Ecosystems of Oceans and Freshwater: Biological Diversity and Water

While it's strange to think about, the open ocean, which makes up about 70% of the planet, has one of the lowest biodiversities we see in an ecosystem! This is because, just like humans, organisms in the ocean need nutrients to grow. The oceans get these essential nutrients from water that has run off from land. So, the further away from land you get, the less diversity you see in the ocean! Another factor that contributes to the biodiversity of the open ocean is light. Light penetrates water in the ocean to about 200 meters, or 600 feet, a region known as the photic zone.

Coral reefs are one of the most diverse ecosystems on the planet. They provide structure for multiple species to hide in as well as crevices for laying eggs and for living in. Therefore, coral reefs provide a nursery ground for raising young.

The majority of organisms found on coral reefs are invertebrates, or animals that don't have a backbone. The list of invertebrates found on reefs is huge! Corals and sponges make up the largest group of invertebrates found on coral reefs; these are the organisms that make up the structure of the reef itself.

Unlike the open ocean and coral reefs, there are several environmental factors that influence the biodiversity of the intertidal zone, all of which are centered on a tidal cycle, or when the tide is in or out.

Just like the open ocean, light is very important to the biodiversity of a lake. Lakes also have a photic zone, but the depth to which this zone extends is more dependent on the depth of the lake than on anything else.

Rivers are a bit like the intertidal zone. Because they are constantly moving, organisms that live in them must either be able to swim well or attach to the bottom or sides of the riverbank. Again, we see the biodiversity of a river dependent upon the primary producers in the river. Fish are, of course, in rivers, as well as macrophytes, which are aquatic plants. As with lakes, you can find amphibians and reptiles in areas where the water moves slowly, and a number of mammals and birds depend upon rivers for feeding grounds.

Species that live in salt marshes and estuaries must endure one of the harshest and most variable habitats on the planet. The salinity in these habitats fluctuates from freshwater to saltwater, which can be problematic for most organisms. Therefore, the biodiversity in these habitats is fairly low for organisms that live in these habitats exclusively. These species typically include plants with special glands that excrete (or get rid of) excess salts, oysters, snails, crabs and small fish.

Biodiversity means 'many different forms of life.' This includes anything from the smallest phytoplankton, which you can't see with your naked eye, to seaweeds that are hundreds of feet long, to the largest mammals in the world, the whales.

Upon completing this lesson, you will be able to: