Lecture 6

Question 1

What is an estuary?

Answer 1

A semi-enclosed area where a river meets the sea

Question 2

What are some types of estuaries?

Answer 2

Drowned river valley estuaries
Bar-built estuaries
Fjords

Question 3

What is the Severn tidal bore?

Answer 3

Funnelling of water at high tide and typical wind direction drive a wall of water

Question 4

Physical characteristics of estuaries

Answer 4

• Salinity: varies
• Tides
• Oxygen
• Nutrients
• Sediment: often high turbidity due to high sediment loads

Question 5

Salt wedge type estuary

Answer 5

Salt water is denser than freshwater so flows along the bottom
Salinity highly variable, and salt wedge can move up and down the estuary with tides
Also daily and seasonal variations in tides and river flows

Question 6

Sediment in estuaries

Answer 6

Large amounts of organic and inorganic particles associated with tide and river flow
Maximum aggregation of particles where seawater and freshwater meet
Settles to form rich mud, but turbidity reduces light penetration reducing photosynthesis

Question 7

What is estuarine turbidity maximum?

Answer 7

Where organic matter accumulates where it meets the salt wedge

Question 8

What is the name for marine organisms with a narrow tolerance to salinity changes?

Answer 8

Stenohaline

Question 9

What is the name for marine organisms with broad tolerance to a range of salinities?

Answer 9

Euryhaline

Question 10

What is brackish water?

Answer 10

Water with intermediate salinity

Can contain both stenohaline and euryhaline organisms and brackish water species

Question 11

Where do most estuarine animals originate from?

Answer 11

Marine environments

Question 12

What are the two methods to deal with salinity?

Answer 12

• Osmoconformer = a perfect osmoconformer has blood with a matching salinity to water
• Osmoregulator = a perfect osmoregulator has blood which stays at a constant salinity even though external salt concentration varies

Question 13

Salinity and species richness

Answer 13

Most marine species find it hard to tolerate freshwater and vice versa
Estuaries have low diversity and high productivity

Question 14

Primary producers in estuaries

Answer 14

• Phytoplankton e.g. dinoflagellates
• Macroalgae e.g. seaweed
• Macrophytes e.g. seagrass
• Benthic biofilm e.g. microphytobenthos
• Saltmarsh plants e.g. halophytes

Question 15

What are mudflats? + Features of mudflats

Answer 15

Deposits of sediment in sheltered intertidal areas
Salinity changes are less dynamic in interstitial water, so there is a more stable environment
Mud can be organic rich
Bacteria can use up all of the oxygen in the interstitial water leaving anoxic sediment
Hydrogen sulphide accumulates in mud and can be toxic
Anaerobic bacteria thrive
Plentiful nutrients so primary production high

Question 16

What dominates areas of sedimentation? (like salt marshes and mudflats)

Answer 16

Diatoms (microphytobenthos)

Important source of primary productivity

Question 17

What type of species are well suited to estuaries?

Answer 17

Benthic (infaunal) species due to the deposition of sediment

Many live in burrows for shelter and have differing methods for obtaining food

Question 18

Features of Hydrobia

Answer 18

Genus of snails
Responds to eutrophication and reach very high densities
Grazer and feeds via gills on diatoms, bacteria and mucus

Question 19

Features of Lugworm

Answer 19

Arenicola marina
Annelid worm
Lives in characteristic burrow and ingests sediment to feed on detritus and micro-organisms within
Can absorb dissolved organic matter through body wall
Work irrigates burrow to maintain oxygen

Question 20

Features of Ribbed Horsemussel

Answer 20

Lives in saltmarsh half-buried in sediment

Suspension feeder

Question 21

Features of Macoma

Answer 21

Genus of clams
Buried in mud
Extends two narrow siphons to the bottom surface
Through siphons feeds on organic matter on the sediment surface or in the water

Question 22

Two types of temporary visitors to the estuary

Answer 22

Anadromous: migration from sea to freshwater to spawn e.g. salmon
Catadromous: migration from freshwater to sea to spawn e.g. eels

Question 23

Features of blue crab

Answer 23

Females undergo long migrations to spawn at sea before their young move into the estuarine environment

Question 24

What is a saltmarsh?

Answer 24

Upper intertidal zone between land and open salt water or brackish water that is partially flooded by high tides
Dominated by salt tolerant plants
Often associated with estuaries
Replaced by mangroves in tropical regions

Question 25

Problem with saltmarsh plants

Answer 25

Unpalatable to consumers
Must be broken down physically and biologically
Colonised by bacteria and fungi and converted to detritus
Carbon:nitrogen ratio changes (more N)

Question 26

Two types of carbon supply

Answer 26

1. Allochthonous: depends on external sources

2. Autochthonous: fixes by primary producers within estuary

Question 27

Features of seagrass beds: (Ealgrass)

Answer 27

Found as neighbouring habitats to estuarine regions
Grow in submerged photic zone and most occur in shallow and sheltered coastal waters
Angiosperms: up to 50 different species
Have a rhizome and leaves are blade like
Common in tropics and temperate zones
Depositional areas
Affected by currents, water depth, light

Question 28

What animals inhabit sea grass beds?

Answer 28

Queen conch - eat grasses, algae and floating organic debris

Dugongs and manatees