Distribution of Hydromedusae in the Indian Ocean
279
density and reproductive rate, as well as intra- and interspecific competition for space and
food, determined by population density. The idea that meaningful patterns of species
distribution exist among plankton is linked to two ancillary ideas that we considered in the
analysis of the data: 1) species distribution is regulated by environmental parameters,
while population density at any given time or place is regulated by the amount of food
1Vailable and the age of the ecosystem; 2) in the world of plankton, patterns of higher
0
10
20
30°C
32
33
3{'
35
36 %05
0 '"
%05 ) ,
( T ... -
(-...)
i
1 i
{'OO
!
I
i
: I
i
Zoncleo
dubio
~ I
./
I
,
- 800
I
E
j i
J
.c.
! I
g.1000
/
0
I
/
1200
!
/
I
. 5t. 285 --1{'00
! 5t. 298 -
I
5t. 15 ---5t. 5{' .. .......
1600
i
1800
0 2 {, 6 mI0:t 1- 1
Fig. 5. Depth distribution of Zanclea dubia, at selected stations plotted over salinity, temperature and
oxygen distribution with depth, at the same stations. Stn 15,07°27' N, 95 ° 18 ' £; Stn 54, 18° 24' N,
90 ° 45'£; Stn285, 14° 22'N, 54° 18'£; Stn298, 12° 33'S, 54° 33'£
order are probably superimposed on the patterns of the distribution of the species. There
are indications that primary producers, grazers, secondary producers, active hunters and
all such ecological categories that are not taxonomic categories, have patterns of
distribution peculiar to themselves.
From the examples cited and the detailed study of the other species we draw some
general conclusions that appear to be corroborated by studies of species belonging to
other taxonomic groups made by the staff of the Indian Ocean Biological Centre at
Cochin.