Coastal ecosystems marshes and mangroves Not strictly biomes
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
marsh/mudflat Variations in coastal substrate: stability, droughtiness, fertility, aeration and salinity beach gravel dune sand
Classification of coastal ecosystems Substrate Rock Gravel Sand Mud Biotic Tidal Regime intertidal supratidal rockweed abiotic marsh, mangrove* reef* *tropical cliff shingle dune swamp forest atoll
st coa ve” ssi “pa “active” coast Distribution of salt marshes and mangroves, North America
34 7 s pp. 28 spp 78 spp Diversity of salt marsh plant communities, North America
Coastal geomorphology and the distribution of marsh and mangrove communities Active coast delta - estuary marsh-mangrove Passive coast barrier-beach lagoon upland barrier-beach
The Fraser River delta as a type example of Pacific coast marshes Lulu I. Boundary Bay
Variations in seasonal river discharge and sediment load (Puget Trough) Vancouver Seattle
Marsh communities display strong zonation with elevation Low brackish marsh High brackish marsh
Vertical zonation on the Lulu Island foreshore % exposure Plant species abundance High marsh Middle marsh Low marsh Tide flats Duration of flooding (Hutchinson 1982, CJB)
Flooding regime and salinity interactions on marsh development Ex. HW rance linity tole Bay low marsh var ns in sa Tideflats Boundary Elevation mid marsh ce MLW . Lulu Is MTL n g tolera floodin ns var in MHW high marsh 0 SALINITY (g/l) 36
Colonizing the mudflat: clonal growth of Scirpus spp. on the Lulu Island foreshore
Root morphologies of marsh plants “guerilla” morphology “turf” morphology
Shoot from root collar Root and rhizome morphology in a local marsh plant Rhizomatous shoot 10 cm rhizome Carex lyngbyei
The low marsh environment: adaptations to daily inundation and anoxic substrates High [O 2] (source) Passive diffusion of oxygen down stem and through root via aerenchyma maintains root respiration; flooding tide diffusion out into soil oxidizes and precipiates iron sulphides, etc. (potential toxins) in the rhizosphere. Low or no [O 2] (sink)
Aerenchyma in stem and root of Distichlis spicata (saltgrass) Aerenchyma (produced by lysis of living cells) Stem (x 48) Root (x 48)
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 weak competition? Low brackish marsh benign environment strong competition? High brackish marsh
A competitive model to explain marsh zonation Field distribution Growth in the absence of competition competitive refuge Ex. HW MTL
Vertical zonation in Atlantic and Gulf Coast marshes
Competition in a bare patch in a high marsh environment annual [guerilla roots] [turf roots]
High marsh colonization sequence YEAR 0 YEAR 1, 2 YEAR 3, 4 Bare spot: high evaporation results in hypersalinity Invasion by salt-tolerant spikegrass and glasswort: plant cover reduces evaporation rate, salinity lowered Immigration and domination by less salttolerant, 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 halophytes Salicornia virginica Batis maritima Other strategies: Salt excretion via specialized salt glands on leaves [e. g. Distichlis spicata]. Succulents do not possess salt glands Succulent plants: 1. have a higher inherent salt tolerance than glycophytes 2. avoid high salt concentrations by increasing cell water content. 3. shed plant parts once salt concentration reaches toxic levels.
High productivity: where does it go? winter summer spring fall 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 Salt pan? HTL na o i s s cce Su Rhizophora Avicennia ce n e u l seq Brugueira/Xylocarpus Lagunculuaria
Mangroves: species – salinity relations Data: Gulf of Fonseca, Honduras; [ Source: mitchnts 1. cr. usgs. gov/ projects/intmangrove. ht
Red mangrove stilt roots
Grey and black mangroves: pneumatophores (and mangrove aerenchyma)
Mangrove lenticels (breathing pores) O 2 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 Conocarp us leaf Rhizophora seedlings: 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 km 2) 198. 1 Annual 2000 1990 change (‘ 000 km 2) 1980 -90 (%) 163. 6 146. 5 -1. 9 Annual change 1990 -00 (%) -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 Images: www. pcebase. org; www. sfrc. ufl. edu
Mangrove forests and coastal protection Restoration of coastal forests for tsunami/storm surge protection is now widespread in SE Asia, although the efficacy of “tsunami forests” is much debated • 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
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