Transcript Salt Marshes, Mangroves and Wetlands

Salt Marshes, Mangroves
and Wetlands
Chapter 5
Salt marshes
• Intertidal zone, emergent vegetation
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Plants have adapted to saline soils, inundation
Salt glands – salt on leaves of Spartina alterniflora
High productivity in marsh due to sunlight
Peat and sediment accumulation in soil
Detritus production high - exported to estuary
Habitat complexity is high (shoot density) - refuge from
predation
• Halophytes – salt-tolerant plants, 600 species in marsh
worldwide
• Species in NC: Spartina alterniflora, Spartina patens,
Salicornia sp., Juncus roemeranus, Distichilis spicata,
Pluchea camphorata (Table 5.1)
Mangroves
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Mangrove – taxonomically, one of eight families of trees, salttolerant, 12 major genera worldwide. In Florida (USA):
 Avicennia – black mangrove
 Rhizophora – red mangrove
 Laguncularia – white mangrove
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All species grow in loose saline soils in intertidal environments.
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"Mangrove" has also been used to describe the whole community of
plants and animals where these trees are found (mangrove swamp
or forest)
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Viviparity – the "propagules" – not seeds, because inside the seeds
have germinated already and are ready to sprout
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Respiratory roots – pheumatophores stick up out of soil (Avicennia)
or are on stilts (prop-roots) in Rhizophora
Latitudinal Zonation
• Mangroves:
• 29 ºN -- 29 ºS – tropics and subtropics
 Mostly 25 ºN -- 25 ºS, but exceptions include:
 Black mangroves scrub at 29 ºN (Dog Island, Florida)
 10-15 ºfurther south in Africa, Australia
 7 º further north in Japan
 Salt Marshes
 From 25 º N -- 65 º N, and 35 º S -- 60 º S
 38 º N -- 65 º N – no above ground winter biomass due to ice
scour
 In southern hemisphere, only salt marshes in South America
Regional Zonation
• Rainfall, ground water seepage may influence the type of
marsh or mangrove found in a region.
• Lots of rainfall = wide band of marsh or mangrove. As
salinity decreases, the plant communities change, individual
species vary in salinity tolerance
• Mangroves –
 Rhizophora, Avicennia, Laguncularia (in polyhaline areas)
 Typha in oligohaline areas
• Salt marshes
 Species diversity declines with increased salinity
• saline marsh: 6 species plants (Juncus, Spartina, Distichlis)
• brackish marsh: 7
• fresh water marsh: 14
Elevation Effects
• Different plants can tolerate different amounts
of inundation (and salt content).
• Salt Marsh
– Spartina alterniflora – near edge, low elevation.
– Juncus roemerianus – higher elevation
– Panicum - highest elevation
• Mangroves
– Trees in mangroves. Rhizophora – Avicennia – Laguncumra
Succession in Marshes
 Primary succession – S. alterniflora in SE marshes
 In marshes in N.E., after disturbance, succession:
 Salicornia europea first to colonize (0-2 yrs)
 Distichlis spicata next to invade, vegetatively (2-3
years)
 Juncas or Spartina will out-compete Distichlis (3-4
years)
 Juncas or Spartina will dominate, but outcome
depends on elevation.
 climax – upland forest
Biological Interactions
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Predation and competition may determine local patterns of
abundance in both salt marshes and mangroves:
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Juncus gerardi competitively excludes Spartina patens at high
marsh/terrestrial zonation boundary.
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Distichlis spicata is out-competed by both and is a disturbance
fugitive species) (Bertness 1991) Ecology 72:125-137
Smith (1987) transplanted propagules of 4 species of mangroves in
Australia (high intertidal – high salt, low inundation; low intertidal –
low salt, high inundation).
Transplanted to zone that was not its "normal" zone – it was zonedominated by Rhizophora racemosa.
Although growth and survivorship was greatest in high intertidal,
number of individuals was greatest in low intertidal.
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Marsh Zonation - caused by physiology?
 Physiological tolerance model not supported by
field studies.
• Lab studies suggest that there are opportunities
for growth
• Multi-factorial experiments on mangroves in which
salinity, pH, redox, soil characteristics, etc. are
varied have not been completed
• Some support indicated – more data needed
Mangrove Zonation
• Tidal Sorting hypothesis
– large propagules not able to be transported to high
intertidal, but take root in low intertidal, high inundation.
– Small propagules are not transported to all intertidal
areas.
• Rhizophora propagules are large and this tree is found in low
intertidal;
• Avicenna propagules are smaller and found in high intertidal
as well as low.
• Unfortunately, there are other examples which suggest the
opposite is true
• This hypothesis not supported by data in literature
Mangrove Seed Predation
 Crabs eat many propagules, graspid crabs
in particular.
 Smith (1987, 1988) tethered propagules across
intertidal in Australia.
• Found inverse relationship between predation
rate on propagules and adults in canopy
• When protected by cages from crabs, Avicennia
propagules grew and survived in areas where
adults not normally found
• Seed predation probably important!
Competition in Marshes and Mangroves
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Mangroves: Smith (1988) tested competition for Ceriops.
– C. tagal and C. australis were grown in mono and polycultures in salinities
0-60%.
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C. tagal grew better than C. australis at low salinities.
– C. australis grew better than C. tagal at high salinities.
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Marshes: Bertness & Shumway (1993) – experimentally created
bare patches followed succession over four years in a Juncus
dominated and Spartina dominated zone
– When Spartina removed, Distichlis % cover increases
– Spartina % cover is the same, whether Distichlis is removed or not
– In high marsh, salt stress inhibits recolonization by Juncus. Juncus
grows back more slowly with other species removed in the unwatered
plots.
– Removal of other species improves growth of Juncus with the watering
and lowering of salt stress.
– Alleviating salt stress shifted the nature of interspecific interactions
from facilitative to competitive.