Chapter 17 Diurnal vertical migration

1. Chapter 17Diurnal vertical migration • Diurnal vertical migration is a very common phenomenon. • A few examples

2. Changes in the abundance of the copepod Calanus finmarchicus in the surface, between 06:00 and 14:00 h during 6 weeks from 21st June to 11th August, 1991, off Californian coast

3. §17.1 Characteristics diurnal vertical migration of zooplankton • samples of night plankton at the surface are notably different from those taken during the day, not only in their faunistic composition but also quantitatively. • The number of ind. colleted in the surface layers become ten times higher between 16:00 and 20:00pm. • The only possible explanation of these variations is vertical migration, representing a rhythm of 24h.

4. Diurnal vertical distribution of the copepod C. finmarchicus females in Loch Fyne, Clyde Sea, Scotland

5. Distribution as a function of the time and maximum depth sampled where the copepod Gaussia princeps is found: solid line, regression curve: z=zo+a cos wt = 487-230 cos wt.

6. Vertical distribution of the copepod C. finmarchicus from the 14th to 16th July, 1933 in Georgia Bank • Top: females • Medium: Copepodid V • Bottom: Females on 17th and 18th July 1933

9. Distance of DVM in some planktonic crustacea

10. Pattern of the migration • Chusing (1951) analysed all the work on crustacea and considered that it is possible to arrange their patterns of migration in the following general scheme: • Rising in the evening from the “day depth” towards the surface • Departure from the surface at about midnight or before it • Rising to the surface just before dawn • Rapid sinking at dawn to the “day depth” • Remaining during the day at a “day depth” more or less variable

11. §17.2 Causes of diurnal migration • Light intensity is of primary importance. • The observations on DVM at high latitudes where during part of the year there is no alternation between days and nights gives a kind of “natural” experiment. • Calanus and other principal species of the zooplankton remain in the superficial layer of water without migration • this also appears again in winter with the return of the change of day to night. During the winter night calanus stays in the depths at a constant level. Hypothesis of phototaxis

12. rather large variations around the optimal light intensity. This species is called “eurylume” species. The zooplankton seem to stay at an optimal light intensity and show a negative phototaxis above certain levels and positive one below that level. Hypothesis of Optimal light intensity

13. Animals must rise to surface in a certain time avoiding of sinking to bottom due to gravity Rising is active, and sinking is passive. Migration is a kind of diurnal alternation of periods of activity and inactivity. geotaxis

14. Feeding and avoiding fed • Zooplankton rises upper layer for Phytoplankton at dark night. • Zooplankton sinks to bottom where the light is dim for avoiding fed at daytime. Hypothesis of food

15. In summary of the DVM reasons • Light is without any boubt the fundamental factor, • Temperature is an important accessory factor • Pressure and gravity are auxilliary factors which may probably not e neglected. • Avoiding fed and active feeding. • Biological behavior, for example, the existence of an internal biological rhythm, must also be considered