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Introduction to Marine Ecology > Chemosynthetic Environments > Flashcards

Chemosynthetic Environments Flashcards

1
Q

How does the change in biomass affect the organisms in the deep sea?

A

It influences many adaptations, e.g. feeding, reproduction, etc.

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2
Q

What are Chemosynthetic environments?

A

In situ sites of primary production in the deep sea. They are exceptions to the general pattern of biomass decline with depth.

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3
Q

What is a photoautotroph?

A

An organism that derives its energy for food synthesis from light and is capable of using inorganic carbon as a source of C.

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4
Q

Define a chemoautotroph.

A

An organism which derives energy from the oxidation of inorganic compounds.

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5
Q

Define photoheterotroph.

A

Organisms that use light for energy, but rely on organic carbon sources for carbon.

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6
Q

Define chemoheterotroph.

A

An organism that gets energy from inorganic oxidation but require organic carbon.

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7
Q

Define chemosynthetic primary production.

A

Fixation of inorganic carbon using chemical energy.

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8
Q

How are inorganic carbon molecules ‘fixed’ in chemosynthetic primary production?

A

“Reduced” chemical compouds (e.g. hydrogen sulphide H2S) + a source of electrons (e.g. O2).

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9
Q

What are the two stages of chemosynthetic primary production?

A

1) production of ‘reducing power’ (chemoautotrophs).

2) fixation of inorganic carbon (e.g. Calvin-Benson-Bassham cycle.)

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10
Q

What does the process of chemosynthetic primary production require?

A

A terminal electron acceptor, e.g. oxygen in aerobic chemosynthesis.

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11
Q

What organisms carry out chemosynthetic primary production?

A

Usually prokaryotic microbes, e.g. Archaea and bacteria.

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12
Q

What are the possible electron donors for chemosynthetic primary production?

A

H2S, CH4, H2, iron Fe(II), manganese Mn(II)

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13
Q

What are the possible elector acceptors for chemosynthetic primary production?

A

Oxygen (O2), Nitrate (NO3-), Sulfate (SO4^2-), iron Fe(III), Sulphur (S).

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14
Q

What are three chemosynthetic pathways used to carry out chemosynthetic primary production?

A

Sulfide oxidation, methanotrophy, Fe & Mn oxidation.

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15
Q

What are the variables that determine which pathway dominates in a chemosynthetic environment?

A

Availability of electron donors, availability of electron acceptors (aerobic vs anaerobic) and energy yield of the reactions.

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16
Q

What is the difference in abundance of prokaryotes in chemosynthetic environments?

A

In ‘normal’ deep sea 10^3 to 10^5 cells ml^-1

Hydrothermal vent environments: 10^6 to 10^7 cells ml^-1.

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17
Q

What can chemosynthetic environments support?

A

Faunal assemblages with high abundance and biomass in the deep sea.

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18
Q

Where do faunal assemblages occur?

A

Where reduced chemicals for chemosynthesis are available at the ocean floor.

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19
Q

What are the three types of chemosynthetic environment? When were they first recognised?

A 
Hydrothermal vents (Late 1970s)
Cold seeps (1984)
Whale falls (1987)
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20
Q

Where are hydrothermal vents found?

A

Along mid ocean ridges and back-arc basins.

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21
Q

How do hydrothermal vents work?

A

As the seafloor separates, a magma chamber forms below the crust surface. Cold seawater is sucked down through the crust, collecting dissolved minerals from the rocks it filters through. It is then heated by the magma/heat source and rises due to its lower density, emerging as a hydrothermal vent saturated with minerals.

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22
Q

How long does it take for the entire global ocean volume to pass through hydrothermal circulation?

A

~ every 10^4 years.

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23
Q

What does hydrothermal circulation remove from seawater?

A

Magnesium and sulfates (SO4).

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24
Q

What does hydrothermal circulation add to seawater?

A

Hydrogen sulfide (H2S), Manganese (Mn), Iron (Fe), Copper (Cu), Lead (Pb), Hydrogen (H2) and methane (CH4).

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25
Q

What are the characteristics of primary (undiluted) vent fluids?

A

+Very hot (up to ~400 degrees C)
+Acidic (pH 3 to 5)
+Anoxic
+Clear

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26
Q

What happens when primary vent fluid mixes with cold, oxygenated seawater at temperatures >225 deg. C?

A

“Black smokers”, where the smoke is precipitating mineral particles - metal sulfides first, then oxides/oxyhydroxides.

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27
Q

What happens when primary vent fluid mixes with cold, oxygenated seawater at temperatures from 100 to 225 deg. C or after greater mixing & conductive cooling?

A

“White smokers”, with shimmering water (caused by diffuse flow at lower temperatures, & the different densities of the water).

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28
Q

Where are the highest temperatures found in hydrothermal vents?

A

They only occur in primary vent fluid (i.e. right at the throat of the vent chimney).

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29
Q

What is the typical background deep-sea temperature?

A

-1.5 to 4.5 deg. C.

