Intertidal Zone Notes

Intertidal Zonation

  • Definition: The intertidal zone is the region of shore between the highest high tide and the lowest low tide.

Tides

  • Height and Time relationship within intertidal zones.

Biotic Zonation

  • Organism distribution is controlled by physical conditions and biological interactions.
  • Physical Conditions: Determine the upper limit of organisms in each zone. "You can’t live outside of your environment."
  • Biological Interactions: Determine the lower limit of organisms in each zone. "You won’t last long where your predator lives."

Rocky Intertidal Biotic Zonation (California Coast)

  • Algae and other encrusting organisms indicate biotic zonation.
  • Zones:
    • Supratidal (Spray) Zone
    • Upper Intertidal Zone
    • Middle Intertidal Zone
    • Lower Intertidal Zone
    • Subtidal (Sublittoral) Zone

Physical Conditions

  • Waves: Bring nutrients and moisture; can detach organisms from the substrate.
  • Exposure Time: Desiccation affects tissue function.
  • Heat & Cold: Temperature changes are more extreme above water.
  • Substrate: Supports diverse communities with varying diversity and abundance.
  • Available Space: Organisms need a place to live; space is a contested resource.

Biological Interactions

  • Predation:
    • Examples: Terrestrial predators, sea stars eat mussels, sea otters eat sea urchins, sea urchins eat kelp.
  • Competition:
    • Space is the most contested resource due to the need for nutrients brought by seawater.
    • Some organisms live on top of others (encrusting).

Adaptation

  • Physiological and morphological ways to deal with physical challenges.

Intertidal Organisms & Adaptations

Common Intertidal Organisms and Their Adaptations

  • Factors: Temperature Variation, Salinity Variation, Time Exposed to Air, Competition, Amount of Sunlight
  • Impact of factors vary depending on intertidal zone.

Barnacles

  • Crustaceans related to crabs and lobsters (infraclass Cirripedia).
  • Exclusively marine, live in shallow and tidal waters, typically in erosive settings.
  • Sessile suspension feeders with two nektonic larval stages.
  • Adaptations against water loss:
    • Impermeable calcite shells.
    • Two plates that slide across apertures when not feeding (also protect against predation).

Periwinkle Snail

  • Found mainly on rocky shores in the upper and middle intertidal zone; sometimes in small tide pools.
  • Larger shell volume allows more water storage for desiccation resistance, allowing survival higher in the intertidal zone.
  • Defense Mechanism: When exposed to extreme cold or heat, withdraws into shell and rolls to potentially fall into the water.

Mussels

  • Live in intertidal areas attached to rocks and other hard substrates using strong byssal threads secreted by byssal glands in their foot.
  • Shells open when submerged to filter plankton.
  • Shells close during low tide to prevent dehydration.
  • Sea stars are major predators.

Limpets and Chitons

  • Limpets: Aquatic snails with a broadly conical shell and a strong, muscular foot.
  • Chitons: Shell composed of eight separate shell plates or valves that overlap and articulate.
  • Mobile grazers that feed on algae when submerged.
  • Clamp down (suction via foot) to avoid desiccation when exposed.

Crabs

  • Store water in gill chambers.
  • Move to concealed areas or into the water if necessary.
  • Examples: Fiddler crab, Sally Lightfoot crab, Hermit crab (not a true crab), Ghost crab.

Sea Anemones

  • Single polyps related to corals and jellyfish.
  • Feed using tentacles to paralyze and consume prey.
  • Close up tight when seawater recedes during low tide to prevent drying out.
  • Structures: Pedal disc (foot).

Starfish and Sea Urchins

  • Echinoderms (spiny-skinned).
  • Use tiny tube feet to attach to surfaces.
  • Starfish eat by covering prey with their stomach, digesting the food, then pulling the stomach back in.
  • Sea urchins have a round shell with spines for protection.
  • Mouth underneath; main food is brown seaweed.
  • Avoid desiccation by attaching to rocks or moving into tide pools.

Marine Macroalgae (Seaweeds)

  • Photoautotrophic
  • Aquatic
  • Eukaryotes
  • Unicellular or Multicellular
  • NOT plants (lack specialized tissues; e.g., blade \ne leaf, stipe \ne trunk, holdfast \ne roots).
  • Subdivided into green, brown, and red algae.

Green Algae (Chlorophyta)

  • Ancestor gave rise to terrestrial plants.
  • Closest relation to terrestrial plants.
  • Cell walls made of cellulose (like terrestrial plants).
  • Can overgrow and kill coral reefs.

Brown Algae (Phaeophyta)

  • Largest of all algal species (giant kelp can grow to hundreds of feet).
  • Largest component of “kelp forests” (contain ~800 distinct species).
  • Structurally most complex of all seaweeds.
  • Contain the pigment fucoxanthin, responsible for their distinctive greenish-brown color.

Red Algae (Rhodophyta)

  • Able to inhabit deep water environments.
  • Better at absorbing blue light, which penetrates deeper than other wavelengths.
  • “Coralline” species secrete CaCO3CaCO_3 skeletons.
  • Some encrust other algae.

Traditional Harvesting

  • Abalone are often poached in large quantities for commercial selling along the California Coast despite restrictions.
  • The Sherwood Valley Band of Pomo Indians have been harvesting abalone for generations.
  • Clam gardens in Kanish Bay, Quadra Island, British Columbia. Evidence for past clam gardens extend from Alaska all the way down to Washington State.