Occurrence of mono-species bloom of the diatom Asterionella
glacialis (Castracane) in the coastal waters of Gopalpur sea, north-western Bay
of Bengal and its impact on the water quality and phytoplankton community
structure is reported in this paper. The bloom period persisted for about two
weeks, from third week of March to 4
$^{th}$
April 2004.
Population density of phytoplankton discerned manifold increase from 4.63
× 10
$^4$
cells l
$^{-1}$
on
22
$^{nd}$
February 2004 to 3.96 ×
10
$^7$
cells l
$^{-1}$
on
26
$^{th}$
March 2004. An overwhelming dominance of
Asterionella contributing about 99.5% of the total phytoplankton count was
observed during peak bloom period. Chlorophyll-a contents also showed an
exponential increase that rose to 237.5 mg m
$^{-3}$
during
peak bloom period from its pre-bloom concentration of about 3.26 mg
m
$^{-3}$
. The stable hydrographic conditions coupled with
increased nutrient concentrations have triggered the blooming of this diatom
species. Termination of bloom occurred with the depletion of nitrate and
silicate in the medium water. Phytoplankton community structure in terms of
their species diversity, species richness and evenness showed distinct
variations during the pre-bloom, bloom and post-bloom periods.
