Estuaries and Salt Marshes

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Chapter 8

• Estuaries and Salt Marshes

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Types of Estuaries

• What is an estuary?
• Classification based on geomorphology and
  geological history
• Classification based on stratification of water
  salinity distribution

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Estuaries contd.

• Partially enclosed coastal body of water
• Interaction of
• River runoff
• Seawater
• Seasons

4
Estuaries contd.

• Classified by origin
• Coastal plain (e.g. Chesapeake Bay)
• Fjord (common along coasts on Alaska Canada)
• Bar built (common along the U.S. Gulf East
  Coasts)
• Tectonic (e.g. San Francisco Bay)

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Bay or Lagoon Behind a Barrier Beach (North
Carolina Coast)
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Tectonic Estuary San Francisco Bay
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Milford Sound in Fiordland, New Zealand
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Mixing in estuaries

• Vertically mixed
• Typically shallow and broad
• Slightly stratified
• Highly stratified
• Salt wedge
• Typically deep and narrow

Fig. 12-5
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Positive (Salt-wedge) Estuaryb) Negative Estuary
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Physical Characteristics of Estuaries

• Salinity
• Substrate
• Temperature
• Wave action currents
• Turbidity
• Oxygen

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Physical Characteristics of Estuaries contd.

• Salinity
• Fluctuate in estuaries in relation to
• Seasons
• Tides
• Coriolis effect (rotation of Earth deflects
  flowing water)

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Change is salinity in an estuary with change in
tide level or change in river discharge
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Comparison of salinity fluctuations in the water
column with that interstitially in the bottom mud
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Result of Coriolis effect on Salinity in the
north-south oriented Chesapeake Bay estuary
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Chesapeake Bay (Purple are represents anoxic
waters)
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Physical Characteristics of Estuaries contd.

• Substrate variable depending on the type of
  estuary
• Most estuaries have soft, muddy substrates
  carried into the estuary by seawater freshwater
• Massive storms their accompanying floods may
  deposit or remove vast amounts of sediment in
  estuaries, causing severe mortality of organisms.

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Physical Characteristics of Estuaries contd.

• Temperature
• More variable in estuaries than in nearby coastal
  waters
• B/c of the smaller volume of water in estuaries
  larger surface area
• Variable freshwater input (rivers on temperate
  zones are colder in winter warmer in summer
  than the adjacent seawater)
• Horizontal temp variation (range)
• Vertical temp variation

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Physical Characteristics of Estuaries contd.

• Wave action and currents
• Relatively calm water small fetch, relatively
  shallow depth
• Currents caused mainly by tidal action river
  flow

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Physical Characteristics of Estuaries contd.

• Turbidity
• High b/c of large amount of suspended particles
• Highest during maximum river flow
• Minimum near the mouth of the estuary
• Major ecological effect of turbidity decreased
  light penetration decreased photosynthesis
  reduced productivity

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Physical Characteristics of Estuaries contd.

• Oxygen
• Usually there is ample supply of oxygen in the
  water column
• Varies depending on temp salinity distributions
  in the estuary
• Depleted in salt-wedge estuaries on deep
  estuaries oxygen depletion may occur in bottom
  waters as a result of vertical salinity
  stratification
• Human activities are contributing to oxygen
  depletion in estuaries coastal waters

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Biota of Estuaries

• Faunal composition in estuaries (3 types)
• Marine (largest group in numbers species)
• Stenohaline animals (unable or barely tolerate
  changes in salinity)
• Euryhaline animals (capable of tolerating varying
  amounts of changes in salinity)
• Freshwater Originate in freshwater cannot
  tolerate salinities gt 5 psu.
• Brackish-water or estuarine fauna Found in the
  middle reaches of the estuary b/w 5 18 psu
  e.g. Nereis diversicolor, Crassostrea,
  Callinectes, Palaemonetes
• Transitional components of estuarine fauna
  migratory fishes e.g. Salmon, Eels Penaeid
  shrimps that spend only part of their lives in
  estuary

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Adaptations of Estuarine Animals

• Physiological adaptations
• Osmosis physical process in which water passes
  through a semipermeable membrane that separates
  two fluids of diff. salt conc., to move from
  areas of lower to higher conc.
• Osmoregulation the ability to control the conc.
  of salts or water in internal fluids
• Osmoconformers cannot control their internal
  salt content
• Osmoregulators have physiological mechanisms to
  control the salt content of their internal fluids

