Zones of the Sea As you go through this presentation you will notice that some words, phrases or sentences are in bold, italicized, and underlined type. These are words or concepts which you are responsible for knowing and understanding.

The oceans can be studied according to different depths, temperatures, proximity to land, latitudes and in many other ways. No one way is the right way.

The ocean by depth. Shallow water over the “continental shelf” which is really just a submerged part of a continent. This region is often teeming with life since the waters are usually warm and sunlight can penetrate through most or all of the water. If light can penetrate, algae and other forms of plant life can grow in abundance. Since these organisms are at the bottom of the food chain (web), they provide the basis upon which all other sea life depends.

Once past the continental shelf, the depth increases sharply along the steep continental slope. Depth quickly increases to about 8 to 10 thousand feet on average. The bottom of the ocean is a flat region called the abyssal plane. Since almost no light penetrates deeper than 500 ft. the bottom of the ocean in this region is absolutely dark. Many organisms that live here have evolved the ability to produce light. This is called bioluminescence.

In some regions sea floor crust may be subducting beneath the continental crust which is less dense. Where this is occurring the sea floor is dragged down forming a deep sea trench. Trenches can be many hundreds of miles long. They are the deepest places in the sea. Deep sea trenches are places where old sea floor is being recycled. It is dragged into the mantle where it melts. The deepest place in any ocean is the “Challenger Deep” which is located in the Mariana Trench off the coast of Japan. It is

,814 feet deep (about 7 miles)! In the 1870s a British ship, the HMS Challenger recorded this record depth by dropping weighted lines over the sides. To date there have been 2 manned and 2 unmanned descents to the bottom. The pressure here, created by the weight of the water above, is about 1100 times greater than normal atmospheric pressure. It would crush any military submarine in seconds.

Near the center of some oceans is a mid-ocean ridge. The mid-ocean ridge is a region of intense volcanic activity where new sea floor is being created.

The ocean can be classified into zones based on the amount of light that penetrates from the surface. The euphotic zone is where most sunlight penetrates. The depth varies according to the clarity of the water. If the water is very clear the euphotic zone might reach down to more than 500 ft. but where the water is murky light might penetrate no more than 50 ft. IMPORTANT: Don’t mistake ‘murky’ with ‘dirty’. Water is often clear because it contains no algae or plankton. Plankton are very small, even microscopic plants and animals that drift in the ocean. They form the basis of many food webs. If water contains a great deal of plankton it may appear murky, difficult to see through, but this is often a healthy sign that the waters are teeming with life.

The disphotic zone is often called the aphotic zone. It is dimly lit. So dimly that photosynthesis cannot take place. That means that all organisms living here directly or indirectly depend on nutrients from the photic zone to survive. Although the light is dim, most organisms living here have adapted so that they can hunt prey and/or avoid predators in low light. The disphotic zone extends from the end of the photic zone (which varies) to a depth of about 1000 feet down.

The aphotic zone is the region where no light penetrates. It is eternally dark. Depth varies but this zone usually begins at about 1000 ft and extends to the ocean floor. All life in this zone is dependent, directly or indirectly, on organic material drifting down from above. Many organisms have evolved bioluminescence, the ability to produce light.

In many cases the light is produced not by the fish, but by bacteria living inside the fish in specialized organs. This is an example of symbiosis in which the fish provide food and the bacteria provide light. Bioluminescence on Camera - YouTube

The LITTORAL zone The zone in the ocean that experiences the effects of the tides. It is the region of the sea between high and low tides. It is sometimes called the intertidal zone.

The littoral (intertidal) zone is immensely important because: It is home to countless species of organisms which are found nowhere else on the planet. Horseshoe crabs Fucus Fiddler crabs

Snails Sea anemones Mussels Clams

In addition to being home to thousands of different species, the littoral zone is often called “the nursery of the sea.” Why? Because so many organisms that spend most of their lives in the open ocean come into the littoral zone to spawn. Sea Turtle Pyjama shark Starfish

With so many animals spawning in the littoral zone it should be no surprise that many other creatures come there to eat the eggs that the spawning animals have deposited. Fish eggs Small fish (fry) Birds feeding on horseshoe crab eggs.

The value of geoduck has increased 500% in the last few years! Why?

There is a tremendous demand in China and these beauties are found only on the Northwest United States coastline.

The littoral zone provides the United States with Clams Oysters Mussels crabs Abelone Lobsters Scallops And MUCH more

Remember this for the test: The bonus word is: