Estuaries Study Notes

Estuaries: River mouths and associated banks/beds affected by tidal flow.
Bound by the river's mouth up to the furthest saltwater detection.
Distribution: Few in Namaqua and South Western Cape, more in Agulhas and Natal BGZ coastlines.
Urban development pressures: Cities/towns on banks of nearly all South African estuaries.

Turbulence and Wave Action:
- Gentle gradient, slow water flow, often with a sand bar at river mouth.
- Promotes sediment deposition (sand, silt, mud flats).
- Burrowing species thrive (prawns, crabs, mussels).
Salinity Levels:
- Fluctuates due to tidal movement and rain patterns.
- Salinity increases over time during low river discharge and evaporation.
- Euryhaline organisms adapt well to salinity changes.
Temperature and Desiccation:
- Extreme temperature fluctuations compared to ocean.
- Animals adapt by burrowing or creating water-filled areas.

High organic load from erosion and river vegetation.
Supports meiofaunal food chains and decomposition processes.
Sediments can become anoxic; adaptations for oxygen access include:
- Prawn and crab burrows, mussel siphons, blood worm structures.

Nurseries for juvenile fish (e.g., Kabeljou, Grunter, Steenbras) that rely on estuarine nutrients.
Habitat for migratory and permanent water birds; vital for food and breeding.