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39 Cards in this Set
- Front
- Back
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Spartina-Dominated Salt Marshes
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-Salt marshes are accretionary environments
=>water tidal areas -Marsh Spartina spp. plants spread by means of a rhizome system ==>maintain structure of marsh sediment and entire salt marsh |
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Spartina salt marshes → dominated by cordgrasses
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-Function as ecosystem engineers by binding fine sediment and causing the buildup of meadows above low water
-Buildup of sediment results in formation of organic peat, colonized by other species at higher levels |
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Succession in Spartina-dominated Salt Marshes
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-SA -> SA + Peat -> other species colonization (SA, SAS, SP)
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Spartina Adaptation
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*Sediments are often anoxic
-tissues are highly vascularized -Aerenchymal tissue- =>allows Spartina to exchange gases, even when surrounded by anoxic soil ==>Provides a connection between leaves (aerobic) and stems and roots (usually in anoxic water) |
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Presence of fiddler crab in marsh
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burrows enhances Spartina growth, perhaps owing to aeration of the soil
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Presence of mussels in marsh
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-aids marsh accretion by trapping sediment and their organic-rich fecal material enhances plant growth
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Salt Marsh Creeks
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-older mature marshes consist of meadows with interspersed creeks
-creek often has strong tidal flow -The creeks have high nutrient input, support large populations of invertebrates and are often nursery grounds for juvenile fishes and crustaceans |
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Threats to Salt Marshes
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-Draining for mosquito control
-Filling for development -Coastal erosion -Accumulation of organic pollutants and metals -Construction of levees -Dredging of channels for boat traffic -Subsidence due to oil and gas extraction -Sea level rise |
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Mangrove Forests
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-common in subtropical and tropical protected shores around the world
-shrub-like or tree-like in form -Mangroves in lower latitudes tend to grow taller than mangroves in higher latitudes -broadly rooted but only to shallow depth in quite anoxic soils -Belowground tissue is exposed to anaerobic ==>slows nutrient uptake and allows toxins to accumulate -Also exposed to decomposing bacteria ==>Tissues have high concentrations of *tannins* (protects against bacterial invasion) |
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Mangrove Roots
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-Roots are adapted for anoxic sediments
-All species - roots have projections into air that allow gathering of oxygen for underground portions of roots |
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Knee roots or pneumatophores
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-are highly chambered and directed upwards into air; oxygen is gathered and directed into chambers and then transported to belowground tissues
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Prop roots
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Mangrove Roots
-extend midway from the trunk and arch downward for support |
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Fine roots
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Mangrove Roots
-are belowground; gather nutrients |
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vadose layer
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-layer of sediment penetrated by roots
-has high salt content (but usually less than full strength sea water) |
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Mechanisms for excluding salt
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-Secrete salt from leaves using salt glands
-Reduce salt intake with ultrafiltration system located in roots ==>Membrane-bound ion channel that can exchange H+ for Na+ ==>Energetically expensive to maintain osmotic gradient |
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Vertical Zonation of Mangroves
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-Zonation is strongly affected by seedling dispersal and predation of seedlings by invertebrates
-In SE Florida and Caribbean ==>Red mangrove (Rhizophora mangle) – dominates seaward portion of forest. First species to colonize unveggetated shorelines, has prop roots and tolerates full strength seawater and tidal inundation ==>Black mangrove (Avicennia mangle) – lies shoreward of red mangroves; tolerates occasional seawater inundation (usually at the highest high tides) ==>White mangrove (Laguncularia racemosa) – may be found landward of black mangroves; rarely inundated by seawater |
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Seeds of Red Mangroves
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-Germinate while still on tree; develop and dangle from parent until they drop off
-Fall into water and are carried away to another muddy shore where they will root in sediment ==>Seedling coat is shed, gives seedling *negative buoyancy* and causes it to drop to bottom |
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Competition with Upland Species
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-Florida hammock species are intolerant of salinity, but mangroves can grow in upland habitats with freshwater in soils
-So, mangroves must be competitively excluded from upland habitats by hardwood hammock species |
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Mangroves and Productivity
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-High primary productivity
-High supply of particulate organic matter, especially falling leaves, which subsidize animal growth -Roots support a rich assemblage of sessile marine invertebrates (mussels, barnacles), mobile invertebrates (crabs, shrimp, snails, etc.), and seaweeds -Deposit feeders dominant on roots and in sediments in seaward part of mangrove forests -Serve as nursery habitat for several fish species (ex. Goliath grouper) |
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Threats to Mangroves
