MARS2014 Lecture 10: Unit 10 - Primary Production (Key Players)
Unit 10: Primary Production (Key Players)
1. Who are the (7) key players in photosynthetic communities?
o Mangroves
o Seagrasses
o Algae
o Microphytobenthos
o Attached large seaweeds
o Phytoplankton
o Bacteria & Archaea
2. Hard and soft substrates
o Which organisms live in hard substrates?
▪ Macroalgae (live in both but prefer hard)
▪ Coral
▪ Microphytobenthos
o Which organisms live in soft substrates?
▪ Macroalgae
▪ Seagrass
▪ Microphytobenthos
▪ Mangrove
▪ Salt marsh
3. Which ecosystems/primary producers are important in the blue carbon cycle?
o Mangroves
o Seagrass
o Salt marshes
o They are all highly productive ecosystems and good at sequestering carbon
o They live in anoxic soil which prevents other organisms from using the carbon
4. Mangroves
o What are they/who are the key players?
o Mangroves are marine angiosperms (flowering plants)
o The grey mangrove (Avicennia marina)
o The red/river mangrove (Rhizophora)
o What is their environment?
o They live in the intertidal zone (between mean tide and highest tide,
submerged/inundated approx. 50% of the time)
o Soft sediment with high nutrient concentration, sheltered from large wave
action
o What kinds of mangrove forests are there?
o Forests associated with estuaries
o Forests on river deltas
o Forests on coastal embayments
o Forests on lagoons
o How are mangroves classified?
o By size and species composition
o As
▪ Tall riverine forests
▪ Seaward fringing forests
▪ Scrub forests (when mangroves are at thermal limits, <2m tall)
o What is their global distribution?
o Correlates with shallow coral reef distribution (tropical to sub-tropical) but
extends a little further north and south
o Most of their diversity is in the coral triangle
o Need a low wave energy (unlike coral)
o What influences mangrove zonation?
o Salinity
o Tidal inundation
o Nutrients
o Wave action
o What are their ecosystem services?
o They fix CO2
o They are the “kidneys” of the ocean --> clean up nutrients and remove any
suspended sediments
o Their roots provide a 3D structure and habitat for organisms --> this structure
also provides traction for soil and slows tidal water, in doing so trapping
sediments and nutrients
o Their dropped leaves in the sediment powers the detrital food cycle, which is
important for all the organisms in the sediment
o How have mangroves and salt marshes adapted to living in a salt environment?
o Some species limit uptake of salt through their roots
▪ e.g. Rhizophora
▪ This specialised mechanism to restrict salt uptake uses a "symplastic
over apoplastic transport", where the spaces around the cells (the
apoplast) through which nutrients can usually flow freely through are
blocked off, so that transport of nutrients into the roots can be
mediated by the symplast on the inner side of the cell membrane
o Some species have salt glands in their leaves
▪ e.g. Avicennia
▪ Salt is toxic to the cytoplasm so plants secrete it into their vacuoles and
expel it through their leaves
▪ This is not a trait associated with salt tolerant plants
o All mangroves use both mechanisms to a degree, but prioritise one over the
other
o To limit water loss, plants have a steep leaf angle (less surface area exposed to
sun) and don't leave their stomata open for very long
o Mangroves also use osmolyte biosynthesis, where they produce osmolytes
(compounds used in osmosis) to create a concentration gradient and draw the
nutrients across
- How have mangroves adapted to living in anoxic conditions?
o They develop aerenchyma, roots which have used programmed cell death to
create holes in the tissue to capture more oxygen from the air before the
roots get to the soil
o These air channels are usually formed in the leaf/stem/roots of mangroves
(and in many marine terrestrial plants)
o These provide low-resistance pathways for air to enter and be transported
around the plant
o Aerenchyma also provide ecosystem services such as sediment trapping,
nutrient cycling/carbon sequestration and nursery habitats
- Why do mangroves need oxygen?
o Oxygen allows metabolism and growth
o It defines the microbial community
o It alters the availability of nutrients (nitrificiation occurs in the presence of elevated
levels of oxygen)
- What are the different kinds of mangrove roots and how do they tolerate inundation?
o Prop roots
▪ Prop roots stem from high up the tree trunk
▪ They dig into the ground before branching out again
▪ Draw in oxygen from the air and draw it down into the lower roots
▪ A large surface area (e.g. taller roots) allow for more O2 capture
▪ e.g. Rhizophora
o Pneumatophores
▪ Like snorkels sticking out of ground
▪ Don't do well in high inundation – need top of root to be above water level
▪ Mangroves that grow higher up the slope use pneumatophores
▪ e.g. Avicennia
o Knee roots
▪ Come and go (not constant)
▪ Work by a similar mechanism as pneumatophores
▪ Close to trunk
▪ e.g. Bruguiera
o Floating buttress roots
▪ Fully attached to trunk the whole way down
▪ Large surface area to capture oxygen
▪ Only occur in mangroves higher up, not right on the water's edge
▪ e.g. Ceriops
- What modes of reproduction do mangroves use?
o Some mangroves are viviparous
▪ "Live birth"
▪ These propagules germinate while on the tree, and are ready to sprout as
soon as they fall and find somewhere to colonise
▪ e.g. Avicennia, Rhizophora
o Other mangroves produce "true seeds"
▪ These have a germination period after they fall from the tree
▪ This can be another factor in zonation, because the seeds that land in a
certain position will be the ones who can germinate under those
conditions
▪ e.g Osbornic sp.
o What are their trade-offs?
o They live in anoxic soils and require sprawling root systems
▪ Bacteria live in salty, nutrient-rich sediments and consume all the
oxygen
o They have to put resources into pneumatophores that could otherwise give
them height and biomass
Document Summary
Why do mangroves need oxygen: oxygen allows metabolism and growth. It alters the availability of nutrients (nitrificiation occurs in the presence of elevated levels of oxygen) Large surface area to capture oxygen: fully attached to trunk the whole way down, only occur in mangroves higher up, not right on the water"s edge, e. g. ceriops. What modes of reproduction do mangroves use: some mangroves are viviparous. Important in ecosystem services flow: break down leaf litter in sediments, have lots of larvae possibly another reason for presence of fish in mangroves. Us: in more temperate environments the diversity is higher, they are irregularly inundated with salt water, and the freshwater input is restricted to rainfall, what is their typical zonation pattern, the low marsh (beside mangroves/open ocean) Is inundated at high tide (twice a day: common species: spantina sp, the middle marsh.
