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Rocky Shore Trail
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Zooplankton

As the name suggest this is the animal component of plankton. The majority are microscopic although in small rockpools it maybe possible to see tiny copepods as tiny dots swimming in a jerky fashion. There are large planktonic creatures, e.g. jellyfish.

Some of these animals will be herbivores eating the diatoms. Nauplii larvae swim rapidly but with quite jerky movement to keep pace with diatoms as they become buoyant and move up the water column. Other species may be carnivorous feeding on the smaller animals. Larval stages of seashore animals are very prolific. Barnacles, limpets, topshells and crabs are just a few of the organisms with such larval forms. Although it is full of food there is a down side to using the plankton. As the larvae enter the plankton they, by definition, cannot determine where they will drift. Inevitably most are lost or eaten. The ocean will take them away from the ideal environment and so fail to become an adult. As a consequence animals using the plankton as a way of feeding and dispersing young will have to produce huge numbers of offspring. Crabs can get close to a million whilst some sea slugs may be four or five times this number.

These larval forms of shore organisms are temporary members of the plankton. Using it for dispersal of young. Some animals have all teh phases of their life living in the plankton, e.g. copepods.

Copepod naupliusCopepod nauplius lava Copepod adult Copepod adult

Buoyancy is an important issue for the animals chasing food. In some like zooea larvae they may have buoyancy aids like spines and swellings that can be expanded. The density of zooplankton is linked to the density of diatoms and often the release of animal young is synchronised with the time of year and blooms.


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