Chemosynthetic environments

Question 1

Chemosynthetic PP

Answer 1

Fixation of inorganic C using chemical energy
Reduced compounds provide a source of electrons
Requires terminal electron acceptor.
Variety of pathways

Question 2

Dominant pathway

Answer 2

Depends on microenvironment
- availability of donors
- availability of acceptors
- Energy yield of reaction

Question 3

Prokaryotes in chemosynthetic environment

Answer 3

High abundance.
High genetic diversity at vents

Question 4

Faunal assemblages

Answer 4

High abundance and biomass of life in the deep sea
Tend to have low species diversity compared to other deep-sea environments

Question 5

Hydrothermal vents

Answer 5

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.

Question 6

Mixing

Answer 6

Primary vent fluid is clear.
Black smoker >225 deg.
Precipitating minerals
Greater mixing and cooling = white smoke at 100 to 225 deg

Question 7

Temperature

Answer 7

Very sharp temperature gradient
Hottest microbe culture at 122 deg
Most animals live <40 deg

Question 8

Hot fauna

Answer 8

Pompeii worm, in tubes where temp is 14 to 80 deg
Sulphide worm can tolerate 50-55 deg

Question 9

Chemosynthesis at vent

Answer 9

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.

Question 10

Animals and PP

Answer 10

Vent animals can exploit chemosynthetic PP
Endosymbiosis
Microbial epibionts
Grazing or suspension feeding of free-living microbes.
Predation/scavenging on primary consumer aniamals

Question 11

Symbioses

Answer 11

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.

Question 12

Mussels

Answer 12

Host bacterial symbionts inside gill cells.
Can hot dual symbioses, sulfide oxidising and methanotrophic bacteria

Question 13

Epibiotic symbioses

Answer 13

Nutrition and detoxification
3 species of Rimicaris vent shrimp have epibiotic bacteria.
Adults feed on epibiotic bacteria which grow on mouth parts

Question 14

Bacterial grazers

Answer 14

Other primary consumers at vents graze on bacteria present either as biofilms or mats of filamentous bacteria.
Grazers include limpets and polychaetes.

Question 15

Zonation of species

Answer 15

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

Question 16

Insular and ephemeral habitats

Answer 16

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

Question 17

Cold seeps

Answer 17

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

Question 18

Cold seep organic compounds

Answer 18

organic compounds from deep resevoir to surface.
Degradation of organic compounds produces methane

Question 19

Chemosynthesis at cold seeps

Answer 19

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.

Question 20

Brine pool cold seeps

Answer 20

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.

Question 21

Cold seeps, insular and ephemeral

Answer 21

Island like and last for long time.
Bicarbonate by-product of methane oxidation underlies sediment, eventually blocks seeping.
Succession pattern leading to stony corals?

Question 22

Whale falls

Answer 22

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

Question 23

Wood falls

Answer 23

Partially chemosynthetic
Xylophagidae can release sulphide
Support other microbes and symbionts

Question 24

Biogeography and evolutionary history

Answer 24

Insular and ephemeral
Dispersal achieved by larval stages.
Interruption to gene flow between populations –> speciation
Caused by tectonic movement

Question 25

Vent molluscs

Answer 25

39 out of 184 vent mollusc species on critically endangered from vent mining

Question 26

Evolutionary history of animals

Answer 26

Most vent animals have relatively recent recent origins (50mya)
Species at chemosynthetic environments have been affected by past climate changes and circulation
Taxa may have adapted first to wood falls and whale falls, then cold seeps and vents
Patterns in phylogenies