CLASSIFICATION OF PLANKTON
I. Based on Composition
A sample of plankton collected from sea water contains
phyto- and zooplankton
(a) Phytoplankton: containing small algae and bacteria. Main
groups are diatoms, dinoflagellates, coccolithophores, and
prochlorophytes. (p. 53, Speight). They are present
throughout the lighted regions of all seas, including under
ice in polar areas. Because the phytoplankton are the
dominant plants in oceans, their role in marine food chain is
of paramount importance. A taxonomic composition of
marine phytoplankton is provided below:
,b) Zooplankton: animal components of plankton community, i.e., the grazers on
phytoplankton in pelagic ecosystems. Marine zooplankton include a number of
protozoan groups and members of most of the phyla, from Cnidaria and Platyhelminths
to Chordata. Most are small a few centimeters or less, but some jellyfish and
pyrosomes are a meter across and several meters long. Animals caught in plankton net
are zooplankton. They may be holoplankton – live in water column throughout their
entire life cycle, and meroplankton that are planktonic larvae
, practice diagram given under III. Upwelling regions
A comparison of food chains in three different marine habitats, top most is: I open ocean
, Harmful algal blooms (HABs)
-profuse growth of microscopic or semi-microscopic algae
which discolors water, may be of short duration, appears
and disappears suddenly called bloom
-cell concentration may range 1-20 mio cells/l, best known
marine blooms - Red tide, gives rust to red water due to high
concentration of dinoflagellates
-Chattonella, Fibrocapsa (class Raphidiophyceae) cause Red
tides of Japan, Trichodesmium (BGA) of Red Sea cause
bloom,Red Sea named after this bloom
-Phaeocystis cause gelatinous bloom in North Sea, common
harmful blooms caused by Gonyoaulux, Gymnodinium,
Prorocentrum, or Ceratium