Chapter 7
Production ecology of marine zooplankton
Zooplanktologists” are interested in the animals themselves, their systematics
(taxonomy), their adaptive schemes for survival, and their places in the marine food
web. Particular studies examine distributional patterns; feeding mechanics and rates;
food selectivity; growth rates and patterns with age; secondary productivity;
reproductive biology and fecundity; mortality (rates, causes, and age distribution);
life-history variations; and vertical migrations. This chapter will consider issues of
feeding and growth, or the trophic aspect of zooplankton, which is the topic of
greatest interest to ecosystem modelers. A very large fraction of the work has been
done on copepods, making other groups seem somewhat neglected by comparison.
That is mostly because copepods are so reliably present in samples. Therefore, they
are always available to study, which is less true of other groups. However, other
groups have had attention, and we know a great deal about them. Distribution patterns
and adaptive strategies are treated in separate chapters.
Feeding Mechanics
(^) Mesozooplankton capture, sort, and ingest food by diverse mechanisms. Particle-
feeders are those animals feeding on prey much smaller than themselves, such as
phytoplankton and protozoans. They essentially filter the water in one way or another,
although filtering the water from around a particle is often a final step after it is
located by a searching procedure.
(^) Phytoplankton and protozoans are small (∼1 μm to hundreds of μm) compared to
most mesozooplankton (∼200 μm to ∼20 mm) that feed upon them, and they are
dilute relative to the water that suspends them (Box 7.1). A few parts per million is a
rich soup. Therefore, lots of water must be processed to acquire meals. The animals
most correctly described as filtering are the salps and doliolids, which strain water
through a literal mesh constructed of mucus. By injecting particles of various sizes
(usually size-graded plastic beads) at the incurrent opening, then collecting at the
excurrent opening those particles not captured on the filter, it is possible to determine
the effective pore size of the filter cone (Fig. 7.1; Plate 6.12). The results show that
particles larger than 2–4 μm are captured with high efficiency. Since the
polysaccharides in mucus are usually charged molecules, it is also possible that some