Is Mesozooplankton Secondary Production Controlled by
Temperature or Food Availability?
(^) Reviewing the approaches to secondary production makes clear how difficult it is
actually to measure all of secondary productivity, or even tissue production by one
species population. Obtaining field estimates can depend upon measurements that we
have no means to make (as for applying Vidal’s results) or upon assumptions difficult
to evaluate. Still, we would like a measure of how much production there is of, say,
mesozooplankton, or even just the copepods. To repeat, we would like to know how
much food the ocean produces for animals that we harvest like herring, anchovy, cod,
and pollock. In order to make predictions, perhaps about the effects of climate change,
we need to know what controls the rates. The likely candidates are temperature and
food availability. Several short-cuts to evaluating control have been suggested and
rather extensively studied. We will examine two.
The Huntley–Lopez Model
(^) A paper by Huntley and Lopez (1992) caused a minor storm in the community of
zooplanktologists. They suggested, based on recalculations of sets of old data, that
copepods, and possibly other zooplankton, grow everywhere at all times at rates
controlled primarily by habitat temperature. First, they made the broad assumption
that copepods grow exponentially at a nearly constant rate from hatching to
maturation. This is almost true for some copepods; see, for example, data from Lee et
al. (2003) for Pseudocalanus at full nutrition. Huntley and Lopez surveyed the
literature, finding data from many species at all latitudes for the mass of an egg, for
adult mass (carbon or dry weight), and for development time, D, from egg to adult. In
applying their assumption, they used the equation: