Oceans

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Oceans

• Ours is a water planet
• The ocean covers 71 percent of the surface area
  of the globe
• It constitutes over 90 percent of all habitable
  space on Earth
• Its total volume is around 300 million cubic
  miles
• And weighs approximately 1.3 million million
  million tons

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• Oceanographers divide the ocean into five broad
  zones according to how far down the sunlight
  penetrates

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• The epipelagic, or sunlit zone the top layer of
  the ocean where enough sunlight penetrates for
  plants to carry on photosynthesis
• The mesopelagic, or twilight zone a dim zone
  where some light penetrates, but not enough for
  plants to grow
• The bathypelagic, or midnight zone the deep
  ocean layer where no light penetrates

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• The abyssal zone the pitch-black bottom layer of
  the ocean the water here is almost freezing and
  its pressure is immense
• The hadal zone the waters found in the oceans
  deepest trenches

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• Intertidal area (also called the littoral zone)
  is where the land and sea meet, between the high
  and low tide zones. This complex marine ecosystem
  is found along coastlines worldwide. It is rich
  in nutrients and oxygen and is home to a variety
  of organisms.

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• An Inhospitable, Changing EnvironmentMuch of
  this inhospitable environment is washed by the
  tides each day, so organisms that live here are
  adapted to huge daily changes in moisture,
  temperature, turbulence (from the water), and
  salinity.

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• Moisture The littoral zone is covered with salt
  water at high tides, and it is exposed to the air
  at low tides the height of the tide exposes more
  or less land to this daily tide cycle. Organisms
  must be adapted to both very wet and very dry
  conditions.

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• Water MovementThe turbulence of the water is
  another reason that this area can be very
  difficult one in which to survive - the rough
  waves can dislodge or carry away poorly-adapted
  organisms. Many intertidal animals burrow into
  the sand (like clams), live under rocks, or
  attach themselves to rocks (like barnacles and
  mussels).

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• Temperature The temperature ranges from the
  moderate temperature of the water to air
  temperatures that vary from below freezing to
  scorching.

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• Salinity Depressions on the shores sometimes
  form tide pools, areas that remain wet, although
  they are not long-lasting features. The salinity
  of tidepools varies from the salinity of the sea
  to much less salty, when rainwater or runoff
  dilutes it. Animals must adapt their systems to
  these variations. Some fish, like sculpin and
  blennies, live in tide pools.

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Vertical Zones

• Vertical Zones The littoral zone is divided
  into vertical zones. The zones that are often
  used are the spray zone, high tide zone, middle
  tide zone, and low tide zone. Below these is the
  sub-tide zone, which is always underwater.

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• Spray Zone Also called the Upper Littoral, the
  Supralittoral Fringe, the Splash Zone, and the
  Barnacle Belt. This area is dry much of the time,
  but is sprayed with salt water during high tides.
  It is only flooded during storms and extremely
  high tides. Organisms in this sparse habitat
  include barnacles, isopods, lichens, lice,
  limpets, periwinkles, and whelks. Very little
  vegetation grows in this area.

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• High Tide Zone Also called the Upper
  Mid-littoral Zone and the high intertidal zone.
  This area is flooded only during high tide.
  Organisms in this area include anemones,
  barnacles, brittle stars, chitons, crabs, green
  algae, isopods, limpets, mussels, sea stars,
  snails, whelks and some marine vegetation.

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• Middle Tide Zone Also called the Lower
  Mid-littoral Zone. This turbulent area is covered
  and uncovered twice a day with salt water from
  the tides. Organisms in this area include
  anemones, barnacles, chitons, crabs, green algae,
  isopods, limpets, mussels, sea lettuce, sea
  palms, sea stars, snails, sponges, and whelks.

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• Low Tide Zone Also called the Lower Littoral
  Zone. This area is usually under water - it is
  only exposed when the tide is unusually low.
  Organisms in this zone are not well adapted to
  long periods of dryness or to exteme
  temperatures. Some of the organisms in this area
  are abalone, anemones, brown seaweed, chitons,
  crabs, green algae, hydroids, isopods, limpets,
  mussels, nudibranchs, sculpin, sea cucumber, sea
  lettuce, sea palms, sea stars, sea urchins,
  shrimp, snails, sponges, surf grass, tube worms,
  and whelks.

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Tides

• Tides are periodic rises and falls of large
  bodies of water. Tides are caused by the
  gravitational interaction between the Earth and
  the Moon. The gravitational attraction of the
  moon causes the oceans to bulge out in the
  direction of the moon. Another bulge occurs on
  the opposite side, since the Earth is also being
  pulled toward the moon (and away from the water
  on the far side). Since the earth is rotating
  while this is happening, two tides occur each
  day.

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Problem facing oceans

• Over fishing
• Pollution
• Coastal Habitat Destruction
• Climate change and global warming

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Fisheries reaching depletion

• According to the United Nations Food and
  Agriculture Organization (FAO), an estimated 70
  percent of global fish stocks are
  over-exploited, fully exploited, depleted
  or recovering from prior over-exploitation.
• By 1992, FAO had recorded 16 major fishery
  species whose global catch had declined by more
  than 50 percent over the previous three decades

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• The fishing of commercially exploited species is
  not just affecting population levels of the
  targeted species. In many cases, fishing and
  habitat destruction go hand in hand.
  Approximately three quarters of commercially
  exploited fish species inhabit, breed, or
  reproduce within coastal ecosystems. The bottom
  of the sea is teeming with diverse life, but is
  fragiletargeted species from the sea grass beds,
  coral reefs, and the ocean floor are extracted
  often at the expense of their environment.

