L6 Estuaries and saltmarshes

Question 1

What physical characteristics do estuaries have that are different to other coastal habitats?

Answer 1

-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
-

Question 2

What is a salt wedge?

Answer 2

FW from the river is less dense than SW.

Steep change in salinity as haloclines/hypnoclines vary with horizontal distance and depth.

Question 3

Where is the highest tidal range in the world?

Answer 3

Severn estuary >12m

High level of turbulance causes much turbidity of sand, clay and organic particles.

Question 4

What is ETM>

Answer 4

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.

Question 5

what is a mudflat?

Answer 5

Deposits of sediment in sheltered intertidal areas

Question 6

Why are mudflats more stable environments than estuaries?

Answer 6

salinity changes are less dynamic

Question 7

What types of microorganisms live in mudflats

Answer 7

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.

Question 8

What can be toxic in mudflats?

Answer 8

H2S can accumulate

Question 9

even though biodiversity may be low…

Answer 9

Primary production can be high, as there are plentiful nutrients in the mud.

Question 10

What is a saltmarsh?

Answer 10

Upper intertidal zone, between land and open saltwater or brackish water - partially flooded by hightides.
Dominated by salt tolerant plants

Question 11

Are there saltmarshes all over the world?

Answer 11

In tropical regions they are replaced by mangroves.

Question 12

5 types of estuarine organisms

Answer 12

• phytoplankton (eg dinoflagellates, HABs)
• Macro algae
• Macrophytes (eg seagrass)
• Benthic biofilms (microphytobenthos)
• Saltmarsh plants (halophytes)

Question 13

What are infauna, 4 types

Answer 13

Benthic organisms that live within the bottom substrate
Burrow to avoid predation and shelter from currents
Snails, polychaete worms, clams, crustaceans

Question 14

Stenohaline
Euryhaline
Brackish

Answer 14

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

Question 15

give an example of an animal very tolerant to changes in salinity

Answer 15

Ragworm - almost a perfect osmoconformer, but at lower salinities it must regulate blood salinity

Question 16

Perfect osmoconformer

perfect osmoregulator

Answer 16

Osmoconformer - salinity of blood matched water
Osmoregulator - salinity of blood stays constant (can increase blood salinity through active transport, gills and kidneys help)

Question 17

Anadromous

Catadromous

Answer 17

Anadromous - SW to FW migration eg Salmon [to spawn]

Catadromous - FW to SW eg eels

Question 18

2 examples of temporary visitors to estuaries

Answer 18

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.

Question 19

Allochthonous

Autochthonous

Answer 19

Allochthonous - depends on external carbon sources

Autochthonous - fixed primary producer eg Saltgrass in saltmarshes provide large source of C.

Question 20

How do saltmarsh plants provide

Answer 20

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

Question 21

What is another important source of primary productivity in areas of sedimentation?

Answer 21

Diatoms

Question 22

What eats benthic organisms and how do they feed?

Answer 22

Preyed on by birds and fish- predators determined by beak length.
Deposit feeders eg Californian hornsnail.
Suspension feeders eg Spaghetti worms - catch falling detritus

Question 23

3 examples of organisms adapted to feeding in estuaries

Answer 23

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

Question 24

What is Arenicola marina and describe its burrow

Answer 24

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.

Question 25

How many species of angiosperm live in seagrass beds?

Answer 25

about 50, Tiny rhizome, bladelike leaves

Question 26

Where are seagrass beds?

Answer 26

grow in submerged photic zone, shallow, sheltered waters.
depositional areas
common in tropics and temperate zones.

Question 27

What else lives in seagrass beds?

Answer 27

many animal inhabitants: Queen conch in carribean

Provide food source for manatees and dugongs - could reduce seagrass beds by 96%.

Question 28

What threatens seagrass beds?

Answer 28

Seagrass wasting disease

Eutrophication, boat damage

Question 29

Which type of birds are the most important predators in mudflats?
How is this an example of resource partitioning?

Answer 29

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.