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MEPS prepress abstract   -  DOI:

Photosynthetic pigments of co-occurring Northeast Atlantic Laminaria spp. are unaffected by decomposition

Luka Seamus Wright*, Andy Foggo

*Corresponding author:

ABSTRACT: Along Northeast Atlantic coasts, the genus Laminaria dominates kelp forests. Two species, L. digitata and L. hyperborea, are cold temperate whilst the third, L. ochroleuca, is warm temperate. In northern France and the southern British Isles, all three species now co-occur, with a gradual rise in predominance of L. ochroleuca evident over recent decades due to climate-driven range shifts. Despite recent focus on the export of photosynthetically viable macroalgal detritus, the effect of decomposition on detrital pigment concentration remains unknown for northern hemisphere kelps. Furthermore, notwithstanding its importance in determining habitat suitability, the photosynthetic pigments of all three species have not yet been assessed comparatively within the same forest. Here we present results of a field experiment aimed to test potential changes in the pigments of decomposing kelp blade fragments. Using spectrophotometry and Gaussian peak spectral deconvolution to quantify pigments, we found that shallow benthic decomposition over one month does not affect major photosynthetic pigment concentrations in any of the examined species. Moreover, the two boreal species were similar in their sporophyte pigment stoichiometry and had more chlorophyll a, chlorophyll c, fucoxanthin and minor carotenoids (β,β-carotene and zeaxanthin) than L. ochroleuca. This resulted in total pigment content that was 82% and 74% higher in L. digitata and L. hyperborea than L. ochroleuca. These differences correspond approximately to each species’ latitudinal distribution and photosynthetic performance.