Fatty acid and elemental composition of littoral “green tide” algae from the Gulf of Finland, the Baltic Sea

Abstract

Coastal eutrophication leads to a shift in primary producer communities from perennial species to ephemeral fast-growingspeciesofmacroalgae,whichisknownas"green tides" phenomenon. In brackish water habitats of the Baltic Sea,theopportunisticgreenalgae,Cladophoraglomerataand Ulva intestinalis, replaced the brown alga Fucus vesiculosus, while in freshwater estuarine parts they replaced epilithic microalgae. We studied Baltic populations of the macroalgae, C. glomerata and U. intestinalis, and epilithic and epiphytic microalgae, with respect to their nutritive quality, such as content of essential polyunsaturated fatty acids (PUFAs) and elemental composition. Fatty acid profiles of the two macroalgae were significantly different, including levels of essential PUFAs. We found a relatively high content of eicosapentaenoic acid (EPA; 20:5n�3) in C. glomerata bio- mass (4.14 mg g �1 C), whereas U. intestinalis had a lower value (0.45 mg g �1 C). Comparison with literature data showed that C. glomerata appeared to be a more valuable food for potential invertebrate consumers in respect to EPA content and stoichiometric C/P ratio than perennial F. vesiculosus and U. intestinalis. Thus, replacement of F.vesiculosusand epilithicmicroalgaebyC. glomeratawould not decrease the potential nutritive value of coastal algal communities for invertebrates. In turn, if U. intestinalis dom- inate in algal community, the nutritive value of primary pro- ducers in coastal zone would decrease. However, in following works, other important indicators of nutritive value, such as sterols and amino acids, should be included in the estimations of green tide algae species.