Bijoy, Nandan S; Lathika, Cicily Thomas; Padmakumar, K B; Smitha, B R; Asha Devi, C R; Sanjeevan, V N(Polish Academy of Sciences, Institute of Oceanology, 2013)
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Abstract:
The phytoplankton standing crop was assessed in detail along the South Eastern
Arabian Sea (SEAS) during the different phases of coastal upwelling in 2009.During phase 1 intense upwelling was observed along the southern transects
(8◦N and 8.5◦N). The maximum chlorophyll a concentration (22.7 mg m −3) was
observed in the coastal waters off Thiruvananthapuram (8.5◦N). Further north
there was no signature of upwelling, with extensive Trichodesmium erythraeum
blooms. Diatoms dominated in these upwelling regions with the centric diatom
Chaetoceros curvisetus being the dominant species along the 8◦N transect. Along
the 8.5◦N transect pennate diatoms like Nitzschia seriata and Pseudo-nitzschia sp.
dominated. During phase 2, upwelling of varying intensity was observed throughout
the study area with maximum chlorophyll a concentrations along the 9◦N transect
(25 mg m−3) with Chaetoceros curvisetus as the dominant phytoplankton. Along
the 8.5◦N transect pennate diatoms during phase 1 were replaced by centric diatoms
like Chaetoceros sp. The presence of solitary pennate diatoms Amphora sp. and
Navicula sp. were significant in the waters off Kochi. Upwelling was waning during
phase 3 and was confined to the coastal waters of the southern transects with
the highest chlorophyll a concentration of 11.2 mg m−3. Along with diatoms,
dinoflagellate cell densities increased in phases 2 and 3. In the northern transects
(9◦N and 10◦N) the proportion of dinoflagellates was comparatively higher and was
represented mainly by Protoperidinium spp., Ceratium spp. and Dinophysis spp.
The main objective of the study was primarily to determine the effect of hydrographical parameters especially nutrients which were supplied externally to the seawater while culturing the diatom Chaetoceros calcitrans, under laboratory conditions, and to determine its optimum concentration for ideal growth of the culture, in such a condition of increased rate of pollution due to the industrialization and effluents. Also an attempt was made to study the possible correlation of diatom abundance in the South west Coast of India with the landings of the pelagic fishery resources, especially sardine, mackerel and anchovy, since these fishes are largely diatom feeders. Positive correlation was found between the diatoms and pelagic fish landings of Thalassery and Vizhinjam area while at Cochin there was less significant correlation between the two variables