FISHERY BULLETIN: VOL. 70, NO. 4 



if the ambient temperature were subject to 

 fluctuations of a few degrees. 



ESTIMATES OF THE SPECIFIC 



GROWTH RATES OF 



PHYTOPLANKTON IN THE SEA 



REVIEW OF METHODS 



Measurement of the phytoplankton specific 

 growth rate in nature is not a routine procedure 

 both because of the lack of widely accepted meth- 

 odology and because the utility of such data is 

 not well appreciated. J.W.G. Lund, J. F. Tailing, 

 L. A, Lanskaya, T. J. Smayda, J. D. H. Strick- 

 land, and S. Ichimura and his colleagues have 

 been the pioneers in such measurement in nat- 

 ural waters while R. W. Krauss and J. Myers 

 have promoted the measurement of ix for lab- 

 oratory cultures. 



Minimal values of /u, can be calculated from 

 rates of increase of cell concentration or of 

 chlorophyll during the spring bloom in temperate 

 waters, although advection, diffusion, and graz- 

 ing complicate their interpretation. Recent ex- 

 amples of this technique are provided by Bunt 

 and Lee (1970), Pechlaner (1970), and Happey 

 ( 1970) . Samples of water can also be incubated 

 in bottles for cell counting at intervals (see, for 

 example. Tailing, 1955; Smayda, 1957). In 

 oligotrophic waters the period of growth neces- 

 sary to allow a precise estimation is likely to 

 result in the depletion of nutrients and the grad- 

 ual diminution of yu, with time. In rich water 

 if growth were extensive, changes in jx would 

 be expected as a result of the decrease in effective 

 illumination in the bottles due to self-shading. 

 Short-term incubations of less than 24 hr may 

 be complicated by diel periodicity in the property 

 measured, by synchronous cell division, or in- 

 sufficient change for meaningful calculations. 

 Such problems are eased in shipboard cultures 

 provided with adequate nutrients for growth, 

 but here rates may be unreasonably high if am- 

 bient nutrient or light levels in the natural water 

 are not duplicated. 



Estimates of /u. are obtained routinely in terms 

 of ^"^N-nitrogen assimilation rate per unit par- 

 ticulate nitrogen in the sample, but such rates 



will underestimate fjL to the extent that the par- 

 ticulate nitrogen analyzed includes detrital and 

 other nonphytoplankton nitrogen (Dugdale and 

 Goering, 1967). 



Carbon assimilation rates per unit phyto- 

 plankton carbon have also been calculated but 

 suffer from the errors inherent in measuring 

 the latter as well as from the uncertain reality 

 of incubation conditions (Riley, Stommel, and 

 Bumpus, 1949; McAllister, Parsons, and Strick- 

 land, 1960; McAllister et al., 1961; Antia et al., 

 1963; McAllister, Shah, and Strickland, 1964; 

 Strickland, Holm-Hansen, Eppley, and Linn, 

 1969). What is needed is an instantaneous 

 method not confounded by the complexities of 

 long incubation either in situ, in enclosed ves- 

 sels, or in shipboard cultures. Unfortunately, 

 no such method is in view. 



In this laboratory two methods have been em- 

 ployed for estimating the carbon content of the 

 crop. In the first of these, all the cells in the 

 sample are counted and their dimensions mea- 

 sured so that the cell volume of each species 

 can be calculated (see Kovala and Larrance, 

 1966, for dealing with cell shape problems) . The 

 carbon content of a cell is then computed from 

 its volume, or "plasma volume," using empirical 

 equations developed from laboratory culture 

 (Mullin, Sloan, and Eppley, 1966; Strathmann, 

 1967). The carbon in each species is then ob- 

 tained from the concentration of cells of that 

 species, and the total carbon of all species is 

 summed. Several applications of this method 

 have been published (Strickland, Eppley, and 

 Rojas de Mendiola, 1969; Holm-Hansen, 1969; 

 Eppley, Reid, and Strickland, 1970; Reid, Fug- 

 lister, and Jordan, 1970; Zeitzschel, 1970; Beers 

 et al., 1971; Hobson, 1971; Eppley et al., in 

 press) . In the second method, only recently put 

 into practice, the adenosine triphosphate (ATP) 

 content of particulate matter retained on a fine 

 porosity filter is determined (Holm-Hansen and 

 Booth, 1966) . The ATP is apparently restricted 

 to living cells but may include contributions from 

 bacteria, protozoans, and other colorless micro- 

 organisms, as well as phytoplankton, even if 

 larger animals are removed by passing the sam- 

 ple through netting. However, phytoplankton 

 appear to be predominant in water samples from 



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