Lecture 7 - Intertidal Zone

Intertidal zone

Region between high and low tide that alternates between aquatic and terrestrial conditions

Zonation

Vertical distribution of organisms across tidal gradients driven by abiotic and biotic factors

Spray zone

Highest zone exposed to air inhabited by lichens and highly desiccation-resistant organisms

Upper intertidal

Zone with extreme desiccation and temperature stress where organisms tolerate air exposure

Middle intertidal

Zone with both abiotic stress and strong biological interactions such as competition and predation

Lower intertidal

Zone mostly submerged where predation and competition dominate

Desiccation

Water loss due to exposure to air during low tide

Crustose algae

Algae that grow tightly adhered to rocks and incorporate calcium carbonate for protection

Acorn barnacle

Sessile crustacean that uses cirri to filter feed and exhibits strong allee effect

Cirri

Modified appendages used by barnacles to filter plankton from water

Blue mussel

Filter-feeding bivalve that attaches to substrate using byssal threads and dominates space

Byssal threads

Strong protein fibers used by mussels to attach to rocks

Dog whelk

Predatory gastropod that drills into shells of mussels and barnacles using a radula

Sea star

Keystone predator that feeds on mussels and maintains biodiversity

Foundation species

Species that structures a community by dominating space or resources

Keystone species

Species with a disproportionately large effect on ecosystem structure relative to its abundance

Allee effect

Correlation between population density and individual fitness measured as per capita growth rate dN/dt

Strong allee effect

Population has a critical threshold below which growth becomes negative and population declines

Weak allee effect

Fitness increases with density but population can still grow at low density

Estuary

Transition zone between freshwater and seawater with variable salinity

Coastal plain estuary

Drowned river valley formed by sea level rise

Bar-built estuary

Estuary separated by barrier islands with restricted tidal exchange and extreme salinity fluctuations

Delta estuary

Estuary formed by sediment accumulation at river mouths with shifting channels

Tectonic estuary

Estuary formed by land subsidence due to tectonic activity

Fjord

Glacially carved deep estuary with strong stratification and a sill

Sill

Shallow barrier at fjord entrance that restricts water exchange

Flushing time

Time required to replace freshwater in an estuary

Tidal prism

Difference in water volume between mean high tide and mean low tide

Salt wedge estuary

Highly stratified estuary where freshwater flows over denser seawater

Vertically mixed estuary

Estuary with uniform salinity due to strong tidal mixing

Isohaline

Line connecting points of equal salinity

Eutrophication

Nutrient enrichment leading to algal blooms and oxygen depletion

Salt marsh

Temperate coastal wetland dominated by halophyte grasses

Halophyte

Plant adapted to grow in high-salinity environments

Euhalophyte

Plant that dilutes salt within tissues

Recretohalophyte

Plant that excretes salt through glands or hairs

Pseudohalophyte

Plant that blocks salt uptake at roots

Pickleweed

Succulent halophyte that stores water and salt in tissues

Anoxic sediment

Low oxygen environment caused by high decomposition rates

Sulfate-reducing bacteria

Anaerobic microbes that dominate in low oxygen sediments

Detritus

Dead organic material that fuels the food web

Blue carbon

Carbon stored in coastal ecosystems such as salt marshes and mangroves

Nutrient loading

Excess nutrients increase shoot growth but reduce root stability leading to marsh collapse

Inundation

Flooding due to sea level rise that increases anoxia and kills plants

Coastal squeezing

Loss of marsh due to urban barriers preventing landward migration

Invasive species

Non-native organisms that outcompete native species and alter ecosystems

Green crabs (Carcinus maenas)

Invasive crab that disrupts sediment and preys on native species

Common reed (Phragmites australis)

Invasive reed that suppresses competitors and alters marsh hydrology

Genetic paradox of invasion

Invasive species succeed despite low genetic diversity due to advantageous gene combinations

Phenotypic plasticity

Ability of an organism to change phenotype in response to environment

Mangrove

Tropical coastal ecosystem dominated by salt-tolerant trees

Prop roots

Structural roots that stabilize mangroves in soft sediment

Pneumatophores

Aerial roots that allow oxygen uptake in anoxic mud

Vivipary

Seeds germinate while attached to parent plant

Tropicalization

Replacement of salt marsh by mangrove due to warming

Mudflat

Soft sediment tidal habitat exposed at low tide

Infauna

Organisms that live within sediment

Bioturbation

Mixing of sediment by organisms which redistributes oxygen and nutrients

Deposit feeder

Organism that consumes organic material from sediment

Filter feeder

Organism that filters particles from water

Pacific razor clam

Burrowing bivalve that uses a siphon to feed and can switch to anaerobic respiration

Holdfast

Structure that anchors macroalgae to the substrate and does not absorb nutrients

Stipe

Central stem-like structure of macroalgae with no true vascular tissue

Blade

Thin flattened leaf-like structure of macroalgae

Pneumatocysts

Gas-filled structures that provide buoyancy to macroalgae

Sill effect

Restriction of water exchange in fjords due to a shallow barrier at the mouth

Wind-driven mixing

Mixing of water in shallow estuaries primarily caused by wind rather than tides

Extreme salinity fluctuations

Rapid changes in salinity in bar-built estuaries due to isolation or evaporation

Carbon sequestration

Long-term storage of carbon in sediments and biomass