Download Estuaries and Intertidal zones

Estuaries and Intertidal
Communities
Chapters 11 and 12
Intertidal Communities
• The effects of the tides and the nature of
the community depends on the substrate.
• Two major types of intertidal communities:
•
Rocky shore communities
•
Soft bottom tidal communities
Rocky Shore Communities
• Occur mostly on active margins.
• Most rocky shore inhabitants live on the
rock surface- called epifauna.
• Low tide- epifauna are exposed to the air.
•
Emersion time- time spent out of the
water.
• Emersion time is longer the higher up the
intertidal you go.
Challenges to epifauna
• Water loss- they will dessicate if exposed
too long.
• Two mechanisms for coping•
Run and hide, or ‘clam up’
• Run and hide- escape to tide pools or hide
in crevices
• Clam up- protective shell to hold in water.
Some Shelled Residents
Whelks
Cross-Section of Whelk
Temperature and salinity
• Exposure to the air creates greater
changes in temperature and salinity.
• Air has greater daily temp. range, and is
flooded with fresh water during rains.
• Tide pools can experience very large
temperature and salinity variations.
Feeding strategies
• Filter feeders cannot feed at low tide.
•
must be submerged to filter
•
often clam up during low tide
• Deposit feeders are rare in the rocky
intertidal zone – few sediments to “hold”
nutrients
• Animals higher in the intertidal have less
time to feed, often grow more slowly than
animals lower in the intertidal.
Wave Energy
• Incoming waves refract along the shore.
• This causes waves to come in parallel to
the shore.
• Headlands receive the most wave impact.
• Bays receive less wave energy.
Wave Refraction
Wave energy on a coastline
Coping with wave energy
• Organisms that live on exposed shores
must deal with waves.
• Strategies:
•
Holdfasts
•
Strong attachments
•
Thick shells
•
Low Profiles
•
Flexibility
•
Finding Shelter
Limiting Resources
• In rocky intertidal communities, food is
abundant.
• Space is the greatest limiting factor- all
sessile organisms will die if not strongly
attached.
• Competition for space is intense.
• Rocky intertidal zones exhibit vertical
zonation- distinct bands at different
heights.
Vertical Zonation on Rocky Shores
• Upper intertidal- lichens, cyanobacteria,
and periwinkles.
• Middle Intertidal- Barnacles dominate in
upper area. Lower areas compete with
mussels and predators.
•
Mussels are the dominant space
competitors. They are limited by air
exposure and predation by sea stars.
• Lower intertidal- red, green and brown
seaweeds.
Vertical Zonation
Vertical Zonation
Soft bottom intertidal communities
• Substrate is sediment- sand, clays, mud.
• Fine sediments are often found in calm
areas.
• Coarse sediments on coasts that
experience wave action.
• Many animals burrow into the sediments,
they are called infauna.
Sediment sizes
Life in the sediment
• Less dessication- sediments hold water.
• Many deposit feeders- most feed on detritus.
Fine sediments have more detritus, sand has
less.
• Oxygen- decaying organic matter uses up
oxygen- therefore interstitial water often is
lacking in oxygen.
• Anaerobic bacteria thrive here- produce H2S.
• Other infauna must pump O2- rich water from
above the sediment, or have extra hemoglobin
and slow metabolism.
Life in the sediment- cont’d
• Some worms help to oxygenate the
sediment by mixing up the sediment.
• Mobility- many soft bottom animals burrow
in the sediment.
•
clams use their muscular foot.
• Many tiny species live in between the sand
grains, they are called meiofauna.
Clam Locomotion
Feeding strategies
• Most soft bottom species feed on detritus.
• Some plankton is also in their diet.
• Deposit feeders- sea cucumbers and
worms eat sediment, and digest the
organic matter.
• Sand dollars- use tube feet to pick up
organic particles.
• Clams use long siphons to reach nutrient
rich surface sediment.
Predation
• Moon snails burrow in the sediments
looking for clams.
•
use their radula to drill through the clam
shell and eat it.
• During low tides, birds are important
predators.
Zonation in
Soft Bottom Intertidal Communities
• Less obvious than on rocky shores.
• Upper beach- Beach hoppers (sand fleas),
ghost crabs and fiddler crabs.
• Lower beach- Polychaete worms, clams,
moon snails.
• Just below tide line- sand dollars, blue
crabs, sea cucumbers
• On muddy shores- very little zonation.
Estuaries
• Estuaries are semi-enclosed areas where
fresh and sea water meet.
• Low in biodiversity, but high in productivity.
• Often among the most affected by human
activity.
• Large cities are often built in estuary areas
or along the rivers that feed them.
• Dredging or filling in of these areas, as
well as pollution can be disastrous.
