Enhancing coral photosynthesis: The power of manganese-alginate gels

Scleractinian corals rely on symbiosis with Symbiodiniaceae, a family of marine dinoflagellates, for photosynthetic products, which sustains their growth in nutrient-poor environments. Manganese (Mn) is a critical element for photosynthesis as an essential cofactor for the oxygen-evolving complex of the photosynthetic machinery. Also, Mn is an essential metal involved in antioxidant mechanisms that maintain normal cellular function in heat stressed corals.

This study aims to investigate the effects of different Mn species on photosynthetic efficiency in the coral Stylophora pistillata under thermal stress. A Mn-alginate device for controlled Mn supplementation was developed for this purpose.

Coral nubbins were exposed to the following Mn species: manganese(II) chloride (MnCl₂), manganese(II) ethylenediamine-N,N'-disuccinate (MnEDDS), manganese(II) desferrioxamine (MnDFO), and manganese(III) citrate (MnCIT). Photosynthetic parameters were measured using fluorometry. Mn-alginate gel dishes were prepared for controlled release, and their impacts on coral health indicators were evaluated at 26 °C and 31 °C, including photosynthetic efficiency, oxygen production, and symbiont density.

Free Mn(II) (MnCl₂) and MnEDDS significantly enhanced photosynthetic efficiency. Mn-alginate effectively delivered Mn in controlled bursts. Under thermal stress, Mn supplementation improved photosynthetic activity and favored symbiont density. Mn-alginate dishes were stable in seawater and biocompatible, releasing Mn optimally at elevated temperatures.

Mn-alginate gel dishes are an efficient and safe method for improving coral photosynthesis and mitigating thermal stress impacts, supporting reef conservation efforts in a changing climate.