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Diffusion

• Molecules move from higher concentration of
  substance to lower concentration

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Osmosis

• Water molecules move through semipermeable
  membrane from less concentrated to more
  concentrated

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• Marine hypotonic fish
• Drink water
• Secrete salt
• Concentrated urine

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Numbers of species in each of the three major
components-marine, freshwater, and brackish-water
species
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Some typical estuarine animals
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Changes in the body fluids of Nereis diversicolor
with changes in salinity wt. changes occurring
after the animals are transferred to 20 seawater
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Osmotic concentration of body fluids in relation
to salinity change
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Change in salinity of the blood of the crab,
Australoplax tridentata with a change in the
salinity of the external medium
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Behavioral Adaptations of Estuarine Animals

• Burrow into the mud (some invertebrates)
• Interstitial water has less variation in salinity
  temp than open water has
• Less likely to be consumed by surface- or
  water-dwelling predators
• Migration of adults of estuarine crabs (e.g. Blue
  crabs) to adjacent sea to breed
• Juveniles of many fish species enter estuaries
  where they feed migrate back to the sea as they
  grow

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The life cycle of the blue crab Callinectes
sapidus in estuaries of the Atlantic coast of the
United States
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Productivity, Organic Matter and Food Sources in
Estuaries

• Phytoplankton, Benthic Diatoms, Sea Grasses, Salt
  marshes
• Primary productivity by algae is considered low
  relative to salt marshes in some areas
• Salt marsh productivity relatively high
• Estuaries act as sinks for organic matter brought
  down by rivers in from sea
• Estuaries have few herbivores that feed directly
  on plants
• Most of the plant material are broken down to
  detritus by bacterial action b/4 entering the
  various food webs

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Food Webs in Estuaries

• Long thought to be primarily detritus based
• Most detritus is digested by bacteria other
  microorganisms
• Macroorganisms that consume detritus actually
  feed, are dependent on, those microorganisms to
  break down the detritus into a usable food
  resource
• Suspension feeders (e.g. clams)
• Deposit feeders (e.g. polychaete worms)

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Food Webs in Estuaries contd.

• Dominant predators in estuaries Fishes birds
  (e.g. ducks, geese, shorebirds, wading birds,
  gulls, terns
• Ontogenetic shift in prey consumption by fish
  from eating zooplankton to macroinvertebrates, to
  other fishes
• Trophic Relay Much of the productivity of
  fishes is ultimately lost to the estuary when the
  fishes move offshore

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The Food Web of a Typical Estuary
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Food Webs in Estuaries contd.

• Modern estuarine food webs have been affected by
  humans
• Eutrophication can lead to algal blooms that
  preclude seagrasses from living in estuaries
• Overexploitation of oysters other filter
  feeders has probably had massive impacts on our
  estuaries

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Salt Marshes

• Found in temperate sub-polar estuaries
  protected marine shores embayments
• Are communities of emergent herbs, grasses, or
  low shrubs rooted in soils inundated drained
  alternately by tidal action
• Are Halophytes can grow in soils with a high
  salt content
• Develop where sediment accumulates
• Dominate intertidal coasts of Atlantic North
  America South of New England northern coast of
  Gulf of Mexico Atlantic coast of South America
• Less common on Pacific coasts of North South
  America

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The Distribution of Salt Marshes in the World
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Areal Extent of Salt Marshes on the Atlantic
Coast of the United States
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Salt Marshes contd

• Buffer shorelines from storm damage erosion
• Serve as biochemical filters on runoff water
  entering estuaries
• Serve as nursery grounds for juveniles of many
  marine fish crustaceans
• Impacted by human activities

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Environmental Services Provided by Salt Marshes
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Environmental Characteristics of Salt Marshes

• Show wide variations in environ. factors, e.g.
  salinity, D.O. in soil
• Salinity can vary from 20 to 40 psu may even
  reach gt 100 psu in high marsh soils
• Marsh sediments can be highly anoxic due in part
  to high microbial activity

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Composition Distribution of Salt Marshes

