Protein, lipid, phosphorus, and organic carbon contents, as well as electron transport system (ETS) activity, lactatedehydrogenase activity, and gut evacuation rate, were measured in four interzonal species of Pacific copepods:
Calanus australis, C. pacificus, Eucalanus inermis, and
E. elongatus f.
hyalinus, collected at the upwelling areas off Peru (8°S) and California (27°N), and in the middle of the North Pacific (30°N), from February to April 1987. The two Eucalanidae species —
E. inermis and
E. elongatus — have distinctive biochemical and elemental body composition and rates of main physiological processes. Relative protein, lipid, phosphorus, and organic carbon contents (µg mg
–1 wet weight) in these species were, respectively, ca. 1/7 to 1/10, 1/5 to 1/20, 1/5 to 1/10, and 1/5 those in
Calanus spp. Likewise, oxygen uptake rate per unit of wet weight (based on ETS activity) in
E. inermis and
E. elongatus was 5 to 10% of that in calanids; a similar difference was found in phosphorus excretion rate. In addition, gut evacuation rates in
E. inermis and
E. elongatus were ca. one-fifth of those in
Calanus spp. Based on these data, we considered the eucalanids as belonging to a distinctive physiological group, figuratively named jelly-body copepods. In contrast with calanids, active lactatedehydrogenase has been found in the bodies of
E. inermis and
E. elongatus, apparently allowing them to survive for a long time in layers of extremely low oxygen content (<0.2 ml l
–1). The adaptive value of physiological features in these eucalanids and typical calanids is compared.
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