Migrations of marine animals #001

Vertical migrations of some animal species are observed much more often than previously thought — it turns out that there are species that spend their entire lives climbing and descending, somewhat resembling naughty children playing with an elevator. However, unlike children, these animals have very good reasons to spend some of their energy on these incessant journeys up and down (after all, even lowering them is not always passive, otherwise it would not be fast enough). Most of the migrations of animals occur in accordance with the rhythm of alternating day and night (diurnal rhythm). There are a small number of species that rise into the surface layers during the day and descend at night; however, as a rule, movement occurs in the opposite direction: animals rise at night and descend during the day. Such vertical migrations sometimes cover several hundred meters, but they do not necessarily reach the surface or the water layers closest to it: they can also occur where, at least to the human eye, there is constant darkness (except for the light emitted by the animals themselves); the shrimp Hymenodora glacialis, for example, stays during the day. at a depth of 1000 m, and at night at 800 m, while Acanthephyra purpures prefers a depth of about 800 m at noon and about 200 m at midnight. Migration can be influenced by both the sex of animals and their age: for example, females of the oar-footed crustacean Calanus finmarchicus, which is very common in northern Atlantic waters, have a larger amplitude of vertical migrations than males or young individuals; nauplius and juveniles of a large number of crustaceans can be found near the surface during the day, while adults stay lower at this time. It also happens that migrations occur in different ways according to the changing seasons: if, for example, as a result of summer warming of the surface layer at about a depth of 50 m, a pronounced thermocline forms, some species that rise at night almost to the surface in winter may be blocked from above by this "roof" of heated water in summer. water. The causes of diurnal vertical migrations are undoubtedly numerous and are still a matter of debate. Only two causes have been precisely identified, although the mechanism of their action, at least the first of them, is not yet known. One of them is undoubtedly the light, which causes the daily lowering of a significant number of species that avoid daylight. The proof of this is quite often observed phenomenon: individuals of the same species are closer to the surface when the sky is covered with clouds, and further away from it when it is cloudless. Les internautes apprécient la simplicité de onewin.com.ci .