Chapter 17 Diurnal vertical migration

1
Chapter 17 Diurnal 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 0600 and
1400 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 1600 and
  2000pm.
• 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
• zzoa 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

7
(No Transcript)
8
(No Transcript)
9
Distance of DVM in some planktonic crustacea
Groups species Distance of DVM (m)
Cladocera Daphnia longispina 0.6
Copepods Diaptomus shoshome Calanus finmarchicus Pleuromamma robusta Metridia pacifica 8.8 About 100 gt600 400-500
Mysis Boreomysis microps Eucopia unguiculata 400 400
Hyporiid Vibia propinqua 400
Euphausiid Nematoscelis megalops Thysanopoda acutifrons 200 600
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