SPATIAL AND SEASONAL-VARIATIONS IN ABUNDANCE AND SPECTRAL CHARACTERISTICS OF PHYCOERYTHRINS IN THE TROPICAL NORTHEASTERN ATLANTIC-OCEAN

A simple and rapid spectrofluorimetric method to quantify phycoerythri ns (PEs) from the area below the fluorescence excitation spectra is pr oposed. In contrast to other methods which used measurements at fixed wavelengths, this method takes into account the spectral diversity of these pigments. It was applied in the tropical northeastern Atlantic d uring the EUMELI program at three stations which were characterized by different trophic status (eutrophic, mesotrophic and oligotrophic). S ampling was made at various periods of the year. The results showed th e constant presence of phycoerythrin nearly always associated with cya nobacteria (Synechococcus). At the oligotrophic site, high phycourobil in (PUB) populations and a great stability in the abundance and spectr al characteristics of PE were observed. The eutrophic and mesotrophic sites showed higher PE abundance and spectral variability, and were es sentially dominated by high phycoerythrobilin (FEB) populations. A gen eral increase with depth in the PUB/PEB ratio at the eutrophic and mes otrophic sites was observed. This increase could be regular or relativ ely sharp through physical discontinuity (thermocline or halocline). T he presence of Cryptophyceae PE was occasionally noted. The PE diversi ty was most probably related to the presence of different populations, but some variations could be also influenced by photoacclimation proc esses. Further progress in the spectrofluorimetric analysis of PE coul d be achieved by using three-dimensional spectra. (C) 1997 Elsevier Sc ience Ltd.