Abstract
Unprecedented mass coral bleaching events due to global warming and overall seawater pollution have been observed worldwide over the last decades. Although metals are often considered as toxic substances for corals, some are essential at nanomolar concentrations for physiological processes such as photosynthesis and antioxidant defenses. This study was designed to elucidate, the individual and combined effects of nanomolar seawater enrichment in manganese (Mn) and iron (Fe), on the main physiological traits of Stylophora pistillata, maintained under normal growth and thermal stress conditions. We provide, for the first time, evidence that Mn is a key trace element for coral symbionts, enhancing cellular chlorophyll concentrations, photosynthetic efficiency and gross photosynthetic rates at ambient temperature. Our experiment also highlights the key role of Mn in increasing coral resistance to heat stress-induced bleaching. While Mn-enriched corals did not bleach and did not reduce their rates of photosynthesis and calcification, control corals experienced significant bleaching. On the contrary to Mn, Fe enrichment not only impaired calcification but induced significant bleaching. Such information is an important step towards a better understanding of the response of corals to seawater enrichment in metals. It can also explain, to some extent, species susceptibility to environmental stress.
Highlights
Coral reefs are one of the most biodiverse, complex and productive ecosystems on Earth[1,2]
Mn is an essential component of the Oxygen Evolving Complex (OEC) of photosystem II, whereas Fe is needed for the structure of the chlorophyll, of the photosystems I and II, the cytochrome b6f complex, and the ferredoxin[34,35,36]
Principal Coordinate Analysis (PCoA) comparison of coral physiological traits maintained under the eight Mn-Fe-temperature conditions revealed a similar response between duplicated tanks (Fig. 1)
Summary
Coral reefs are one of the most biodiverse, complex and productive ecosystems on Earth[1,2]. The only three studies which have focused on the combined effects of thermal stress and metal pollution (copper and nickel)[12,25,26], have highlighted an increased bleaching susceptibility of adult corals under metal pollution[13,26] and a reduced thermal tolerance of coral larvae[25] Many metals, such as mercury[27], copper[28] or lead[21], are toxic for living organisms, even at nanomolar concentrations, some of them can play key roles in the functionning of photosynthetic organisms (e.g. phytoplankton, plants, algae) (reviewed by[29]). We hypothesize that an enrichment in Mn and/or Fe can increase the coral resistance to bleaching; iii) we hypothesize that a combined enrichment in manganese and iron has additive effects compared to an enrichment in either manganese or iron alone
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
