spring. At least in A. californiensis there is a short “refractory” period. That is, the
eggs must experience a certain interval of cold conditions before they will respond to
warming by developing. This isn’t very strict, as is the refractory phase of diapause in
some insects, but it ensures that transient warmings won’t initiate development of all
the eggs in the sediment, only to be chilled to death almost immediately. In
Labidocera aestiva, production of resting eggs also depends upon temperature, but the
dependence varies according to the daylength (Marcus 1982).
(^) Third, most species of the abundant oceanic copepod family Calanidae can rest in
one or more of the older copepodite stages, termed a copepodite diapause. Most
typically, if a generation is going to include a diapause, the fifth copepodite (C5) stage
feeds near the surface and accumulates a large mass of oil in a thin-walled sac (Plate
8.1) as a reserve of organic matter and energy. Then it descends to a considerable
depth in the ocean and remains there during a diapause on the order of a half year.
During this time there usually is no feeding, although Calanus finmarchicus has been
caught taking “midnight snacks” in the Gulf of Maine during November. Respiration
is strongly suppressed, and activity is nil. Recent work shows that many genes are
down-regulated (no mRNA generated), while others are up-regulated during the onset
and maintenance of diapause (Tarrant et al. 2008). Apparently, only one gene for a
small heat-shock protein (an HSP or a “molecular chaperone”, a protein that protects
enzymes from unfolding and degrading), HSP22, is up-regulated during diapause
(Aruda et al. 2011). Large HSPs (e.g. HSP70 and HSP90) are typical of diapauses in
many other animals. Fifth copepodites seem to approach neutral buoyancy closely and
just hang suspended. They do remain alert and dart away when poked or when the
water eddies near them. Because their metabolism is shut down, resting individuals do
not recover rapidly from such an escape effort, and they essentially get only one or
two tries at escape from a predator. In most Calanidae, diapause is initiated in late
spring, with the warmest, less-productive summer–fall period spent at depth. One
tropical species, Calanoides carinatus, spawns and grows actively near the surface
during periods of large-scale coastal upwelling. It is found most abundantly in the
Gulf of Guinea and the Arabian Sea, sites where upwelling occurs for about half the
year. The C5s from the last of about six generations (Binet & Suisse de Sainte-Claire
1975), and perhaps some C5s from all generations, enter diapause at mesopelagic
depths far seaward of the upwelling centers occupied during the growing phase of the
phenology.
(^) Diapause phases apparently evolve readily. There are about as many variant patterns
as there are species, and within species the patterns vary across the oceans. This
suggests that since habitats suitable for feeding and growth are only available part of
the year, it is an urgent task to make a close match of life-cycle events to those
periods. Emergence from copepodite diapause is coupled to the maturation molt, C5
advancing to C6 males and females. In Calanus finmarchicus of the subarctic