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Benthic Communitites

1. Rocky shores - intertidal communities

  • Harsh environment: loss of water at low tide; physical forces of waves; variation in temperature; UV radiation; ice formation; variation in salinity (rain exposure)
  • Adaptation to life between water and air
    • Hard shells and solid attachement against wave action
    • High temperature and water-loss tolerance (60-90% of water in some algae)
    • Retreat into shells and housings at low tide to minimize water loss and exposure to grazers
    • Synchronized spawning
    • Cluster formation
  • Kelp forests: large brown algae, outside the 20°C isotherms, sublittoral down to 20-40 m depending on water clarity; Growth rates up to 50 cm per day; high primary production and habitat for numerous microalgae and animals

2. Sand Beaches
  • Wave action makes the beach best for infauna
  • Typically shallow slope: sand drains and dries slowly
  • Remember vertical oxygen gradient in sands and muds with hydrogen sulfide (H2S) at deeper layers! Slow draining of sand causes little water and oxygen exchange at depth

  • Primary production: microalgae (diatoms), few macroalgae
  • Low diversity in macrofauna, but meiofauna most diverse, including the unique interstitial fauna

  • Examples for interstitial fauna
  • Vertebrate animals include flat fish, and birds are important grazers
  • Most infauna is mobile
  • Most infauna (98%) do not produce planktonic larvae
  • Often, only one to few eggs are produced, and often parents bread and take care of their offspring
3. Estuaries Where Land Meets Sea
  • An estuary is a coastal embayment isolated from open ocean conditions, whose waters are diluted by freshwater input from rivers. Estuaries are classified by their circulation patterns, and by the vertical distribution of salinity.
  • Salt wedge estuary: controlled by rate of river discharge in a thin layer above a salt wedge

  • Partially mixed estuary: strong surface river flow and strong inflow of seawater at the bottom

  • Well mixed estuary: strong tidal mixing and low river flow 

  • Fjord-type estuary: least mixed, weak tidal flows, stratification; fresh water at the surface, seawater enters slowly at depth. The bottom water in fjords may become stagnant and anoxic due to slow rate of replacement.