Life on the Ocean

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Life on the Ocean

• Chapter 13

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• The marine environment is a hard ecosystem to
  study for several reasons
• it's hard to get to
• cruise down in a deep-sea submersible
• Are expensive to build, and to operate.

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• it's hard to get your samples back to the lab in
  one piece
• Animals are built to withstand the huge pressures
  of great water depths,
• When they are brought to the surface they blow
  up.
• The whole system is permeated with hydrogen
  sulfide, which is the smell of rotten eggs

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• We can define each part of the ocean on the basis
  of the following characteristics
• temperature
• amount of light
• currents
• salinity
• nutrient supply
• water depth
• nature of the sediment on the bottom

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TEMPERATURE

• The most important, for all organisms, not just
  the coral.
• Most oceanic organisms are cold-blooded
  (poikilothermic).
• they cannot regulate their internal temp.
• Their body temperature is near the temperature of
  the water they live in.
• Animals that can maintain a warmer-than-surroundin
  gs internal temperature are homeothermic.

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• Only organisms that left the sea for land or
  freshwater and returned to the sea are
  homeothermic
• Marine mammals
• Big fish like marlin, tuna, and tarpon are
  homeothermic.

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METABOLISM

• The process by which all organisms extract energy
  from food, is a chemical reaction that is
  strongly influenced by temperature.
• The warmer the temperature, the faster metabolism
  will be.
• Organisms that normally live in cooler waters may
  burn themselves up if taken to warmer water.

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• And organisms that normally live in warm waters
  won't have enough energy to power their vital
  organs, like the brain and heart, if they move to
  cooler waters.
• Organisms living in warmer waters tend to grow
  faster, have a faster heartbeat, reproduce more
  rapidly, swim more swiftly, and live shorter
  lives than those living in cooler waters.

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• Remember, AMOUNT OF DISSOLVED GAS in the ocean
  is also determined by temperature.
• Fast swimmers such as salmon, trout, and pike
  need to live in cold waters because their oxygen
  demand is high.

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AMOUNT OF LIGHT

• Determines how productive plants can be.
• determined by water depth and water turbidity
  (how much sediment is suspended in the water).
• Light is composed of different colors and most
  light penetrates only about 100 m into the water,
  
• less if there is much suspended sediment in the
  water
• Blue light can penetrate deepest, to about 450 m.

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• Green light can penetrate to about 300 m water
  depth, but plants do not use green light-they
  reflect green light.
• This is why plants look green to us.

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• The depth to which light can penetrate defines an
  important area to plants the PHOTIC ZONE.
• Plants have enough light to photosynthesize in
  the photic zone.
• They can't photosynthesize in deeper water.

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CURRENTS

• determines how successful filter-feeders can be.
• They need some current to bring food particles
  their way, but not so much current that it just
  blows the food past.
• Currents can drag plankton along to colder or
  warmer waters than the plankton prefer.

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  SALINITY

• We are all composed of cells that are surrounded
  by a membrane.
• That membrane can allow water to pass through it
  readily, but not salt.
• An organism's body fluids must be the same
  salinity as seawater, or the organism needs to
  exert energy to either keep water in its body, or
  keep water out.

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• The process whereby water moves across the
  membrane but salt doesn't is called OSMOSIS (fig.
  13.15-16)

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• If an organism is less salty than seawater, water
  from the organism's body moves out (to increase
  its salinity).
• The organism will dehydrate if it doesn't
  actively drink water and get rid of excess salt
  that comes from drinking seawater.

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• If an organism is more salty than seawater, water
  from the ocean moves into the organism's body and
  it blows up.
• For higher marine organisms, such as the
  arthropods and chordates, the problem is the
  former we are slightly less salty than seawater.

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A marine fish

• Its salinity is only 18 parts per thousand.
• It loses water by osmosis to increase its
  salinity, but gains it by drinking.
• However, seawater is too salty for it, so it
  secretes salt via the gills, and produces hardly
  any urine.

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A fresh water fish

• Its salinity is higher than the environment.
• It gains water by osmosis decreasing its
  salinity, avoids drinking water.
• However, fresh water moves in, so it produces
  copious urine.

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NUTRIENT SUPPLY

• Determines how abundant life can be.
• include organic compounds such as proteins,
  vitamins, and inorganic compounds, called
  'minerals', such as calcium, magnesium, selenium,
  etc.
• Nutrients for plants are all inorganic and
  include nitrogen, phosphorus, potassium, and a
  host of others.
• The nutrient supply to plants is the more
  important. Without plants, there can be no
  nutrients for the animals.

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• Nutrients for plants come from one of two places
  
• runoff from continents products of chemical
  weathering.
• upwelling from the sea floor.

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• Where upwelling occurs?
• divergent ocean currents
• eastern boundary currents

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  WATER DEPTH

• determines the amount of pressure an organism
  experiences and the amount of light it has.
• Water depth defines ocean provinces.
• A province is an area where we expect to find
  similar plants and animals, depending on other
  environmental factors (temperature, current,
  salinity, nutrient supply)(f.13.19)

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• Provinces have different names depending on
  whether we are considering benthonic organisms or
  nektonic and planktonic organisms.

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• Pelagic Provinces
• (nekton, plankton)
• Benthic Provinces
• epipelagic 0-200 m
• littoral intertidal (foreshore)
• mesopelagic 200-1000 m

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• sublittoral 0-200 m (continental shelf)
• bathypelagic 1000-4000 m
• bathyal 200-4000 m (continental slope and rise
  mid-ocean ridges)

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• abyssopelagic 4000-6000 m
• abyssal 4000-6000 m (abyssal plains)
• hadalpelagic gt6,000 m
• hadal gt6,000 m (trenches)

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• Most plankton live in the epipelagic, photic
  zone.
• Most light penetrates into the epipelagic and
  littoral to sublittoral zones.
• Some whales and giant squid live in the
  mesopelagic and even into the top of the
  bathypelagic province.
• We still have so much to learn about life in the
  meso-, bathy- and abyssopelagic realms!

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Nature of the bottom

• sediment (sandy, muddy, carbonate), or rocky.
  Particularly important to the benthos.
• All of the physical factors interplay.
• If the sun warms up water at the equator, water
  may evaporate from the ocean and raise the
  salinity.

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• Dissolved oxygen levels will go down, but plant
  growth will speed up which can raise oxygen
  levels back up during the day, but drive them
  down again at night.

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• All the physical factors together make up a
  province.
• Each province of the ocean then has a unique set
  of plants and animals that are adapted to that
  province.
• The set of plants and animals is a community.
• A community is all of the organisms living in the
  same environment (province) and interacting with
  one another.

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• In the ocean, we see that animals and plants fit
  into one of four basic lifestyles
• planktonic
• nektonic
• nekto-benthonic
• benthonic

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• Each community has its share of plankton, nekton,
  and benthos.
• The really defining members of most communities
  would be the BENTHOS because some nektonic
  organisms can swim into an area and swim out of
  it again.

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• So a particular community exists because it
  shares the following characteristics
• physical characteristics of the water
• temperature
• amount of light
• vigor of the currents
• salinity
• nutrient supply
• water depth
• characteristics of the sea floor the benthos live
  on or in (sandy, muddy, rocky, carbonate) and
• the types of animals and plants within each.