|It is not essential to dive at night to observe zooplankton. By being a little attentive, even in broad daylight, it is common to see small living organisms drifting with the currents.|
Plankton includes all living organisms that float and drift in open water. This word comes from the Greek planktos which means "wandering". The organisms that make up the plankton are capable of limited movements and cannot move against the current. Plankton is pelagic, that is to say living in open water (in contrast, organisms living at the bottom are said to be benthic). Very diverse in nature, these organisms have sizes ranging from 0.2 micrometers to several centimeters or even several decimeters for the largest, such as salps.
Plankton is divided into 2 major kingdoms, plant plankton or phytoplankton and animal plankton or zooplankton. Many organisms belong to plankton: unicellular algae, small crustaceans and other invertebrates, eggs and larvae of fish, molluscs, echinoderms... Plankton plays an essential role in the functioning of ecosystems being, among other things, the base of the food chain.
Zooplankton are animal plankton. It feeds on living matter, with some species being herbivorous and others carnivorous. Zooplankton is easily differentiated from phytoplankton by more complex shapes: presence of legs, antennae. It rises to the surface at night to feed on phytoplankton and descends during the day to deeper waters, which is called a daily vertical migration. However, you can also see a lot of zoo and phytoplankton during the day.
Phytoplankton feed in particular myriads of small crustaceans which form krill which itself feeds other animals including seabirds such as albatrosses, storm petrels, shearwaters, petrels, penguins... Krill feeds also fish, seals and giants like whale sharks, basking sharks, manta rays and baleen whales (Mysticetes). In return, the droppings of all these animals feed the phytoplankton. The development of phytoplankton is therefore maintained by the animals that feed on it. The cycle is virtuous!
Here are some pictures of zoo and phytoplankton. From right to left and top to bottom: 1- Juvenile Argonaut using a salp as a means of transport 2- Cerianthus larvae 3- Veligera 4- Sea Tunneler (t