L6 Estuaries and saltmarshes Flashcards
What physical characteristics do estuaries have that are different to other coastal habitats?
-Huge variation in salinity from tides mixing with FW
-Drop in O2 can be caused by much suspended matter from river, depending on flow rate and O2 content
-Can be more polluted due to pesticide run off
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What is a salt wedge?
FW from the river is less dense than SW.
Steep change in salinity as haloclines/hypnoclines vary with horizontal distance and depth.
Where is the highest tidal range in the world?
Severn estuary >12m
High level of turbulance causes much turbidity of sand, clay and organic particles.
What is ETM>
Estuarine turbidity maximum
max aggregation of particles in layers of salinity in an estuary, especially in the salt wedge. It settles to form a rich mud, but turbidity reduces light penetration.
what is a mudflat?
Deposits of sediment in sheltered intertidal areas
Why are mudflats more stable environments than estuaries?
salinity changes are less dynamic
What types of microorganisms live in mudflats
Bacteria use up all the O2 in intersitial water, so it is anoxic below 1-2cm. Anaerobic bacteria thrive, and archaea can live in anoxic conditions.
What can be toxic in mudflats?
H2S can accumulate
even though biodiversity may be low…
Primary production can be high, as there are plentiful nutrients in the mud.
What is a saltmarsh?
Upper intertidal zone, between land and open saltwater or brackish water - partially flooded by hightides.
Dominated by salt tolerant plants
Are there saltmarshes all over the world?
In tropical regions they are replaced by mangroves.
5 types of estuarine organisms
- phytoplankton (eg dinoflagellates, HABs)
- Macro algae
- Macrophytes (eg seagrass)
- Benthic biofilms (microphytobenthos)
- Saltmarsh plants (halophytes)
What are infauna, 4 types
Benthic organisms that live within the bottom substrate
Burrow to avoid predation and shelter from currents
Snails, polychaete worms, clams, crustaceans
Stenohaline
Euryhaline
Brackish
Stenohaline - narrow tolerance to salinity changes, orgs limited to the upper and lower end of estuary.
Euryhaline - broad tolerance to a range of salinities
Brackish - intermediate salinity, contains steno and euryhaline organisms
give an example of an animal very tolerant to changes in salinity
Ragworm - almost a perfect osmoconformer, but at lower salinities it must regulate blood salinity
Perfect osmoconformer
perfect osmoregulator
Osmoconformer - salinity of blood matched water
Osmoregulator - salinity of blood stays constant (can increase blood salinity through active transport, gills and kidneys help)
Anadromous
Catadromous
Anadromous - SW to FW migration eg Salmon [to spawn]
Catadromous - FW to SW eg eels
2 examples of temporary visitors to estuaries
Atlantic medhaden (Brevoortia tyrannus) breeds at sea. Larvae move into nursery in estuary until they can fully survive SW Blue crabs- eggs carried from estuary to open sea, larvae released in open sea. Females undergo long migrations to spawn at sea.
Allochthonous
Autochthonous
Allochthonous - depends on external carbon sources
Autochthonous - fixed primary producer eg Saltgrass in saltmarshes provide large source of C.
How do saltmarsh plants provide
get broken down physically and chemically by bacteria and fungi that colonise it. Not many animals eat saltmash plants.
Converted into detritus - Carbon:Nitrogen ration changes (N increases) and carbohydrate falls
What is another important source of primary productivity in areas of sedimentation?
Diatoms
What eats benthic organisms and how do they feed?
Preyed on by birds and fish- predators determined by beak length.
Deposit feeders eg Californian hornsnail.
Suspension feeders eg Spaghetti worms - catch falling detritus
3 examples of organisms adapted to feeding in estuaries
Ribbed horse mussel - Half buried suspension feeder, ‘gapes’at low tide to take in oxygen.
Malcoma - clams buried in mud, extends 2 siphons to sediment surface, inhalant and exhalant, to feed and get O2.
Hydrobia - snails, respond to eutrophication by reaching v high densities of 34000 per m2. Grazer, feeds on diatoms, mucus and bacteria via gills
What is Arenicola marina and describe its burrow
Lugworm - builds a characteristic burrow, ingests sediment to feed on detritus and microbes within.
Irrigated burrow to maintain O2. Increases bacterial growth and nutrients replenished via mineralisation at the anoxic sediment interface. Ciliates live in ‘garden’ feeding off the bacteria. Burrow may have nematodes and copepods which worm feeds on.
How many species of angiosperm live in seagrass beds?
about 50, Tiny rhizome, bladelike leaves
Where are seagrass beds?
grow in submerged photic zone, shallow, sheltered waters.
depositional areas
common in tropics and temperate zones.
What else lives in seagrass beds?
many animal inhabitants: Queen conch in carribean
Provide food source for manatees and dugongs - could reduce seagrass beds by 96%.
What threatens seagrass beds?
Seagrass wasting disease
Eutrophication, boat damage
Which type of birds are the most important predators in mudflats?
How is this an example of resource partitioning?
Wading shorebirds eg Willet, godwit, plovers.
Feed on polychaets,shrimp, clams
Varying length of bills shows specialisation as prey species at different depths in mud.
Some probe mud other look for movements.
