Week 10 Salt marshes, Plants

Question 1

Describe a saltmarsh.

Answer 1

Saltmarshes:
-upper end (trees plants)
-upper marsh (high salinity levels) M.H.W.S.T.L. (doesn’t encounter seawater often)
-most of marsh:
Mid upper marsh-species rich communities
Lowmid marsh 
Pioneer zone – most plants
Mudflap- mostly underwater
-M.H.W.N.T.L encounters water often 
Herbaceous vascular vegetation on sheltered particulate shores between MHWNTL and MHWSTL.

Question 2

What role do plants play in marshes?

Answer 2

• Plants of terrestrial origin invading a stressful
environment.
Inverse relationship between elevation and
sediment accretion rate. (the higher the marsh, the less sediment)
Mature marshes are flat as deposition to seaward is initially higher because it is lower and later plants intercept sediment and stabilise it. Plants on top of mud-sediment

Question 3

How can saltmarshes act as coastal defense?

Answer 3

Saltmarshes dissipate wave energy, reduces damage to, and overtopping of, sea walls.
• With 80 m of saltmarsh a sea wall needs be only 3 m high and cost £400 per linear m.
• With no marsh wall needs to be 12 m high and costs £5000 per linear metre.
• In Essex alone, where there are 440 km of sea walls protecting a subsiding coast, saltmarsh value = £600m.
• Creates a seawall- protects us from erosion of coast.

Question 4

What is the importance of saltmarshes?

Answer 4

• Very high primary productivity. Similar to TRFs! (tropical rainforest) however not many and very big
• Most (plant material) is exported as detritus to food webs in adjacent habitats – including mudflat invertebrates and then fish/birds.
• Some species are nationally rare or scarce e.g. Laxflowered sea lavender.

Question 5

What creatures feed or live in saltmarshes?

Answer 5

-Habitat for Birds:
• Many birds nest in saltmarshes particularly Redshank (60% of UK population).
• Upper marshes may not be reached by spring tides from May to August. (good place of shelter for birds)
-Roosts:
• Saltmarshes provide convenient (close to food) and relatively undisturbed roosting areas for waders (especially on neap tides).
• Geese and Widgeon eat some saltmarsh
plants (now contain more N than previously)
-Invertebrate fauna:
The polychaete Nereis diversicolor. Eats diatoms, seeds and seedlings, plankton and small invertebrates. (does everything) (closely related to earthworms) Corophium volutator and amphipods also found in saltmarsh. Carcinus maenas tunnels into the banks of creeks in salt marshes.
-Birds coexist/live with invertebrates.
-Fishes:
• Fishes use saltmarshes, especially creeks. (important shelters, bigger fish cant get there) (especially for zero group fish/babies)
• e.g. 0 group bass feed only when in saltmarsh or mudflat habitats.

Question 6

How important are saltmarshes to humans?

Answer 6

• 88% of UK saltmarshes are designated one or more of:
• SSSI (site of special scientific interest)
• National Nature Reserve, Local Nature Reserve (UK).
• Special Area of Conservation, Special Protection Area (EU).
• Ramsar (International). (weapons treaty)

Question 7

How are saltmarshes formed?

Answer 7

• Saltmarshes are assumed to form through
facilitated succession. (diatoms)
• Sand/mudflat with benthic diatoms – secrete EPS (extracellular polymeric substances) that bind and stabilise the sediment - which rises to an elevation suitable for pioneer zone vascular plant species (e.g. Salicornia europaea). (turns it into a film, plants can take root and stabilize it more)

Question 8

What plants are found in saltmarshes?

Answer 8

-Elytrigia atherica (sea couch grass)
-Puccinellia maritima (saltmarsh grass)
-Salicornia europaea (marsh samphire)
Further enhance sediment accretion to levels suitable for higher species.

Question 9

How do the plants and the marsh succeed (grow)?

Answer 9

• The marsh develops upwards and extends seawards (progradation).
• Plant species show a vertical zonation. Lower limit is dependent on their tolerance to physical and chemical factors (esp. salinity) and the upper limit by interspecific competition. (more species)

Question 10

What is saltmarsh erosion and why does it occur?

Answer 10

• Saltmarshes are disappearing rapidly with annual losses of 1-2% worldwide. (we expect them to grow/they grow well, however opposite happens)
• Causes include land claim (reclamation) and erosion suggested to be due to:
• increased storms (no evidence).
• sea level rise and coastal squeeze (no evidence).
• nutrient pollution.
-Reduced to about 10% of former levels (marshes), mostly by land claim from Medieval times.
• For past 50+ y a further two thirds has gone through erosion mostly from the pioneer zone.
• A major conservation and flood defence problems (annual cost £6 m)

Question 11

What’s an example of a salt marsh?

