Clathromorphum Nereostratum(corallinales, Rhodophyta): The Oldest Alga?¹

The longevity of organisms is intrinsically interesting and can provide useful information on their population structure and dynamics and the dynamics of associated communities. With the exception of perennial Laminariales that have rings in the stipe, the life spans of most perennial macroalgae are unknown or based on anecdotal observations. Using morphological analyses combined with the location and time of the rise in 14 C from atmospheric nuclear testing within the thallus, we determined that the growth rate of a specimen of Clathromorphum nereostratum Lebednik from Adak Island was 0.30 mm·yr −1 , the 3 0 bands within the thallus were annual, and the specimen sampled was 61–75 years old. Living crusts of this species from the same geographic region are reported to be up to 20 cm thick. Assuming our growth rate is typical, C. nereostratum can be approximately 700 years old, the oldest known living alga. This longevity and consistent banding within the thallus suggest that smaller scale sampling and additional chemical analyses of this alga could provide a detailed long‐term record of environmental variation at high latitudes in the North Pacific.