Noctiluca scintillans bloom in a coastal site of northwestern Bay of Bengal
Subhashree Sahoo
DST,INSPIRE Fellow
Dept. of Marine Sciences, Berhampur University
Bhanjabihar, Odisha-760007, India
What is algal bloom ? ? ?
 Sudden and explosive growth of one or few species of
algae (macro or micro) in an aquatic ecosystem
 Bloom
can
turn
water
in
to
red, orange, yellow, brown, green, white or pink
depending upon the causative species.
 Common
natural event in temperate and tropical
waters.
 Favorable
conditions like nutrient enrichment and
stable hydrographic conditions are conducive .
 About
300 phytoplankton species can form
blooms, mainly from diatoms dinoflagellates & bluegreen algae in which about 80 species have the
capacity of producing harmful algal toxins.
Harmful algal bloom ! ! !
 When the blooms are
associated with any one or
more of these adverse affects they are known as
Harmful Algal Bloom (HAB).
 Some bloom forming species have spiny structures
which causes irritation to fish gills.
 The anoxic conditions in surface layers may cause
the suffocation and mass mortality of fishes and
invertebrates.
 The poisonous toxins may reach to man
through
the consumption of intoxicated fish and shellfish
may cause a series of illness.
 The dense bloom of phytoplankton cause hindrance
to fishing operations and damage to fishing gears.
Red Tide in coastal waters off Rushikulya eastuary
 This
region is internationally recognized for the
episodic mass congregation event of vulnerable Olive
Ridley sea turtles.
 Periodic
pre-monsoon
phytoplankton
blooms
associated with coastal upwelling is a prominent
biological feature.
 Experiences tropical monsoonal climate.
 The southwest (SW) monsoon sets in between June and July and withdraws in October.
Average rainfall of 1,210 mm/year.
 Identified for long-term time-series bio-optical measurement under SATellite Coastal and
Oceanographic REsearch (SATCORE) programme coordinated by Indian National Centre
for Ocean Information Services (INCOIS).
Brown to dull red discolouration of coastal water
during April, 2014………………
Active phase
Decline phase
Study methodology
 Five field surveys were carried out onboard a fishing
trawler at three selected stations.
 Covered three depths (0, 10, 20 m) during April 2014
[observation 1 (O1) on 13th, observation 2 (O2) on
16th, observation 3 (O3) on 20th, observation 4 (O4) on
23rd and observation 5 (O5) on 27th]
 Water
samples for analysis of physico-chemical
parameters (dissolved oxygen, salinity, total suspended
matter, nitrite, nitrate, phosphate, silicate) following
Grasshoff et al (1999).
 Phytoplankton identification was done by microscopy.
 Size fractionated chlorophyll concentration were determined by subjecting water samples to
sequential filtrations through 20 µm (for microplankton), 2 µm (for nanoplankton) and 0.2
µm (for picoplankton) polycarbonate filter papers .Subsequent estimation of Chl-a was done
spectrophotometrically.
Observations………
 Taxonomic
analysis confirmed the presence of
Noctiluca scintillans (NS).
 NS is
a common bloom forming dinoflagellate results
in red or green tides in coastal and offshore waters.
 Depending upon the ingested material and geographic
location, these colourless heterotrophic species imparts
green or red colouration.
 In certain conditions, NS can act as vector of toxins to
higher order of food chain by grazing on toxigenic
microalgae.
 NS
varied between 0.15 and 32.87x 104 cells l-1
representing its bloom.
 Bloom persisted for 12 days during its peak to waning phase.
 The phytoplankton community was composed of two major groups, viz. diatom (30 species)
and dinoflagellates (6 species) during the observation period.
Observations………
 Dinoflagellates with the dominancy of NS were more abundant than diatoms during O1, O2
and O3, which grouped these days as the peak phase of the bloom.
 The relative abundance of NS subsequently decreased to 20.44% (O4) and finally 6.67%
(O5) indicating decline phase of the bloom.
 During peak phase of the bloom, picoplankton were found to be significantly contributing to
total Chl-a (49.48% to 66.14%) followed by nanoplankton (22.32% to 33.32%) and
microplankton (11.54% to 18.58%).
 The present observation is the first report of picoplankton biomass during a NS red tide
event in Indian waters
Observations………
 In oligotrophic conditions, approximately 60 to 98% of the standing stock of chlorophyll is
contributed by the pico and nanoplankton.
 Concomitant high concentration of picoplankton during peak phase of the bloom implied its
non-predation by NS.
The above observations lead us to hypothesize as:
"During peak bloom phase, NS grazed on microplaknton providing conducive
environment for opportunistic picoplankton to uptake the available nutrients and
proliferate. During decline phase, evolution of microplankton, dominated by
diatom, begins to consume the residual nutrients resulting in depletion of
picoplankton".
Observations………
 Parallel
sporadic swarming of gelatinous
macro zooplankton (jelly fish).
 The
jelly fishes might have grazed on
populations of herbivorous zooplankton
(particularly copepod), which outcompeted
NS to avail diatom prey.
Observations………
 Salinity varied
between 34.19 to 34.78 psu with
low standard deviation of 0.14 presenting a
conducive environment for NS cell division and
population growth.
 The reduction in DO concentration can cause lethal
and sublethal effects in a variety of organisms,
specifically in fish.
 The enrichment of NH4 during the decline phase of
the bloom was due to excretion by organisms in the
developing food chain and degradation of NS.
 May be harmful for the coastal fishery by reaching
up to a toxic level by interacting with neurotoxic
chemical producing dinoflagellates, Gonyaulax spp.
and Alexandrium spp.
 Exhaustion of SiO4 in the prebloom period might
have promoted the luxuriant growth of NS with
reduction in diatom abundance.
Conclusion………
 Depletion of DO with information on fish evasion during decline phase of the bloom is
apprehensive.
 NS bloom exhibited a significant effect on the nutrient status
 High salinity values with poor variation indicated no riverine influence on NS bloom
 Picoplankton community declined with increase in micoplankton at the waning phase of
NS bloom
 exhaustion of nutrients, especially silicate, in the water column with decline in diatom
abundance during pre-bloom was conducive for NS to proliferate
 parallel sporadic swarming of Jelly Fish during the NS bloom period outcompeted NS to
avail diatom prey
 Need
of further research to encapsulate the reason of recurrences of NS red tide
particularly in coastal waters of present study area in east coast of India.