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-Coastal development
-Shrimp farms -Sea-level rise from global warming |
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Estuary
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-partially enclosed section of the coast where freshwater from rivers mixes with seawater
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Watershed
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-the surrounding land that provides freshwater input to the estuary
==>Provides input of nutrients and pollutants to estuary |
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Drowned river valleys/coastal plain estuary
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-formed when sea level rose at the end of the last ice age (~18,000 years ago)
==>Examples – Chesapeake Bay, mouth of Delaware River, mouth of the St. Lawrence River, mouth of the River Thames |
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Bar-built estuary
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-accumulation of sediments along coast builds up – creates sand bars and barrier islands that act as a wall between the ocean and freshwater from rivers
==>Examples – estuaries along Texas coast, North Carolina coast |
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Tectonic estuaries
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-created when the land subsided due to movements of the Earth’s crust
==>Example – San Francisco Bay |
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Fjords
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Type of estuary created when retreating glaciers cut deep valleys along the coast; valleys partially submerged when sea level rose; rivers flow into the valleys
==> Examples – common in southeastern Alaska, Norway, British Columbia, Columbia, Chile, New Zealand |
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Salinity zonation in an estuary
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-Estuaries range from open marine → range of successive zones of decreasing salinity → tidal freshwater and associated creeks and marshes → freshwater
-Polyhaline -> mesohaline -> Oligohaline -> Tidal freshwater -> Nontidal freshwater |
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Estuarine structure
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-controlled by seaward flow of freshwater combined with tidal mixing
-Salinity structure of an estuary is determined by: ==>Watershed topography ==>Slope and size of river(s) feeding into main part of estuary ==>Size of main estuary channel ==>Tidal flow -river discharge important to salinity transitions within estuaries ==>Increased river flow in spring moves freshwater further down estuary ==>In summer, river influence might not be as strong due to low river discharge, low tidal flow -Storm events (hurricanes, etc.) can lower salinity throughout estuary |
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Salt wedge/highly stratified
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Estuarine Structure
-have a distinct low-salinity layer flowing towards the sea, with a compensating deeper high salinity flow moving upriver from ocean. Strong flow and low tidal mixing |
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Partially mixed
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Estuarine Structure
-partial mixing occurs by wind and tidal action. Has a stretch near opening of estuary where mixing occurs; salinity is still lower on surface than at depth |
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Vertically homogenous
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-usually very small and shallow estuaries. Wind fully mixes water to the bottom
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Estuarine Species and Salinity
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-Marine species can generally tolerate salinity fluctuations as long as salinity stays above 10-15 ppt
==>Some invertebrates can handle low salinities better than others -Estuaries with vertical stratification- ==>bottom organisms can go farther upstream than planktonic species -In mixed estuaries – ==>infaunal species experience less salinity fluctuation than epifaunal species b/c of buffering effect of sediment pore waters |
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Estuarine Species
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-Are some species (e.g. striped bass, salmon, killifish, blue crabs) that can osmoregulate quite well and can cross large salinity gradients in relatively short amounts of time (days to weeks)
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Estuary may serve as:
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-A nursery for juvenile fishes
-A spawning ground -Adult habitat |
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Buoyant flow
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-seaward net flow of low salinity surface waters in an estuary
-Some species have adaptations to counteract seaward flow and remain within estuary, others use this flow to be transported to the continental shelf |
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Suspension Feeders in Estuaries
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-Usually have large populations of suspension-feeding bivalves
-*Retention time* = the average number of days that a phytoplankton cell stays in an estuary -*Turnover time* = the number of days that it takes for a bivalve population to completely filter the water column -In *well-mixed estuaries*, bivalves may be able to greatly reduce phytoplankton densities (top-down effect) ==>Increases in phytoplankton have been observed in estuaries where the numbers of bivalves have been greatly reduced |
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What prevents all the water in an estuary from being filtered by bivalves?
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-Stratification
-Spatial heterogeneity of current flow |
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Top-down and Bottom-up Effects in Estuaries
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-Increased nutrient inputs (bottom-up)
==>High levels of phytoplankton in water column can decrease water clarity and have detrimental effects on SAV ==>Ungrazed phytoplankton dies and sinks to bottom; if too much sinks, it can overwhelm the deposit feeders on the bottom; results in bacterial decomposition and anoxic conditions at the sediment surface -Loss of top predators due to overfishing (top-down) can have cascading effects on lower trophic levels |
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Threats to Estuaries
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-Pollution
-Shoreline habitat alteration -Biological invasions |
