11. ECOLOGY OF DISTRIBUTION
337
The central Atlantic has not been sampled intensively enough as yet
to determine the parameters limiting the distribution of the different
species in any detail. Moore (1952) argues that since euphausiids
perform a diurnal vertical migration they in fact live in two environments, the surface layers a t night and the deeper layers during the day,
and that the temperatures of both the deeper and the surface layers
will affect their horizontal as well as vertical distribution. A species
living in deeper layers of optimal temperature and unable to enter the
surface layers because the temperatures are too high (or low) will,
therefore, have less chance of access to food than a species that lives in
an area where temperatures a t all depths are suitable for it. Consequently, Moore plotted the curves (Fig. 124) relating abundance of a
species to temperature at the sea surface and at the depth of the 1O-I2
level of surface illumination, and obtained rather distinct curves. It is
significant that Moore, using these two temperature regimes, drew a
map illustrating the theoretical distribution of Euphausia hemigibba in
northern subtropical regions of the Atlantic and obtained excellent
agreement between it and his map of the actual distribution of this
species.
A summary chart is presented in Pig. 125 of the vertical and horizontal distribution of species throughout the Atlantic. The order in
which the species are presented against the vertical scale within any
one bathymetric group is in many cases arbitrary because of lack of
sufficient comparative knowledge of the vertical layering of species but
where such knowledge exists shallower living species have been placed
nearer the top of the table, deeper living species nearer the bottom. The
Antarctic species have been included to complete the picture.
Pacijic Ocean
Much more detailed knowledge of the distributions of these animals
is available for the Pacific Ocean than elsewhere owing to the work of
Brinton, Ponomareva and Nemoto. Consequently, their distribution
can be discussed in much more general terms in this area than in the
Atlantic. Brinton (1962~) has examined the errors and artefacts liable
to arise in plotting geographical distributions of euphausiids when
insufficient information is available on the methods used for sorting and
counting animals in the plankton hauls, the type of nets used, the time
of day and season when hauls were taken, and the extent of the water
column sampled. Further anomalies arise when different methods of
plotting the data on maps are used. Many of these criticisms apply to
the present data concerning distributions of Atlantic species and
consequently no attempt was made to use contour lines to show the
337
The central Atlantic has not been sampled intensively enough as yet
to determine the parameters limiting the distribution of the different
species in any detail. Moore (1952) argues that since euphausiids
perform a diurnal vertical migration they in fact live in two environments, the surface layers a t night and the deeper layers during the day,
and that the temperatures of both the deeper and the surface layers
will affect their horizontal as well as vertical distribution. A species
living in deeper layers of optimal temperature and unable to enter the
surface layers because the temperatures are too high (or low) will,
therefore, have less chance of access to food than a species that lives in
an area where temperatures a t all depths are suitable for it. Consequently, Moore plotted the curves (Fig. 124) relating abundance of a
species to temperature at the sea surface and at the depth of the 1O-I2
level of surface illumination, and obtained rather distinct curves. It is
significant that Moore, using these two temperature regimes, drew a
map illustrating the theoretical distribution of Euphausia hemigibba in
northern subtropical regions of the Atlantic and obtained excellent
agreement between it and his map of the actual distribution of this
species.
A summary chart is presented in Pig. 125 of the vertical and horizontal distribution of species throughout the Atlantic. The order in
which the species are presented against the vertical scale within any
one bathymetric group is in many cases arbitrary because of lack of
sufficient comparative knowledge of the vertical layering of species but
where such knowledge exists shallower living species have been placed
nearer the top of the table, deeper living species nearer the bottom. The
Antarctic species have been included to complete the picture.
Pacijic Ocean
Much more detailed knowledge of the distributions of these animals
is available for the Pacific Ocean than elsewhere owing to the work of
Brinton, Ponomareva and Nemoto. Consequently, their distribution
can be discussed in much more general terms in this area than in the
Atlantic. Brinton (1962~) has examined the errors and artefacts liable
to arise in plotting geographical distributions of euphausiids when
insufficient information is available on the methods used for sorting and
counting animals in the plankton hauls, the type of nets used, the time
of day and season when hauls were taken, and the extent of the water
column sampled. Further anomalies arise when different methods of
plotting the data on maps are used. Many of these criticisms apply to
the present data concerning distributions of Atlantic species and
consequently no attempt was made to use contour lines to show the