Red algae, typically known for their namesake color derived from light-harvesting pigments, might potentially be using color in a far more complex way than previously understood. New research suggests that certain species employ structural coloration – producing blue hues at their growth tips and white hues elsewhere, including fruiting structures – as a form of inter-species communication. This groundbreaking finding links color production with anti-herbivory chemicals, indicating a complex defence mechanism.

The Diver’s Curiosity

The investigation began with observations made while diving.Being a diver, I have long been aware that some red algae have a much whiter appearance than their usual red when observed in water, said a researcher. Also, in a recent diving survey I noticed that the tips of young shoots in one of the species seemed to have a blueish hue. These observations made me curious, and I wanted to clarify the mechanism of these colors.

Challenges in deep-Sea Research

Studying these algae presented significant hurdles. These species grow deep underwater below the tidal zone, which requires scuba diving for their observation and collection, the researcher explained. in addition, many deep-water species are very fragile, and it is arduous to conduct detailed observations and experiments in the laboratory while they are still alive. Also, it requires special techniques to enable looking at the detailed structures with an electron microscope. Despite these challenges, researchers successfully gathered enough samples, drawing on prior experience with brown algae studies.

Microspheres and Color Creation

The research team published their findings in the European Journal of phycology.They discovered specialized cells, known as “gland cells,” containing tightly packed microspheres of light-reflecting material. In the growth tips of the red alga Asparagopsis taxiformis, these microspheres are uniform in size, reflecting blue light. As the gland cells mature,the microspheres become less uniform,reflecting all colors and resulting in a whitish appearance.

The structural color of red and brown algae living in shallow water has been explained to protect the photosynthetic pigments or to optimize photosynthesis. However, little is known about the structural color seen in deep water species, the researcher noted.

A Warning and Camouflage System

The location of these colors suggests their function. The inside of the structure that causes the coloration contains a substance that is highly reactive and may act as a feeding repellent to algae-eating fish, the researcher stated. Such a repellant is more effective when combined with a warning color such as the blue hue at the algae’s growth tips. And where these structures are white, around where the organism’s fruiting structures are located, they may act as a camouflage of their original red color against grazers using sight to find their food.

Global Warming Implications

the prevalence of algae-grazing fish in tropical waters, due to higher temperatures aiding digestion and increased visibility, may explain the concentration of structural coloration in red algae in these regions. However,this has implications for global warming.

As warm-water fish migrate further north, they might pose a significant threat to the algae there that are not protected by such coloration.
Researcher

Collaboration

This research was conducted in collaboration with a researcher from Hokkaido University.