythm of the reef — Diel cycles of the coral holobiont