MICROPLANKTONIC POLYUNSATURATED FATTY-ACID MARKERS - A MESOCOSM TRIAL

The fatty acid composition of total lipid was determined in microplank ton (< 200 mu m) from control, diatom-dominated and coccolithophore-do minated mesocosms. There was a good correlation between the abundances of chlorophyll a and total fatty acids in the three mesocosms. Analys es of fatty acid markers characteristic of diatoms (16:1n-7, 16:2n-3, 16:3n-3, 16:4n-1 and 20:5n-3) and of coccolithophores (18:5n-3 and 22: 6n-3) established that in the diatom-dominated mesocosm, an increase i n coccolithophore biomass, preceded the diatom bloom. Similarly, an in crease in the levels of diatom fatty acids preceded the coccolithophor e bloom in the coccolithophore-dominated mesocom. These transient incr eases in microplanktonic marker fatty acids levels were not evident fr om measures chlorophyll a, or estimated carbon contribution derived fr om cell counts. There was appreciable 22:6n-3 derived from coccolithop hores in the diatom-dominated bloom suggesting that the amount of this key nutrient at the base of the marine food-web may often be underest imated, with important consequences for higher trophic levels. (C) 199 8 Academic Press Limited.