An adequate and clean supply of fresh water is vital to our survival and to Earth’s ecosystems, but recall that fresh water makes up only 2,5% of our planet’s water. Fully 97,5% is salt water, comprising the oceans that cover 71% of our planet’s surface. The oceans influence global climate, teem with biodiversity, facilitate transportation and commerce, and provide us many resources.

The world’s five major oceans – Pacific, Atlantic, Indian, Artic, and Antartic – are all connected, comprising a single vast body of water. Ocean water is salty primarily becase rivers and winds carry sediments and sals from the continents into the ocean. Evaporation then removes pure water, leaving a higher concentration of salts. If we were able to evporate all the water from the ocean, the world’s ocean basins would be covered with a layer of dried salt 63m (207 ft) thick.

Surface waters of the oceans are warmer than subsurface waters because the sun heat them and because warmer water is less dense. Deepbelow the surface, water is dense and sluggish, unaffected by winds and storms, sunlight, and daily temperature fluctuations. Ocen water moves in currents, vast riverlike flows that move in the upper 400m of water, horizontally and for great distances. Wind, solar heating and coling, gravity, density differences, and the Coriolis effect drive the global system of ocean currents. hese lon lasting patterns influence global climate, El Niño andLa Niña events, and navigation and human history.

Marine and coastal ecosystems are diverse. Their variation in topography, temperature, salinity, nutriens, and sunlight, marine and coastal environments feature  variety ofecosystems:

  • Near-surface pelagic ecosystem – areas oft he open ocean where the photosynthetic productivity is concentrated near the suface in regions o nutrient-rich upwelling. Phytoplankton constitute the base of the marine food chain. Pedators at higher trophic levels include larger fish, sea turtles, shraks, and seabirds.
  • Deep ocean – little-known, the deep ocean’s animals have adapted to deal with extreme water pressures and to live in th dark without food from photosynthesizers. Some of these bizarre-looking creatures scavenge carcasses or detritus that fall from above.

 

  • Kelp forets - large brown algae, or kelp, grow from the floor of continental shelves, reaching toward the sunlit surface for up to 60m  (200 ft) in height.  Dense stands of kelp form underwater forests in many temperate waters. Kelp forests supply shelter an food for invertebrates and fish, which in turn provide food for predators such as seals, sharks, and seaotters. Kelp forests also absorb wave energy and protect shorelines from erosion. People derive alginates from kelp, which serve as thickeners in a wide range of consumer prducts, from cosmetics to foods to pains to paper to soaps.

  • Coral reefs - is an underwater outcrop of calcium carbonate composed of the skeletons o tiny marine aimals known as corals. Corals attach to rock of existing reef nd capture passing food with stinging tentacles. They also derive nouishment from symbiotic algae, known as zooxanthellae, that inhabit their bodies and produce food through photosynthesis. Most corals are colonial, and the colorful surface of  coral reef consists of thousands of millions of densely packed individuals. As corals die, their skeletons remain part o the reef while new corals grow atop them, increasing the reef’s size. They absorb wave energy, protect shorelines, and host as much biodiversity as any other type of ecosysem. The likely rason is that coral reefs provide complex physical structure in shallow nearshore waters, which are regions of high primary productivity. Besides the staggering diversity of anemones, sponges, hydroids, tubeworms, and other sessile invertebrates, innumerable molluscs, crustaceans, flatworms, seastars, and urchins patrol the reefs, and thousans of fish species fnd food and shelter in reefnooks and crannies. Larger predators, such as grouper and mora eels, feed on the smaller fish.

  • Intertidal zones – where he ocean meets the land, intertidal, or littoral, eosystems extend between the farthest reaches of the high and low tides, which are the periodic rising and falling of the ocean’s heigh at a given location, caused  by the graviational pullof the moon and sun. Intertidal organisms spend part of each day submerged in water, part of the day exposed to the air and sun, and part of the day being lashed by waves. Sessile nimals such as anemones, mussels, and barnacles live attached t rocks, filter-feeding on plankton in the water that washes over them.

 

 

 

 

 

 

  • Salt marshes – along many of the world’s coaslines at temperate latitudes, salt marshes occur where the tides wash over gently sloping sandy or silty substrates. Rising and falling tides fow into and out of channels, and at highest tide, water spills over onto elevated marsh flats. Marsh flats grow thick with rushes, shrubs, and grasses. Salt marshes boast very high primary poductivity and provide critical habitat for shorebirds, waterfowl, and the adults and young of many commercially important fish and shellfih species.

  • Mangroe forests – in tropical and subtropical latitudes, mangroveforests occur along sandy and silty coasts. Mangroves are trees with odd rots, some of which curve upward like snorkels to attain oxygen lacking in the mud, and some of which curve downward, serving as silts to support the tree in changing water levels. Fish, shelfish, crabs, snakes, and other organisms thrive amont the root network, and bird feed and nest in the foliage of these coastal forests. Mangroves protect coastlines; studies fter the 2004 South Asian tsunami indicated that coasts wth intact mangrove forests suffered less damage than deforested coasts.

  • Estuaries - many salt marshes and mangrove forests occur in or near estuaries, water bodies where river flow in the ocean, mixing fresh water with salt water. Biologically productive ecosystems, estuaries experience significant fluctuations in salinity as tital currents and freshwater runoff vary daily and seasonally. For shorebirds and for many commercially important shellfish species, estuaries provide critical habitat.

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