Explain the seasonal migration of calanus What differences are there with lattitude and where is the line drawn? Why do they do the seasonal migration?

Seasonal migration: During winter calanus is usually deeper down. The juviniles migrate down towards the end of the season. And migrate up to mate towards the end of winter. North of lofoten they only have one generation each year, and south they have several generations each year. Copopods in the north migrate down to overwinter to avoid predators. Deeper waters is usually much colder with the depth. They keep metabolic rate low. Currents are also slower in the ddep water. They somehow sense the change and migrate up again in early spring. It is common for them to enter a resting stage (diapause) in the deep. at depth they can keep metabolic activity very low. Whats the point?: at deep depths advection(skubbet rundt af strømme osv) is limited because of few currents. fewer predators at deep depths.