Rocky Intertidal Ecology

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Rocky Intertidal Ecology

• Rocky - hard substrate
• Intertidal - area between high tide and low tide
  marks
• Ecology - the study of the interactions that
  determine the distribution and abundance of
  organisms
• Interactions can be between organisms or
  between organisms and their environment

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Intertidal zone

• This area is is exposed to the air usually twice
  a day as the tides ebb and flood
• Tides create a partly aquatic and partly aerial
  environment
• Locally the tidal range is about 3 meters
• Rocky, sand, estuaries, mangroves, coral reefs,
  etc.
• Patterns are similar worldwide

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Vertical zonation

• Banding pattern on the rocky shore as a result of
  the rise and fall of the tides
• The distribution of organisms is in horizontal
  bands
• Upper, middle and low zones
• Caused by differing tolerances of organisms to
  stresses, both biotic and abiotic
• Examples?

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Limits of organisms

• Upper limits are set by abiotic factors such as
  desiccation, temperature, salinity, food and
  oxygen availability, light
• Lower limits are set by biotic factors such as
  competition, predation, herbivory

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Abiotic factors

• 1. Desiccation water loss drying out
• Occurs at low tide due to air exposure
• Can increase with wind
• Some species are more tolerant to being in the
  air (e.g. limpets, Fucus, Porphyra) and can live
  higher in the intertidal zone
• Adaptations
• - close up e.g. barnacles, mussels
• - lose water then rehydrate e.g. Fucus

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2. Temperature

• Water temperature varies only slightly over the
  year (7-12oC)
• Air temperature, however, can vary drastically
  (0-30oC)
• Organisms out of the water are subject to greater
  variations in temperature
• Adaptations
• Evaporative cooling by mussels
• Eurythermal enzymes

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3. Salinity

• Salinity can increase with evaporation or
  decrease with fresh water input (e.g. rain)
• Euryhaline - tolerant to wide variations in
  salinity e.g. mussels, barnacles
• Stenohaline - can only tolerate a narrow range of
  salinities e.g. sea stars
• Adaptations
• Close up e.g. barnacles, mussels
• Ion pumps e.g. crabs

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4. Food oxygen availability

• Many marine organisms get their food from the
  water (as plankton!) they can only feed when
  underwater
• Also, many marine organisms obtain oxygen from
  the water
• Organisms living high in the intertidal zone have
  a limited time in which they can feed and acquire
  oxygen
• Adaptations
• - scaleless fish e.g. clingfish
• - feed whole time they are underwater

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5. UV light

• Marine organisms can get sunburns too
• Especially when out of the water
• Adaptations
• Sun screen - natural compounds that absorb UV
• Protective shell

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Biotic factors

• Competition use or defense of a resource that
  reduces its availability to other individuals
• Interference - direct interaction
• Exploitative - differential use of resource
• Interspecific - between species
• Intraspecific - between individuals of the same
  species

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2. Predation

• Animals eating other animals
• Predators can be generalists (eat a wide range of
  food) or specialists (eat a single prey type)
• Refuges from predation
• Size e.g. some mussels are too big to be eaten by
  Pisaster
• Space e.g. limpets living on vertical surfaces to
  avoid predation by birds
• Height in the intertidal e.g. Pisaster / mussel
  interactions (Paine experiments)

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3. Herbivory

• Animals eating plants
• Similar to predation interactions
• Refuges from herbivory
• Chemical defenses e.g. sulphuric acid in
  Desmarestia, bromine in Prionitis
• Physical defenses e.g. calcium carbonate in
  coralline algae
• Height in the intertidal e.g. Ulva and Porphyra
  live very high to avoid being eaten

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A reminder

• Upper limits are set by abiotic factors such as
  desiccation, temperature, salinity, food and
  oxygen availability, light
• Lower limits are set by biotic factors such as
  competition, predation, herbivory