New Insights on the Diurnal Mechanism of Calcification in the Stony Coral, Stylophora pistillata

Abstract

Scleractinian corals are evolutionary-successful calcifying marine organisms, which utilize an endo-symbiotic relationship with photosynthetic dinoflagellate algae that supply energy products to their coral hosts. This energy further supports a higher calcification rate during the day in a process known as light enhanced calcification. Although this process has been studied for decades, the mechanisms behind it are still unknown. However, photosynthesis and respiration also cause daily fluctuations in oxygen and pH levels, resulting in the coral facing highly variable conditions. Here we correlated gene expression patterns with the physiological differences along the diel cycle to provide new insights on the daily dynamic processes, including circadian rhythm, calcification, symbiosis, cellular arrangement, metabolism, and energy budget. During daytime, when solar radiation levels are highest, we observed increased calcification rate combined with an extensive up-regulation of genes associated with reactive oxygen species, redox, metabolism, ion transporters, skeletal organic matrix, and mineral formation. During the night, we observed a vast shift toward up-regulation of genes associated with cilia movement, tissue development, cellular movement, antioxidants, protein synthesis, and skeletal organic matrix formation. Our results suggest that light enhanced calcification is related to several processes that occur across the diel cycle; during nighttime, tissue might elevate away from the skeleton, extending the calcifying space area to enable the formation of a new organic framework template. During daytime, the combination of synthesis of acid-rich proteins and a greater flux of ions to the sites of calcification facilitate the conditions for extensive mineral growth.

Nutritional exchange between reef-building corals and algal endosymbionts buffers the energetic demand of larval development and metamorphosis

“…Our finding that gene expression and metabolism increased concurrent with elevated symbiont photosynthesis are aligned with previous observations that carbohydrate metabolism and transport genes are upregulated during the day in adult tissues of the confamilial species Acropora cervicornis when photosynthetic activity is highest (74). However, there is variability by species and life stage in metabolism and carbohydrate usage dependent on diel cycles and energetic priorities (e.g., investment in calcification or reproduction) (75, 76). Shifts in carbohydrate utilization should be examined across life stages in the context of energy demands in future work.…”

Transcriptional responses indicate acclimation to prolonged deoxygenation in the coral Stylophora pistillata

“…Accordingly, some corals appear to regulate energy metabolism through adjustments of cellular/ metabolite fluxes rather than use metabolic gene expression alterations to adjust to the diurnal oxygen dial cycle. However, some coral species, like S. pistillata, alter metabolic gene expression in response to short-term deoxygenation or natural diurnal hypoxia (Alderdice et al, 2020;Neder et al, 2022). Therefore, it is hard to predict how corals will acclimate to prolonged deoxygenation based on the response to short-term or natural diurnal hypoxia, emphasizing the importance of our two-week long study.…”

Viral infection arrests coccolithophore calcification and nutrient consumption, and triggers shifts in organic stoichiometry

“…Duplicate samples of 10 mL were filtered through 0.2 μm filters (Sterivex, Millipore) and kept at 4°C until further analysis. Alkalinity was measured by acid-base titration following (Neder et al 2022), via automatic titrator (Titroline 7000 Si analytics), and calculated using a gran plot with a precision lower than 20 mEq. Phosphate (as dissolved reactive phosphate) was measured by colorimetric spectroscopy using the Mo-Blue method (Cary 8454 UV-vis spectrometer, Agilent) with a precision of 0.1 mM and detection limit of 0.1 μM (Holman 1943).…”

“…Alkalinity was measured by acid-base titration following (Neder et al 2022), via automatic titrator (Titroline 7000 Si analytics), and calculated using a gran plot with a precision lower than 20 mEq. Phosphate (as dissolved reactive phosphate)…”