The Open Ocean

Source: Food and Agriculture Organization of the United Nations, 2013, Caroline Hattam, Plymouth Marine Laboratory,   "The Youth Guide to Biodiversity" 1st Edition (Chapter 8) Youth and United Nations Global Alliance. Reproduced with permission.

Chapter 8. Verbatim.

Diatoms.

© C. Widdicombe/PML

The Open Ocean Contains Small Populations Of Very Many Different Species

The open ocean has few nutrients available, so despite its enormous size, it is not home to dense populations of organisms, but the diversity of these organisms is very high. Here you find trillions of small single cell organisms known as phytoplankton (e.g. diatoms, dinoflagellates and coccolithophores) and larger zooplankton (e.g. copeopods and foraminifera). You also find many kinds of fish and whales.

Only a very small amount of light passes below 100 to 200 m, and no light reaches beyond 500 to 1000 m. This environment far below the surface is very stable, cold and dark. Many of the organisms that live in this part of the ocean have evolved special adaptations that help them to survive in this environment. For example, some organisms swim up to the upper zones of the oceans to feed at night. Others have developed special body parts called photophores which are bioluminescent (they produce light). Some fish have developed enormous mouths with very sharp teeth and their jaws can be unhinged to catch big prey.

Diatoms.

© E. Fileman/PML

Dinoflagellates.

© C. Widdicombe/PML

Coccolithophores.

© PML

Copeopod.

© PML

The Sea Bed Provides An Important Habitat For Marine Life

We know much more about the creatures that live on the sea bed than we do about some of those that live in the water, mostly because the bottom-dwellers don’t move very quickly and are easier to catch! In shallow, light areas, it is possible to find marine plants (e.g. seagrasses) and algae (or seaweeds) which look like plants but actually are not very closely related. In and on the seabed you can also find starfish, sea urchins, polychaete worms, sea cucumbers, anemones, sponges, corals and shelled animals such as clams, mussels and scallops… the list is almost endless.