BOMO: salt marshes

salt marsh

intertidal habitat w/ sediment/peat as substrate- sediment is bound up & supported by plant roots

“most terrestrial marine habitat” - most organisms are terrestrially derived

autogenic structure

structure built by & persisting b/c of organisms that reside in it

where do salt marshes occur

calm, protected, low flow coastlines with high sediment supply- broad, flat shorelines on passive margins

salt marshes re self-perpetuating

colonizing grasses decrease water flow via friction with above ground biomass, which enhances sedimentation

aggressive vegetative growth & root expansion stabilizes marsh structure & binds sediments together

as marshes age, the high marsh zone expands bc of sedimentation

rhizome

horizontal underground root network capable of producing new plant shoots

low marsh zone

inundated every day, very stressful, characterized by spartina alterniflora, which is halophytic

Spartina alterniflora

tall form found at seaward border bc there are more nutrients, salt doesn’t build up b/c flushed more often, lower soil

short form found behind tall form in higher soil that has bad draining

mid/high marsh

characterized by Spartina patens, Juncus gerardii, Salicornia europaea, & distichlis spicata

high marsh/ terrestrial border

characterized by iva frutescens, solidago semipervirens, limonium carolinianum, boloboschoenus robustus, spartina pectinata, and phragmites australis

salt marsh stressors

water logged soil & salinity

waterlogged soil

anoxia occurs, reduced below ground metabolism

roots & microbiota consume o2 below ground

o2 diffused slower in water- no more air pockets in soil

avoiding waterlogged soil

grow in higher elevations that are rarely inundated or waterlogged or the seaward edge thats flushed more or grow near bioturbating animals that increase sediment o2 lvls

have anaerobic metabolic pathways, which helps to withstand temporary periods of anoxia

keep rhizomes near the air-sediment interface to maximize o2 exchange with air

facilitate transport of o2 to soil using aerenchyma

aerenchyma

tissue of air-passage conduits extending from leaves to below ground- o2 in leaves passively diffuses to roots & creates an o2 halo around roots in anoxic environ

salinity (stressor)

external hypertonic conditions lead to cellular dehydration- too many internal inorganic salts interfere with metabolism

avoiding salinity stress

reduce water loss by making roots hypertonic to sediments (increase concentration of organic solutes)- limits osmotic water loss & draws in fluid or having a succulent body plan (thick waxy coverings, reduced leaves, reduced stomata) or store a lot of water by having enlarged h2o storage vacuoles

excrete salts- cellular pumps actively excrete salts across membranes, salt glands excrete salts onto leaves, concentrate salts into certain tissues & then drop them

mobile grazers in the salt marsh

insects & vertebrates (terrestrially derived), gastropods & crabs (marine derived)

herbivory on low-salt marsh plants- protected by structural & chemical defenses- reproductive tissues more heavily grazed

suspension feeders in the marsh

restricted to low marsh, marine derived

barnacles, infaunal clams, oysters, & the ribbed mussel (geukensia demissa)

geukensia demissa

feed primarily on phytoplankton & form dense beds at the base of s. alterniflora, gregarious, & semi-infaunal

symbiotic relationship between Geukensia demissa & spartina alterniflora

s alterniflora keeps g demissa from sinking in mud & excretions fm g demissa provides s alterniflora w. nutrients

predators

shrimp, crabs, fish, & birds

decomposers/detritovores/deposit-feeders

bacteria & fungi break down decaying material

amphipods, worms, gastropods, & crabs feed on decaying matter or bacteria/fundi on decaying matter

salt marsh zonation

lower limits set by physiological stress, upper limits set by competition for terrestrially derived animals

salt marsh ecology is dependent on positive species interactions…

mutualism btwn g demissa & s alterniflora

habitat amelioration btwn adjacent plants

bioturbation facilitates plant growth

succession after disturbance

bare patch is hypersaline & anoxic→ colonized by opportunistic/stress-tolerant species that ameliorates patch & facilitates later successional species that displace competitive subordinates

ecosystem services provided by salt marshes

source of production for neighboring habitats

nursey ground for young fish, crabs, & shrimp b/c of the reduced predation in shallow water full of plant stems

coastal buffering- roots prevent shoreline erosion, protect from storms/waves, & intercept nitrogenous runoff from land

salt marsh uses

used to be used for harvesting & livestock grazing, ditching & draining for mosquito control,

used for dredge material, eliminating salt marshes

coastal squeeze

salt marsh cant go landward b/c of humans & cant migrate fast enough to avoid sea lvl rising