A single copepod species, Neocalanus plumchrus (Marukawa), makes up much of the mesozooplankton biomass in the subarctic Pacific. Its vertical distribution and developmental sequence are both strongly seasonal. Together, they produce a strong and narrow (<60 days duration) annual peak of upper ocean zooplankton biomass in spring and early summer. At Ocean Station P (50°N, 145°W), seasonal phasing of this annual maximum has shifted dramatically between 1956 and the present. Both time series observations of N. plumchrus stage composition ratios and measurements of total upper ocean zooplankton biomass produce consistent pictures of this change. Population development was very late in the early 1970s (biomass maximum in mid-July to late July), early in the late 1950s (late May - early June), and very early in the 1990s (early May to mid-May). The changes in timing are strongly correlated with large-scale year-to-year and decade-to-decade ocean climate fluctuations, as reflected by spring season temperature anomalies in the surface mixed layer within which the juvenile copepodites feed and grow (r2 = 0.56, development about 60 days earlier in warm than in cold years). But the change in developmental timing is too large to be explained solely by physiological acceleration of individual development rate. We suggest instead that the cause is interannual differences in survival among early versus late portions of the annual copepodite cohort.

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All stages from egg to adult of the North Pacific copepod,Euchaeta japonica contained wax esters in their lipid stores, while triglycerides were important only in the eggs, early naupliar stages, and adults. The large lipid reserves of the eggs were wax esters and triglycerides (58% and 19% of the lipid, respectively), both of which were used rapidly during the early stages of development. Wax esters continued to decrease after triglycerides had been utilized completely for energy. The slow metabolism of lipid during starvation indicated that lipid stores in adult females may be conserved for egg production. The dominant alcohols of the wax esters of all stages were tetradecanol (24–42% of the total) and hexadecanol (25–65%). Only minor amounts of polyunsaturated alcohols were observed. There was, however, a high proportion of polyunsaturation in the wax ester fatty acids, even though octadecenoic was generally predominant (16–46% of the total wax ester fatty acids). The polyunsaturation of the wax esters fatty acids and the presence of 21∶6 hydrocarbon suggest phytoplankton in the diet of adults and in the younger stages. Cholesterol was the main sterol, but there were minor amounts of desmosterol (1–12% of the total sterols) present. The latter sterol has not been found previously in copepods, although reported from Cirripedia and Decapoda.