S. Sathyendranath et al., SOME BIOOPTICAL CHARACTERISTICS OF PHYTOPLANKTON IN THE NW INDIAN-OCEAN, Marine ecology. Progress series, 132(1-3), 1996, pp. 299-311
Light absorption by phytoplankton and the parameters of the photosynth
esis-light curve were measured in the NW Indian Ocean in January to Fe
bruary 1993. The light absorption characteristics of phytoplankton sho
w some regional differences, probably reflecting changes in the phytop
lankton population: cyanobacteria (Synechococcus spp.) were present in
all 3 regions and dominated the phytoplankton biomass in the Somali C
urrent area; prochlorophytes were mainly confined to samples from the
Somali Current area; and larger algal species, including diatoms, were
found in the Red Sea and Gulf of Aden. The initial slope alpha(B) and
the assimilation number P-m(B) of the photosynthesis-light curve had
dynamic ranges of 3.7 and 3.9, respectively, and appeared to be correl
ated with environmental co-variables such as nutrient concentrations a
nd ambient light levels as well as phytoplankton absorption in the blu
e and red parts of the spectrum. Even though the sampling was confined
to the mixed layer, there was some evidence of photoadaptation, sugge
sting that the rate of vertical mixing in the mixed layer was rather s
low, compared with photoadaptation rates. The quantum yield of photosy
nthesis varied over a factor of 6, and was correlated with relative ch
anges in absorption in the blue and red parts of the spectrum. The imp
lications of these results for computation of primary production using
photosynthesis-light models are discussed, with special reference to
applications of remotely sensed data on ocean colour.