Chapter 12Chapter 12

Estuaries: Where Rivers Meet the Sea

Estuaries: Where Rivers Meet the Sea

EstuaryEstuary

• Semi-enclosed areas where fresh water and seawater meet and mix

• Close interaction between land and sea• Among the most productive

environments on earth• Among the environments most effected

by humans• Many cites are located along them (NY,

London, Tokyo)

• Semi-enclosed areas where fresh water and seawater meet and mix

• Close interaction between land and sea• Among the most productive

environments on earth• Among the environments most effected

by humans• Many cites are located along them (NY,

London, Tokyo)

Environmental ImpactsEnvironmental Impacts

• Dredged or filled and transformed into marinas, seaports, industrial parks, cities and garbage dumps

• Dredged or filled and transformed into marinas, seaports, industrial parks, cities and garbage dumps

Origins and Types of Estuaries

Origins and Types of Estuaries

• Scattered along the shores of all the oceans and vary widely in origin, type and size

• May be called lagoons, bays

• Drowned river valleys or coastal plain estuaries (formed when the sea invaded lowlands and river mouths)

• Scattered along the shores of all the oceans and vary widely in origin, type and size

• May be called lagoons, bays

• Drowned river valleys or coastal plain estuaries (formed when the sea invaded lowlands and river mouths)

• Bar built estuary – formed from the accumulation of sediments that build up and create sand bars and barrier islands dividing fresh and salt water

• Tectonic estuaries – formed when the land sank – San Fransicso Bay

• Fjords – created from deep cuts by glaciers that later filled in by rivers

• Bar built estuary – formed from the accumulation of sediments that build up and create sand bars and barrier islands dividing fresh and salt water

• Tectonic estuaries – formed when the land sank – San Fransicso Bay

• Fjords – created from deep cuts by glaciers that later filled in by rivers

• Passive margins have broad well developed estuaries

• Passive margins have broad well developed estuaries

Physical Characteristics

of Estuaries

Physical Characteristics

of Estuaries

• Have a unique combination of physical and chemical characteristics from the mixing of salt and freshwater

• Have a unique combination of physical and chemical characteristics from the mixing of salt and freshwater

SalinitySalinity

• Fluctuates dramatically from place to place and time to time

• Seawater 35 o/oo and freshwater 0 o/oo so salinity is somewhere in between

• Decreases as you move upstream

• Varies with depth – salinity increases as you go down because of density

• Fluctuates dramatically from place to place and time to time

• Seawater 35 o/oo and freshwater 0 o/oo so salinity is somewhere in between

• Decreases as you move upstream

• Varies with depth – salinity increases as you go down because of density

• Salt wedge – seawater is more dense and flows along the bottom with fresher water on top – moves back and forth with the tides

• Salt wedge – seawater is more dense and flows along the bottom with fresher water on top – moves back and forth with the tides

SubstrateSubstrate

• Sand to soft mud

• Particles are carried in by the river and settle out as the river slows

• Mud (mix of silt and clay) is rich in organic material

• Sediments are often anoxic – decay bacteria use up the oxygen in the interstitial water

• Sand to soft mud

• Particles are carried in by the river and settle out as the river slows

• Mud (mix of silt and clay) is rich in organic material

• Sediments are often anoxic – decay bacteria use up the oxygen in the interstitial water

Other Physical FactorsOther Physical Factors

• Water temperature varies because of shallow depths and surface area

• Large amounts of suspended sediments are typical – reduces water clarity – reduces light

• Water temperature varies because of shallow depths and surface area

• Large amounts of suspended sediments are typical – reduces water clarity – reduces light

Estuaries as EcosystemsEstuaries as Ecosystems

• May look like a wasteland

• Really are tremendously productive

• Home to large numbers of organisms that are of commercial importance

• Provide vital breeding and feeding grounds

• May look like a wasteland

• Really are tremendously productive

• Home to large numbers of organisms that are of commercial importance

• Provide vital breeding and feeding grounds

Living in an Estuary

Living in an Estuary

• Live revolves around the need to adapt to extremes in salinity, temperature and other physical factors

• Change rapidly and in many ways

• Life is not easy so few species have successfully adapted to estuarine conditions

• Live revolves around the need to adapt to extremes in salinity, temperature and other physical factors

• Change rapidly and in many ways

• Life is not easy so few species have successfully adapted to estuarine conditions

Coping with SalinityCoping with Salinity

• Maintaining the proper salt and water balance of cells and body fluids is one of the greatest challenges facing estuarine organisms

• Maintaining the proper salt and water balance of cells and body fluids is one of the greatest challenges facing estuarine organisms

In GeneralIn General

• Marine fish – have a lower concentration of salts in their blood as compared to the seawater – constantly drink water – secrete small volume of very concentrated urine – salt also excreted by gills

