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Dieren en planten

Animals   Crustaceans   Copepods   Marine fauna   Animal plankton   Sea fish   Seabirds   Marine mammals   
Zooplankton, NIOZ, www.nioz.nl

Animal (or zoo)plankton

Plankton is the collective term for all free-floating organisms in water. Zooplankton account for the animal category. Zooplankton are able to move around themselves, but are not strong enough to fight the currents. Belonging to this category are microscopically small one-celled animals to larger animals such as jellyfish. Even the free-floating larvae of fish and other larger marine animals fall under the zooplankton. Three-quarters of all of the plankton biomass in the North Sea consists of the zooplankton copepod.

  • Types and sizes

    Zooplankton come in all sorts of shapes and sizes. The smallest animals consist of one cell. They cannot be detect with the naked eye, however their fantastic shapes can be admired under a microscope. As far as numbers are concerned, the one-celled protozoa form the largest group within the zooplankton in the coastal waters. Not all zooplankton are so small. Copepods and larvae from fish as well as benthic animals can grow to a few millimetres. Krill are shrimp-like animals approximately three centimetres long. Krill form the most important food source in the oceans for many whales. Jellyfish grow much larger than krill: some species can reach more than one meter in diameter.
    Just like phytoplankton, a number of zooplankton possess protrusions. These enlarge their ability to float and hide from predators. Especially one-celled zooplankton often possess this adaptation. A number of one-celled species also use drops of oil as a floating organ. Fish larvae have a yolk sack which increases their floating ability immensely. Copepods use their long antennae to stay afloat. They can also move around in a vertical direction: sometimes with a speed of 60 meters per hour. Krill can cover 100 to 400 meters in an hour. Jellyfish move about by contracting their umbrella-like bell. The swimming combs of the sea gooseberries consist of a number of plates. Each plate contains ciliate hairs with which it makes stroking movements. Thus every sort has its own way of remaining afloat and thereby remaining in the area where their food is.

  • Link between plants and animals

    An enormous amount of variation in plants and animals live in the sea. All of this sea life cannot live without carbohydrates, proteins and fats. Animals are not capable of producing these building materials themselves, but plants can. All marine animals are therefore dependent upon phytoplankton for their basic elements. They obtain their building materials either directly or indirectly by eating algae or algae-eaters. Some zooplankton eat phytoplankton. The rest of the zooplankton, benthic animals and fish, in turn, eat the zooplankton, and thereby come indirectly in contact with their building materials. And they, in turn, are eaten by larger fish, seabirds and marine mammals. This series of eat and be eaten is called a food pyramid, food chain or food web.