Intertidal Zonation on the Rocky Shore

Introduction to the Intertidal Zone

• The intertidal zone is an area on the seashore.
  • Exposed and above sea level at low tide.
  • Underwater during high tide.
• Varies greatly depending on habitat (sandy beach, mangrove swamp, rocky shore).

Features of the Rocky Shore

• Solid surface for attachment of organisms.
• Experiences horizontal zonation due to physical and biological stresses.

Zonation on the Rocky Shore

• Divided into four general zones:
  1. Spray Zone
  2. Upper Intertidal Zone
  3. Middle Intertidal Zone
  4. Lower Intertidal Zone
• Below the lower intertidal zone is the sub-tidal zone.

Determining Limits for Organisms

• Upper limit: Determined by physical stresses (e.g., desiccation, temperature fluctuations).
• Lower limit: Determined by biological factors (e.g., predation, competition).

Spray Zone (Supra-littoral Zone)

• Highest zone where marine organisms are found.
• Mostly dry; wetted by wave splash.
• Sparse organisms due to physical stresses (air exposure, desiccation).
• Common organisms: Barnacles, limpets, periwinkles (all have protective coverings).

Upper Intertidal Zone

• Covered by water only during high tides.
• Subject to high levels of biological and physical stress.
• More diverse than spray zone; higher competition and predation.
• Common organisms: Barnacles (dominant, adapted to physical elements), periwinkles, limpets, chitons, shore crabs, marine snails, and green algae.

Middle Intertidal Zone

• Regularly covered by water; submerged twice daily.
• More diverse than the upper intertidal zone, with increased biological stress.
• Physical stresses (desiccation, air exposure) reduced due to less exposure time.
• Adaptations for strong attachment due to wave action.
• Common organisms: Barnacles, sponges, algae, mussels, sea stars, sea anemones, shore crabs, and gastropods.
• Interactions:
  • Barnacles found higher up due to mussel presence limiting their lower range.

Lower Intertidal Zone

• Usually submerged, exposed only at very low tides.
• High diversity with minimal physical stress.
• Dominant biological stresses are competition and predation.
• Presence of brown algae, encrusting sponges, shore crabs, sea urchins, gastropods, sea cucumbers, abalone, and small fish.

Sub-tidal Zone

• Rarely exposed.
• Habitat for predator species like octopus and larger fish that prey on lower intertidal organisms.

Conclusion

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