Download Midlittoral Zone - HWSY15-16

Intertidal Communities
The Rocky Shore
Key Concepts
• The intertidal zone is the coastal area
alternately exposed and submerged by
tides.
• Organisms that inhabit intertidal zones
must be able to tolerate radical changes
in temperature, salinity, and moisture
and also be able to withstand wave
shock.
Key Concepts
• Organisms on rocky shores tend to be found
in definite bands, or zones, on the rocks.
• In contrast to sandy shores, rocky shores
provide a relatively stable surface for
attachment.
• Tide pool organisms must be able to adjust to
abrupt changes in temperature, salinity, pH,
and oxygen levels …abiotic factors.
Key Concepts
• Biotic factors are most important in
determining the distribution of
organisms on rocky shores, whereas
physical factors are most important on
sandy shores.
Characteristics of the Intertidal
Zone
• Daily fluctuations of the environment
– organisms must tolerate radical changes in
temperature, salinity and moisture, and endure the
crushing force of waves
• Inhabitants are most active during high tide,
when area is submerged
– water provides food for filter feeders
• As the tide retreats, organisms adjust to
exposure to air and sunlight
Rocky Shores
• Composed of hard materials
• Found from California to Alaska on the west
coast and from Cape Cod northward on the
east coast of North America
• Coasts may be recently uplifted, formed from
lava flows, or highly eroded by wind and
waves
Rocky Shore Zonation
• Zonation—separation of organisms into prominent
horizontal bands defined by color or distribution of
organisms
• Rocks provide a stable surface for attachment of
organisms
• As tide retreats...
– upper regions exposed to air, changing
temperatures, solar radiation, desiccation
– lower regions exposed only a short time before
tide returns to cover them
Zonation
Rocky Shore Zonation
• Zone system for rocky shore proposed
by Alan and Anne Stephenson
– Supralittoral (maritime) Zone — area
above high water that may extend several
miles inland
– Supralittoral fringe (splash zone) —
uppermost area covered only by the
highest (spring) tide, usually just
dampened by spray of crashing waves
Rocky Shore Zonation
• Supralittoral fringe of rocky shores
– receives very little moisture
– exposed to drying heat of the sun in summer and
extreme cold in winter
– few organisms inhabit this harsh area
– gray and orange lichens composed of fungi and
algae are common
– sea hair – a filamentous alga
– most common animal = periwinkles, molluscs of
Littorina and associated genera
Lichen zone
Gray & Yellow lichen and the Green lichen
– Gray & orange lichens common in this zone
– Symbiotic relationship: mutualism between and algae and
a fungus.
– Fungus traps traps the water; alga undergoes
photosynthesis and produces food
Rocky Shore Zonation
• Supralittoral fringe (continued)
– other inhabitants include limpets and isopods
– some periwinkles and isopods breathe air
• Midlittoral zone of rocky shores
– inhabitants must avoid desiccation, maintain gas
exchange, and deal with temperature extremes as
the tide moves in and out
– wave shock—force of the waves as they crash
against the rocks during low tide
Littorina littorea
Periwinkles (Littorina cincta) get through low tide by
clustering in a moist, shady crevice. They also seal
against the rock to retain moisture.
Rocky Shore Zonation
• Midlittoral zone (continued)
– Upper midlittoral zone
• typical organisms = acorn barnacles and rock barnacles
• barnacles permanently attach to surfaces
• barnacles open their shells to filter feed during high tide,
and close them to trap water inside during low tide
• barnacles cool themselves by opening the shell slightly
and allowing a little water to evaporate
Dog Whelk Snail & Barnacles
Rocky Shore Zonation
• Midlittoral zone (continued)
– Middle and low midlittoral zone
• oysters, mussels, limpets, and periwinkles dominate
• oysters and mussels survive low tides by trapping water
in their shells
• limpets and chitons graze algae at high tide
• common periwinkles bury themselves in seaweed to
retain moisture during low tide
• rock urchins survive wave shock by hollowing out a
space in the rock and wedging into it
Midlittoral Zone
• Major organism is
predominately Mytilus sp.
