_
Dnrrrmc LIFE
125
the greatest quantities of animal life. Such indeed is'the case.
The abundance of that little Creature, the Calanus, and of the
-shrimp-like euphausiids, has already been dwelt upon and
they too are to be found chiey in the regions.outlinedab0ve.
But. while the plankton' is present in greatest quantitiès '
in these: northern waters, it is remarkable that compared
with thepl'ankton of the warm and tropical regions“ the
numbers of different kinds of animals are extremely few.
.
The‘catches made in the northern waters can almost be
‘
described as monotonous in composition, that is, although
they are so large, they will be made up of only c0mpa'ratively
few species of animals.
To the collector then the catChes
-
made in warmer regions prove vastly more interestingon
account of the wealth of different species to be f0und there,
even though they
Only in small numbers.
One
example is sufcient to show how marked this difference is.
Of roughly ve hundred species of copepods, while eighty
per cent. are to be found in the warm regions, only four per
,
_
cent. are found in the cold northern region andîonly eight
per cent. in the southern;
This phenoïnenon holds good
for all the different groups of. animals represented in the
plankton.
'
-
-.
'
_
Ÿ
Apart from.the excessive abundahce of‘drifting
the
it is to be noticed that
the
coastal regions are considerably' ‘richer‘ than the waters of
the open ocean.
The central regions of the North and
_
South Atlantic oceans are the poorest in plankton'life,
that
is the areas lying a little“ north and a_ little south of the
eqüator.
equatorial regions the plankton is a
little cher;
The deep blue Sargasso Sea, in the centre
of the North Atlantic, is probably als barren as any règiOn
'
in theWorld.
There are several factors that together are
'
responsible for the abu‘ndance or poverty of plankton‘ life,
but of greatest importance is the presence or absence of