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THE OCEAN ENVIRONMENT

Two-thirds of the surface of the Earth is covered by the oceans. Life on the Earth is shaped by these bodies of salt water. They have a major influence on our climate and weather. The masses of unexplored oceans support a great diversity of life and any changes in our oceans, even ever so slight, can affect ecosystems in water as well as on land.
 
Today, only about 5% of the Earth's ocean volume remains almost totally unaffected by human intervention. Through a joint venture with the National Geographic Society, these areas are being designated as Exclusive Economic Zones (EEZs). One EEZ recently established as such a marine reserve is an area extending 200 nautical miles from Pitcairn Island's coastline (Pitcairn is the island where Fletcher Christian and his crew landed following their mutiny on the ship HMS Bounty in 1790).
 
Our oceans consist of four zones: (1) the Intertidal Zone (areas which experience tides) such as flats, marshes, estuaries, swamps and coastlines; (2) the Continental Shelf, with depths down to about 650 feet; (3) the Continental Slope, with depths down to about 3,500 feet; and (4) the ocean bottom, about 7 miles below the surface.

Animals that live in the marine environment of the ocean are very different from those that live on the land. Marine animals must be able to withstand these conditions in order to survive and reproduce. What conditions present a challenge to a marine animal, and in particular, to the marine mammal called the Bottlenose Dolphin?
 

Salinity

The oceans in which the Bottlenose lives are marine; that is they are filled with, among other things, a number of salts. Salts cause the world’s oceans to be 800 times denser than air. The ocean’s salts must be at a rather specific concentration for the animals that live in it, including the dolphin. A basic scientific principle (called "diffusion") requires molecules to move from more concentrated areas to less concentrated areas. In other words, they try to make both areas equal in concentration. When diffusion forces these concentrated molecules up against a semi-permeable membrane and to pass through that membrane in order to make both sides equal in concentration, it is called "osmosis". If the ocean was too salty, water in the dolphin’s body would tend to move outward from the skin in an “attempt” to bring the ocean’s salt concentration down, dehydrating the dolphin. If the ocean wasn’t salty enough, water would tend to move into the animal through the skin, attempting to make the ocean’s salt more concentrated, making the dolphin’s body bloat. Salt water also affects the tendency of a body to sink or float in it. The more salt in the ocean environment (and, thus, the more dense it is), the more the animal tends to float. The less salt, the more likely the animal would tend to sink in the water. Floating in salt water aids the dolphin, as floating while swimming requires less energy. Sinking in a less salty environment would require the animal to expend energy both to stay afloat and to move forward. Animals which float in the dense salt water environment are able to pump blood throughout their body more easily than land animals. This is because the heart does not have the strong gravitational forces of land to deal with in an ocean-floating body. Additionally, molecules of salts dissolved in the ocean water provide for better conduction of sound. Sound is transmitted much easier and for longer distances in a salty environment than in a body of fresh water. Sound travels 4.5 times faster in salt water than in air. Finally, dense water tends to keep small objects suspended within it, providing nutrients for fish, squid and crustaceans on which the dolphin feeds. Such fish, squid and crustaceans may even swim near the dolphin, requiring less effort to hunt its meals.

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Temperature

The Earth’s oceans range in temperature from about 28 degrees to 105 degrees F. Being a mammal, the dolphin is warm-blooded, requiring it to keep a constant body temperature. Ocean temperatures change less from day to day than do temperatures on land. This feature requires less energy be expended by the dolphin to maintain its body temperature. An ocean’s temperature is able to remain more stable because if the water warms, molecules evaporate from the surface, leaving cooler areas of water. Additionally, the movement of water within the ocean allows cooler waters from below to mix with the warmer surface waters, maintaining a more stable temperature. Of course, if the dolphin needs to, it can just swim to an area within the ocean with a more desirable temperature.

Pressure

Water, like all other matter, has weight. The deeper the dolphin dives, the more water is weighing on its body, creating greater pressure on the animal. Marine animals like the dolphin must be able to adapt to various water pressures associated with diving to various depths in the ocean.

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Light

Sunlight can penetrate only through the upper levels of the ocean. Although the limit of visibility in the ocean is typically only about 100 feet, animals like the bottlenose which live in these lighted upper levels need to be camouflaged so as not to be seen easily by their predators. Just below these lighted upper levels the ocean provides a dark environment in which vision is often very limited. The dolphin must rely on other methods to “see” in its environment in order to hunt, avoid predators, communicate, and navigate.

 

Viscosity

Fluids have a thickness, or viscosity about them. The viscosity of the ocean is 800 times greater than the viscosity of air. Thus, the thickness of the ocean's salt water provides friction or drag on the dolphin as it passes through it. This friction or drag must be overcome, or at least minimized, in order to conserve its vital energy stores.

Other Factors

Other factors associated with life in the ocean such as parasites present in the water, predators of the dolphin, pollution, boat strikes that injure dolphins, intentional capture of dolphins, maternal abandonment, diseases, and unintentional capture due to poor fishing practices affect the world's dolphin populations.

Environmental Change

Climate change threatens life on our planet. Melting of polar sea ice is causing sea temperatures and water levels to rise. This, in turn, affects the numbers and type of prey available to dolphins and affects their migratory pattern and range. The ability of dolphins to breed successfully may eventually be affected by these changes. Much of our current climatic change is being caused by the increase in gasses produced by man's activities. These are called "greenhouse gasses" because of their ability (like a greenhouse) to allow the sun's heat to enter our atmosphere, and then trap it from leaving.

Another human activity that affects dolphins is that which produces unnatural sound under water. Dolphins use sound they produce to find food, attract mates, avoid predation, navigate, and communicate with other dolphins. They must do this in an environment where there are significant natural sounds such as those coming from wave action, other marine mammals (such as whales), thunder storms and earthquakes. Sounds produced by man make it more difficult for dolphins to function. These manmade sounds include those coming from ships, fuel research and exploration equipment, military activity (such as sonar and explosions), construction and dredging. Such sounds may change the dolphin's migration patterns, breeding, feeding and communication. They may also mask the natural sounds the dolphin needs to hear to perform its daily functions. Perhaps unnatural sound may be one of the causes of stranding, a phenomenon discussed in the "stranding" section of this site.

Finally, marine debris can injure and kill dolphins. It may pollute the water, concentrate in the animal's blubber and be transferred to its young through the mother's milk. Solid liter may be swallowed, choking the dolphin or may entangle the animal causing it to drown and strand.

The following excellent video provided by NOAA (the National Oceanic and Atmospheric Association) summarizes the threat of marine debris to the ocean's inhabitants. 

Site Content
 
Understanddolphins.com contains information condensed from a number of reputable technical sources, peer reviewed journal articles, and respected dolphin research facilities, as well as from my personal experiences and observations as a dolphin VIP Tour Guide and Educator.
 
I have made every attempt to support the information presented in this site with video and still photographic images. On a regular basis I plan to produce more of these images and will continue to update the site with these as well as with any new and scientifically verified information which becomes available.

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