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What is an estuary?

A semi-enclosed area where a river meets the sea


What are some types of estuaries?

Drowned river valley estuaries
Bar-built estuaries


What is the Severn tidal bore?

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


Physical characteristics of estuaries

-Salinity: varies
-Sediment: often high turbidity due to high sediment loads


Salt wedge type estuary

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


Sediment in estuaries

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


What is estuarine turbidity maximum?

Where organic matter accumulates where it meets the salt wedge


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



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



What is brackish water?

Water with intermediate salinity
Can contain both stenohaline and euryhaline organisms and brackish water species


Where do most estuarine animals originate from?

Marine environments


What are the two methods to deal with salinity?

-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


Salinity and species richness

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


Primary producers in estuaries

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


What are mudflats? + Features of mudflats

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


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

Diatoms (microphytobenthos)
Important source of primary productivity


What type of species are well suited to estuaries?

Benthic (infaunal) species due to the deposition of sediment
Many live in burrows for shelter and have differing methods for obtaining food


Features of Hydrobia

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


Features of Lugworm

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


Features of Ribbed Horsemussel

Lives in saltmarsh half-buried in sediment
Suspension feeder


Features of Macoma

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


Two types of temporary visitors to the estuary

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


Features of blue crab

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


What is a saltmarsh?

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


Problem with saltmarsh plants

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)


Two types of carbon supply

1. Allochthonous: depends on external sources
2. Autochthonous: fixes by primary producers within estuary


Features of seagrass beds: (Ealgrass)

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


What animals inhabit sea grass beds?

Queen conch - eat grasses, algae and floating organic debris
Dugongs and manatees