regression line approach 1 d−1 above 10°C and would be primarily those for small
copepods, in modest disagreement with Huntley and Lopez. Significantly, growth was
nearly independent of body mass up to ∼20 μg carbon, falling off somewhat for older
stages of large species, most of which in the data were free-spawners. Finally, both
free- (Fig. 7.20c) and sac-spawners showed strong effects of food availability,
approximated as chlorophyll concentration near the depth of capture. However, even
at very low chlorophyll values, many species showed growth near the asymptote of
Hirst and Bunker’s hyperbolic function. All in all, the Huntley and Lopez analysis
comes out reasonably well.
(^) Having found definite effects of several factors, Hirst and Bunker offered multiple
regression formulas for free and sac spawners: log 10 (growth rate) as functions of
temperature, body weight, and, for free-spawners, chlorophyll. To get at secondary
production, one would measure T and chlorophyll concentration, appropriately
analyze a plankton sample into classes by spawning mode and body weight, and then
apply them in those equations. However, the equations “explain” (R^2 values),
respectively 39% and 29% of the variances, so there is considerable room for
variation among species, seasons, and locations. Finally, one would sum the products,
giWi, over all body weights, obtaining a secondary production estimate for copepods.
(^) Such an analysis has been done by Roman et al. (2002) using a similar equation
(not including chlorophyll) from Hirst and Lampitt (1998). They used a series of
sieves to partition 200 μm mesh plankton samples (0–200 m) from time-series
stations (HOT near Hawaii and BATS near Bermuda) into five size categories,
determined their carbon biomass, and ran the calculation. There was seasonal
variability driven by both T and BW. Averages for samples over four years were 13
and 6 mg C m−2 d−1, respectively, at HOT and BATS. These were ∼2.7% and ∼1.3%
of mean measured primary production (1°P) available for transfer to predators.
Perhaps these are reasonable estimates for the very large subtropical oceanic areas.
The amount of food ingested would have been on the order of three-fold greater, 9%
and 4% of annual 1°P. Compare those estimates to the global estimate, mentioned
above, of 25–30% of 1°P of Hernández-León and Ikeda (2005). Additional copepod
production as egg output was not included. Similarly approximate estimates for higher
latitudes are scattered in the literature. Zhou (2006) shows an alternate approach in
which community biomass is partitioned by size (using automated, optical, size-
determining counters) into a spectrum (numerous small animals grading progressively
to few large ones) and production is calculated from sundry approximations.
(^) As can be seen by examining the scatter in Fig. 7.20, we have not solved the
problem of quickly and reliably estimating mesozooplankton productivity in the sea.
Perhaps some averages are of the right order of magnitude, but estimates from
different perspectives come up with very different fractions of measured primary