ESTIMATING THE CONTRIBUTION OF MICROALGAL TAXA TO CHLOROPHYLL-A IN THE FIELD - VARIATIONS OF PIGMENT RATIOS UNDER NUTRIENT-LIMITED AND LIGHT-LIMITED GROWTH
R. Goericke et Jp. Montoya, ESTIMATING THE CONTRIBUTION OF MICROALGAL TAXA TO CHLOROPHYLL-A IN THE FIELD - VARIATIONS OF PIGMENT RATIOS UNDER NUTRIENT-LIMITED AND LIGHT-LIMITED GROWTH, Marine ecology. Progress series, 169, 1998, pp. 97-112
Cellular concentrations of chlorophylls and carotenoids were measured
in nutrient- and Light-limited cultures of marine microalgae to determ
ine the utility of accessory pigments as proxies for the biomass of sp
ecific groups of microalgae in the ocean. rn most species, concentrati
ons of chlorophyll a (chl a) and photosynthetically active pigments va
ried linearly with growth rate in nitrate-limited continuous cultures
or with the logarithm of the irradiance in light-limited and light-suf
ficient batch cultures, as has been observed before. Rates of pigment-
concentration change as a function of irradiance or growth rate did no
t covary with rates of maximum growth. Concentrations of carotenoids c
ovaried with chl a in most species analyzed; intraspecies variations o
f chl a-carotenoid ratios were usually smaller than variations of chl
a:b or chl a:c ratios. These results were used to critically evaluate
the assumptions underlying iterative methods used to determine the con
tribution of different algal taxa to chl a from ratios of chl a and ac
cessory pigments. Estimates based on chl a:b or chl a:c ratios are pro
ne to error because these ratios can vary by up to an order of magnitu
de among species and within species as a function of irradiance, thus
violating an assumption of the iterative methods. Instead, such method
s should rely on ratios of chl a and photosynthetically active caroten
oids. Using simple models and field data from the Chesapeake Bay, USA,
we showed that iterative methods are either prone to error when diffe
rent populations of microalgae co-vary or do not give discrete solutio
ns. As an alternative we suggest methods that rely more strongly on em
pirically determined pigment ratios.