Coastal salt marshes Steven Pennings

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Coastal salt marshesSteven Pennings

• Marsh tour
• Disturbance
• Stress
• Tidal gradients in plant size
• Zonation patterns
• Positive interactions

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1) Marsh tour distribution of salt marshes and
mangroves(sheltered coasts where fine sediments
can accumulate and plants can survive)
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Maine
wrack
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MA
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CT
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GA
Plant create marsh by trapping sediment
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LA marsh loss
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Germany
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Spain
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Easy to manipulate Strong gradients Ecosystem
highly productive
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2) Disturbance

• Ice
• Wrack
• Foraging
• Anthropogenic

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Ditching
wrack
Plant zones
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Eutrophication

• Estuaries accumulate nutrients from entire
  watershed
• Salt marsh plants are nitrogen limited
• Marshes are a good filter blocking nutrients
  coming from upland from entering water column
• But added nitrogen shifts competitive balances,
  changes species distributions

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Geographic variation in salt marshes
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3) Stress

• Flooding
• Salinity
• Marshes are low diversity systems because few
  species can tolerate both stresses together

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Flooding

• Flooded soils become anaerobic (no oxygen), plant
  roots need to respire
• Biogeochemistry of flooded soils produces
  sulphides, which are toxic

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Aerenchyma Anaerobic metabolism
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Salinity

• Flooded with salt watersalty
• Evaporation can increase salinity to several
  times seawater concentration
• Plants salt lowers osmotic potential of water,
  similar to drought conditions. Salt also
  interferes with N uptake, and is directly toxic
• Animals fluctuating salinity creates osmotic
  problem

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Geographic variation in salt marshes
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Physical stresses (?) can cause severe episodes
of marsh die-back (LA, GA)
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4) Tidal height gradients in plant size

• Gradients in salinity and flooding create
  gradients in plant height (10-fold)
• Occur in all salt marsh plant species
• Phenotypic plasticity, not genetic variation

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Increased physical stress stunts Iva at lower end
of zone
Reduced exchange of tidal water stunts Spartina
at upper end of zone
Rhode Island
Spartina alterniflora
Spartina patens
Juncus gerardi
Iva frutescens
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5) Zonation of plants

• Salt marsh plants commonly occur in zones
• Best studied in New England
• Lower limit set by increasing physical stress
• Upper limit set by competition

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Rhode Island
Increased physical stress stunts Iva at lower end
of zone
Reduced exchange of tidal water stunts Spartina
at upper end of zone
Mark Bertness
Spartina alterniflora
Spartina patens
Juncus gerardi
Iva frutescens
Upper limits of each species set by competition
Lower limits of each species set by flooding
Increasing flooding and salt stress
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6) Positive interactions

• Between plants
• Between invertebrates and plants

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Positive interactions between plants

• Aerenchyma help oxygenate soil
• Plant canopy minimizes salt accumulation
• Positive interactions increase diversity in
  stressful habitats

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Positive interactions in the marsh
Plants shade soil and limit salt buildup,
benefiting rare forbs, and shifting
zonation boundaries seaward
Plants oxygenate soil, stimulating further plant
growth
Plants trap sediment and create low- marsh habitat
Fiddler crabs aerate soil and increase nutrient
supply, stimulating plant growth
Mussels stabilize and fertilize soil,
benefiting plants
Plants support burrows, shelter crabs from
predators, and contribute detritus to diet
Plants provide sites for mussels to attach,
and contribute detritus to diet
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Summary

• Physically stressful habitat because intertidal
  (flooding, salinity)
• Low diversity because of stresses
• Strong gradients in stress create patterns in
  plant height, zonation
• Positive interactions occur when organisms can
  alleviate stress

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