MEPS 201:91-106 (2000)  -  doi:10.3354/meps201091

Bio-optical characteristics of diatom and prymnesiophyte populations in the Labrador Sea

V. Stuart1,2,*, S. Sathyendranath1,2, E. J. H. Head1, T. Platt1, B. Irwin1, H. Maass1

1Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada
2Oceanography Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada

ABSTRACT: During the spring of 1996, phytoplankton samples were collected along a transect from South Wolf Island (Labrador) to Cape Desolation (Greenland). Dense blooms of diatoms were found over the shelf near the coast of Labrador, whereas high concentrations of the colony-forming prymnesiophyte Phaeocystis pouchetii were found close to Greenland. Phytoplankton samples were separated into 2 major groups (diatoms or prymnesiophytes) on the basis of chlorophyll (chl) chl c3/chl a ratios (determined by HPLC analysis), and the effects of species composition on the absorption and photosynthetic characteristics of these 2 high-latitude phytoplankton populations were studied. At all pigment concentrations and all wavelengths examined (apart from 623 nm), the diatom population had a much lower absorption coefficient than the prymnesiophyte population; this was attributed to an increased pigment-packaging effect in the larger diatom cells. Varying proportions of photoprotective pigments also influenced the absorption characteristics of these populations. The low specific-absorption coefficient of the diatom population resulted in a higher maximum photosynthetic quantum yield relative to that of the prymnesiophyte population. The initial slope of the photosynthesis-irradiance (P E) curve (αB) also appeared to be taxon-specific, with higher αB values being recorded for the smaller prymnesiophytes than for the larger diatom cells. The implications of species-dependent variations in phytoplankton absorption coefficients for the retrieval of remotely-sensed chl a are discussed.

KEY WORDS: Phytoplankton absorption · Bio-optical characteristics · Photosynthesis-irradiance curve · High latitudes · HPLC pigments

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