The Ecology of Phytoplankton

of their ecologies. The C–S gap is spanned by
genera such as Dinobryon, Dictyosphaerium,
Coenochloris, Pseudosphaerocystis, Eudorina and,
arguably, Volvox (Reynolds, 1983b), and by
Aphanocapsa and Aphanothece. The series spans
diminishing sv −1 ratios, maximum growth rates
and low-temperature tolerance but increasing
ability to exploit and conserve nutrient
resources. Algae in the C–R axis include predominantly
centric diatoms of varying tolerance of
turbidity and the Scenedesmus–Pediastrum element
of enriched shallow ponds and rivers). The R–S
possibility is represented by the slow-growing,
long-surviving, acquisitive but highly acclimated
species of density gradients, like Planktothrix
rubescens and Lyngbya limnetica. Certain (not
all) members of the genus Cryptomonas show a
blend of the characteristics of all three primary
strategies in being unicellular, having cells of
moderate size (1–4 ×10 3 µm 3 )andofintermediate
sv −1 (0.3–0.5 µm −1 ), and being capable of
intermediate replication rates (r20∼10 × 10 −6
s −1 ; r0∼0.9 × 10 −6 s −1 ).
It is right to point out that Grime’s CSR concept
of plant stategies is not universally accepted
and it has been subject of vehement and challenging
debate (see Tilman, 1977, 1987, 1988;
Loehle, 1988, a.o.). Although there is much common
ground shared by the adversaries and, in
truth, the differences are more of perspective
and emphasis (Grace, 1991), the differences have
never been entirely resolved. The application to
plankton has not been so criticised and some
(Huszar and Caraco, 1998; Fabbro and Duivenvorden,
2000; Gosselain and Descy, 2000; Kruk
et al., 2002; Padisák, 2003) but by no means
all (Morabito et al., 2002), have found the arguments
convincing and helpful to interpretation.
The applicability of a scheme devised for plant
species is not a barrier: it is now quite evident
that the idea has a long pedigree among
other ecological schools (Ramenskii, 1938) and
has been applied successfully to the ‘violent’,
‘patient’ and ‘explerent’ strategies of zooplankton
(Romanovsky, 1985). The CSR model has been
applied to fungi (Pugh, 1980) and periphyton
(Biggs et al., 1998).
An updated application to phytoplankton
is set out in Box 5.1. A notable modifica-
REPLICATION RATES UNDER SUB-IDEAL CONDITIONS 211
tion recognises that motility and large size
are not necessary adaptations to function in
chronically very resource-depleted pelagic environments.
Indeed, resource gathering in spatially
continuous, rarefied environments is favoured
by small size, whereas the low levels of diffuse
biomass is an unattractive resource for
direct grazing by mesozooplankters (see Chapter
6). The adaptive strategies for surviving
the ‘resource desert’ of the ultraoligotrophy of
the oceanic pelagic are accorded the additional
stress-tolerant category SS.
The original ascriptions of C, S and R categories
to phytoplankton (Reynolds, 1988a) separate
quite satisfactorily on the plot of the areas
projected by various species of phytoplankton
and the product of maximum dimension and
surface-to-volume ratio (msv −1 ) Fig. 3.12). Nearspherical
forms align close to msv −1 [d × 4π(d/2) 2
÷ 4π(d/2) 3 /3] = 6 but separate broadly in to
C and S species according to size, because the
carbon and chlorophyll contents vary with v =
4π(d/2) 3 /3 but the light interception increases
as a function of the disk area, a = π(d/2) 2 .
The morphological attenuation of the R species
pulls out the plot to much higher msv −1 values.
Thus, we distinguish species that are capable
of rapid growth in benign, resource-replete
environments, those that are able to go on
squeezing out increased biomass from diminishing
light income and those who are physiologically
or behaviourally adapted to function in
spite of developing nutrient stress. The model
appears in various guises later in the book,
demonstrating the power and flexibility of the
strategy–process–ecosystem interactions. It even
provides the bridge to the light : nutrient hypothesis
(Sterner et al., 1997) insofarasthespecies
best adapted to cope with low doses of I ∗ are most
able to cope with high particulate content in the
water andtheC:Pratioofthesestonavailable
to secondary consumers.
5.4.6 Resource exhaustion and survival
It is reasonable to assume that the growth of
phytoplankters distinguished by efficient, highaffinity
resource-gathering capabilities may continue
until they deplete their growth-limiting
resource to near exhaustion. It was often and