coastal ecosystems: marshes and mangroves not strictly “biomes” position at land-sea interface...
Post on 21-Dec-2015
218 views
TRANSCRIPT
Coastal ecosystems: marshes and mangroves
• Not strictly “biomes”• Position at land-sea interface creates
gradational environment and communities
• Character strongly determined by variations in substrate
• Common management and jurisdictional problems
Variations in coastal substrate:
stability, droughtiness,
fertility, aeration and salinity
marsh/mudflat
beach gravel
dune sand
Classification of coastal ecosystems
Tidal Regime Substrate intertidal supratidal
Rock rockweed cliffGravel abiotic shingle
Sand abiotic duneMud marsh, swamp forest
mangrove*Biotic reef* atoll
*tropical
Coastal geomorphology and the distribution of marsh and mangrove
communities
Active coast Passive coastdelta - estuary barrier-beach lagoon
marsh-mangrove upland barrier-beach
Vertical zonation on theLulu Island foreshore
Low marsh
High marsh
Middle marsh
Plant species abundance
Duration of flooding
% exposure
(Hutchinson 1982, CJB)
Tide flats
Flooding regime and salinity interactions on marsh
development
0 36SALINITY (g/l)
Ele
vati
on
MLW
MTL
ExHW
Tideflats
low marsh
MHW mid marsh
high marsh
Bou
nd
ary
Bay
Lu
lu Is
.
var
ns in
floodin
g to
lera
nce
varn
s in s
alin
ity t
ole
rance
Root and rhizome
morphology in a local
marsh plant
Carex lyngbyei
10 cm
Rhizomatous shoot
rhizome
Shoot from root collar
The low marsh environment: adaptations to daily inundation and
anoxic substrates
High [O2](source)
Low or no [O2](sink)
flooding tide
Passive diffusion of oxygen down stem and through root via aerenchyma maintains root respiration; diffusion out into soil oxidizes and precipiates iron sulphides, etc. (potential toxins) in the rhizosphere.
Aerenchyma in stem and root of Distichlis spicata
(saltgrass)
Stem (x48) Root (x48)
Aerenchyma
(produced by lysis of
living cells)
Marsh aggradation: from low to high marsh
Stems filter out
sediment in suspension
in tidal waters
Benthic microorganisms (esp. diatoms and cyanobacteria)
stabilize the mud
harsh environment benign environmentweak competition? strong competition?
Low brackish marsh High brackish marsh
A competitive model to explain marsh zonation
MTLExHW MHW
Gro
wth
in
th
eabse
nce
of
com
peti
tion
Field distribution
competitive refuge
High marsh colonization sequence
YEAR 0
Bare spot:high evaporation results in hyper-
salinity
YEAR 1, 2
Invasion bysalt-tolerant
spikegrass andglasswort:
plant cover reduces
evaporation rate, salinity lowered
YEAR 3, 4
Immigration anddomination by
less salt-tolerant, but
highly competitive(turf roots)black rush.
Dealing with high salinities
e.g. Batis maritima growing in hypersaline (80-100 g/l) lagoonal soils in Sinaloa, Mexico
Salt marsh halophytesBatis maritima
Succulent plants:1. have a higher inherent salt tolerance than glycophytes2. avoid high salt concentrations by increasing cell water content.3. shed plant parts once salt concentration reaches toxic levels.
Salicornia virginica
Other strategies:Salt excretion via specialized salt glands on leaves [e.g. Distichlis spicata]. Succulents do not possess salt glands
Mangroves: vertical zonation
HTL
Rhizophora Avicennia Brugueira/Xylocarpus Lagunculuaria
Successional sequence
Salt pan?
Mangroves: species – salinity relations
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Data: Gulf of Fonseca, Honduras; [ Source: mitchnts1.cr.usgs.gov/ projects/intmangrove.html]
QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.
Grey and black mangroves:
pneumatophores (and mangrove aerenchyma)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Other adaptations:salt glands (on
leaves and roots) and vivipary (Rhizophora
seedlings can float and remain viable for
a year)
Salt glands
on Conocar
pusleaf
Rhizophoraseedlings:
a) on parent plant;
b) in mud
Crocodilians as geomorphic agents in mangroves
Alligators and saltwater crocodiles keep upper reaches of tidal channels open, thereby increasing ebb flows, and slowing invasion by late successional species such as Conocarpus
Mangrove crabs
Crabs are often considered the keystone species in mangrove ecossytems.They shred and eat leaf litter, making smaller particles available for bacterial and fungal colonization. Their faeces provide a direct nutrient source in the forest, and larval crabs are prey for many small fish. Their burrowing activities aerate the anoxic soils.
Images: www.sfrc.ufl.edu; www.kingsnake.com
Mangrove distribution
World
1980(‘000 km2)
1990 (‘000 km2)
2000(‘000 km2)
Annual change1980-90
(%)
Annual change1990-00
(%)
198.1 163.6 146.5 -1.9 -1.1
Data and chart: FAO
Mangrove deforestation
• Causes:conversion to fish and rice farms;logging for fuelwood and charcoal
• Effects:loss of subsidy to neighbouring neritic ecosystems;loss of nursery function;reduction in protection of coastal settlements (e.g. typhoons, tsunamis, etc.)
Mangrove –– shrimp farm conversion
above: coastal shrimp farms and mangrove remnants on the Pacific coast of Honduras, 1997;
below: the same area in 1987 (one shrimp farm in NW quadrant).
Images: wikipedia
Mangrove primary production
•700 - 2000 g m-2 a-1 production
•~90% leaves (salt removal)•Very little herbivore activity•Most production is exported by tides or consumed in detrital food chain
Mangrove nurseries
“The submerged roots of mangroves provide protection and habitat diversity and their leaves start the food web. Mangrove leaves that fall into the water feed fungi, bacteria, and protozoa that in turn feed invertebrates, and they in turn feed juvenile fish. Of course the small fish attract larger picivorous fish like barracuda.”
Wildlife of Mangrove ecosystems www.sfrc.ufl.edu
Images: www.pcebase.org; www.sfrc.ufl.edu
Mangrove forests and coastal protection
• Wanduruppa, set within degraded mangrove forests, was severely affected by the Indian Ocean tsunami: 5,000 to 6,000 people died.
• Nearby Kapuhenwala, surrounded by 200 hectares of dense forest, lost only two villagers – the lowest death toll of any village in the country.
Source: IUCN
Banda Aceh coast, post-tsunami
Mangrove nursery, Thailand
Restoration of coastal forests for tsunami/storm surge
protection is now widespread in SE Asia, although the
efficacy of “tsunami forests” is much debated