A Quick Overview of Marine Plankton
Every month there will be differences in the variety of life in the plankton although some groups will always be present. Diatoms are single-celled algae constituting the phytoplankton, the main component carrying out photosynthesis. Likewise there will always be a few copepods and larval forms, the zooplankton. Copepods are generally cylindrical shapes often with long antennae and represent crustaceans that remain permanently in the plankton world. These permanent creatures form the holoplankton while the meroplankton is the name given to those organisms using this world for just part of their life cycle. For example, barnacles and periwinkles living on a rocky shore have nauplius and veliger larvae, respectively.
Yet another way of categorising the life living in this environment is by size. Here is an approximate guide of sizes and examples:
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Femtoplankton - Viruses up to 0.2 micron
Picoplankton - bacteria & cyanophytes 0.2-2 micron
Nanoplankton - some flagellates 2-20 micron
Microplankton - tintinnids & diatoms 20-200 micron
Mesoplankton - copepods, many larvae 0.2 -20mm
Macroplankton - arrow worms 2 - 20cm
Megaplankton - large jellyfish up to 2 metres
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Plankton sample with low magnification. The green circles and shapes are large diatoms while copepods form the bulk of the zooplankton here.
All of these are single-celled organisms or Protists
Click on photos
The marine worms, polychaetes, may live permanently in the plankton or as a larva
Crustaceans: Clockwise, large copepod (Calanus), water flea Podon, larva of a barnacle and larva of a porcelain crab
Molluscs are represented by larval forms in the Milford Haven plankton. Called veligers they have a large organ covered in cilia for movement
Jellies: A tiny medusa, sea gooseberry or ctenophore
The larva of a sea anemone
To find out what these are click on the photo and it will take you to their section
