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These
include viruses, bacteria, plants (phytoplankton) and animals (zooplankton)
that drift in the sea. Most are microscopic, but some - such as
the various species of jellyfish and sea-gooseberry - can be much
bigger.
Diatoms
and dinoflagellates dominate the phytoplankton. Although they are
microscopic plants, diatoms have hard shells and dinoflagellates
have little tails that propel them through the water. Phytoplankton
populations in the Irish Sea have a spring "bloom" every April and
May, when the seawater is generally at its greenest.
Crustaceans,
especially copepods, dominate the zooplankton. However, many animals
of the seabed, the open sea and the seashore spend their juvenile
stages as part of the zooplankton. The whole plankton "soup" is
vitally important, directly or indirectly, as a food source for
most species in the Irish Sea, even the largest. The enormous Basking
Shark, for example, lives entirely on plankton and the Leatherback
Turtle's main food is jellyfish.
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