Genus-specific response of kelp photosynthetic pigments to decomposition

Abstract

Detritus is widely considered to be dead organic matter. However, recent studies have shown that kelp detritus can be functionally equivalent to the attached plant. This is significant, because detritus makes up ~ 42% of all plant biomass. In the Northeast Atlantic, studies on detrital photobiology have been restricted to the genus Laminaria. Here, we present data from a 46 d in situ experiment investigating the effect of decomposition on detrital photosynthetic pigment concentrations and stoichiometry in four Northeast Atlantic kelp species from three genera. We corroborate the lack of a decomposition effect on pigments of cold temperate Laminaria species as identified by previous studies but show that the photophysiology of other kelp genera responds differently. While Saccharina latissima displays an idiosyncratic parabolic response, the annual and thermally plastic kelp Saccorhiza polyschides seems to become less pigmented with increasing detrital age. If S. polyschides becomes increasingly dominant in future parts of a warmer Northeast Atlantic, this may translate to lower detrital photosynthetic potential at the forest scale. However, given our somewhat ambiguous data on this species, this conjecture requires further investigation into detrital photosynthesis.