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30
Q

What is the usual temperature gradient at hydrothermal vents?

A

Very sharp - 360 to 2 deg. C over 10s of centimetres.

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31
Q

Where was the hottest known microbe cultured?

A

122 deg. C.

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32
Q

Where do most vent animals live?

A
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33
Q

Why do vent animals prefer cooler water?

A

There is more oxygen, and it is less acidic.

34
Q

What is an example of an organism which can live in high temperatures?

A

Alvinella pompejana, the “Pompeii worm” inhabits tubes where temperature varies from 14 to 80 deg. C. The molecular structure of its collagen may be adapted for thermotolerance.

35
Q

What is the ‘sulfide worm’?

A

Paralvinella sulfincola, able to tolerate 50-55 deg.C and prefers 25-50 conditions.

36
Q

What is the typical change in biomass with depth?

A

There is usually an exponential decline in biomass.

37
Q

What are some of the adaptations of worms that allows them to live near vents?

A

They grow bristles which have bacteria grow on them, which they can then eat. They are less active above temperatures >12 deg.C, potentially because oxygen is more limited.

38
Q

What is the dominant form of chemosynthesis at vents, in terms of carbon fixation? Why?

A

Sulfide oxidation, because hydrogen sulfide is readily available in vent fluids and oxygen is readily available in background deep-sea water.

39
Q

What other forms of sulfide may be used in other geological settings?

A

Methane (CH4) and Hydrogen (H2).

40
Q

Which chemosynthetic pathway may dominate in high temperature fluids?

A

Anaerobic pathways, e.g. methanogenesis.

41
Q

What are the ways that animals can exploit chemosynthetic primary production by microbes?

A

+via endosymbiotic relationships.
+via microbial epibionts.
+by grazing/suspension feeding of free-living microbes.
+by predation/scavenging on primary consumer animals.

42
Q

What is an epibiont?

A

An organism that lives on the surface of another living organism.

43
Q

What is an example of an animal-microbe endosymbioses at vents?

A

The vent tubeworm Riftia pachyptila, classified as a siboglinid polychaete. They form huge colonies and grow up to 2m high in a matter of months. 15% of the total body weight is bacteria.

44
Q

Why do Riftia endosymbionts need inorganic carbon?

A

Heterotrophia CO2 from their tissues forms 1/2 of the symbiont demand. Tubeworm blood is alkaline & favours DIC as bicarbonate (HCO3-), helps to maintain diffusion gradient as seawater DIC is CO2.

45
Q

How does hydrogen sulfide affect animal tissue?

A

It is highly toxic - it poisons the cytochrome c oxidase electron transport enzyme and usually replaces oxygen at the binding sites of haemoglobin.

46
Q

How does Riftia transport hydrogen sulfide without adverse effects?

A

Hydrogen sulfide is favoured at pH 6 but Riftia take up bisulphide (HS-) as it’s less toxic for cytochrome c oxidase.
HS- is carried in the blood by highly adapted haemoglobin molecules, which have separate binding sites for HS- in addition to O2.

47
Q

How does Riftia access oxygen in vent waters?

A

Riftia haemoglobin has high affinity for O2, helping to maintain the uptake gradient. Haemoglobin affinity for O2 is reduced at elevated temperatures.

48
Q

How does the environmental temperature gradient along Riftia’s body affect haemoglobin?

A

As it’s warmer at the trophosome than the plume, it may aid unloading of O2 at the trophosome.

49
Q

What is another animal-microbe endosymbiosis?

A

Bathymodiolus spp mussels. Host bacterial symbionts inside gill cells, including dual symbioses (sulfide-oxidising and methanotrophic bacteria.)

50
Q

What are the roles of epibiotic bacteria?

A

Nutrition and detoxification.

51
Q

What are other primary consumers at vents?

A

Grazers, which feed on bacteria present either as biofilms or mats of filamentous bacteria, including limpets and polychaetes. There are also filter-feeders liked Eolepadid stalked barnacles.

52
Q

What are some predators/scavengers at vents?

A

Some crabs, zoarcid fish, anemones, possible octopus species. There are also opportunistic “non-vent” predators/scavengers.

53
Q

What is the zonation at vents like?

A

There are steep physico-chemical gradients at vents on a similar scale to rocky intertidal environments.

54
Q

What are some of the gradients that define zonation at vents?

A

Temperature, sulfide & O2 concentration.

55
Q

What is the insular nature of hydrothermal vents?

A

They occur in ‘fields’: clusters of chimneys within the area of a few hundred metres squared.

56
Q

What does the occurrence of vent fields depend on?

A

Underlying geology, availability of a heat source and pathways for circulation.

57
Q

What does the speed of spreading have to do with vent fields?

A

+On a fast spreading mid-ocean ridge (East Pacific rise) fields may be 10s of km apart.
+On a slow spreading ridge (Mid Atlantic ridge) fields may be 100s of km apart.

58
Q

What effects the duration of a hydrothermal vent?

