Summary of Estuaries and Mangroves

Overview of Estuaries and Mangroves

• Definition of Estuaries: Semi-enclosed coastal waters where seawater is diluted by freshwater from land drainage (Pritchard, 1967).

• Types of Estuaries:

  • Coastal Plain: Flooded river valleys, <10,000 years old (e.g., Thames, Chesapeake Bay).
  • Tectonic: Formed by land subsiding (e.g., San Francisco Bay).
  • Semi-enclosed Bay: Sand bars/spits create brackish conditions (e.g., Great South Bay).
  • Fjord: Flooded glacial valleys with deep sides and shallow sills, may harbor anoxic basins.

• Living Conditions: Highly variable, stressful environment for organisms due to tide, salinity, currents, sediment, and temperature.

• Organism Adaptations: Physiological and behavioral adaptations to osmosis, burrowing, and migration.

• Mangroves Definition: Woody trees/shrubs thriving at tropical estuaries' land-sea interface, forming mangal habitats.

• Distribution: Generally found within 20°C isotherm, replaced by salt marshes at higher latitudes.

• Mangrove Types:

  • Riverine: Large areas in deltas, low tidal range
  • Tide-dominated: Intertidal with high wave action.
  • Basin: Landward of fringing mangroves with variable salinity.

• Adaptations of Mangroves: Special adaptations to waterlogged soil and salt, including knee roots (Bruguiera), aerial roots (Rhizophora), and pneumatophores (Avicennia).

• Mangrove Reproduction: Vivipary, where seedlings grow while still attached to parent plants.

• Ecological Importance:

  • Coastal protection from storms (e.g., Indian Ocean tsunami).
  • Contributions to marine productivity and carbon cycles.
  • Nursery grounds for coral reef fish, enhancing biodiversity.