Seasonal Variation of Phytoplankton Pigments in the Laccadive Sea off Cochin
185
When dealing with phytoplankton pigments, the effect of grazing cannot be overlooked. One of the consequences of grazing would be the production of degraded forms
of inactive chlorophyll which would interfere with the spectrophotometric determination
of chlorophylls. Off Cochin, during the SW monsoon the percentage of phaeopigments is
about 10 to 40% at various depths; during the other months the upper layers have very
little, while at 15 m depth there are about 10%. This indicates heavy grazing during the
rich monsoon months. However, no data on the seasonal variation of zooplankton in
this area are available so that any further interpretation will have to await further
studies.
As a general conclusion it may be stated that hydrobiologically 2 distinct periods,
"May - October" and "November - April" may be identified. The former is characterized
by upwelling and high pigment content and the latter by sinking, followed by stable
conditions and low plant pigment content. Now that information on the quantity of plant
pigment present during different months in the coastal region off Co chin is available, it
is possible to make a rough estimate of the phytoplankton pigments at any given time of
the year if the colour of the sea is observed and the Secchi disk measured, provided the
influence of the changing hydrographical conditions is also borne in mind.
185
When dealing with phytoplankton pigments, the effect of grazing cannot be overlooked. One of the consequences of grazing would be the production of degraded forms
of inactive chlorophyll which would interfere with the spectrophotometric determination
of chlorophylls. Off Cochin, during the SW monsoon the percentage of phaeopigments is
about 10 to 40% at various depths; during the other months the upper layers have very
little, while at 15 m depth there are about 10%. This indicates heavy grazing during the
rich monsoon months. However, no data on the seasonal variation of zooplankton in
this area are available so that any further interpretation will have to await further
studies.
As a general conclusion it may be stated that hydrobiologically 2 distinct periods,
"May - October" and "November - April" may be identified. The former is characterized
by upwelling and high pigment content and the latter by sinking, followed by stable
conditions and low plant pigment content. Now that information on the quantity of plant
pigment present during different months in the coastal region off Co chin is available, it
is possible to make a rough estimate of the phytoplankton pigments at any given time of
the year if the colour of the sea is observed and the Secchi disk measured, provided the
influence of the changing hydrographical conditions is also borne in mind.