• Marine fish – have a lower concentration of salts in their blood as compared to the seawater – constantly drink water – secrete small volume of very concentrated urine – salt also excreted by gills

• Freshwater fish – concentration of salt in their blood in greater than the surrounding water so they constantly gain water through osmosis over their skin and gills

• Do not drink, secrete large volume of dilute urine, salts are absorbed by gills

• Freshwater fish – concentration of salt in their blood in greater than the surrounding water so they constantly gain water through osmosis over their skin and gills

• Do not drink, secrete large volume of dilute urine, salts are absorbed by gills

Osmosis in an estuaryOsmosis in an estuary

• Most estuarine organisms are marine species that have developed the ability to tolerate low salinities

• Euryhaline – organisms that can tolerate a wide range of salinities – most estuarine organisms are

• Stenohaline – tolerate a narrow range in salinity

• Most estuarine organisms are marine species that have developed the ability to tolerate low salinities

• Euryhaline – organisms that can tolerate a wide range of salinities – most estuarine organisms are

• Stenohaline – tolerate a narrow range in salinity

BrackishBrackish

• Water is intermediate salinity

• Some organisms are adapted to this type of environment

• Water is intermediate salinity

• Some organisms are adapted to this type of environment

Dealing with OsmosisDealing with Osmosis

• Since most estuarine organisms are from a marine background they tend to take on water through osmosis

• Move

• Osmoconformers – body fluids change with the salinity (mollusks and some polychaete worms)

• Since most estuarine organisms are from a marine background they tend to take on water through osmosis

• Move

• Osmoconformers – body fluids change with the salinity (mollusks and some polychaete worms)

• Osmoregulators – keep the salt concentration of their body fluids more or less constant

• Salinity lower than blood – get rid of excess water through active transport

• Fishes, crabs and some mollusks

• Osmoregulators – keep the salt concentration of their body fluids more or less constant

• Salinity lower than blood – get rid of excess water through active transport

• Fishes, crabs and some mollusks

Adapting to MudAdapting to Mud

• Nothing to hold on to• Organisms must burrow or

live in permanent tubes beneath the sediments surface

• Hard to move in mud – stationary or slow moving

• Salinity does not change as much

• Nothing to hold on to• Organisms must burrow or

live in permanent tubes beneath the sediments surface

• Hard to move in mud – stationary or slow moving

• Salinity does not change as much

• Oxygen concentrations are low from the decay

• Pump oxygen rich water

• Blood that contains hemoglobin that holds oxygen

• Oxygen concentrations are low from the decay

• Pump oxygen rich water

• Blood that contains hemoglobin that holds oxygen

Types of Estuarine

Communities

Types of Estuarine

Communities

• Consist of few species

• Species present are in large numbers

• Consist of few species

• Species present are in large numbers

Open WaterOpen Water

• Type and abundance of plankton varies tremendously with the currents, salinity and temperature

• Murky water also limits photosynthesis

• Rich supply of fish and shellfish in or near the estuary

• Nurseries for young – abundant food

• Type and abundance of plankton varies tremendously with the currents, salinity and temperature

• Murky water also limits photosynthesis

• Rich supply of fish and shellfish in or near the estuary

• Nurseries for young – abundant food

MudflatsMudflats

• Bottoms of estuaries that become exposed at low tide

• Can be extensive where there is a large tidal range and a gently sloping bottom

• Bottoms of estuaries that become exposed at low tide

• Can be extensive where there is a large tidal range and a gently sloping bottom

Low tide in a mudflatLow tide in a mudflat

• Desiccation

• Variations in temperature

• Predation

• Variations in salinity

• Desiccation

• Variations in temperature

• Predation

• Variations in salinity

Mudflat organismsMudflat organisms

• Primary producers are not present• Benthic diatoms• Bacteria• Infauna – feed on detritius – deposit and

suspension feeders• Bivalves (quahog - Mercinaria

mercenaria and soft shelled clam Mya arenaria and razor clams Ensis), fiddler crabs

• Primary producers are not present• Benthic diatoms• Bacteria• Infauna – feed on detritius – deposit and

suspension feeders• Bivalves (quahog - Mercinaria

mercenaria and soft shelled clam Mya arenaria and razor clams Ensis), fiddler crabs

Mya arenaria

Razor Clam

• Fishes and birds – important predators• Fishes – high tide• Birds – low tide• Important stopover and wintering areas for

many migratory birds

• Fishes and birds – important predators• Fishes – high tide• Birds – low tide• Important stopover and wintering areas for

many migratory birds

Salt MarshesSalt Marshes

• Estuaries in temperate and subartic regions usually bordered by extensive grassy areas that extend inland from the mudflats