Answer 11

Tollesbury (Essex) saltmarsh
• Typical extensive creek system. (river)
-land reclamation (lots of the marsh lost this way)
-mudflap-normal marsh
-quite a bit of greenery

Question 12

What is creek erosion?

Answer 12

• A few saltmarshes are eroding at the seaward face, but most erosion is by expansion of creeks- erosion of mud which erodes the plants
• Both have a different/additional biological explanation: nutrient pollution

Question 13

What is nutrient pollution and what does it have to do with marsh erosion?

Answer 13

• Deegan et al. 2012: large scale experiments (in NE USA) nutrients (N and P fertilisers) added to incoming tidal currents in creeks for 9 years.
• Decrease in root biomass, increase in aboveground biomass, and increased vulnerability of plants to herbivores (plants do not have to grow roots as nutrients readily available)(high nitrogen content makes them more attractive to herbivores)
• Led to collapse of creek banks; saltmarsh converted to mudflat. Changes not apparent for several years (and probably overlooked by a standard research project).
-Normal nutrient levels- narrow creek/deep rooted plants, lots of organic matter
-High nutrient level- big plants with low roots ,creek banks collapsing, wide creeks, less organic matter, eroding
.Creek erosion - a rotational slump (the whole area falls, the bottom falls in the water)

Question 14

What is eutrophication?

Answer 14

EUTROPHICATION: (too much nutrients)
• Eutrophication (post war) has increased
sediment surface resources, encouraging…
• Deposit-feeding (rather than filter-feeding) (deposits on surface of water) by Nereis.
• Increased population densities of Nereis. (algae on top of water surface)
-leads to Sediment erosion

Question 15

How can food webs be analyzed through stable isotopes?

Answer 15

Two main stable isotopes of carbon 13C/12C and nitrogen 15N/14N. Their ratios are useful in food web studies -as there is a mean enrichment of 15N and 13C between different trophic levels because metabolism (and excretion) preferentially uses the lighter isotope.

Question 16

What problems exist with nitrogen enrichment?

Answer 16

Waste-water nitrate is more enriched with 15N (typically 10-20‰) than natural 15N values (2-8‰) because bacteria preferentially metabolise 14N in denitrification etc. Consequently the terrestrial sources of some pollutant N can be identified. Direct nitrate runoff can’t be identified via this method as the Haber-Bosch process uses N2 gas as its N source (and N2 gas is the reference against which the isotope ratio is measured). (no difference with N2 gas)

Question 17

Is nereis increasing?

Answer 17

• Nereis abundance has seemingly increased in the past few decades. Why?
• Nereis is known to favour organically enriched (sewage polluted) areas (and to decrease in abundance on clean-up).(nereis tied to excess nutrients)
• Marja Aberson (2011) examined variations in food sources and abundances (biomass) in sewage affected sites and “clean” sites in 4 estuaries (and 4 seasons).
-“Across all estuaries studied Nereis was mainly deposit feeding on sediment organic matter, Ulva sp., but with suspension feeding being more important at the cleaner sites”. (where theres more nutrient pollution, more diatoms, nereis growing more)
• In almost all dates/sites biomass was higher in polluted sites then clean ones.
• The N signal indicated significant enrichment in their diet from terrestrial sources.

Question 18

What effect does Nereis abundance have on the saltmarshes?

Answer 18

Nereis are more abundant, and their rates of deposit feeding are higher, at the saltmarsh-mudflat interface, because of nutrient enrichment.
• Leading to loss of saltmarsh vegetation - directly through herbivory, and indirectly through increased sediment instability (on mudflats and in creeks).
-Nereis exclusion experiments demonstrate absence of pioneer zone vegetation where the sediment is high enough is due to bioturbation and herbivory (they eat seeds and seedlings)
-Sediment accretion on Nereis exclusion mats in a creek at Tollesbury. Nereis destabilises the creeks, leading to a positive feedback of flow rates.
-Nereis exclusion can lead to sediment accretion over relatively large areas, and (potentially) reverse the feedback of increased erosion. (new colonization,more creeks/biomass, more roots)(slowly being repaired/can be repaired)

Question 19

Can saltmarsh erosion stop?

Answer 19

• Saltmarshes are important as habitats for species and coastal defence.
• Saltmarshes have been lost historically through land reclamation but are now at threat from erosion.
• Eutrophication from agricultural runoff causes major changes to plants and animals leading to conversion to mudflats.
• This may be reversible.

