Where is the intertidal zone? Covered by water at the highest tide Exposed to air at the lowest tide Air exposure occurs daily! Intertidal zone can be sandy or rocky Cabrillo National Monument, Pt. Loma San Diego http://www.nps.gov/cabr/naturescience/a-virtual-visit-to-the-tidepools.htm High Tide Low Tide

Intertidal Life is Stressful!  Risks due to air exposure: Summer = too hot Winter = freezes Rapid change = air temp can be very different from water temp Salinity Sunny = tidepools are saltier Rainy = tidepools are fresh Drying out Gills = have to stay wet Cells = lose water and not function Predation Ocean predators = fish, crabs, sea stars Land predators = birds, people

Intertidal Life is Stressful!  Risks due to waves: Brings in logs, rocks that crush critters Carried away Leaves animals vulnerable to predators Erodes sediment leaving critters homeless

Adjusting to Intertidal Stressors Location is Everything! Cracks in rocks, cliffs, overhangs reduce amount of stress Provides shade Provides protection from waves Distance away from water determines time exposed to air Farther away from water = more air exposure Closer to water = less air exposure

Adjusting to Intertidal Stress Conserve water! Cliffs, cracks and overhangs stay wet more of the time Animals retreat into wet areas Sandy tide region: dig deeper! Rocky intertidal: move into pools or hide under algae Store water Close up with water inside right before low tide Reflect light (reduces evaporation) Light colored shells help do this!

Adjusting to Intertidal Stresses Waves Sandy intertidal Dig deeper: do this to avoid be washes out to sea Rapid digger: IF washed out..dig back in quickly Rocky intertidal Stay low: reduces drag, less likely to be pulled off rocks Strong anchor: keeps animal securely attached Barnacles: cement head to rocks Mussels: have byssal threads Snails, chitons & limpets: large foot to cling onto rocks Algae: strong holdfasts

Rocky intertidal

Rocky Intertidal Competition for space (limiting resource) Critters need something to attach to BUT…only so much space on the rocks How do critters deal with limited space?? Reduced feeding time: animals can only feed during high tide (sandy tide critters can hunt for food at ALL times)

Zones of the Intertidal Division of intertidal into obvious zones defined by: Time exposed to sun Distribution of organisms Splash zone  HIGHEST Upper intertidal Middle intertidal Low intertidal Subtidal  LOWEST

Splash Zone (supralittoral fringe) Exposed majority of the time, infrequently covered by water Lichen / Enteromorpha Tiny periwinkle snails small brown/gray barnacle

High Intertidal (upper midlittoral zone) Exposed daily (during each low tide) High intertidal organisms: Shore crabs Acorn barnacles Limpets/ larger snails

Middle Intertidal (middle and low midlittoral zones) Only exposed during lowest part of low tide (6 hours daily) Common organisms: Mussels Sea anemones rockweed

Middle Intertidal (middle and low midlittoral zones) Middle midlittoral zone:  mussels Low midlittoral zone:  agregating anemones High Middle

Low Intertidal (infralittoral fringe) Only exposed during minus spring tides Common organisms: kelps/surfgrass Sea star Giant green anemones

Maintaing Zonation How do the organisms stay in a specific area? Upper limit: established by physiology (how well critter can deal with exposure) Lower limit: established by biological interactions (competition and predation)

Connell’s Barnacles

Role of Pools Tidepools Reduce impact Organisms found in higher zone than normal Larger tidepool  more organisms living inside Smaller tidepool  less organisms

Keystone Species in the Rocky Intertidal Mussels often dominate middle intertidal Don’t spread upward because of physiology Could spread downward but don’t because of Ocher stars (Pisaster ochraceus) Predation by a small number of Ocher stars keeps the mussels out of the lower intertidal

Oregon Coast British Columbia Coast Channel Islands, CA

Soft Sediment Intertidal Rocky intertidal better known because of wide variety of animals BUT soft sediments (mud & sand) are also intertidal habitats Advantages of soft sediments Less exposure: animals in sediment, not on surface More moisture: water retained in spaces between sand grains Continual feeding: deposit feeders can eat during low tide

Mud Flats Common in estuaries & other areas protected (from waves) Often smells like rotten eggs because oxygen in the mud has been used up

Sandy Beaches Unstable (the sediment moves) Few algae: nothing to anchor to Difficult to live on surface: sand scour Sand grain size depends on wave strength stronger waves = larger grain size (pebbles), less water retained in the sediment weaker waves = smaller grain size (mud), more water retained in the sediment http://www1.istockphoto.com/file_thumbview_approve/3125905/2/istockphoto_3125905_coarse_sandy_beach.jpg http://www.gtp.gr/showphoto.asp?FN=MGfiles%5Clocation%5Cimage16715%5B6479%5D.jpg&Q=100&MW=520

Sandy Beaches Zones determined mostly by wave action Upper Beach (Supralittoral) Middle Beach (Midlittoral) Subtidal (below water for most of time)

Intertidal Zones: Upper Beach Defined as: High tide line to terrestrial plant line Dominated by amphipods (beach hoppers ) and terrestrial insects (kelp flies)

Intertidal Zones: Middle Beach Defined as: Area exposed at low tide Dominated by burrowers: worms, crabs, clams

Vertical Zonation within middle beach Dry & drying sand: no or little moisture moisture retention zone: damp Water retention zone: wet Water saturation zone (most animals): liquid water present

Intertidal Zone: Subtidal Defined as: Below low tide line, almost never exposed Many less hardy organisms: sand dollars, brittle stars, crabs, snails, cockles