Chemosynthetic environments Flashcards
Chemosynthetic PP
Fixation of inorganic C using chemical energy
Reduced compounds provide a source of electrons
Requires terminal electron acceptor.
Variety of pathways
Dominant pathway
Depends on microenvironment
- availability of donors
- availability of acceptors
- Energy yield of reaction
Prokaryotes in chemosynthetic environment
High abundance.
High genetic diversity at vents
Faunal assemblages
High abundance and biomass of life in the deep sea
Tend to have low species diversity compared to other deep-sea environments
Hydrothermal vents
Along MORS, super heated water loses and gains minerals from deep rocks.
Entire ocean through every 10,000 years.
Removes Mg and sulohate, adds H2S, Mn, Fe, Cu, Zn, Pb, H, CH4
Rapid mixing with cold oxygenated water.
Mixing
Primary vent fluid is clear.
Black smoker >225 deg.
Precipitating minerals
Greater mixing and cooling = white smoke at 100 to 225 deg
Temperature
Very sharp temperature gradient
Hottest microbe culture at 122 deg
Most animals live <40 deg
Hot fauna
Pompeii worm, in tubes where temp is 14 to 80 deg
Sulphide worm can tolerate 50-55 deg
Chemosynthesis at vent
Sulfide oxygenation appears to be dominant
H2S readily available
Oxygen available in background deep water
Anaerobic thought to be less important but may dominate in high temperature fluids.
Animals and PP
Vent animals can exploit chemosynthetic PP
Endosymbiosis
Microbial epibionts
Grazing or suspension feeding of free-living microbes.
Predation/scavenging on primary consumer aniamals
Symbioses
Riftia pachyptila
- microbes in trophosome.
- carbonic anhydrase in worm tissue adds CO2 uptake as it prefers HCO3.
- HS highly toxic, HS carried in blood by special haemoglobin
- Supply of O and HS can be separated.
Environmental temperature gradient along worm body, warmer at base
Haemoglobin affinity for O reduced at elevated temperature.
Mussels
Host bacterial symbionts inside gill cells.
Can hot dual symbioses, sulfide oxidising and methanotrophic bacteria
Epibiotic symbioses
Nutrition and detoxification
3 species of Rimicaris vent shrimp have epibiotic bacteria.
Adults feed on epibiotic bacteria which grow on mouth parts
Bacterial grazers
Other primary consumers at vents graze on bacteria present either as biofilms or mats of filamentous bacteria.
Grazers include limpets and polychaetes.
Zonation of species
Steep gradients at vents of temperature, sulfide and O concentration.
Closest dominated by epibionts
Next zone dominated by endosymbiosis species
e-protobacteria can oxidise H2 and respire S and ). Can thrive close to vents when there are many donors and less O available as an e acceptor.
g-proteobacteria may be more productive than e-proteobacteria, competitive advantage over e in that zone.
Filter feeders further from vent
Scavengers/predators in periphery.
Non-vent animals 100s of m from vent
Insular and ephemeral habitats
On fast spreading MOR, vent fields 10s of km apart
Slow MOR, 100s of km apart.
Venting doesn’t last forever.
Tectonic activity can affect it
On fast can last for 10s of years
Slow last 1000s years
Fauna must be able to disperse
Cold seeps
Non-volcanic geological process generate reduced chemicals at the seafloor to support chemosynthesis.
Typically found on continental margins but also in ocean trenches.
Soft-sediment settings
Cold seep organic compounds
organic compounds from deep resevoir to surface.
Degradation of organic compounds produces methane
Chemosynthesis at cold seeps
Anaerobic subsurface microbes in seafloor oxidise methane using sulfates:
- CH4 + SO4 HCO3 - + HS- + H2O
HS = energy for chemo.
At cold seep there is a typically flux of sulfide and methane at the seafloor.
Brine pool cold seeps
Salt diapirism
bed of mussels that have gill symbionts
Grazers, scavengers, species zonation follows gradients in sulfide and O
Different species from hydrothermal vents.
Vent and seep tubeworms, seep acquire sulfide by roots not plumes.
Cold seeps, insular and ephemeral
Island like and last for long time.
Bicarbonate by-product of methane oxidation underlies sediment, eventually blocks seeping.
Succession pattern leading to stony corals?
Whale falls
Partially chemosynthetic
V rich in lipids, anaerobic bacteria break this down, sulphate to sulfide in process.
Sulfide flux can support chemosynthetic PP.
Animals exploit by symbiosis
Adipicola mussels host endosymbionts
Grazers, scale worm
Insular and ephemeral
Wood falls
Partially chemosynthetic
Xylophagidae can release sulphide
Support other microbes and symbionts
Biogeography and evolutionary history
Insular and ephemeral
Dispersal achieved by larval stages.
Interruption to gene flow between populations –> speciation
Caused by tectonic movement
