Abstract

Authors: Jef Huisman, Tadzio Holtrop, Maayke Stomp, Levi Biersteker, Jeroen Aerts, Théophile Grébert, Frédéric Partensky, Laurence Garczarek and Hendrik Jan van der Woerd   Which colours of light are available in the aquatic ecosystems of our planet? And how do these colours affect the biogeographical distributions of phototrophic organisms, such as cyanobacteria, anoxygenic phototrophic bacteria and eukaryotic algae? Stretching and bending vibrations of water molecules absorb photons of specific wavelengths, a phenomenon that constrains light energy available for aquatic photosynthesis. Previous work suggested that these absorption properties of water create a series of underwater light colours or ‘spectral niches’. However, the theory was still too simplified to enable prediction of the spectral niches in real aquatic ecosystems. Here, we show with a state-of-the-art radiative transfer model that the vibrational modes of the water molecule delineate a series of distinct spectral niches, in the violet, blue, green, orange, red and infrared parts of the light spectrum. These distinct spectral niches are effectively captured by different photosynthetic pigments (chlorophylls, bacteriochlorophylls, phycobilin pigments), providing insight into how different groups of phototrophic organisms can flourish in different underwater light environments. We predicted the global distributions of the spectral niches by satellite remote sensing, and show that they matched well with observed distribution patterns of cyanobacterial pigment types. Our findings provide an elegant explanation for the large-scale biogeographical distributions of phototrophic organisms across the lakes and oceans of our planet.