Saltmarshes

Where do salt marshes develop?

• Wherever sediment accumulates

• Transition area between aquatic and terrestrial ecosystems

• Dominate intertidal areas, especially on the Atlantic coast of North and South America and in the Gulf of Mexico

• Far less common component of intertidal habitats on the west coast

Why do estuaries tend to be a lot shorter on the west coast?

Steep mountains with a narrow continental shelf

What makes up salt marsh communities?

Emergent herbs, grasses, and low shrubs

How does tidal action affect salt marshes?

Alternating inundation and draining happens several times a day

What is the dominant plant in many salt marshes?

Smooth cordgrass

What is smooth cordgrass?

• Spartina/Sporobolus alterniflora

• Genus Spartina reclassified as Sporobolus in 2014

• Ecosystem engineer

• Extensive rhizome system

• Broad salinity tolerance

• Broad geographic range

• Aerenchymal tissue

• Native on the east coast of the Americas but invasive on the west coast

• Widespread in British Columbia

Why does smooth cordgrass have aerenchymal tissue?

To transport oxygen throughout the plant even when it is underwater

What is an ecosystem engineer?

• Species able to create, modify, maintain, or destroy habitat

• Huge impact on species richness (sometimes positive, sometimes negative)

Where in a salt marsh does smooth cordgrass grow?

At the seaward edge

How many native Spartina species are on the west coast of the Americas?

2

What are the vegetational zones of a salt marsh?

• Low/intertidal marsh

• High marsh

• Upland border

What are vegetational zones?

Distinct zones that are characterized by specific plant species

What is the low/intertidal marsh?

• Ground found between mean low water and mean high water

• Where smooth cordgrass is found

• Nothing else can survive there

• Underwater for 2/3 of the day

• At the seaward-most parts, smooth cordgrass can grow to 2-3 m, depending on the tide

• Flushed by tidal current daily

• Water is quite clear

What is the high marsh?

• Mean high water to spring high water

• Inundated only for very short periods, usually just during the highest tides

• Lots of time for sediment and root material to accumulate

• Brown layer of marsh peat

Which species inhabit the high marsh?

• Other species of Spartina that are not as tolerant of salt

• Form of smooth cordgrass that is a lot shorter

• Spikegrass

• Blackgrass

• Number of other species in other places

• Salicornia

What is marsh peat?

Organic material that accumulates and decomposes

Where is marsh peat the thickest?

High marsh

Why is marsh peat the thickest in the high marsh

Not swept away by the tides

What is the upland border?

• Beginning of land vegetation

• Might have reeds

Why does a pattern of zonation exist in salt marshes?

• Gradient of salinity

• Flooding tolerance

• Competition

What are salt marsh creeks?

• Macrohabitats within salt marshes

• Sometimes called tidal creeks

• Offer a completely different habitat from the top of the salt marsh

• Very dynamic environments

• Sediment may erode (creek broadens) or accrete (creek narrows)

• Influenced by the tide

• One of the main places where the tide comes in

• Bottom tends to have sandier, heavier sediments

• Edge is much more silty/clay

• No algae living at the bottom largely because of tidal flow

• Introduce variation in habitat in the salt marsh ecosystem

Which species only live in salt marsh creeks?

• Marsh mussels live at the ecotone between mud and plants

• Fiddler crabs hang out where the mud is just right to build burrows

What are key environmental features of salt marshes?

• Salinity

• Oxygen availability

What is salinity like in salt marshes?

• Fluctuates widely

• Fluctuations are more severe than estuaries

• Can go from 0 to 35 ppt in a matter of hours

• Added stress of evaporation in the summer increases salinity

• Has been measured to over 100 ppt in places with lots of evaporation

What is oxygen availability like in salt marshes?

• Marsh sediment is often quite anoxic

• High productivity of marshes leads to sediment that has high organic content and high microbial activity, which depletes the sediment of oxygen

• Aerenchymal tissue is one solution to this problem

What are the primary producers in salt marshes?

• Mainly salt marsh plants

• Much smaller contributions by phytoplankton and mud diatoms

What is primary productivity like in salt marshes?

• Daily input of marine nutrients from changing tides

• High growth rate and productivity

• Salt marsh in Florida can produce 10 tons of vegetation per acre while a wheat field in the midwest can produce 7 tons of wheat

• Little direct consumption by herbivores

• Source of detritus

What % of salt marsh plant material is consumed directly by herbivores?

≈5-6%

What is the base of salt marsh food webs?

Detritus

What are the 2 distinct salt marsh food webs?

• Pelagic pathway

• Benthic pathway

What is the pelagic salt marsh food web?

• Relies primarily on detritus from smooth cordgrass in the low marsh, phytoplankton, and benthic algae

• Seen in salt marsh creeks

What is the benthic salt marsh food web?

• Depends on other Spartina species and other high marsh species

• Seen in marsh platforms

What are salt marsh food webs like?

• 2 distinct food webs

• Species that make up each food web are very distinct

• Relatively species-poor because of the relatively harsh conditions

• Taxonomic similarity across salt marshes in the world

• Genus assemblages are very similar from place to place

How did lesser snow geese affect salt marshes in the 1970s?

• Historically, lesser snow geese would migrate north in the summer to salt marshes of La Perouse Bay, Manitoba to breed

• Thinned plants by eating roots and rhizomes

• Provided nutrients by defecating

• Caging experiments were done in the 1970s to exclude geese from the area

• When geese were excluded from the system, plant biomass decreased

• Nutrients that the geese brought into the system were more than enough to make up for the consumption of salt marsh plants

• Needed geese in the system for the marsh plants to do well

How did lesser snow geese affect salt marshes in the 1990s?

• Population increased from 1970-2010

• Marked increase in the early 1990s

• Started overwintering on golf courses and agricultural fields rich in nitrogen from the use of fertilizers instead of more natural habitat that is limited in nutrients

• Great effect on overwinter survival

• More geese were able to migrate north and breed

• Destroyed 100s of 1000s of acres of salt marshes

• Similar exclusion experiments showed opposite results

How are salt marshes controlled?

• Traditionally thought to be controlled from the bottom-up

• Now thought to be controlled from the top-down

What are ecosystem services of salt marshes?

• Important nursery habitat for commercially important species of fishes and invertebrates

• Coastal protection from storm surges and erosion

• Water filtration: filter out contaminants and sediments that come from land before they reach the ocean

What are threats to salt marshes?

• Filling and draining to extend the land seaward and be used for agriculture or housing

• Coastal development: hardening of shores to prevent erosion

• Invasions by non-native species