A

Volcanic eruptions or tectonic activity can disrupt their ‘plumbing’. Ephemeral duration depends on how frequently those occur.

59
Q

How does rate of spreading affect the ephemeral nature of vents?

A

+Fields on a fast spreading ridge may last for 10s of years.

+Fields on a slow spreading ridge may last for 1000s of years.

60
Q

What are cold seeps?

A

Environments where non-volcanic geological processes generate reduced chemicals at the seafloor to support chemosynthesis.

61
Q

What are the types of cold seep environments?

A

Salt diapir systems, mud volcanoes, asphalt seeps, gas hydrate beds.

62
Q

Where are cold seeps typically found?

A

On continental margins, but cal also occur in ocean trenches. Generally found in soft-sediment seafloor settings.

63
Q

How does chemosynthesis occur at cold seeps?

A

Geological processes forces organic compounds from deep reservoirs up through seafloor sediments (e.g. at subduction zones). The organic compounds involved are of ancient photosynthetic origin (e.g hydrocarbons) and degradation of those compounds produces methane.

64
Q

What is the main way to produce sulfides at cold seeps?

A

Anaerobic processes. Anaerobic subsurface microbes in seafloor sediments oxidise methane using sulfate to produces HS-. This produces an energy source for chemosynthesis, along with unoxidised methane. This is VERY slow.

65
Q

How is the flux of sulfide and methane used at seeps?

A

Chemosynthetic microbes use these reduced compounds and animals exploit this in similar ways to those at hydrothermal vents.

66
Q

What is an example of a cold seep?

A

The brine pool cold seep, Gulf of Mexico. It’s anoxic & hypersaline & surrounded by a bed of mussels that harbour gill endosymbionts. Grazers/scavengers include gastropods, polychaetes, shrimp & lobsters.

67
Q

What is the difference between siboglinid tubeworms found in brine pools and those that are found in hydrothermal vents?

A

Genera and species differ, but seep worms acquire sulfide via roots rather than plumes, though O2 still taken up via plume. They are also slow growing and long living (up to 250y)

68
Q

What is the ephemeral nature of cold seep sites?

A

Cold seeps are on timescale of centuries.

69
Q

What causes the end of a cold seep?

A

Bicarbonate by-product methane oxidation forms biogenic carbonate rock, which eventually blocks seeping at the site.

70
Q

What does carbonate rock formation at seep sites drive?

A

It may drive a succession pattern - dominance by mussels, then tubeworms (able to reach sulfides by roots) then scleractinian corals.

71
Q

What are the differences between hydrothermal vents and cold seeps?

A

+There is a reduced temperature gradient in seep systems.
+Seeps are less ephemeral (vents tend to be live fast/die young).
+Fluid chemistry is based on a different process - this determines the flora and fauna.

72
Q

What is a whale fall?

A

A dead whale on the ocean floor. Scavengers rapidly remove flesh from whale skeleton (typically within a few months). Whale bones are very rich in lipids.

73
Q

What is the chemosynthetic process at whale falls?

A

Anaerobic bacteria break down the lipids in whale falls, reducing seawater sulfate (SO42-) to sulfide (S2-) in the process. The resulting sulfide flux from the bones can support chemosynthetic primary production by other microbes.

74
Q

What is the typical fauna found at whale falls?

A

The animals exploit the primary production in similar ways but not many species are shared with vents and seeps. Endosymbiont hosting-species are Adipicola mussels (extra- & intracellular gill symbionts).

75
Q

What is Osedax spp?

A

The “bone-eating” or “zombie” worm, a siboglinid polychaete with heterotrophic bacteria living in the root, which break down bone material directly. Able to live on cow & even fish bones.

76
Q

What is the ephemeral & insular nature of whale falls?

A

+Whale skeleton lipids depleted after decades - natural mortality of grey whales –>~1600 new carcasses per year w/ distances of 10s of km.
+(Only 7 natural whale falls studied so far).

77
Q

What is the evolutionary history of chemosynthetic fauna?

A

Most vent animals have relatively recent evolutionary origins, sharing evolutionary history with other deep sea fauna - have been affected by changes in climate, ocean circulation & deepwater anoxic events.

78
Q

Where did shallow water taxa first adapt to?

A

Most likely first to whale falls & similar environments, then to vents and seeps. So, within a taxon, radiations can occur between diff. types of chemosynthetic environments.

79
Q

How does speciation occur in chemosynthetic fauna?

A

By interruption to gene flow between populations, such as movement of plates, ridges & continents/changes to ocean currents. Speciation –> different species living in different regions.

80
Q

What is the significance of chemosynthetic primary production?

A

+CPP can support fauna w/ high abundance & biomass in deep sea.
+Insular & ephemeral - model system for studying dispersal & evolution in largest biome.

81
Q

Define chemoautotrophy.

A

To fix inorganic carbon into carbon-based molecules by oxidation of substances from the environment, usually inorganic minerals.

Introduction to Marine Ecology (7 decks)

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