Iridescent cystoseira

This remarkable seaweed is harvested in Brittany, France, on the Côtes d'Amor. It grows in a protected ecosystem and is harvested by hand according to responsible harvesting methods. It has a surprising feature: when outside the water at low tide it is a green/brown colour but becomes an iridescent blue once it is submerged. Hence, it is also known as "rainbow wrack". (It is also compared to a multicolour sea diamond.) This iridescence results from the presence of a dynamic, three-dimensional opalescent system, similar to that of the chameleon, another wonder of nature. Iridescence may help develop photoprotection in this seaweed through the activation of defence mechanisms which allow it to cope with the stress caused by exposure to light.