WATER COLUMN TRANSPARENCY AND THE DISTRIBUTION OF SPECTRALLY DISTINCTFORMS OF PHYCOERYTHRIN-CONTAINING ORGANISMS

Predominance of Type I (phycourobilin-containing) and Type II (phycour obilin-lacking) phycoerythrins (PE) was examined using scanning fluore scence spectroscopy at 176 stations in the northwestern Atlantic off t he northeast coast of the United States. Simultaneous optical measurem ents were made at 75 stations, permitting an analysis of the distribut ion of spectral types of PE-containing organisms based on geographic p osition of the stations and on the relative penetration of blue and gr een wavelengths of light. Stations dominated by Type I PE occurred alm ost exclusively in very transparent water with high transmissivity for blue light [domnwelling attenuation coefficient; K-d(440) < 0.12] and relatively low attenuation of blue light relative to green light. Thi s pattern was reversed for Type II PE, which dominated in less transpa rent waters with relatively high attenuation of blue light relative to green light. Type II PE tended to dominate on the continental shelf a nd slope, and Type I PE tended to dominate in the Sargasso Sea. Regard less of geographic location, there was a transition from dominance by Type I PE to Type II PE as the ratio K-d(440)/K-d(550) exceeded 1.25. Our data suggest that optical parameters are important niche dimension s for marine Synechococcus and that nearshore waters may be classified optically by phycoerythrin characterization.