Characterising photo-physiological responses of three coral species to low light for enhancing ex situ culture and the restoration of extreme reefs
摘要
Rapid coastal urbanisation has led to the growing prevalence of reefs characterised by suboptimal water conditions, such as extreme low light. Reef restoration initiatives for these reefs require a better understanding of how corals respond under extreme environmental conditions, so that ex situ mariculture practices supporting these efforts can be enhanced with acclimation regimes to improve post-transplantation survivorship. The current study investigated the effects of various intensities of photosynthetically active radiation (PAR) on the physiological responses of three common scleractinian coral species from Singapore’s extreme, low-light reefs, characterised by highly fluctuating PAR regimes. Fragments of Pachyseris speciosa, Merulina ampliata and Porites lutea were exposed to four levels of PAR (Very Low: 40–80 μmol m−2 s−1; Low: 100–140 μmol m−2 s−1; Medium: 230–270 μmol m−2 s−1; High: 320–360 μmol m−2 s−1) in flow-through aquaria tanks for six weeks. Corals from all species regulated their photosynthetic and respiration processes within two weeks of increased PAR. Species-specific responses were observed, with P. speciosa and M. ampliata fragments exposed to the lower PAR levels quickly registering higher effective quantum yields. Apart from P. lutea, zooxanthellae counts varied significantly over time, while chlorophyll-a concentrations decreased significantly for all species, suggesting its active role in photo-acclimation to decreasing light. No significant changes in storage lipids suggest that energy reserves were not utilised even under low PAR. Our findings suggest that corals from extreme low-light reef environments such as Singapore may already be pre-acclimated to low-light conditions and that they can acclimatise to extreme changes in PAR within six weeks without compromising growth and physiological health.