‘’Floating or weakly swimming
animals that rely on water currents
to move any great distance’’
"zoon -animal", "planktos -drifter"
Without environmental factors which keep reproduction of
some species of zooplankton (such as Filinia) under control,
entire world would be covered with 3-feet-thick layer of
zooplankton in 130 days.
1 st size classification of zooplankton was given by (schutt 1892)
CATEGORY SIZE RANGE DESCRIPTION
Femtoplankton 0.02-0.20 um marine viruses
Picoplankton 0.2-2 um
small eukaryotic protists; bacteria;
Nano plankton 2-20 um
feeding on bacteria
Microplankton 20-200 um Protozoans like ciliates
Mesoplankton 0.2-20 mm Metazoans (Copepod, Medusa etc..)
Macroplankton 20-200 mm
Members of hydromedusae, mysids,
ctenophores, eel larvae
> 200 mm (almost 8
Metazoans (Jelly fish)
Classification based on size
Based on developmental stages
Meroplankton only partially planktonic life cycle
(eg) crab zoea, snail veliger, Bipinnaria of
Holoplankton remain plankton for their entire
life cycle (eg) pteropods , chaetognaths,
siphonophores, and copepods.
Characterized by either a long tail used for
swimming (flagellates) OR
by hair-like structures called cilia (Ciliates
contains the colonial siphonophores and
the scyphozoans—also known as the true
Most are non-motile, about 100 species are
Rotifers eat bacteria, detritus, other rotifers,
algae or protozoa.
Rotifers are highly efficient reproducers
Most macrozooplankton are copepods found in
marine and freshwater ecosystems.
Swim using an antenna and frontal structures
• Arrowwormsare mostly holoplanktonicand are abundant worldwide.
• These transparent wormsare approximately3 cm long and have fins on
the sidesof their bodies.
larvae of benthic molluscs usually found in coastal
waters including heteropods or pteropods.
class of annelid worms, generally marine.
Each body segment has a pair of fleshy
protrusions called parapodia that bear many
bristles, called chaetae, which are made of chitin
planktonic crustaceans found in
coastal waters; swim using second
larvae of the midge Chaoborus is the only
widely known insect larvae classified as
classes Appendicularia and Thaliasia. Both
are filter feeders
Appendicularia consumes small food
particles using a mucous filter.
Other types of tunicates are benthic and are
only planktonic during their larval stages
Classified under Euphausids
found all over the world.
can be 3 cm large and are an
important source of food for many
types of whales.
Serves as an indicator organism for
the presence of baleen whales in the
All the organisms living or inhabiting in the bottom regions of the aquatic environment
are termed benthos.
Macro benthos are organisms that are
larger than 1 mm
E.g. oysters, starfish, lobsters, sea
Meio benthos are between 0.1 and 1 mm
E.g. ciliates, annelids
Micro benthos are very tiny organisms.
They are smaller than 0.1 mm E.g.
bacteria and ciliates
CLASSIFICATION BASED ON SIZE…..
Endobenthic organisms are the
meiofaunal sized organisms which move
within the sediment by displacing particles
eg. Sand dollar
Mesobenthic organisms are the
meiofaunal organisms living and moving
within the interstitial spaces of the grains.
eg,. Sea cucumber
Epibenthic organisms are those that living
at the sediment-water interface
Eg. Rock Cod
CLASSIFICATION BASED ON LOCATION…..
Based on the mode of life
Epifaunal organisms : animals which
live on the substratum.
Infaunal organisms : are those that
animals live into the substratum.
Burrowers : Organisms that penetrate or
burrow into the unconsolidated bottom
sediments are called burrowers.
Borers : organisms those that penetrate
or bore the hard rock or substrate
materials are called borers.
Based on mobility
1. Sessile benthos
- do not have any mobility, attached
or fixed with the substratum - rely on
currents or other mechanisms to
bring food to them.
E.g. enthic algae, sea grasses ,corals
2. Vagrant benthos
- are those that have locomotory
powers and either they can move
rapidly or slowly.
E.g. Only animals are included under
Arthropods : The crabs and lobsters are the largest and fastest of the vagrant benthos. In
addition, they have some swimming ability, using either their tails and/or specially adapted legs.
Echinoderms : They have numerous appendages in the form of sucker feet or spines that are
used for locomotion.
The sea urchins live on hard substrates where they feed on debris.
Sand dollars have the poorest mobility but they can move slowly by the whisker-like feet that
surround their body.
Sedentary or Vagrant epifauna: They may live on rigid substrate, firm sand or
soft mud. While some move very slowly, others move very quickly.
Foraminifera: less than a millimetre in dia
with different shaped tests and most of
which are multi-chambered
Many organisms are attached to the substrate throughout their
maturity and have no mobility at all. These include,
Brachiopods: attach with a stem like foot that extends from
near the hinge line that holds the shells together.
Mussels are about the same size and they attach themselves to
a hard surface with strong thread like structures, called byssus
threads which develop at the hinge line
includes various meiofaunal and macro fauna such as snails,
clams, worms, sea urchins, and crustaceans.
Some groups are entirely infaunal, tusk shells
two different models of life
1. Some graze or plow through the sediment (sediment
2. others construct extensive burrow complexes that they
occupy and in which they move about (sediment
Nekton vs Plankton vs Benthos
o Nekton live throughout the water column whereas plankton live
closer to the water surface.
o Unlike nekton and planktons, benthos linked to the ocean floor.
o Unlike the planktons and benthos, nekton can propel themselves
either by swimming or other means.
o Many planktons are microscopic or small animals, when
compared to the other two types.
o Some benthos are free living, while others live attached to the
seabed. However, all the nekton are free living animals.
Lalli, C. and Parsons, T.R., 1997. Biological
oceanography: an introduction. Butterworth-Heinemann.
Schütt, F., 1892. aus: Biological Oceanography, An Early
MAY BE THROWN BY US…
A VIEW OF littersin VERSOVA BEACH DURING neap tide