Environmental Engineering Reference
In-Depth Information
Table 2.1
Differences between centric and pennate diatoms
Point
Centric diatom
Pennate diatom
Cell shape
Discoid, solenoid or cylindrical
Elongated and fusiform, oval, sigmoid or roughly
circular
Ornamentation
Radial in nature, i.e., the arrangement of
the markings is radiating from the centre
Bilateral in nature, i.e., the arrangement of the
markings is on either side of the apical (main) axis
occurrence has been recorded in coastal waters.
They form important diet components of
(a) On the basis of size, the phytoplankton may
be grouped under
lter-
ve categories (Table
2.2
).
(b) Phytoplankton can also be classi
feeding animals.
Coccolithus
sp. and
Isochrysis
ed on the
basis of the cell characteristics (Table
2.3
).
galbana
are
common
coccolithophores
of
oceans, seas and estuaries.
2.1.2 Seaweeds
Blue-Green Algae
These include both unicellular and multicellular
organisms. The blue colour in them is due to the
presence of a pigment known as phycocyanin. Of
the various organisms belonging to this category,
the most important is
Seaweeds or benthic marine algae are the group of
plants that live either in marine or brackish water
environment. They are macroalgae and contain
photosynthetic pigments. Like the terrestrial pro-
ducer community, the seaweeds can prepare their
own food with the help of sunlight and nutrient
present in the sea water. Seaweeds are found in the
coastal region between high tide to low tide and in
the subtidal region up to a depth where 0.01 %
photosynthetic light is available. They require
hard substratum for their growth, which may be
tree trunks (preferably mangroves) that get sub-
merged during the high tide or even brick or
boulders that are often laid to enter the island from
the adjacent bays or estuaries (Fig.
2.8
).
Plant pigments, light, exposure, depth, temper-
ature, tides and the shore characteristic combine to
create different environment that determines the
distribution and variety among seaweeds. The
important criteria used to distinguish the different
algal groups based on the recent biochemical,
Trichodesmium erythraeum
because in certain seasons of the year, its bio-
mass increases greatly resulting in the formation
of clumps.
Green Algae
Microscopic green algae present in the plank-
tonic community largely occur in coastal waters.
The green colour in them is due to the presence
of chloroplasts. They are widely distributed in
the warmer (tropical) seas, and only few species
are found in the Arctic and Antarctic oceans.
Some common species of microscopic green
algae that are planktonic in nature are
Chlorella
marina
,
Chlorella salina
, etc.
Table 2.2
Classication of phytoplankton on the basis of
size
Plankton category
Classification of Phytoplankton
The phytoplankton community consists of a
variety of organisms, namely diatoms, dino
Maximum dimension (
ยต
m)
fl
ag-
Ultraplankton
<2
ellates, blue-green algae, silico
agellates, and
coccolithophores which ranges in terms of size
from 0.001 to 0.2 mm.
Phytoplankton may be classi
fl
Nanoplankton
2
20
-
Microplankton
20
-
200
Macroplankton
200
2,000
-
ed variously
from different angles which are discussed here:
Megaplankton
>2,000
