What is the definition of the intertidal zone?
- shoreward fringe of the sea-‐bed between the highest and lowest extent of the tides. -Productive areas which receive rich nutrient supply terrestrial nutrients and coastal phytoplankton -Very close proximity to humans ␣ which means they are well studied ecosystems and also highly exposed to human impacts
What are some examples of intertidal zones?
-mangrove forests, seagrass beds, mud flats, beaches, rocky coastline
What is typical of the intertidal zone?
-zonation is typical of intertidal zone, across a short gradient even just meters
-over just tens of meters completely different organisms= different species
What cause zonation in the intertidal zone?
1. Physiological tolerance 2. Wave shock 3. Larval and adult preferences 4. Competition 5. Predation -Similar patterns of species vertical ranges combined with sharp boundaries suggests zonation is caused by simple factors
How does physiological tolerance and wave shock determine the zones in the intertidal zone?
-Species found higher on the shoreline are generally more tolerant of dessication, reduced feeding time, reduced access to oxygen and extreme temperatures. Organisms lower in the intertidal are more resistant to wave shock. example:because of their ability to seal themselves inside their test, barnacles are found higher in the intertidal than anemones
How does body size and the surface to volume ratio influence water loss?
-As body size increases, the surface area relative to body volume decreases, and this aids in reducing water loss.
-However, a decreased surface area to volume ratio comes with increased size which is a disadvantage for heat loss
-Intertidal organisms trade off water loss and heat loss in their body sizes
How does shape influence water loss and hence zonation?
- Long thin organisms lose water more rapidly than spherical organisms - E.g. sea anemones contract into a small cylinder at low tide to reduce surface area and water loss
What are the adaptations to heat stress?
-Evaporative cooling and circulation of body fluids - Higher intertidal animals better adapted to heat stress than lower intertidal species - e.g. species of the intertidal gastropod Nerita that reside higher in the intertidal zone retain cellular function at higher temperatures
How are feeding mechanism affected as an adaptation to heat stress?
-feeding capabilities differ for upper intertidal and lower intertidal organisms -e.g. movement of the feeding appendages (cirri) in a lower intertidal and an upper intertidal dwelling barnacle differs in response to temperature i.e. upper intertidal barnacle increases its feeding rate at higher temperatures (up to an upper thermal limit)
How do periwrinkles adapt to heat stress?
close their operculum(the bottom opening) to remain moist during low tide when exposed to air
How do limpets adapt to heat stress?
-make the edge of their shell fit the exact configuration of the rock where they live, keeping water inside. These spots on the rock are known as home scar
What is the example of heat stress adaptation where the colour of an organism changes?
-Colour may vary with latitude -e.g. proportion of brown and black colour morphs of the blue mussel Mytilus edulis Varies with latitiude on the east coast of the U.S.A. -the brown are more common than black closer to equator -warmer region= more brown individuals
How are crabs adapted against dessication?
-Many intertidal organisms have gills which they can use to breathe when exposed to air as long as the gills are moist -High intertidal crab Scopimera has a mambrane on each leg designed to exchange gas from the air for uptake into arterial blood
In what three ways can waves damage intertidal organisms?
-1. Abrasion (sand in suspension, floating debris, or whipping seaweed fronds against rock) -2. Pressure (Crushing of delicate or compressible structures e.g. gas-‐filled air bladders of seaweeds) -3. Pressure drag (directional force of waves may rip apart or dislodge organisms or dislodge just their support structures such as hold fasts and the byssal threads of mussels)
How are mussels adapted to wave shock?
Wide range of morphological adaptations to wave shock: -Mussels have thick shells and thick byssal threads for attachment -Mytilus edulis changes its attachment strength with season i.e. secretes more byssal threads in winter so it can resist winter storms -Individual mussels more vulnerable to waves. Dense beds dissipate wave forces along the surface of the mussel bed. Flow within mussel aggregations is 0.1% to 10% of free-‐ stream velocity.
How is the production of byssal threads affected by the velocity of water?
-4 different species looked at -the mussels make fewer byssal threads with high velocity= so it is not the increase in threads that allows them to stick there -put plaster rods to test how much it falls away= the ones in dense mussel beds= less flow less worn out so they resits the high energy environment by assembling as groups
How is the sea star Pisaster ochraeus adapted to wave shock?
- Sea star Pisaster ochraeus living in the intertidal zone have a harder and thicker integument compared to individuals living in sheltered waters
How do larval and adult preferences affect the zonation in the intertidal zone?
-Most invertebrates in the intertidal produce larvae -Larvae must settle into a suitable habitat -Larvae of many species are able to locate the tidal height suitable for adults of their own species -Preferential settlement on adults of their own species (e.g. the Australian barnacle Hexaminius popeiana= can recognise the chemicals -Mobile animals can adjust their tidal height by a combination of responses to light, gravity and moisture but for sessile really crucial where they settle
How does predation affect zonation in the intertidal zone?
-Predators often limited by the time of immersion as predators must be moist as they move to locate and ingest prey -Susceptibility to dessication limits sea stars and snails to the lower shore or to refuges where water exists in the intertidal -E.g. dog whelks (Nucella) emerge from moist cracks to prey upon barnacles -Mussel beds in California have a sharp lower limit due to predation by a large sea star (Pisaster)
How does competition affect zonation in the intertidal zone?
-Intertidal habitats may be severely space limited -Species capable of undercutting or overgrowing others can dominate the shore level where they do well physiologically -E.g. mussels are able to move by forming and detaching byssal threads -This allows them to climb on top of competitors and smother them -As a result, mussels frequently dominate the lower shore