the ratio (P : B) of carbon added in the incubation interval (production rate, P) to
carbon biomass (B) is the same as the specific rate of increase in B (i.e. ΔB/[BΔt] ), or
equivalently the slope of ln(B) vs. time. In several of Kimmerer’s experiments, the
relation of ln(B) to time was indeed reasonably linear, and almost all the P : B results
ranged from 0.2 to 0.32 mg C (mg C d)−1. Most of the production was growth of the
copepodite stages, since nauplii grow as fast or faster but are relatively much smaller.
Production totals for volumes or areas can be obtained by estimation of the biomass
density, say milligrams of A. inermis below each square meter of Kaneohe Bay, and
multiplying by the P : B ratio. Kimmerer (1983) did not report such a result.
Artificial Cohorts
(^) There have been very few studies that precisely followed that “Kimmerer protocol”,
but a large number have used various approximations to arrive at a guess about the
weight increment during incubation (reviewed by Kimmerer et al. 2007). Most
popular are variations of an “artificial cohort” technique applied to copepods. A
gently collected net sample is poured through a fine screen to remove young stages of
one or more target species. The animals on the screen are then resuspended in filtered
water and refiltered through a coarse screen to remove old stages and predators.
Animals passing the coarse screen are an “artificial cohort” (AC). They are given a
substantial volume of the fine screen filtrate as both temporary habitat and food
supply, and then incubated, sometimes in containers suspended at depth in the ocean
(or estuary). With the youngest stages removed, there will be no recruitment to the
younger stages in the AC. Stages older than those in the initial AC and appearing
during incubation will all have been produced by growth. In one approach, the stage
composition is evaluated both before and after the incubation. If incubated for a
substantial fraction of the stage development time, some will have molted, generating
a difference. The before-and-after stage compositions are assigned biomass estimates
by multiplying numbers of each stage by measures of its stage weight. Mean stage
weights from field samples were applied by Kimmerer and McKinnon (1987). Using:
(^) they found P : B estimates of 0.025 to 0.25 d−1 (mean = 0.11 d−1 ) for Acartia fancetti
in a tropical coastal embayment, which were multiplied with a time-series of biomass
estimates giving 130 mg C m−3 yr−1, about 1% of primary production.
(^) A substantial number of AC studies have been done instead by measuring samples
of copepodite lengths (which change substantially only at molting) before and after
incubations, then used length–weight regressions based on field samples to determine
both the biomass and the change in biomass during incubation. This is fraught with
issues that are reviewed by Hirst et al. (2005). However, for smaller tropical copepods
that grow and molt rapidly, and with incubations lasting through, say, all of the