Soft Bottom Intertidal

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Soft Bottom Intertidal
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General Information

• Bottom consists of sediment instead of rock
• Unstable and constantly shift in response to
  tides, waves and currents
• No place for organisms to attach
• Most animals burrow into the bottom
• These organisms are referred to as infaunal
• Very few marine plants

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Physical limits for life

• Sediment grain size
• Whether it is clay, silt or sand
• Sediment sorting
• How much of each type of sediment is present
• Desiccation
• Sandy sediment dries out faster than clay or silt
• Not as big an issue as in a rock shore

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Oxygen Availability

• Since no light penetrates the sediment no
  photosynthesis takes place no oxygen is
  produced
• Sandy sediments are more porous than muddy
  sediments therefore, water associated with sandy
  sediments is mixed with water from the water
  column more efficiently and has a higher oxygen
  content
• Muddy or clay sediment is densely packed and does
  not exchange water so it becomes anoxic quickly
• Animals that live in this biome pump water into
  their burrows with siphons, some are very
  sluggish reducing the need for oxygen, and some
  have symbiotic bacteria

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Anoxic Waters

• Refers to those waters that have no oxygen
• Some have a rotten egg smell due to the presence
  of hydrogen sulfide produced by anaerobic
  bacteria
• Areas that have a lot of this bacteria have black
  sediment layer because the bacteria reduce iron

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Mobility

• Some mollusks burrow using their radula
• Heart urchins use their spines and tube feet to
  burrow
• Some animals eat their way through the sediment
  sea cucumbers and worms
• Some animals are so small they can squeeze
  between the grains in the sediment called
  meiofauna

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Feeding

• Detritus is the main food source
• Many organism eat the sediment extracting
  whatever nutrients they can
• Some organisms collect particles as they settle
  out of the water column
• These are considered suspension feeders
• Some carnivores burrow through the sediment
  looking for organisms that have burrowed in and
  then consume them
• Some fish come into the area at high tide an
  nibble on the exposed siphons

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Zonation

• Not as obvious as in the rocky shore area
• Sandy beaches have the most zonation of any soft
  bottom shore
• Water drains quickly from the high tide areas
  creating physical limits to life
• Upper beaches tend to be drier than lower beaches

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Upper Beach

• Dry
• Inhabited by beach hoppers, isopods, ghost crabs
  and fiddler crabs

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Lower Beaches

• Wet covered with water for a lot of the time
• Inhabited by polychaetes, clams and other
  organisms