Studies on Limacina inflata d'Orbigny (Thecosomata, Gastropoda) in the Indian Ocean 397
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Fig. 13. The distribution of Limacina inflata in relation to the thermocline (in terms of number
perm 3 )
July. As Limacina inflata is an eurythermic form inhabiting tropical to polar waters, the
temperature may not act as a barrier to the up and down migration of this species. As
diurnal variation is remarkable, light may be the major factor in the vertical distribution
of Limacina inflata.
Even though no correction factor was applied to the varying depth of thermocline
hauls (30-120 m), the occurrence and abundance of Limacina inflata above and below
the thermocline show more or less the expected vertical distribution. When the data were
converted in terms of number per m 3 (Fig. 13), 28 of the 35 night stations below the
thermocline show negative values, giving the impression that no organisms are present.
This might be due to the non-random distribution of the organisms, the population of
Limacina inflata being more dense above than below the thermocline at night, or it might
be an artefact of the method used.