6: Mangroves Flashcards
What are 4 adaptations of mangrove vegetation that makes them suitable mangrove environments?
1 root structure
- breathable roots
- vivipary and proagule seed dispersal
- Salinity tolerance
What are vivipary and propague seeds? How does this aid their survival and dominance in mangrove environments?
They are seeds that have started to grow before they disperse from the plant . This means that they can stick to the ground once they fall which gives them greater resistance against tides so they can get a foothold and they can also root quickly in to the ground once this has happened as they are already fairly matured
Where are mangroves located usually and outline the Australian difference?
They are typically located in the tropics but in Australia they strangely stretch further towards the poles.
Where did mangrove species first derive from? What happened once they left this area?
Central Pacific - once the species dispersed further from this area either East or West they developed in to two very dissimilar species
What was the name of mangrove species that dispersed west?
Indo-West Pacific
What was the name of the mangrove species that dispersed east?
Atlantic East Pacific
Which area has the highest diversity/concentration of mangrove species?
Indonesia
What happens to mangrove species diversity with latitude?
Decreases
Why is the mangrove species diversity in the south hemisphere much greater?
Because there is more ocean and less land
What is the limit of the southern hemisphere mangrove distribution and why?
Corner Islet, after this is the Bass Strait which features too cold water temperatures
What forms in mangroves and why?
Zones of different species due to different tolerances of salinity, fluidity and oxygen concentrations
What distinguishes mangroves in N. Australia?
They are usually a lot thicker and taller at the front when it progrades outwards and forward
How to describe saltmarshes in relation to mangroves and why?
Cousins - they are usually found in more temperate regions (e.g. Tasmania)
What are the rough 6 zones of mangrove zonation?
Bare mudflats, seaward amrgins, Rhizophora, Transition, Tidal Flat, Salt Flat
What allows the identification of different mangroves’ zones?
Compiling images of mangroves at highest 10% of high tides and lowest 10% of low tides. This enables identification of composites from which spectral signature can be inferred and used to define the vegetation and therefore zones of the mangrove
What is the role of tides in mangrove environments?
Bring sediment/material to the mangroves at high tide. When at high tide and following the retreat of the tide line they deposit the material at high tide
What effect does the sedimentation at high tide have upon the mangrove environment?
Progradation at upper sections of the mangrove and relative subsiding of the lower sections of the mangrove.
What are the 8 physical factors that affect the development of mangroves over time, in order of bigger to smaller timescales of operation?
Tectonism Eustatic sea level Ocean circulation Steric sea level channel migration floods and storms waterbody mixing tides
What are the 7 biological factors that affect the development of mangroves over time, in order of bigger to smaller timescales of operation?
Evolution Mangrove life history competition epidemic disease propagule viability Organism interactions Microorganisms
What spatial factors affect the distribution of species in mangrove environments?
Dominance of freshwater/saltwater
Differing amount of fluvial/marine deposition
Outline the likely mangrove setting in lagoon environments?
Lagoons do not have an inlet and so the tidal range is limited. This also means that the substrate is thinner as there is no repeat pattern of deposition. This simple environment also means there is likely to be homogeneous vegetation
Outline the likely mangrove setting in fringe environments
Opposite to lagoon. They have a good access to tidal variation and so the supply of sediment to the substrate is fairly consistent meaning the mangroves become fairly strong
Outline the likely mangrove setting in island environments
They are basically to exposed to the coastal tidal variation because of their low elevation and so the mangroves are overwhelmed meaning they cannot develop well
Which area was found to have a set of additional unique factors affecting the distribution/environment of mangroves?
Australia
What affected mangroves at the (1) global scale; (2) environmental setting; (3) hydrology and topography?
global scale = temperature
environmental setting = geomorphic type
hydrology and topography = ecology
What were the 3 scales that Colin proposed for affecting mangrove environment and associated factors to these scales?
Macro = climate and sea level change Meso = Hydrodyanmics and sedimetn supply Micro = Geomorphic processes and biologic processes
What were some examples of things in the macro scale for things affecting mangrove environments?
Climate = temperature, precipitation and storms
Sea level = SLR and subsidence
What were some examples of things in the meso scale for things affecting mangrove environments?
Hydrodyanmics = inundation and salinity
Sediment supply = inorganic and organic material
What were some examples of things in the micro scale for things affecting mangrove environments?
Geomorphic processes = accretion, nutrient addition, autocompaction, shrink/swell
Biological = above-ground biomass production, below-ground biomass production, decomposition
What is the tidal frame?
The difference betweent eh highest astronomical tide and the mean neap tide in relation to occupation over the substrate (vertically or translated laterally)
What section of the tidal frame is usually occupied by mangroves?
Half plus a bit extra towards inland (this half is usually the more inland section from just before the highest astronomical tide mark and a bit before the mean sea level mark
What is the name given to the area that the mangrove environments occupy?
Available accommodation space
What is the total accommodation space?
Where material/sediment is deposited from the influence of tides (this includes the available accommodation space)
What makes the total accommodation space so suitable for mangrove environments as opposed to just the underlying substrate?
The realised accommodation space is composed of sediment that is softer which is easier for mangroves species to occupt
What is the realised accommodation space?
The area where vegetation can grow and because the deposited material is softer it increases the available accommodation space
What happens to the available accommodation space with the knowledge that the tides have deposited softer substrate? What does this mean for vegetation on mangroves?
It gets bigger and so the vegetation can now grow further out towards the sea
What happens to the tidal frame and therefore all the different accommodation space categories in light of sea level rise?
Vertical range of the tidal frame shifts upwards. This causes the accommodation spaces to shift or extend further inland depending upon the condition of the realised accommodation space (deposited material above the substrate_
What happens to the state of the realised accommodation space due to SLR and why?
It extends further inland and this then also means that it receives more organic material due to vegetation life cycles
What are the 8 ways that the available accommodation space can increase due to SLR?
Eustatic SLR Deep subsidence Tectonism Hydrological changes along estuaries Organic matter decomposition Root zone collapse Substrate compaction or consolidation
What happened to sea level around Australia around 8 and 6 ka?
At 8ka it started to rise slightly and then by 6ka it stabilised a bit but then continued to rise abit
What happened to mangroves in Australia in light of the sea level changes that took place?
At 8ka the sea level is not high enough and so there is no sediment and therefore no suitable mangrove environments. But then at 6ka it has risen sufficiently so that sedimentation can occur. Mangroves start to occur as vegetation is supported. But SLR is too much and so eventually the sedimentation becomes too much as well resulting in the many mangroves becoming uplifted too much to form floodplains. Mangroves are forced to the interior of valleys.
What has enabled us to see how the environment changed its sedimentation rate and therefore species changed from those seen in mangroves to floodplains? Which paper was this found in btw and which area does it apply to?
Sediment cores. Woodroffe et al. (1985) in Northern Australia
What happens to vegetation at the three stages of SLR in northern Australia? (in Woodroffe et al. 1985)
Firstly there is a lot of low elevation species (Rhizophora) then species diversification occurs as SLR due to Rhizophora being outcompeted in a range of environments that are not all ideally suitable to that species. As sedimentation continues the mangrove retreats back to the shoreline as more inland areas are no longer inundated by tides as they are too high. Instead saline flats form behind the mangrove
