Coastal Zones: Formation, Dynamics, and Communities

Posted on Dec 3, 2024 in Geology

The Coastline

The coastline is the land between the upper and lower limits of the coast and adjacent areas directly influenced by the sea. It’s the contact zone between land and sea.

The Coast as an Interface

In the littoral zone, four Earth subsystems interact:

Atmosphere

  • High moisture content, water particles, and salts.
  • Winds influence currents, waves, intertidal life, and geology.

Hydrosphere

  • Mainly marine waters.
  • Models geology and provides habitat for coastal life.

Geosphere

  • Determined by materials, lithology, and geological processes.
  • Affected by the atmosphere, hydrosphere, and living organisms.

Biosphere

  • Diverse biological community due to varied habitats.
  • Rich in resources and unique environmental features.

Coastal Zoning

Boundaries within the coastal strip are fuzzy and variable:

Supralittoral Zone

Between the high tide line and the limit of storm wave action. Terrestrial vegetation begins here.

Foreshore or Intertidal Zone

The coastal strip between the low and high tide lines.

Subtidal Zone

From the low tide line to the lower limit of wave action during calm periods.

Dynamic Wave Coast

Waves are the main agents of coastal erosion, sediment transport, and deposition:

  • Erosion: Occurs when waves hit rugged shores.
  • Transport: Waves carry materials of varying sizes (solution, suspension, saltation, and drag).
  • Deposition: Occurs mostly in low-slope areas like beaches, where waves lose strength and leave sediment.

Littoral drift is the movement of sediment by currents along the coast, parallel to the shoreline, influenced by prevailing winds.

Tides

Tides are less important for coastal morphology due to their lower strength but play a significant role in sediment transport in shallow waters.

Coastal Morphology

Refers to the shape and relief of the coast.

Cliffs

Result from continuous wave erosion and littoral drift on coastal salients. An abrasion platform or shore forms at the cliff’s base.

Beaches

Formed by the combined action of waves and longshore currents in low-energy coastal areas. Sedimentation occurs as waves deposit material on the shore.

Forms Associated with Beaches
  • Arrows: Formed when sand accumulates on a coastal projection.
  • Coastal Bars: Similar to arrows but isolated from the coast.
  • Tómbolos: Coastal arrows connecting to a nearby island, forming a peninsula.
  • Albuferas: Lagoons formed when an arrow closes off a cove.

Rias and Fjords

Large sea inlets creating indented coastlines.

  • Estuaries: Ancient river valleys flooded by sea-level rise or tectonic subsidence.
  • Fjords: Glacial valleys flooded by the sea, with U-shaped walls and steep slopes.

Deltas and Estuaries

Formations caused by river and coastal dynamics, where rivers meet the sea.

  • Deltas: Formed when rivers deposit large amounts of sediment in areas with weak currents.
  • Estuaries: Formed at river mouths with strong currents and significant tidal ranges.

Coastal Communities

Coastal Land Community

People and species living in the supralittoral zone and above, composed of terrestrial species.

  • Terrestrial Plants: Halophilic species tolerant of high salt concentrations.
  • Terrestrial Animal Communities: Many vertebrates, especially birds, adapted to coastal environments.
    • Terrestrial Invertebrates: Mainly insects.
    • Terrestrial Vertebrates: All vertebrate classes except fish.

Landlocked Marine Community

Organisms living in the intertidal and subtidal zones, directly interacting with water.

  • Pelagic: Organisms floating on or near the surface (e.g., plankton).
  • Benthic: Organisms living on the seabed (e.g., algae, corals, gastropods, bivalves, echinoderms).
  • Nektonic: Organisms swimming freely (e.g., fish, cephalopods, marine mammals).

Plankton

Pelagic organisms, mostly microscopic, floating in the water column.

  • Phytoplankton: Microscopic photoautotrophs living near the surface.
  • Zooplankton: Microscopic heterotrophs.

Marine Plant Community

Macroscopic algae and benthic multicellular organisms.

  • Intertidal Zone: Green and brown algae in rocky areas.
  • Subtidal Zone: Abundant green, brown, and red algae, especially on rocky bottoms.

Planktonic and Marine Animal Community

Includes benthos, nekton, and some pelagic organisms. High faunal diversity due to abundant resources.

  • Invertebrates: Dominant in both intertidal and subtidal zones.
  • Vertebrates: Mostly fish, abundant and diverse.