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Bustillos-Guzman et al.: Taxon-specific pigment variation and
hydrographic structur e 253
(ng I-')1:: 1!!
J A S O N D1992
Fig. 5 Vert~ cal istribution of chlorophyll a ( C h l a ) ,
ucoxanthin Fig. 6. Vertical distribution of chlorophyll b (Chl b )
, eaxan-and 19 ' -hexanoyloxyfucoxanthn t
19'-butanoyloxyfucoxanthin thin and divinyl chlorophyll a (DV-Chla)
concentration at(19'-HF+19'-BF) concentration at Stn B between
March 1992 Stn B between March 1992 and April 1993.Uppermost par t
ofand April 1993. Upper most par t of figur e refers to
stratification figure refers to stratification conditions as def
ined in Fig. 1
conditions as defined in Fig. 1 (stratification ndex)
(stratification index)
which is a pnori impossible to set up for open oceanwaters,
allowed us to investigate in detail the closelinkage between
hydrodynamic and phytoplanktondynamics and , in particular, allowed
us to evaluate thetime necessary for the system to become stable
again.
The recorded average chl a + DV-Chla (24 mg m- 2)is well within
the ra nge of thos e zones consid ered asoligotrophic (e .g.
Packard & Dortch 1975, Dortch &Packard 1989, Ondrusek et
al. 1991, Li et al. 1992).However , the variability of this auto
tro phic biomassconcentration (range = 13 to 48 mg chl a + DV-chl
am-', variation coefficient = 34%) ,as well as the changein
phytoplankton community structure, shows that thesystem displays a
wide ran ge of tr ophic conditionswhich are principally linked to
hydrodynamics. Let us
examine in detail the phytoplank ton sign ature of typi-cal
hydrological situations.Diatoms are recognized as the most
opportunistic
species as far as taking advantag e of nu trient avail-ability
is concerned (Fog g 1991) and a s such, are alikely contributor to
new production in the o pen ocean(Goldman 1993, Claustre
1994).Nevertheless, evidencealso suggests that, in deep mixed
layers, diatoms donot dominate, probably a s a conseque nce of
limitedphotoadaptational ability. Therefore, most of thediatom
bloom records are generally restricted to thespatio-temporal
transition between mixed and strati-fied conditions (Kiorboe 1993,
Claustre et al. 1994).These conditions offer the best compromise
betweenlight and nutrient availability because the associated
