Thursday, December 8, 2011

The Intertidal Zone

An Inhospitable, Changing Environment:
Much 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.
sea star

  • 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.
  • Water Movement:The 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).
  • Temperature: The temperature ranges from the moderate temperature of the water to air temperatures that vary from below freezing to scorching.
  • 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. 
Vertical Zones:
knobbed whelkThe 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.
  • 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.
  • 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. sea anemone
  • 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.
  • 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 extreme 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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