Underwater Light Modulators: Iridescent Structures of the Seagrass Posidonia Oceanica

Colors are crucial for animals and plants to interact with their environment and other organisms. Especially the bright, iridescent colors in nature often rely on micro- and nanoscale features made by organic materials. The occurrence and shape of these structures causing the colors is not only fascinating, but it is becoming increasingly important for biomimetics and bioinspired devices that imitate functional principles of living systems. Many plants developed structural colors based on photonic crystals, e.g., in the cuticle of fruits to attract animals. Here, we report the first time on the iridescent structures in the seagrass Posidonia oceanica and provide evidence that the resulting color likely relies on a multilayered 1D photonic crystal consisting of multiple liquid and organic layers. The structure evolves and changes throughout the leaf blade (from its base to the top) resulting in different light interactions on the same leaf. Photonic structures become increasingly important in bioinspired optical devices, also integrated in robots as sensors, as organism-machine interacting element, or photoprotection and the here described structures could be especially interesting as inspiration for developing light modulators for applications in underwater scenarios.