Question 20

What is the importance of plants?

Answer 20

-Plants are important as sources of food
-as sources of fuel, fibre and medicines (willow- salix spp. to salicylic acid to aspirin)
-as sinks of CO2 and sources of O2 (Photosynthesis releases oxygen – respiration releases CO2)
-Plants also provide habitats for other plants Climbing plants have evolved to use other plants as habitats (and in some cases as food)
-and habitats for animals (eg. fruit bats,wasp nests, woodpeckers)
Plants provide many benefits to humans – e.g. hedgerows
house natural enemies of pest species…and pollinators of
crops

Question 21

What effects do plants have on ecosystems?

Answer 21

Ecological experiments have shown that “ecosystem
functioning” is positively related to plant biodiversity
- e.g. Cedar Creek experiment in America – demonstrated importance of species richness for enhancing overall plant growth

Question 22

How many plant species are there on earth?

Answer 22

Scientists estimate there are approximately 300,000 plant species on Earth

Question 23

How is plant diversity distributed globally?

Answer 23

• the closer to the equator, the more plants
• Temperature determines large scale patterns of biodiversity
• distributed in the major biomes of vegetation

Question 24

What are the major biomes of vegetation?

Answer 24

• mountains: Alpine meadow plant assemblage – flowers above the treeline
• tundra: Moss forms thick carpets – eventually building deep peat beds
• tropical rainforest: Hotspots of biodiversity and extreme specialisation (e.g. Titan Arum Lily)
• savanna: Baobab trees in the Serengeti (above) have thick, fire resistant bark and can store large volumes of water during the dry season
• desert: Saguaro cacti in Mexico can live for hundreds of years, reach heights of many metres & are extremely drought tolerant
• chaparral: Cork oak in the Mediterranean – the thick bark acts as a defence against fires and drought.
• Northern conifer forest: Cathedral Grove in Canada holds some of the largest organisms on the planet – some of these Giant Sequoias (Sequoiadendron giganteum) are >3,000 years old
• temperate forest: The natural vegetation type for almost all of Britain – most of the original “wildwood” has been cleared progressively since the Neolithic. Less than 1% now remains.
• tropical seasonal forest: Monsoon rains and forest fires create a dynamic and challenging environment
• temperate grassland: The Pampas of S. America – gauchos manage herds of cattle raised on the vast grassy plains – these ecosystems provide much of the world’s crops and livestock

Question 25

Which biome is predicted to lose the most species by 2050?

Answer 25

• warm mixed forest

- followed closely by temperate deciduous forest

Question 26

What limits plant distribution?

Answer 26

• Temperature & rainfall both determine vegetation biomes, however temperature changes over time (as well as space)
• As the continents have migrated over the planet, their climates and vegetation have also changed ( 150 mybp Earth had two supercontinents – Laurasia & Gondwana – these split and the new land masses moved across the Earth, eventually forming our contemporary continents)

Question 27

How has plant distribution changed over time?

Answer 27

-50 million years ago much of the continental land masses
were covered with tropical forest (“Petrified forests” of ancient fossilised trees can be found in now arid regions)
-32 million years ago the climate was drier and savanna had replaced many of the tropical forests
-10 million years ago many biomes broadly represented their current distribution
-Rainforests have also contracted and expanded over more recent time
-Long term shifts in N. American vegetation tracks climate change cycles - Post-glacial warming trend in N. American vegetation

Question 28

What role do thermal trends play in change in vegetation?

Answer 28

-Thermal gradients have strong influences on the spatial distribution of individual species -e.g., temperature & altitude constrain the ecological “niche”
-Thermal limits to species distributions in Europe- e.g. Small-leaved lime (Tilia cordata) has a
clear temperature “envelope” that maps its spatial distribution in Europe

Question 29

How can we detect adaptation?

Answer 29

• Detecting adaptation – transplant experiments :
  1. Umbilicus rupestris, after 8 years growing in Sussex from a population in mild-wintered area in S. Wales. Survival was better for the Sussex population – revealing local thermal adaptation to colder conditions
  2. Sapphire rockcress from drought-prone low elevation sites & high elevation sites were raised together – the former had better water efficiency and grew better (e.g., broader rosettes)

Question 30

What do we know about plants?

Answer 30

• Plants have a critical role to play in ecosystems
• Have numerous benefits to humans
• Plant distribution mediated by temperature (min and max) and rainfall
• Many are at risk of loss
• Local adaptations within populations are known