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Marine Botany
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Monterey
Bay Flora
Methods PHYCOLOGICAL SOCIETY OF AMERICA |
Why do Animals Swim? A digressionMany people consider movement to be one of the essential features that separating animals from plants. In terrestrial environments, it is certainly true that most of the animals move about the landscape, and most of the plants stay put. The animals probably move to forage for food, to find a mate, and to escape from predators. Plants get their "nutrition" in a very different way, from sunlight and carbon dioxide in the air. Plants don't have to move very much to collect either of these. Terrestrial plants also have evolved special mechanisms to accomplish other tasks which land animals have to move to do. For example, plants have reproductive strategies which may include airborne pollen or a host of sophisticated mechanisms to attract mobile animals that assist with pollenation and seed dispersal. Plants can defend themselves against being eaten with body parts like wood that animals can't digest, spines and prickles, and poisons. In the ocean, our stereotypes about plants and animals break down. There are many rooted, immobile types of animals, and most plants float and drift in the currents. However, the floaters are in some ways not mobile, because they do not move relative to the water immediately surrounding them. In this situation, any plant or animal builds up a boundary layer, a layer of water around the cell or organism where nutrients or oxygen are depleted. If the organism can't swim to escape the boundary layer, and the boundary layer is never disrupted, it is as if the cell is living in a little desert. In the ocean, water motion serves to break up boundary layers near stationary species. Floating species have the real trouble, because no matter how much the water moves, the floater doesn't escape. That's one good reason why some pelagic (open-water-dwelling) animals swim. Plankton, or pure floaters, need other mechanisms get out of the desert and back into nutrient-rich waters. Photo Gallery
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