• Also develop along sheltered open coasts

• Partially flooded at high tide

• Also known as tidal marshes

• Estuaries in temperate and subartic regions usually bordered by extensive grassy areas that extend inland from the mudflats

• Also develop along sheltered open coasts

• Partially flooded at high tide

• Also known as tidal marshes

• Wave action is minimal to allows the accumulation of muddy sediments

• Tidal creeks, freshwater streams and shallow pools frequently cut through the marsh

• Have extremes in salinity, temperature and tides like the mudflats

• Muddy bottom held together by the roots

• Wave action is minimal to allows the accumulation of muddy sediments

• Tidal creeks, freshwater streams and shallow pools frequently cut through the marsh

• Have extremes in salinity, temperature and tides like the mudflats

• Muddy bottom held together by the roots

Plants of the Salt MarshPlants of the Salt Marsh

• Hardy grasses dominate

• Salt tolerant land plants

• Pronounced zonation of plants

• Cord grasses (Spartina alterniflora) – occupy the fringe above the mean low-tide level

• Another cord grass (S. patens)

• Rushes and pickle weed

• Hardy grasses dominate

• Salt tolerant land plants

• Pronounced zonation of plants

• Cord grasses (Spartina alterniflora) – occupy the fringe above the mean low-tide level

• Another cord grass (S. patens)

• Rushes and pickle weed

Spartina alterniflora

S. patens

Pickle Weed

Zonation results from:Zonation results from:

• Effects of flooding

• Competition for space

• Increased soil salinity in warm areas due to evaporation

• Effect of burrowing animals

• Effects of flooding

• Competition for space

• Increased soil salinity in warm areas due to evaporation

• Effect of burrowing animals

Animals of the Salt MarshAnimals of the Salt Marsh

• Decay bacteria• Diatoms• Thick mats of filamentous green algae• Cyanobacteria• Nematodes• Small crustaceans• Larvae of land insects• Fiddler crabs

• Decay bacteria• Diatoms• Thick mats of filamentous green algae• Cyanobacteria• Nematodes• Small crustaceans• Larvae of land insects• Fiddler crabs

• Coffee bean snails (Melampus)• Marsh periwinkles (Littorina, Littoraria)• Ribbed or horse mussel (Geukensia

demissa)• Killifish and juvenile silversides

• Coffee bean snails (Melampus)• Marsh periwinkles (Littorina, Littoraria)• Ribbed or horse mussel (Geukensia

demissa)• Killifish and juvenile silversides

Melampus

Mangrove ForestsMangrove Forests

• Tropical equivalents of salt marshes• Mangroves – flowering land plants

adapted to live in the intertidal• Mangel – dense forest of trees and

shrubs• Typical in tropical and subtropical areas• Grow on protected coasts where muddy

sediments accumulate

• Tropical equivalents of salt marshes• Mangroves – flowering land plants

adapted to live in the intertidal• Mangel – dense forest of trees and

shrubs• Typical in tropical and subtropical areas• Grow on protected coasts where muddy

sediments accumulate

• Mangroves must get rid of salts from the water

• Salt glands on the leaves of some species excrete salts

• Prop roots which branch downward and support the tree-like stilts

• Mangroves must get rid of salts from the water

• Salt glands on the leaves of some species excrete salts

• Prop roots which branch downward and support the tree-like stilts

Mangrove OrganismsMangrove Organisms

• Crabs• Mudskippers• Sponges• Polychaetes• Mud shrimps• Clams• Birds make their homes in the

mangrove branches

• Crabs• Mudskippers• Sponges• Polychaetes• Mud shrimps• Clams• Birds make their homes in the

mangrove branches

• Food on fishes, crabs and other prey• Snakes, frogs, lizards, bats and other land

animals also live in the mangrove trees

• Food on fishes, crabs and other prey• Snakes, frogs, lizards, bats and other land

animals also live in the mangrove trees

Feeding Interactions

among Estuarine Organisms

Feeding Interactions

among Estuarine Organisms

Estuaries have high primary production because:

Estuaries have high primary production because:

1. Nutrients brought in by the tide and rivers, together with those generated by nitrogen-fixing organisms and the decomposition of detritus are used by plants, algae and bacteria the primary producers

1. Nutrients brought in by the tide and rivers, together with those generated by nitrogen-fixing organisms and the decomposition of detritus are used by plants, algae and bacteria the primary producers

2. Nutrient trap in deep estuaries

3. Surplus detritus is exported to the open and neighboring ecosystems in a process known as outwelling – valuable source of food and nutrients to other ecosystems

2. Nutrient trap in deep estuaries

3. Surplus detritus is exported to the open and neighboring ecosystems in a process known as outwelling – valuable source of food and nutrients to other ecosystems

The End ……The End ……