The influence of light on phlorotannin content of brown macroalgae

Phlorotannins are phenolic compounds unique to brown macroalgae, known for their wide spectrum of bioactive properties, which have sparked increasing industrial interest. Understanding how environmental factors influence phlorotannin production is crucial for evaluating the commercial potential of brown seaweeds. However, their plasticity makes it difficult to elucidate a clear link, if any, between phlorotannin content and any single environmental variable.

Phlorotannins have been reported to act in inducible defence responses, with secondary roles in photoprotection. However, with production pathways not yet fully understood, there is still no definitive evidence as to whether phlorotannin production is induced by intensity or wavelength of light. Photosynthetically active radiation, also known as visible light (PAR, 400–700 nm), drives photosynthesis, whereas ultraviolet radiation (UVR, 100–400 nm) triggers stress responses, such as oxidative damage. This distinction is important because studies on phlorotannins often examine whether their production is influenced by the amount of light (intensity) or the type of light (UVR vs. PAR). Given UVR’s higher stress potential, it may play a stronger role in phlorotannin induction. This review therefore provides an overview of the published literature that shows variation in natural light characteristics, both temporal and spatial, to be a factor influencing phlorotannin content for a range of brown macroalgal species, with a comparison to studies using artificial sources of light in an effort to induce phlorotannin production.

Overall, this review finds that a general consensus appears to have been reached in the literature that characteristics of light do influence phlorotannin content in both intertidal and subtidal brown macroalgae, supporting the proposal that phlorotannins act in a photoprotective mechanism and tolerance-raising role.