David Attenborough was recently interviewed by Rove McManus on The Project television show. When asked to play a word association game he described ‘exquisite’ with ‘plankton’. We asked our awesome Underwater Observatory tour guides to give us the low-down on plankton.
A planktonic organism is one that floats freely in the water. Plankton can be small plants that photosynthesise, these are called phytoplankton, or they can be small animals, these are called zooplankton.
Plankton are often sorted into different size classes, starting at femtoplankton which are less than 0.2um or 0.0002mm long (such as some bacteria and viruses), up to megaplankton which are over 20cm (such as jellyfish).
Plankton includes many viruses, bacteria’s, jellyfish, comb jellies and larvae of larger species.
Seeing plankton is often difficult because they are so small, sometimes they are so small they just make the water cloudy, sometimes we might see little dots floating in the water.
Underneath the Jetty the most common type of plankton we see are comb jellies. These are a macro/mega-plankton which are a bit bigger (up to 10cm) and therefore easier to spot. Comb jellies are a beautiful, transparent jelly-like animals, but are not to be confused with jellyfish or stingers as they have no external tentacles or harmful stinging cells. When the sunlight illuminates them, you can see the most exquisite rainbow colours of the rows of cilia (combs) along their bodies. At night comb jellies are often bioluminescent.
Plankton are the drivers of the biggest mass-movement of animals on earth – oceanic diel vertical migrations. In the oceans at night zooplankton swim up from the depths to a few hundred metres below the surface where their food phytoplankton lives. The phytoplankton need the sunlight for photosynthesis that is only present in the first few hundred metres of water, and the zooplankton swim up at night because they have the protection of darkness. This attracts many other, and larger, species, beginning a nocturnal marine feast.