123
true, in situ growth rates? Some growth rates of natural populations
enclosed in. dialysis tubes are high relative to other published data.
(Eppley, 1972; 1981).
If my results
(Table
Growth rates in
5)
reflect
cages exceed these estimates.
the actual potential maximum
exponential growth rates for several diatom species, then additional
consideration must be given to earlier in situ estimates. If division
rates for natural populations of S. costatum in cage cultures are in
-1
-
the range of 4.8 - 5.9 day
(Furnas, 1982a,b) then we must also
reconsider some laboratory results.
Such growth rates are rarely
attained in culture under supposedly ideal growth conditions.
Differences observed between growth rates measured using dialysis
tubes
and
cages
should not be viewed
as
entirely being a
methodological problem.
Growth rates based on both techniques are
high, therefore we may have to reconsider some concepts of the
potential maximum growth rates that can be achieved by diatoms in
-1
situ. How common are growth rates of greater than 3-4 doublings day
in diatoms? Are they an artifact of the method in the sense that
since cages act as nutrient concentrators, encapsulating a population
simply allows it to grow under nutrient sufficient and otherwise ideal
conditions thereby achieving a true ~max?
The hypothesis presented by Goldman et al. (1979) and Goldman
(1980) states that phytoplankton populations in oligotrophic, oceanic
waters are not nutrient limited and have high relative growth rates
(~/~max ~ ~max)·
A low, steady-state biomass must be maintained by a
combination of nutrient regeneration and loss rates.
Growth rates for several species in the slope and shelf-break
waters (Table 5) tend to support their hypothesis, however, not all
species grew at such high rates.
It would not be illogical to assume
that some species in an assemblage would have the intrinsic ability to
outcompete others over short time periods. Certainly the high growth
rates of several estuarine and coastal diatoms presented by Furnas
(1982a,b) and my results (Table 5) indicate that some diatoms do have
intrinsically high growth rates.
There is no reason to assume that
rapid growth would not be realized in natural populations if
environmental conditions can support high turnover rates. Temperature
and light are not normally considered to be limiting growth in oceanic
surface waters.
My dilution series results (Table 4) suggests that
the Central Gulf population was nutrient limited. Any type of a cage
culture acts as a nutrient concentrator. Enclosing a population in a
cage sets up a high diffusive gradient .between the inside and outside
of the cage. In effect nutrient availability increases until membrane
transport equals uptake.
Populations enclosed within the cage should
true, in situ growth rates? Some growth rates of natural populations
enclosed in. dialysis tubes are high relative to other published data.
(Eppley, 1972; 1981).
If my results
(Table
Growth rates in
5)
reflect
cages exceed these estimates.
the actual potential maximum
exponential growth rates for several diatom species, then additional
consideration must be given to earlier in situ estimates. If division
rates for natural populations of S. costatum in cage cultures are in
-1
-
the range of 4.8 - 5.9 day
(Furnas, 1982a,b) then we must also
reconsider some laboratory results.
Such growth rates are rarely
attained in culture under supposedly ideal growth conditions.
Differences observed between growth rates measured using dialysis
tubes
and
cages
should not be viewed
as
entirely being a
methodological problem.
Growth rates based on both techniques are
high, therefore we may have to reconsider some concepts of the
potential maximum growth rates that can be achieved by diatoms in
-1
situ. How common are growth rates of greater than 3-4 doublings day
in diatoms? Are they an artifact of the method in the sense that
since cages act as nutrient concentrators, encapsulating a population
simply allows it to grow under nutrient sufficient and otherwise ideal
conditions thereby achieving a true ~max?
The hypothesis presented by Goldman et al. (1979) and Goldman
(1980) states that phytoplankton populations in oligotrophic, oceanic
waters are not nutrient limited and have high relative growth rates
(~/~max ~ ~max)·
A low, steady-state biomass must be maintained by a
combination of nutrient regeneration and loss rates.
Growth rates for several species in the slope and shelf-break
waters (Table 5) tend to support their hypothesis, however, not all
species grew at such high rates.
It would not be illogical to assume
that some species in an assemblage would have the intrinsic ability to
outcompete others over short time periods. Certainly the high growth
rates of several estuarine and coastal diatoms presented by Furnas
(1982a,b) and my results (Table 5) indicate that some diatoms do have
intrinsically high growth rates.
There is no reason to assume that
rapid growth would not be realized in natural populations if
environmental conditions can support high turnover rates. Temperature
and light are not normally considered to be limiting growth in oceanic
surface waters.
My dilution series results (Table 4) suggests that
the Central Gulf population was nutrient limited. Any type of a cage
culture acts as a nutrient concentrator. Enclosing a population in a
cage sets up a high diffusive gradient .between the inside and outside
of the cage. In effect nutrient availability increases until membrane
transport equals uptake.
Populations enclosed within the cage should