• Attaches firmly to rocks via
byssal threads
Mussels & barnacles
Rocky Shore Zonation
• Midlittoral zone (continued)
– Seaweeds of the midlittoral zone
• rockweeds (brown algae) grow on rocks without full
exposure to the sea
• rockweeds compete with barnacles for space by
sweeping the rocky surface with their blades, preventing
cyprid larvae of barnacles from settling
• some rockweeds are toxic to deter grazing
• rockweeds produce a gelatinous covering that retards
water loss and prevents desiccation
• they form large mats that trap water and provide a haven
for animals during low tide
Bladderwrack Fucus vesiculosus
•
Bladderwrack Fucus vesiculosus Bladderwrack is the most well
known of the wracks. Can be found in large beds on Cornwallsﾕ rocky
shores. With a quick look at bladderwrack it appears that there are two
types of bladder. The knobbly bladder like organs at the end of some of
the fronds, are receptacles. In spring the female receptacles are
covered by orange mucus and the males by green mucus.
Rocky Shore Zonation
• Midlittoral zone (continued)
– Tide pools—depressions in the rocks which retain
water during low tide
• water loses oxygen as it heats in the sun
• salinity may change owing to rainfall or evaporation of
water by the sun
• oxygen in tide pools containing algae may change
drastically – high during the day when algae are active,
low (+ low pH) at night
• salinity, temperature, pH abruptly returned to ocean
conditions when tide reaches the pool
Rocky Shore Zonation
• Midlittoral zone (continued)
– Tide pool organisms
• e.g. algae, sea stars, anemones, tube worms, hermit
crabs, molluscs
• many are filter feeders
• biotic interactions help structure tide pool communities
• e.g., in New England, Irish moss lives in tide pools where
common periwinkles eat the green alga Enteromorpha,
which normally outcompetes Irish moss
When the tide goes out, a bit of ocean spray stays in this small tide pool.
Organisms like these chitons (Sypharochiton sp.) and snails (Diloma sp.)
move to the pools to keep moist. Even here, life is tough as the water often
undergoes drastic changes in salinity, dissolved oxygen (D.O.) content and
temperature.
Rocky Shore Zonation
• Infralittoral fringe of rocky shores
– transitional area submerged except at spring tides
– rich flora and fauna of organisms that can tolerate
limited air exposure
– rocks may be covered with seaweeds
– in cooler waters, molluscs, sea stars and brittle
stars live among large kelps
– other animals include hydrozoans, anemones,
sea urchins, spider crabs
Infralittoral Fringe
• surf zone includes the edge of the lower
rocky platform and parts of the reef
• rocks may be covered with algae such as
Sargassum
• boring urchins, anemones, sponges, bryozoa,
sea cucumbers, keyhole limpets
Subtidal Zone
• Relatively barren compared to subtidal zone
in temperate climates
• Small, turf-forming red algae dominate
– lack of larger algae present in higher zones
thought to be owing to herbivory
– in experiments, exclusion of herbivores
permitted erect algae to establish
themselves where they were not found
previously
Intertidal Fishes
• Resident species
– Typically have special adaptations for surviving
harsh intertidal conditions
• small size; absent, reduced or firmly attached scales;
compressed/elongate or depressed body shape; absent
or reduced swim bladder; greater body density
• tolerant of temperature and salinity changes
• some intertidal fish can leave the water to feed
• Temporary inhabitants
– tidal, seasonal and accidental visitors
Ecology of the Rocky Shore
• East coast rocky shores
– barnacles dominate upper zones
– below the barnacles are mussels
– algae and consumers survive on protected shores
• West coast rocky shores
– barnacles compete with algae; mussels displace
barnacles by growing over them
– balance maintained by ochre sea stars, the
keystone predator
The Rocky Shore Habitat
REVIEW
• Rocky shores are the most densely inhabited by macroorganisms.
• Have the greatest diversity of animals and seaweeds.
• On the east coast, rocky shores are found from Cape Cod northward.
• Rocky shores are defined by prominent hoizontal bands, defined by color and
distribution of organisms.
• The separation of organisms into definite bands is called zonation.
• Unlike the other habitats we've studied, rocks provide organisms with a stable
surface for attachment.
• The characteristic abiotic factors of intertidal zones apply here.
• Organisms present may vary depending upon wave action, tidal cycle, climate,
length of exposure, amount of light, shape of shore and type of rock.
• The uppermost area of rocky shore which is covered only by the highest.
(spring) tides and is usually just dampened by the spray of the crashing waves is
the supralittoral fringe or splash zone.
•
Above this is the supralittoral or maritime zone, an area above the high water
mark.
•
Below the supralittoral fringe is the midlittoral zone (true intertidal zone).
•
Below the midlittoral zone is the infralittoral fringe, which extends from the
lowest of low tides to the upper limits reached by the large kelps.
•
The subtidal zone (infralittoral) is the region of shore covered by water, even
during low tide.