Assessment of the coral health of Platygyra carnosa through in-situ and ex-situ measurements of metabolic rates
Involved Member: Dr. Leo Lai CHAN
Underwater visual monitoring methods are used broadly to evaluate coral reef conditions in the natural environment, but quantitative measurements of the coral holobiont has been largely restricted to photo-physiological assessment of the endosymbionts. An underwater respirometer has been designed to make routine, diver-operated, non-invasive measurements at coral surfaces, but the realistic in situ accuracy and precision capabilities of this device have not been critically assessed; an essential step if these measurements are to be useful for quantifying spatial and seasonal patterns of coral metabolism. We developed specific protocols for this system to survey shallow coral colonies and detect metabolic profiles (respiration, photosynthesis, and biocalcification), diel cycles (day and night), and photosynthesis-irradiance curves. Analysis of data from in situ and laboratory-controlled conditions showed good agreement among coral colonies and high precision measurements of temperature, oxygen and pH fluxes over 15-min incubation times without noticeable detrimental effects on coral health. Moreover, marked differences were observed in coral calcification rates between estuarine-influenced and coastal marine conditions, despite the absence of significant differences in visual appearance or other health indicators, revealing the system’s potential for early detection of marginally adverse conditions for coral metabolism.
Stress-tolerant coral species, such as Platygyra spp., are considered to be well adapted to survive in marginal reefs, but their physiological response to short term exposure to abnormally high temperature and lowered salinity remains poorly understood. Using non-invasive techniques to quantitatively assess the health of Platygyra carnosa, we identified the plasticity of its energetics and physiological limits. Although these indicators suggest that it can survive at high temperature (25–32 °C), its overall energetics were seriously diminished at temperatures >30 °C. In contrast, it was well adapted to hyposaline waters (31–21 psu) but with reduced calcification, indicating a short-term adaptation for expected future changes in salinity driven by increased amounts and intensities of precipitation.
Our findings provide useful insights to the effect of these climate drivers on P. carnosa metabolism and thus better forecast changes in their health status under future climate change scenarios. The ease of operation and rapid quantification of the physiological status of the corals make the underwater respirometer well suited for use by reef scientists, monitoring agencies, and stakeholders in biogenic reefs conservation efforts. Moreover, the high spatial and temporal resolution of these data will have the potential to discriminate the effects of local stressors on coral health from those generated by broader changes associated with climate drivers.
References:
2. Dellisanti, W., Tsang, R.H.L., Ang, P., Wu, J.J., Wells, M.L. and Chan, L.L. (2020). Metabolic performance and thermal and salinity tolerance of the coral Platygyra carnosa in Hong Kong waters. Marine Pollution Bulletin, 153, 111005.