Rocky Shore Intertidal Zone

• The intertidal zone is the area located between the highest high tide and the lowest low tide.
• It's where the land meets the sea.

Rocky Shore Community

• Rocky shore communities are regularly exposed to air due to tidal flow.
• It is also known as the littoral zone because of the abundance of the periwinkle snail, Littorina planaxis.
• These communities are more common on the West Coast of the US.
• They are typically found on recently uplifted or geologically young coasts with hard, rocky bottoms where erosion occurs.
• Temperature and salinity in these communities fluctuate greatly due to tidal flow.
• They consist mostly of epifaunal organisms which live on top of the substrate and can be motile (move) or sessile (attached).
• Snails, anemones, mussels, crabs, and seastars are examples of organisms in the rocky shore community.

Vertical Zonation in Rocky Shore Communities

• Zones are determined by how frequently they are exposed to air and water.

Upper Intertidal Zone

• The Upper intertidal zone is wet only during the highest Spring high tides, and mostly dry, referred to as the spray/mist zone.
• Common organisms in the upper intertidal zone include barnacles and limpets that can trap moisture
• Lichens, which are fungus and plant symbiosis organisms, are also common.

Middle Intertidal Zone

• The Middle intertidal zone is wet and dry every day, also known as the splash/crash zone.
• Ecological succession is prominent here because the replacement of organisms maintains biodiversity.
• Seastars, chitons, mussels, and sea anemones are common organisms in the middle intertidal.

Lower Intertidal Zone

• The Lower intertidal zone is dry only during the lowest Spring low tides and mostly wet, this is the wet/water zone.
• Octopuses, red abalones, sponges, seaweeds, and seagrasses are common organisms in the lower intertidal zone.

Limiting Factors in Intertidal Zones

• Organisms in the upper intertidal zone are limited by physical factors such as heat and air exposure.
• Organisms in the lower intertidal zone are limited by biological factors such as predators.
• Space is a major limiting factor in rocky shore communities.
• Disturbances help create space with driftwood providing substrate.
• Waves can wash away organisms which frees up space on rocks.
• Low disturbance frequency can lead to competitive exclusion, where a dominant species takes over such as seastars which have useful adaptations.
• Constant disturbances result in a healthier balance where ecological succession is more likely.
• High disturbance frequency, such as during a storm prevents any organism from holding on.

Habitat Parameters and Adaptations

• Tides affect habitat parameters causing organisms to develop adaptations.

Incoming Tide (High Tide)

• Problems related to high tides include wave shock, abrasion, increased predation, and decreased temperature.
• Adaptations to high tides include migration, anchors, glue, byssal threads, suction, thick shells, low profiles, flexibility, absence of swim bladders, shells, hiding, closing down, migration, and dark coloration.

Outgoing Tide (Low Tide)

• Problems related to low tides include desiccation, UV radiation, abrasion, increased predation, and increased temperature and salinity.
• Adaptations to low tides include closing down, hiding in moist crevices, suction to trap moisture, staying in a tidepool, covering with shell bits, shells, migration, and light coloration.

Feeding in Rocky Shore Communities

• Sessile organisms like sea anemones use suspension or deposit feeding.
• Mobile organisms like snails feed by grazing, predation, or deposit feeding.
• Bivalves and sponges are usually the only filter feeders in this environment.

Soft Bottom Community

• Soft bottom communities have soft, sandy bottoms composed of gravel, sand, silt, and clay.
• They consist mostly of infaunal organisms which live in the substrate, such as sand crabs and bivalves.
• They also consist of meiofaunal organisms that live in between the sediments, such as worms and copepods.
• Soft bottom communities are more common along the East Coast of the US and also commonly known as beaches.

Habitat Parameters and Adaptations in Soft Bottom Communities

• Shifting sediments are common due to crashing waves.
• The type of sediment affects habitat parameters with the two types of sediment.

Coarse Sediment (Gravel, Sand)

• Sandy bottoms have large, gritty sediments.

Fine Sediment (Silt, Clay)

• Muddy bottoms have small, and smooth sediments.

Sediment Composition

• Composition refers to how tightly packed the sediments are.
• The sequence of settling goes from heaviest to lightest such as gravel, sand, silt, then clay.
• Muddy bottoms have slow water movement, so muddy bottoms are mostly wet.
• Sandy bottoms have faster water movement, so sandy bottoms are mostly dry.
• Since substrates remain wet after the tide goes out, desiccation is not a huge problem.

Drainage

• Water drains quickly in well-sorted sandy bottoms due to interstitial space, this increases desiccation and leads to no organic matter and more oxygen.
• Water drains slowly in well-sorted muddy bottoms due to little space, decreasing desiccation, also there is organic matter trapped leading to anaerobic conditions, no oxygen (anoxic), and a smelly (hydrogen sulfide) environment.
• Water movement is inefficient in poorly sorted (mixed) sediments.

Feeding in Soft Bottom Communities

• Sea cucumbers are more common in mud because detritus is most available and mud is less abrasive.
• Bivalves (clams) use long siphons to filter feed.
• At low tide, shore birds are the most common predators.
• At high tide, fish are the most common predators.