Seasonal Variation of Phytoplankton Pigments and Some of the Associated Oceanographic Parameters in the Laccadive Sea off Cochin

Abstract

Collections were made on board of the RV “Conch” from stations located approximately 7 to 15 km off Cochin (Fig. 1). Most of the monthly collections were made from stations located in area 2, profile studies were made from areas 1, 2 and 3, and one grid study from areas 1, 2, 4, 5 and 6. At stations in the depth range 18 to 20 m samples were collected from 0, 5, 10 and 15 m, and at 25 to 26 m deep stations from 0, 10 and 20 m. Collections were generally made between 1000 and 1300 local time. All samples were collected with Nansen reversing water bottles; the usual practice was to operate a single bottle 2 or 3 times at the same depth and empty the water into a plastic bucket. This water was then poured into 2 or 3 one-liter polyethylene screw-cap bottles for determining the amount of plant pigments and nutrients. Samples for pigment determinations were stored in a cool dark place after the addition of 1 ml magnesium carbonate suspension. On reaching the shore laboratory these samples were filtered through Whatman GF/C glass fibre filters, which were then stored in a desiccator in a refrigerator. The analytical procedures for salinity were described in Barnes (1959) and the rest as in Strickland and Parsons (1965 and 1968). Most of the phytoplankton pigment measurements were made with 10 cm path-length, low-volume cuvettes which were specially fabricated for this purpose. Trichromatic equations designated “P.S.” were used for calculating the quantity of pigments.