Salt Marshes

True or false salt marshes can be found on barrier islands

TRUE

Salt marsh salinity zones (polyhaline, mesohaline, brackish)

• Salt marshes mainly occupy polyhaline (and sometimes euhaline) zones

• Mesohaline marshes often have the same plant communities as polyhaline zones

• “Brackish marsh” is a common term, but not a precise scientific salinity category

• Better to use exact salinity terms like mesohaline instead of “brackish”

• Brackish = informal, not a defined salinity range

Distribution

globally, Greenland to Aucklans NZ

accumulate in LOW ENERGY enviroments including:

estuaruies, embayments, lagoons, splits, back-back

Intertidal and Supratidal

mean high water up to limites of the highest astronomical tide

What factors affect survival through sedimentation in salt marshes?

• Accommodation space = volume available for sediment to build up

• Suspended sediment concentration = how much sediment is in the water

• Proximity to tidal channels/creeks = closer = more sediment delivery

• Hydroperiod = how long the surface is flooded/inundated

• Settling rate = how quickly sediment drops out of water and accumulates

Salt marshes- masters of OM accumulation

High primary production

produces high litter that accumulates nutrients generally in good supply

Salt marshes- masters of OM accumulation

Slow decomposition

Tides (alternating inundated/dryer) limit oxygen which increases accumulation

Zonation order

• Low marsh: Spartina alterniflora

• High marsh: Spartina patens, Distichlis spicata, Juncus roemerianus

• Salt pannes: Salicornia spp. & Sarcocornia spp.

• Upland: not part of marsh system (too high elevation, not regularly flooded)

Salt Pannes

• Shallow, poorly drained depressions

• Usually found in the high marsh zone

• Formed by wrack accumulation or ice scouring after spring high tides

• Can be ponded or contain succulent plants

• Often become hypersaline due to evaporation, especially when vegetated

Extreme systems: Hypersaline Salt Marshes

twice the saline of salt ocean water

maybe 6 worldwide

Laguna madre

Abiotic factors vs Biotic Factors

• Seaward edge: controlled by abiotic factors (physical/environmental stress like flooding, salinity) → determines survival

• Upland edge: controlled by biotic factors (mainly competition between plants) → determines survival

Plant Adaptations

• Salt excretion (recretohalophytes) = removes excess salt

• Halophytes vs glycophytes = salt-tolerant vs non–salt-tolerant plants

• Aerenchyma = air spaces in roots that help move oxygen

• Root oxidation = oxygen released from roots into surrounding sediment

  • oxygen leaves through root zones with aerenchyma

  • occurs where there is no barrier to radial oxygen loss

Spartina alterniflora (Smooth cordgrass)

• True grass (Poaceae)

• Dominant in low marsh (US Gulf & East coasts), often forms monoculture

• High salt tolerance

• Can be invasive (US West Coast, Europe, Asia)

• Adaptations:

  • Salt glands (salt excretion)

  • Aerenchyma (air spaces for oxygen transport)

  • Radial oxygen loss

  • Rhizomatous growth = spreads via rhizomes, adds stability

Juncus roemerianus (Black needlerush)

• A rush (graminoid, not a true grass)

• Dominant in the high marsh (SE & Gulf coasts)

• High salt tolerance, but prefers lower salinity than low marsh species

• Rhizomatous growth = provides sediment stability

• Note: Eye hazard (sharp, stiff leaves)

Spartina patens & Distichlis spicata

• Both are true grasses (Poaceae)

• Found in the high marsh, often together

• Can be co-dominants, or S. patens may be more abundant

• Common in higher latitudes in the USA (less expansive in low latitudes)

• Have extensive root/rhizome systems

Adaptations:

• Spartina patens: curls leaves to protect stomata (gas pores)

  • also helps with drought tolerance → found on dunes too

• Both adapted to survive in both very wet and very dry conditions

Salicornia spp. (Sea beans / glasswort)

• Includes species like Salicornia virginica and Salicornia bigelovii

• Halophytes (salt-tolerant plants)

• Succulent plants → store water

• Water storage helps dilute internal salt concentration

• Common in salt pannes

• Very high salt tolerance

• Edible (“sea beans”)

Interactions

• Connected to unvegetated intertidal flats

• Linked with shellfish beds and reefs

• Connected to seagrass beds located lower in the tidal frame

• These systems are ecologically and physically connected through tides, sediment, and nutrient exchange

Ecosystem Services

• Highly productive ecosystems

• Nursery habitat for marine organisms

• Shoreline protection (reduces erosion, buffers storms)

• Water filtration (traps sediments and pollutants)

• Hotspots of biogeochemical cycling:

  • Nitrogen cycling

  • Sulfur cycling

  • Carbon cycling

  • and more nutrient processing

Salt marsh threats & solutions

Threats:

• Sea-level rise

• Development

• Eutrophication / pollution

• Invasive species

• Marsh dieback

Solutions:

• Thin layer placement (sediment addition)

• Living shorelines

• Planting vegetation

• Restoring tidal flow

Salt marsh physical structure & faunal patterns

• Channels, berms, back marsh areas shape habitat use

• Tidal creeks = main pathway for larvae + nekton movement

• Moving away from channels → changes in:

  • nutrients & sediment input

  • grain size

  • productivity

  • faunal diversity

• Edge → interior changes can happen over just a few meters

Faunal diversity patterns in salt marshes

• Highest diversity in channels + marsh edge

• Diversity decreases toward marsh interior

• Reasons:

  • most organisms are aquatic in origin

  • higher risk of stranding at low tide inland

• Exceptions: insects, birds, some mammals

Primary consumers in salt marshes

• Grazers (less common): insects, snails, mammals, birds

• Detritivores (deposit feeders): oligochaetes, polychaetes, amphipods, snails

• Suspension feeders: oysters, clams, mussels, polychaetes

Detrital food pathway in salt marshes

• Most plant production enters detrital food web

• Breakdown by bacteria + fungi before consumption

• ~80–90% energy loss through trophic steps

• Some carbon is buried (debated amount)

• Also direct producers:

  • periphyton

  • macroalgae

  • benthic microalgae

Resident vs transient marsh fauna

Residents:

• live in marsh full-time (or most life stages)

• ex: grass shrimp, killifish, fiddler crabs

Transients:

• use marsh seasonally/tidally (often juveniles)

• ex: blue crabs, shrimp, flounder, croaker

• mainly use edge habitat (within ~2–5 m)

Why do transient species use salt marshes?

• Food: high invertebrate productivity

• Growth: warmer water → faster growth

• Protection: vegetation = refuge from predators

• Must still move to deeper channels at low tide

Human-use species in salt marshes

• Blue crabs (#1 NC fishery)

• Penaeid shrimp (#2 NC fishery)

• Flounder (nursery + foraging + refuge)

• Diamondback terrapin (species of concern)

• Many birds, oysters, clams also important

Bird use of salt marshes

• Feeding + nesting habitat

• Some are dependent residents (rails, wrens, sparrows)

• Others are migratory feeders (herons, egrets, geese, ducks)

• Back ponds especially important for waterfowl

Threats to salt marsh systems

• Sea-level rise (from earlier topic context)

• Development + dredge/fill

• Water quality decline

• Sediment budget disruption

• Climate change impacts

• Species interactions (e.g. crab impacts)

• Natural erosion & senescence cycles

Salt marsh management strategies

• Preservation: regulations + protected areas

• Water quality management + buffers

• Restoration/creation:

  • replanting vegetation

  • restoring tidal flow

  • designing marsh topography + channels

  • thin-layer sediment addition

• Focus on function, not just structure