Nz. Jiao et Ih. Ni, SPATIAL VARIATIONS OF SIZE-FRACTIONATED CHLOROPHYLL, CYANOBACTERIA AND HETEROTROPHIC BACTERIA IN THE CENTRAL AND WESTERN PACIFIC, Hydrobiologia, 352, 1997, pp. 219-230
Geographic and vertical variations of size-fractionated (0.2-1 mu m, 1
-10 mu m, and >10 mu m) Chlorophyll a (Chl.a) concentration, cyanobact
eria abundance and heterotrophic bacteria abundance were investigated
at 13 stations from 4 degrees S, 160 degrees W to 30 degrees N, 140 de
grees E in November 1993. The results indicated a geographic distribut
ion pattern of these parameters with instances of high values occurrin
g in the equatorial region and offshore areas, and with instance of lo
w values occurring in the oligotrophic regions where nutrients were al
most undetectable. Cyanobacteria showed the highest geographic variati
on (ranging from 27x10(3) to 16,582x10(3) cell l(-1)), followed by Chl
.a (ranging from 0.048 to 0.178 mu g l(-1)), and heterotrophic bacteri
a (ranging from 2.84x10(3) to 6.50 x 10(5) cell l(-1)). Positive corre
lations were observed between nutrients and Chl.a abundance. Correspon
dences of cyanobacteria and heterotrophic bacteria abundances to nutri
ents were less significant than that of Chl.a. The total Chl.a was acc
ounted for 1.0-30.9%, 35.9-53.7%, and 28.1-57.3% by the >10 mu m, 1-10
mu m and 0.2-1 mu m fractions respectively. Correlation between size-
fractionated Chl.a and nutrients suggest that the larger the cell size
, the more nutrient-dependent growth and production of the organism. T
he ratio of pheophytin to chlorophyll implys that more than half of th
e > 10 mu m and about one third of the 1-10 mu m pigment-containing pa
rticles in the oligotrophic region were non-living fragments, while mo
st of the 1-10 mu m fraction was living cells. In the depth profiles,
cyanobacteria were distributed mainly in the surface layer, whereas he
terotrophic bacteria were abundant from surface to below the euphotic
zone. Chl.a peaked at the surface layer (0-20 m) in the equatorial are
a and at the nitracline (75-100 m) in the oligotrophic regions. Cyanob
acteria were not the principle component of the picoplankton. The carb
on biomass ratio of heterotroph to phytoplankton was greater than 1 in
the eutrophic area and lower than 1 in oligotrophic waters.