Lecture 16: Intertidal Communities

• Physical factors of the intertidal zone: tides, wave and current action, air and sunlight exposure, salinity.
• Tide factors include duration of aerial exposure.
• Wave factors include wave shock and drag.
• Adaptations to wave shock: glue self to substrate, living in depressions, adhere to substrate, move with the tides, attachment to substrate.
• Organisms in the intertidal community have rough surfaces to break up surface flow to help prevent drift.
• Air and sunlight exposure categorized by temperature, desiccation (water loss), UV radiation, and respiration.
• Gills are not good at extracting oxygen from the air so species within intertidal communities will have accessory organs for oxygen.
• Zonation within the intertidal zone: Supralittoral, littoral, infralittoral
• Littoral zone broken up into the supralittoral fringe, midlittoral, and infralittoral fringe.
• Wave action affects the vertical width of tidal zones and the slope of the shore affects the horizontal width of the tidal zone.
• Steep slopes have shorter horizontal width.

  Gradual slopes have a larger horizontal width.
• Species diversity is greater in the Atlantic than it is in the Pacific intertidal zones due to an Ice Age affecting the Atlantic and not the Pacific.
• Organisms found in the supralittoral fringe in:

  Temperate climates: lichens, periwinkles, limpets, idopods

  Tropical climates: hermit crabs, isopods, periwinkles, chitons
• Organisms in the midlittoral zone in:

  Temperate: barnacles, bivalves, limpets, periwinkles, rockweeds

  Tropical: boring algae, limpets, rock snails, coralline algae
• Organisms found in the infralittoral zone in:

  Temperate: rich flora and fauna (high diversity)

  Tropical: relatively barren flora (high levels of grazing)
• Temperate intertidal communities have high temperatures, less temperature variations, high predation, mobile inverts, less competition, more refugia and abundant periwinkles
• Tropical intertidal communities have lots of barnacles and muscles, large body size and residents in high intertidal zones, and large impact from microalgae communities.
• Biological factors in the intertidal zone: Settlement preference (soft vs. hard), zonation through sediment preferences, height preferences, physical and biological factors; competition for space and food, prediation
• Fundamental vs. Realized niches

  Fundamental is any space in which an organism can be; realized is the actual space and organism inhabits.
• Chthalamus and Semibalarus barnacles compete in the intertidal zone. Semibalarus grows larger and faster than Chthalamus and outcompetes it for space.
• Common characteristics of Rocky Shores: no strong detrital component, dominated by suspension feeders and macroorganisms, complex predator-prey interactions.

  More dense in the middle intertidal and more diverse in the lower intertidal (due to lack of specialized tolerances needed).
• Tide pools are areas of rocky coast where the sea level is low and the water is shallow.

  Contain salinity changes, temperature changes, and oxygen depletion through warmer water holding less oxygen than colder waters.
• Tide pools have the highest photosynthesis rates during the middle of the day.
• Fish in the intertidal zone: clingfish, gobies, blennies, sculpins.
• Sandy shores have wave and current action that determines the mix of sand mud.
• Smaller particles hold more water but have less curculation.
• Sandy shores have diversity under the substrate.
• Sandy shores have a large detrital community with many burrowers.

  Few herbivore and sediment is not stable enough for algal attachment.
• Typical zonation of sandy shores have diversity and number of organisms increase as you move towards the sea and get deeper in the substrate.
• Sandy shores have daily behavioral cycles of burrowing during the day and coming out at night during low tide
• Mole crabs and coquinas have a feeding behavior that is affected by the tidal influence.

  The greatest amount of food and nutrients are at the leading edge of the waves.