(14)_Rocky_intertidal

Rocky Intertidal Overview

• Course: Biol 3711, Winter 2025

Tides

• Definition: Gravitational pull exerted on water by the moon and the sun.

• Types of Tides:

  • Spring tides: Occur when the sun and moon are in line, leading to higher tidal ranges.

  • Neap tides: Occur when the sun is at a right angle to the moon, resulting in lower tidal ranges.

Tidal Height and Variability

• Tidal Height (cm): Shows ranges influenced by geographical factors.

• Graphical Representation:

  • Tidal variation displays significant increases and decreases over the tidal cycle.

Intertidal Communities

• Definition: Shoreline areas between the extreme high water spring (EHWS) and extreme low water spring (ELWS).

• Environment: Stressful due to physical factors including wind, waves, sunlight, and ice exposure.

• Nutrient-Rich Habitats: Productive for various species.

Rocky Shores

• Characteristics: Most densely inhabited intertidal shores.

• Dominant Organisms:

  • Solitary animals (e.g., mussels, barnacles, gastropods).

  • Clonal animals (e.g., anemones).

  • Seaweeds.

• Competition for Space: High due to limited habitat.

Vertical Zonation

• Definition: Dominance of distinct species in horizontal bands across rocky intertidal zones.

• Influence of Slope: Slope determines vertical extent of these zones.

• Zonation Examples:

  • Notable differences in zonation observed in various locations, such as Scotland and British Columbia.

Universal Zonation Scheme

• Categories Established by Stephenson & Stephenson (1949):

  • Supralittoral fringe: Dominated by littorine snails and lichens.

  • Midlittoral zone: Dominated by barnacles and mussels.

  • Infralittoral fringe: Dominated by Laminarians (brown seaweed).

Wave Exposure

• Definition: Affects different species assemblages and their vertical extent in both protected and waveswept areas.

• Characteristics of Exposed Shores:

  • Have high spray and wave impacts affecting organism survival.

  • Exhibits barnacle and mussel communities.

• Sheltered Shores:

  • Support different seaweed communities and alternative species interactions.

Life in the Rocky Intertidal

• Low Tide Challenges:

  • Heat stress, desiccation, and oxygen shortage.

  • Reduced feeding and reproductive opportunities for organisms.

Wave Shock Effects

• Impact on Organisms:

  • Damage through abrasion, pressure drag, and acceleration.

  • Tolerance to wave shock varies by size, structural strength, and bed formation.

Zonation Patterns

• Wave-exposed Open Coast:

  • Distinct zones of barnacles, mussels, and kelp.

• Protected Coast Zonation:

  • Integrates fucoid canopies, understories with mussels, barnacles, snail grazers, and predatorial interactions.

Factors Affecting Zonation

• Key Factors:

  1. Physiological tolerance.

  2. Larval and adult preferences.

  3. Competition.

  4. Predation and grazing.

Interspecific Competition

• Experimental Evidence:

  • Experiments confirm competition impacts species distribution.

  • Example: Chthamalus overgrown by Semibalanus when transplanted downward.

Competition Among Seaweeds

• Lower Intertidal Dominance:

  • Kelp species outcompete smaller opportunistic seaweeds in specified regions.

Predation and Competition

• Role of Predators:

  • Predation by Pisaster ochraceus can regulate competitive dominances, evident in prey interactions with Mytilus californianus.

Herbivory Effects

• Influence of Limpets (Lottia):

  • Overgrazing can lead to barren rock areas, inhibiting growth of algae and seaweeds by territorial behavior.

Small-scale Patchiness

• Causes of Patchiness:

  • Variables include algal frond action, grazing distribution, recruitment fluctuations, and refuge effects from rock structures.

Patchiness and Predator Refuges

• Refuge Locations:

  • Cracks and tidepools in higher intertidal zones provide shelter for predators.

  • Biological refuges created by mussel beds and seaweeds for carnivores/herbivores.

Mobile Predators and Larval Recruitment

• Recruitment Areas:

  • Mobile predators may aggregate at high larval recruitment sites, particularly noted for Pisaster ochraceus near mussel beds.

Disturbance and Succession

• Post-Disturbance Recovery:

  • Succession follows a predictable sequence after disturbances, starting with opportunistic species like Ulva and progressing to dominant slow-growing species.