interesting polemic (Childress et al. 2008; Ikeda 2008).
Fig. 12.19 Oxygen consumption per unit weight of copepods (open circles with
horizontal regression) compared to that of large crustaceans (×, mysids and shrimp).
All measures corrected to 5°C and equivalent weight.
(^) (After Thuesen et al. 1998.)
Reproduction in the Mesopelagic
(^) Mid-water copepods, like epipelagic ones, divide into free-spawners (e.g. Gaussia,
Megacalanus) and egg carriers (e.g. Oncaea, Euchirella, Paraeuchaeta, Valdiviella).
Presumably, the former produce more eggs at each spawning that then suffer greater
mortality before hatching, although specific data on fecundity and death rates are
lacking. The young of Paraeuchaeta molt through all the naupliar stages before
beginning to feed, probably a common life-history feature in deep-living copepods. At
least some deep-sea chaetognaths (e.g. Eukrohnia bathypelagica) also carry their eggs
and even early larvae in “marsupial” sacs attached to the female gonopore. Other than
that, chaetognath reproduction does not seem to be particularly specialized for the
deep. Deep-living Sagitta (s.l.) are free-spawners. Among deep-sea euphausiids,
females of the genus Stylocheiron carry their eggs glued to their thoracic legs, while
Bentheuphausia and Thysanopoda are probably free-spawners. Eggs of the free-
spawners tend to sink, but apparently not fast enough to reach the seafloor before
hatching. Stylocheiron species produce only a few or a few tens of eggs at a time,
implying very low mortality rates, while at least Thysanopoda females produce
hundreds of eggs per clutch, implying high egg and larval mortality. Shrimp also
divide into massively fecund free-spawners, for example all of the Sergestidae, and
egg carriers, including the most numerous groups of the Caridea. While the eggs of
carriers are protected by the mother’s swimming and escape capabilities, they are
often very numerous. A 7.5 cm Acanthephyra quadrispinosa, for example, was
carrying 1500 eggs (Aizawa 1974). Nevertheless, the general division into low-