19′-hexanoyloxyfucoxanthin may not be the appropriate pigment to trace occurrence and fate of Phaeocystis:: the case of P-globosa in Belgian coastal waters

Two haptophycean strains were isolated from field samples collected in 2001 in Belgian coastal waters (southern North Sea) during the Phaeocystis monitoring program of the AMORE Project. The morphology and pigment composition of these two strains, one identified as Phaeocystis globosa and the other as Imantonia rotunda, were carefully examined. The comparative analysis of their pigment signature revealed the presence of two fucoxanthin derivatives, 19'-butanoyloxyfucoxanthin and 19'-hexanoyloxyfucoxanthin (but-fuco and hex-fuco) in I rotunda, which were undetectable in P. globosa. A further comparison of pigments and phytoplankton from field samples showed no significant correlation between hex-fuco concentration and P globosa biomass in the water column. Low concentrations of this pigment were, however, detectable before and at the end of the Phaeocystis bloom. The presence of L rotunda in the area, overlooked by light microscopy, but isolated in pure culture from field samples, might explain the presence of this pigment. We conclude that hex-fuco is not the appropriate pigment to estimate Phaeocystis abundance and trace its trophic fate in Belgian coastal waters. These results also indicate that pigment analysis should be coupled with a precise identification of phytoplankton taxa, present in field samples. (C) 2004 Elsevier B.V. All rights reserved.