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Differences Between Freshwater Organisms & Saltwater Organisms

Organisms have evolved and developed mechanisms that enable them to live in their ecosystem. The marine ecosystem and the freshwater ecosystem are both aquatic ecosystems. The main difference between the two is the level of salinity in the marine ecosystem in comparison to the freshwater ecosystem. The depth and scope of the marine ecosystem is also much broader than that of the freshwater ecosystem. Organisms that live in these aquatic ecosystems have adapted to survive in their environment.

  1. Collapsed Lungs

    • Most marine animals have adapted to survive underneath the water for prolonged periods of time. The level of pressure in huge bodies of water like oceans and seas is enormous. According to Marinebio.org, the level of pressure increases by 14.7 pounds per square inch for every 33 feet of water. Most freshwater organisms cannot survive at the depths that marine organisms can. Some of them, such as elephant seals and Weddell seals, have developed adaptations that allow them to dive as deep as 1 mile into the depths of the ocean. They have lungs that they can collapse as soon as they go into a steep dive.

    Blubber

    • Marine mammals such as seals, whales and manatees have developed adaptations that help them survive in the marine environment. The water in the marine environment can be exceedingly cold, and these mammals have to maintain a body temperature that is above that of the water they are swimming in. One of these adaptations is the development of a protective layer of fat known as "blubber." Blubber serves as a sort of insulator between the mammals and the cold water. Freshwater water mammals do not have this adaptation because it is not necessary. For example, sea otters do not have a lot of body fat. They depend on a thick covering of fur to keep them warm.

    Salt

    • Marine plants and animals have evolved to survive in the marine environment, despite the high salt content. Most marine organisms have specialized processes for filtering out the excess salt from their systems. They have highly adapted kidneys and gills that help them with the process of osmoregulation, which is the process of regulating the osmotic pressure on the fluids inside an organism. This regulation helps them combat any excess dilution or concentration of their bodily fluids. This same process goes for freshwater animals; they have to use osmoregulation to prevent their bodily fluids from becoming too diluted by excess water. Organisms that have adapted to high salinity include crocodiles. Unlike freshwater alligators, they prefer brackish and salty water bodies.

    Tides

    • Plants and animals that live in marine areas with strong tide, like estuaries, have adapted to live in such areas. Organisms like cockles have strong shells to resist the action of the flow and ebb of the tide. Barnacles and mussels have developed apparatus that enable them to cling to rock, protecting them from being washed out to sea. Freshwater and marine mussels have different characteristics; marine mussels have stronger shells and they also have the thread-like appendages with which they secure themselves to rocks.

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