Marker T, Andreassen P, Arashkewich E, Hansen BW
Calanus, lipids, maturation, feeding, mesocosm, 18 m3, Bergen, Norway
Two cohorts of Calanus finmarchicus (Gunnerus),with habitats in Bergen (60 N) and Tromsø (69 N),were reared from copepodite stage III (CIII) in mesocosmsin Tromsø from April 24 1998 to June 30 1998.The aim was to study whether the two cohorts divergedphenotypically with respect to indication of physiologicalpreparation for diapause as opposed to initiatinganother generation. At the end of the experiment thefractions of the cohorts that had reached sexual maturation,based on observed stage shifts to adults, was 45% within the Bergen cohort and 35% for theTromsø cohort, within which males appeared beforefemales. Examination of the mandibular gnathobase ofcopepodites at stage V (CV) revealed that 40% of the Tromsø cohort wereready for ecdysis, eventually to become adults in thesame year. The physiological expression of the range inindividual maturity within the cohorts was revealed inindividual carbon and nitrogen content. Both cohortsincorporated the storage lipids wax esters (WE) andtriacylglycerols (TAG) rapidly, primarily during CV(0.16–0.21 lg total neutral lipid ind)1 day)1), with nosignificant difference. Lipid storage was incorporatedfrom CIII and the maximum was reached at the CVstage. Presumably due to excess food, high WE, TAGand free fatty acid levels were observed in both cohorts.A relative decrease in neutral lipids was observed later infemales from both cohorts. We suggest that part of theBergen population, but also a fraction of the Tromsøpopulation, prepared for diapause in CV. A possiblereason for the sexual maturation among the rest of theCV copepodites could be a shift in life ‘‘strategy’’ causedby an unusually high rise in temperature in the mesocosmsduring the last 10 days of the experiment.