Zooplankton or animal plankton – that is how is called the assemblage of the drifting unicellular and multicellular animals, current-borne in the water masses. Small zooplankton is the central component of the marine ecosystem. Most of zooplankton animals graze mainly the phytoplankton, Thus zooplankton the phytoplankton and the fish. Zooplankton, fish larvae graze mainly zooplankton. Fluctuations in zooplankton (especially, copepods) abundance is very important factor affecting the fish abundance. Zooplankton community is characterized by the wide range of sizes of the animals which belong to variable taxons. It can vary from several microns (e.g. ciliates - Video 1) to 0.5 м and more (e.g. jellyfishes – Video 2).
HOLOPLANKTON and MEROPLANKTON Majority of zooplankton live in plankton only part of their lifespan. They are called MEROPLANKTON in contrast to true zooplankton (HOLOPLANKTON) which live in plankton (in water column) during all their lifespan or on the sea bed.
HOLOPLANKTON HOLOPLANKTON consists of zooplankton animals from various taxons – Ciliates (Video 1), Copepods (e.g. Acartia clausi - Video 3), Cladocerans (Video 4), appendicularians (Video 5), Ctenophora (Video 6) and many others. Copepods are the biggest group of holoplankton. Among copepods most widespread are groups of Calanoid copepods (for example, Calanus sp. - Video 7), Pseudocalanus sp. (Video 8), Acartia sp. (Video 3) ), Harpacticoid Copepods (Video 9) and Cyclopoid Copepods (e.g. Oithona - Video 10). Early stages of copepods are very like tiny spiders, and they are called nauplii (Video 11).
Many Rotifers (or Rotatoria) can be found in the plankton (Video 12A). In the Black Sea, Synchaeta sp. are very abundant among them.
MEROPLANKTON MEROPLANKTON consists mainly of the larvae stages of the animals from various taxons of benthic animals, such as worms, molluscs, crustaceans. Besides, pelagic larvae and eggs are also part of meroplankton, while their adult stages are mainly part of nekton. Some larvae of crustaceans resemble the adult forms (shrimps), other – absolutely different, but molting from stage to stage started to be adult-like. Crustaceans larvae have also fantastic Greek names: nauplii, zoea, mysis, megalopa.
Another group of meroplankton are the larvae of molluscs (Video 13). Their first stage is trohophora, the second one is veliger, which have transparent shell and in two weeks finally settle on hard substrates. Third group of meroplankton includes the larvae of different marine worms, e.g. Polychaeta (“many setas”) (Video 14) . Significant group of meroplankton consists of pelagic fish eggs (Video 15) and larvae (Video 16). The pelagic eggs remain in plankton due to their light oil drop(s) and yolk sac. BUT!!! HOLOPLANKTON have stages that stay (even for a long period of time) in the sea bed – dormant, diapauses, wintering eggs or stages. They stay in the bottom deposits and hatch when meeting favorable conditions. These bottom dormant stages help a lot for reproduction and restoration of estuarine copepods even in variable environmental conditions.
DIVISION of ZOOPLANKTON by Size Groups
-microzooplankton – ciliates, rotifers, etc. – less than 0.2 mm Know more about the Black Sea zooplankton
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ZOOPLANKTON is a diverse, graceful, beautiful animal community. The name “plankton” was proposed by the well-known German physiologist from Keel – Viktor Hensen who developed the sampling of plankton. The word “plankton” is derived from Greek and means “wanderer” or “drifter”. 
Photo: Heteropod Atlanta peronii, Peter Parks © 2001 (
Photo: Starfish larva, Tim Hellier © 2001 (
The research leading to these results has received funding from the European Community´s Seventh Framework Programme (FP7/2007-2013) under Grant agreement n. 217766
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