The water is full of animals, plants, bacteria, and protists so small that they cannot swim against strong currents and are swept in whatever direction the tide is flowing. (Which kingdom of life is left out? Click here for the answer.) These organisms are called the plankton. Many animals, such as crabs, shrimp, and oysters, enter the plankton as eggs or larvae, and leave it when they metamorphose into adults. This sea star larva, for instance, hatched from a very tiny egg in the plankton. When the time comes to begin its adult life, it will drop down to the seafloor. Other animals, such as copepods, live their whole lives in the plankton. Many animals eat plankton, including bay anchovies and oysters.

Type
Copepods | The Salt Marsh
Copepods | The Salt Marsh

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The most abundant animals in the plankton are copepods, such as the one pictured. As adults, they are less than 1 millimeter in length. The abundance and diversity of plankton species are highest in...
Fungi | The Salt Marsh
Fungi | The Salt Marsh

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Fungi are the only kingdom of life not represented in the plankton. Bacteria have only recently been demonstrated to exist in great abundance as our sampling gear has improved enough to capture these...