questions being raised
(Carpenter and Lively,
(Gieskes et al., 1979),
114
about heavy metal and trace metal toxicity
1980~
Fitzwater et al., 1982), bottle size
and ultraviolet radiation (Smith and Baker,
1980). There are also problems associated with phytoplankton biomass
measurements (Sakshaug, 1980) which are required to calculate growth
rates from carbon or nitrogen uptake rates.
Growth rate estimates
based on uptake and biomass measurements also assume that balanced
growth occurs, whereas Eppley (1981) argues that there is no reason to
assume that balanced growth occurs in natural populations over short
time scales.
Cage
culture
techniques
offer
an
alternative
method
for
establishing
potential
growth
rates
for
natural
phytoplankton
-1
populations.
Growth rates greater than 2 divisions day
for
individual species in dialysis culture of natural populations
have
been reported
(Vargo, 1976,1979).
Recently, Furnas (1982a) has
reported that growth in filter-walled cages (modelled after those
developed by OWens et al., 1977) was, at times, 2 to 3 times higher
than for the same populations grown in dialysis tubing.
Our results
suggest that phytoplankton have the intrinsic ability to grow at rates
which are higher than those normally reported in the literature
(Goldman et al., 1979~ Eppley, 1981) and that the type of cage may
influence the max·imum potential growth rate achieved by enclosed
popula~ions.
In this paper I will present some examples of growth of natural
populations in tubes and cages, assess the reasons for expecting
differences or similarities, report growth rates of several species
from the eastern Gulf of Mexico and discuss these results with respect
to current questions being raised about the growth rates of
phytoplankton from oligotrophic, oceanic waters.
Methods
Dialysis tubes were 2.86 cm. in diameter and had a final, filled
length of 24.8 cm. This size tube has a surface area of 229cm 2 with a
volume of approximately 160 ml and an A/V ratio of 1.43.
Replicate
tubes were incubated in flowing sea water suspended in plexiglass
tanks on the wheel arrangement described by Jensen et al. (1972) .
A
small bubble in the tube provided continuous mixing.
Cages were
constructed according to the design of Owens et al. (1977) but were
larger and used a 1 micron pore size, 142mm diameter Nuclepore (R)
filter as cage walls.
Two filters per cage were separated by a 2.54
cm thick plexiglass plate.
Total surface area was 226 cm 2 but the
(Carpenter and Lively,
(Gieskes et al., 1979),
114
about heavy metal and trace metal toxicity
1980~
Fitzwater et al., 1982), bottle size
and ultraviolet radiation (Smith and Baker,
1980). There are also problems associated with phytoplankton biomass
measurements (Sakshaug, 1980) which are required to calculate growth
rates from carbon or nitrogen uptake rates.
Growth rate estimates
based on uptake and biomass measurements also assume that balanced
growth occurs, whereas Eppley (1981) argues that there is no reason to
assume that balanced growth occurs in natural populations over short
time scales.
Cage
culture
techniques
offer
an
alternative
method
for
establishing
potential
growth
rates
for
natural
phytoplankton
-1
populations.
Growth rates greater than 2 divisions day
for
individual species in dialysis culture of natural populations
have
been reported
(Vargo, 1976,1979).
Recently, Furnas (1982a) has
reported that growth in filter-walled cages (modelled after those
developed by OWens et al., 1977) was, at times, 2 to 3 times higher
than for the same populations grown in dialysis tubing.
Our results
suggest that phytoplankton have the intrinsic ability to grow at rates
which are higher than those normally reported in the literature
(Goldman et al., 1979~ Eppley, 1981) and that the type of cage may
influence the max·imum potential growth rate achieved by enclosed
popula~ions.
In this paper I will present some examples of growth of natural
populations in tubes and cages, assess the reasons for expecting
differences or similarities, report growth rates of several species
from the eastern Gulf of Mexico and discuss these results with respect
to current questions being raised about the growth rates of
phytoplankton from oligotrophic, oceanic waters.
Methods
Dialysis tubes were 2.86 cm. in diameter and had a final, filled
length of 24.8 cm. This size tube has a surface area of 229cm 2 with a
volume of approximately 160 ml and an A/V ratio of 1.43.
Replicate
tubes were incubated in flowing sea water suspended in plexiglass
tanks on the wheel arrangement described by Jensen et al. (1972) .
A
small bubble in the tube provided continuous mixing.
Cages were
constructed according to the design of Owens et al. (1977) but were
larger and used a 1 micron pore size, 142mm diameter Nuclepore (R)
filter as cage walls.
Two filters per cage were separated by a 2.54
cm thick plexiglass plate.
Total surface area was 226 cm 2 but the