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• As fishing technology has advanced, so have the
  destructive effects on fish populations and the
  marine ecosystems. Many industrial fishing
  operations use gear and fishing practices, such
  as bottom trawling and traps, which physically
  disturbs different marine habitats.

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Bottom trawling

• Bottom trawlers catch fish by dragging heavy nets
  along the ocean floor.

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Dredges

• Dredges drag large steel frames and chain bags
  over sand and mud, plowing through the seabed in
  search of sea urchins, oysters, and scallops. The
  effects of these methods have been compared by
  many scientists to forest clearcutting, but with
  a much greater areaapproximately 150 times as
  large as all clear-cut forests.

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By catch

• While fishers target only a few commercially
  valuable species, most fishing methods require
  the indiscriminate catch of non-commercial or
  unwanted species. These extras, which equal one
  third of the worlds catch or approximately 27
  million tons, are dumped back into the ocean,
  dead or dying.

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• Driftnets arbitrarily kill millions of marine
  animals, including dolphins, seals, turtles,
  seabirds, and other animals. Bycatch is the most
  serious threat faced by cetaceans, including
  whale, dolphins, and porpoises. Easily caught in
  purse seines, gillnets, and mid-water trawls,
  these creatures drown in the nets.

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Shrimp fishing

• Shrimp fishing is infamous for its deadly effects
  on incidental catch. For every pound of wild
  shrimp caught, an average of 8 pounds of bycatch
  is thrown back into the ocean. According to the
  FAO, approximately one-third of the world's 16
  billion pounds of bycatch is from shrimp fishing.
  The species most threatened by this bycatch
  include endangered sea turtles and finfish.

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Sustainable Fisheries Act

• The Sustainable Fisheries Act is responsible for
  programs related to maintaining healthy fish
  stocks important to commercial and recreational
  fisheries eliminating overfishing and rebuilding
  overfished stocks and, increasing long-term
  economic and social benefits to the nation from
  living marine resources

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Aquaculture

• A December 2000 storm resulted in the escape of
  100,000 salmon from a single farm in Maine, about
  1,000 times the number of  documented wild adult
  salmon in Maine
• A salmon farm of 200,000 fish releases an amount
  of nitrogen, phosphorus, and fecal matter roughly
  equivalent to the nutrient waste in the untreated
  sewage from 20,000, 25,000, and 65,000 people,
  respectively
• Over the past decade, nearly one million
  non-native Atlantic salmon have escaped from fish
  farms and established themselves in streams in
  the Pacific Northwest

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Pollution
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Oil

• The National Research Council has estimated that
  as many as 8.8 million tons of oil enter the
  ocean each year as a result of human activity,
  and that at any given time, the ocean contains
  280,000 tons of tar balls

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Plastic Pollution

• But when plastic reaches our waters, whether it
  be plastic bags or drifting fish nets, it poses a
  threat to the animals that depend on the oceans
  for food. To a sea turtle, a floating plastic bag
  looks like a jellyfish.

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• And plastic pellets--the small hard pieces of
  plastic from which plastic products are
  made--look like fish eggs to seabirds. Drifting
  nets entangle birds, fish and mammals, making it
  difficult, if not impossible to move or eat. As
  our consumption of plastic mounts, so too does
  the danger to marine life.

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Chemical pollutants

• Heavy metals and organochlorine compounds such
  as PCBs and DDT have been associated with a wide
  range of impacts on marine wildlife these
  compounds bioaccumulate
• Striped dolphins in the western North Pacific,
  have concentrations of PCBs and DDT more than 10
  million times higher that that of the water they
  live in

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Habitat Destruction

• Many ocean species rely on coastal habitats for
  breeding, feeding shelter one-third of the
  worlds marine fish species are found on coral
  reefs
• Other coastal habitats, such as mangroves and sea
  grasses, are also vital breeding, feeding and
  nursery areas for fish and shellfish species,
  home to a variety of wildlife species, and
  important protection and shelter against storms
  and coastal erosion

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• Ninety percent of the current world fisheries
  harvest comes from within 200 miles of the coast,
  and most of that within a strip of just five
  miles from the coast

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• The coastal zone is also home to the majority of
  the worlds population. As much as 66 percent of
  the worlds population lives within 40 miles of
  the shore, and coastal populations are growing
  faster than the global population as a whole

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Global warming

• The burning of vast amounts of coal, oil, and
  natural gas is increasing the amount of certain
  gases such as carbon dioxide (CO2) in the
  atmosphere and contributing to climate change.
  These gases are trapping heat inside the planet
  and temperatures gradually rising.

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• While corals are well adapted to their life in
  the tropics, they are not prepared for warmer
  temperatures, and they are falling victim to
  global warming. When it gets too hot the corals
  bleach, i.e. they turn a bright white color,
  which is a sign of sickness. If temperatures
  remain high for an extended period of time,
  corals will die.

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• Recently, as a result of record high
  temperatures, many corals throughout the world
  have died. Scientists are worried that if the
  worlds temperatures continue to rise, we will
  see many other corals sicken and die. And this
  might be worse in those places where the corals
  are already stressed.