122
eastern Gulf of Mexico had doubling rates in excess of 4
-1
day
Nutrient flux could support this growth rate.
The ammonium
concentration at stations 4 and 7 was approximately 0.5 ~g at 1- 1 with
ni trate undetectable.
Using my values for ammonium transport, the
flux rate could support 4.4 divisions in a 24 hour period at the
-1
initial biomass levels of 0.07 and 0.05 ~g Chla 1
for stations 4 and
7 respectively.
Thus the population at both stations was growing at
the maximum rate diffusion would allow.
Growth rates of several
species at other stations were not unexpectedly .high •
There was also considerable areal variation in the growth rate
of the same species.
The growth rate of Rhizosolenia alata ranged
from 0.22 to 4.09 divisions day-1 (Table 5). Such differences may be
attributed to variations in biomass between stations.
Ammonia and
nitrate concentrations were essentially the same at all stations
(about 0.5 ~g at 1- 1 ). However, the initial biomass of each culture
varied by more than an order of magnitude from less than 0.1 ~g Chla
-1
1
for the shelf break and slope station to greater than 1 ~g Chla
1- 1 at near- shore stations.
Therefore, flux rates may have limited
growth at the inshore stations.
Growth rates based on chlorophyll consistently underestimate
those calculated from cell counts.
This suggests that a lag period
occurs with respect to growth as measured by chlorophyll and/or that
the populations were adapted to a lower light regime.
The results
also demonstrate that not all species within an assemblage grow
equally fast.
Other species in each of the assemblages in Table 5
exhibited no growth or a decline. Lack of growth in cage cultures may
reflect the inablility of some species to tolerate the turbulant
condi tions inside the tubes (Furnas, 19B2a,b~ Sakshaug and Jensen,
1978~ Vargo, 1976) or represent the true situation in situ~ i.e. some
species exhibit exponential growth and outcompete others while some
species maintain a minimal population level or decline.
General Discussion
What we are really looking for is the actual growth or production
rates of natural populations unmodified by cage "bars".
Do filterwalled cages or dialysis tubes provide the best estimate or will
division rates based on microscopic observation of paired cells, such
as those reported by Swift and Durbin (1972), Weiler and Karl (1979),
Weiler and Chisholm (1976) and Weiler (1980), be the only way to get
eastern Gulf of Mexico had doubling rates in excess of 4
-1
day
Nutrient flux could support this growth rate.
The ammonium
concentration at stations 4 and 7 was approximately 0.5 ~g at 1- 1 with
ni trate undetectable.
Using my values for ammonium transport, the
flux rate could support 4.4 divisions in a 24 hour period at the
-1
initial biomass levels of 0.07 and 0.05 ~g Chla 1
for stations 4 and
7 respectively.
Thus the population at both stations was growing at
the maximum rate diffusion would allow.
Growth rates of several
species at other stations were not unexpectedly .high •
There was also considerable areal variation in the growth rate
of the same species.
The growth rate of Rhizosolenia alata ranged
from 0.22 to 4.09 divisions day-1 (Table 5). Such differences may be
attributed to variations in biomass between stations.
Ammonia and
nitrate concentrations were essentially the same at all stations
(about 0.5 ~g at 1- 1 ). However, the initial biomass of each culture
varied by more than an order of magnitude from less than 0.1 ~g Chla
-1
1
for the shelf break and slope station to greater than 1 ~g Chla
1- 1 at near- shore stations.
Therefore, flux rates may have limited
growth at the inshore stations.
Growth rates based on chlorophyll consistently underestimate
those calculated from cell counts.
This suggests that a lag period
occurs with respect to growth as measured by chlorophyll and/or that
the populations were adapted to a lower light regime.
The results
also demonstrate that not all species within an assemblage grow
equally fast.
Other species in each of the assemblages in Table 5
exhibited no growth or a decline. Lack of growth in cage cultures may
reflect the inablility of some species to tolerate the turbulant
condi tions inside the tubes (Furnas, 19B2a,b~ Sakshaug and Jensen,
1978~ Vargo, 1976) or represent the true situation in situ~ i.e. some
species exhibit exponential growth and outcompete others while some
species maintain a minimal population level or decline.
General Discussion
What we are really looking for is the actual growth or production
rates of natural populations unmodified by cage "bars".
Do filterwalled cages or dialysis tubes provide the best estimate or will
division rates based on microscopic observation of paired cells, such
as those reported by Swift and Durbin (1972), Weiler and Karl (1979),
Weiler and Chisholm (1976) and Weiler (1980), be the only way to get