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

Distribution of salt marshes

and mangroves

, North America

“acti

ve” c

oast

“pass

ive”

coast

Diversity of salt marsh

plant communities

, North

America78 s

pp

347 s

pp.

28 spp

Coastal geomorphology and the distribution of marsh and mangrove

communities

Active coast Passive coastdelta - estuary barrier-beach lagoon

marsh-mangrove upland barrier-beach

The Fraser River

delta as a type

example of Pacific

coast marshes

BoundaryBay

Lulu I.

Variations in seasonal

river discharge

and sediment

load (Puget Trough)

Seattle

Vancouver

Marsh communities display strong zonation with elevation

Low brackish marsh High brackish marsh

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

Colonizing the mudflat: clonal growth of Scirpus spp. on the Lulu Island foreshore

Root morphologies of marsh

plants

“guerilla” morphology

“turf” morphology

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

Vertical zonation in Atlantic and Gulf Coast marshes

Competition in a bare patch in a high marsh

environment

[guerilla roots] [turf roots]

annual

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

High productivity: where does it go?

winter spring

summerfall

PNW marshes:400-2800 g m-2 a-1

A coastal marsh food web

Lesser snowgeese grazing on young shoots of Carex lyngbyei

Lesser snowgeese (Chen caerulescens) grubbing for bulrush

rhizomes in the Fraser delta marshes

Snowgoose grub hole

Trumpeter swan(Olor buccinator)

grub hole

10 cm

A biotically-cratered marsh landscape

Changing marsh

communities:invasion of

exotics (e.g. Spartina

alterniflora into

Washington State)

Mangrove ecosystems

Mangrove distribution(55 spp in 11 plant families)

Bruguiera spp.

Rhizophora (red mangrove)

Avicennia (grey & black mangrove)

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.

Red mangrove stilt roots

Grey and black mangroves:

pneumatophores (and mangrove aerenchyma)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Mangrove lenticels(breathing pores)

O2

Photo credit: Newfound Harbor Marine Institute

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

Salt pans: e.g. Avicennia subshrub in hypersaline soil, Sinaloa, Mexico

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