Types of Estuaries
• Drowned river valleys- formed after the
last Ice age - like the Chesapeake Bay
•
caused by sea level rise.
• Bar Built estuaries-Sand bars and barrier
islands are common.
•
Formed by deposition that isolates a
body of water from the open ocean- like
the Outer Banks.
Cape
Hatteras
is a barbuilt
estuary.
Types of Estuaries
• Tectonic estuaries- formed when the land
subsided (sank) due to plate movements.
•
Ex- San Francisco Bay
• Glacial estuaries- also called fjords.
•
Formed by retreating glaciers carving
out valleys along the coast.
•
Common in Alaska and Norway.
A fjord in New Zealand
Salinity and Estuaries
• Dramatic fluctuations in salinity are
common throughout the day.
• Salinity drops as you travel upstream.
• Salinity often increases with depth.
•
As salty tidal water come in, it forms a
‘salt wedge’- fresher, less dense water
flows on the surface.
Salinity varies in an Estuary
During High tide
During Low Tide
Coping with Salinity changes
• How far up and estuary an animal can live
depends upon how well it can tolerate low
salinities.
• Animals that can tolerate a wide range are
Euryhaline.
• Stenohaline organisms can only survive a
narrow range- they are less successful in
estuaries.
Dealing with Osmosis
• Estuarine species must be good
osmoregulators or osmocomformers.
• Many species do both, during
extreme salinity fluctuations.
•
Many invertebrates osmoregulate
at low salinities, and osmoconform in
high salinities.
Other Factors in Estuaries
• Substrate- like soft bottom intertidal
communities.
• Often less primary production by plankton
due to poor water clarity.
• Anoxic conditions are common. In these
areas, anaerobic bacteria thrive.
Types of Estuarine Communities
• Open water- Limited primary production.
•
-rich in shellfish- 90% of commercially
important fish and shellfish in the Gulf of
Mexico rely on estuaries.
•
Often called the oceans nurseries
because many juvenile fishes seek shelter
in estuaries.
•
Migration routes for catadromous and
anadromous fishes.
Types of Estuarine Communities
• Mudflats- found mostly where there are gentle
slopes.
• Mud exposed at low tide- community must deal
with dessication as well as salinity changes.
• Only a few producers like sea lettuce
• Bacteria and burrowing infauna are common.
•
Worms, clams, snails, ghost shrimp, fiddler
crabs are common
• Important feeding grounds for shorebirds
Birds feeding on a mudflat
at low tide
Mudflats on Prince Edward Island
Resource Partitioning- the different shapes
and lengths of these birds beaks allow them to
forage for different foods
• Fiddler crabs hide in the sand and come
out at low tide to feed.
• Feed on detritus in the sand.
• Male fiddlers have a one large claw to
attract mates.
• They attract mates by waving their claws
at females, and by fighting each other.
• Different species of fiddler crabs have
different waving patterns to attract the
‘right’ mate
Sandpipers use their bills as
probes in the sand
Plovers use visual cues to feed
Salt Marsh Communities
• Extensive grassy areas that are flooded at
high tide.
• Develop in areas sheltered from strong
wave action.
• Lower area is dominated by cordgrasses.
• Upper areas give way to pickle weeds and
rushes.
Salt Marsh near Atlantic Beach, NC
Animals of the Salt marsh
• Marsh plants provide shelter for many animals.
• Many burrowing animals live in the substrate.
• Air breathing snails live in the upper marsh, such
as coffee bean snails and periwinkles
• Small fish live in the tide pools and move into
marsh grasses during high tide to avoid
predators.
• Fiddler crabs live at the boundary of the salt
marsh and mudflat
• Land birds and mammals forage in the salt
marsh during low tide
The
Atlantic
Horse
mussel
can
breathe air
during low
tide
Salt Marsh
Wading
birds feed
in the Salt
marsh at
high tide
Mangroves
• Often considered the tropical version of
salt marshes.
• Mangroves are trees and shrubs that are
adapted to live in the intertidal.
• 60-70% of sheltered tropical shores are
mangrove forests- not all are estuarine.
• Some need freshwater to live, others can
excrete excess salts through glands on the
leaves.
Animals of the Mangrove
• Both land and marine animals live in mangrove
forests.
• Mudskippers- fish that can spend hours out of
the water feeding, getting oxygen to their gills
form the air.
• Sponges are abundant, attached to mangrove
roots- a mutualistic relationship
• Many shrimp, lobsters and fish mature in the
protection of the mangrove roots.
• Many birds and reptiles live in the canopy
Mudskippers feed on insects up on
the exposed roots of mangroves
Distribution of salt marshes and
Mangroves
Mangroves
Mangroves in Belize
The roots of mangroves provide
shelter for marine life
Oyster Reef in Beaufort, NC