• Are species poor b/c of high salinities anoxic
  conditions in the soil
• Dominant plants are
• Spartina
• Juncus
• Salicornia
• Animals associated with salt marshes are
• Crabs (e.g. Uca, Sesarma)
• Mussels (Geukensia)
• Snails (e.g. Littorina)
• Small crustaceans (e.g. amphipods, shrimp)
• Terrestrial insects, raccoons

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Some Dominant Emergent Salt Marsh Emergent Plants
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Characteristic Animals Present in a Salt Marsh at
Low and High Tides on the Atlantic Coast of North
America
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Tidal Creeks Penetrating into a Coastal Salt
Marsh on the Lower Coastal Plain of Georgia, USA
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Zonation of Salt Marshes

• Lowest Zone creek bank bottom lacks
  macrophytic vegetation contains mainly infauna
• Low Marsh (flooded daily by tides)
• Dominated by S. alterniflora (tall form shorter
  form)
• High Marsh
• Dominated by S. patens next zone is black rush
  (Juncus gerardi) which is less tolerant of salty
  soil flooding that S. patens
• Upper limit of the Marsh
• Marsh elder (Iva frutescens), a woody shrub which
  is intolerant of tidal flooding grows only
  where the soil is well drained

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Zonation Patterns of Salt Marshes of a New
England Marsh, USA
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Zonation Patterns of Salt Marshes of the Southern
USA
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Zonation Patterns of Salt Marshes of the Pacific
Coast, USA (San Francisco Bay)
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Causes of Salt Marsh Zonation

• Plant competition physical stresses
• Grazers are unimportant with regard to zonation
  of salt marsh plants
• Competitive dominance in New England marshes
• Iva frutescens gt Juncus gerardi gt Spartina patens
  gt S. alterniflora
• S. alterniflora is able to live in low marsh area
  which is waterlogged has anoxic sediment that
  S. patens cannot tolerate

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Positive Plant-Animal Interactions in Salt Marshes

• Salt marsh habitats are physically stressful on
  plants that live in them
• Some invertebrates living in marshes help
  alleviate some of the stresses on the plants
• On the seaward border of marshes in southern New
  England, cordgrass growth is limited by
  disturbance nitrogen

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Positive Plant-Animal Interactions in Salt
Marshes contd.

• Mussels help alleviate both problems by
• Filter-feeding depositing high-nitrogen fecal
  matter on the roots rhizomes of the cordgrass
  in the sediment
• Buffer the seaward edge of the cordgrass against
  physical disturbance by binding sediment
  cordgrass roots with their byssal threads
• Cordgrass provide the anchoring material of roots
  for the byssal threads of the mussels

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Facultative Mutualism b/w the Filter-feeding
Marsh Mussel Geukensia demissa and Cordgrass on
the Atlantic Coast of North America
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Change in competitive relations among marsh
plants under high low nitrogen levels
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Consumer control of Marsh vegetation

• Natural marshes may be controlled by consumers
• Introduced rodent (nutria) decreased marsh plant
  primary productivity on Louisiana Gulf coast
• Snow geese control arctic marsh production of
  Hudson Bay by feeding on the marsh plants while
  supplying them with nitrogen through defecation

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Increases in snow goose population of North
America over the past 50 yrs
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Geese exclusion cages, showing the results of
runaway herbivory by geese in Hudson Bay
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Map showing the massive spatial scale of the
destruction (in red) of Hudson Bay marshes over
the past 20 yrs
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Consumer control of vegetation in the extensive
salt marshes of Georgia and the Carolinas
Natural marshes may be Controlled by consumers
Marsh snails (Littoraria irrorata) impacts salt
marshes
Marsh snails at high density Destroy cordgrass
by ingesting them making them more susceptible
to fungal infection through grazing scars
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Impact of Predation on distribution and abundance
patterns of marsh plant organisms

• Predation by blue crab (Callinectes sapidus)
• Restricts the ribbed mussel Geukensia to high
  marsh habitats in southern marshes
• Excludes marsh periwinkles from places where they
  cannot migrate out of the water at high tide
• Killifish predation limits the snail Melampus,
  juvenile fishes, various amphipods to high
  marsh in association with dense vegetation

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The migration of the marsh periwinkle Littoraria
irrorata up the cordgrass blades to avoid
predation by blue crab
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Effects of predation on some of the salt marsh
inhabitants
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Human impacts on Salt marshes