Lecture 9

Question 1

How was ocean depth historically measured?

Answer 1

Lowering a rope on a steam winch

Question 2

When did the HMS Challenger go on a deep sea discovery?

Answer 2

1872-6

Discovered over 4000 species

Question 3

How is depth measured now?

Answer 3

Using multi beam echosounder (sonar) which bounces back signals from sea floor that a computer can convert and produce 3D images from

Question 4

Features of continental shelves

Answer 4

Underwater during interglacial periods
End at shelf break/edge
8% of sea surface area

Question 5

What are continental shelves important for?

Answer 5

• Fisheries
• Shipping
• Hydrocarbons
• Renewable energy
• Aquaculture
• Recreation

Question 6

Types of continental shelf communities

Answer 6

-Soft bottomed benthic
-Hard bottomed benthic
-Kelp forests
+seagrass, coral reefs, etc.

Question 7

Features of soft-bottomed benthic continental shelves

Answer 7

• Characterised by vegetation-free, sediment-rich habitats
• Sediment type determined by water movements (waves, currents, upwelling) and geological history (glacial deposits)
• Typically coarser sediments are found closer to shore

Question 8

How do the type of feeders vary due to the amount of turbulence on soft-bottomed benthic habitats?

Answer 8

When there is less turbulence, the sediment particles are smaller (mud) and there is less oxygen and more detritus. Animals likely to be deposit feeders.
When there is more turbulence, sediment particles are larger (sand) and there is more oxygen and less detritus. Organisms more likely you be suspension feeders

Question 9

Size of macrofauna

Answer 9

> 0.5mm

Question 10

Meiofauna size

Answer 10

0.065-0.05mm

Question 11

Features of hard-bottomed benthic continental shelves

Answer 11

• Harder / shelly substrates harder to burrow into
• Communities dominated by rich epifauna but poor infauna
• Sessile species: sponges, hydroids, anemones, bryozoans, polychaetes, barnacles
• Motile species: urchins, limpets, chitons

Question 12

Features of kelp forests

Answer 12

• Rapid growth
• Canopy forming
• Attached by holdfast (up to 40m deep)
• Cold water environment
• Unique biodiversity

Question 13

Zonation of kelps in kelp forest

Answer 13

• Canopy: grinds on surface of midwater
• Understorey: fronds erect or close to bottom
• Algal turf: short clumps, filaments and encrusting algae

Question 14

What is an example of a ‘top down’ interaction involving kelp forests?

Answer 14

Shifts in killer whale behaviour led to declining sea otter numbers
This resulted in an explosion in sea urchin numbers
They overgrazed the kelp

Question 15

Deep sea benthos

Answer 15

• Organic rich, soft sediment
• 1-3% of primary productivity reaches sea floor
• Very few suspension feeders due to slow water movement and scarce food
• More deposit feeders

Question 16

Deep sea benthic meiofauna

Answer 16

Nematodes
Foraminifera
Copepods

Question 17

Deep sea benthic macrofauna

Answer 17

Polychaetes
Amphipods
Bivalves

Question 18

How does macrofaunal community structure change with depth?

Answer 18

Sessile species become less common
Scavengers become more common such as Holothurian
Biomass decreases
Size decreases, reflecting food supply

Question 19

What is the exception to size of organisms decreasing with depth?

Answer 19

Scavengers increase in size in relation to depth

Question 20

What is a seamount?

Answer 20

Seamounts rise >1km above the abyssal sea floor
They are often extinct volcanoes
Usually 3-5km below sea surface
Found along fault lines

Question 21

How do seamounts affect oceanic organisms?

Answer 21

Interact with ocean currents, driving eddies over the seamount
Can promote upwelling
Provides a hard substrate for sessile macrofauna
High diversity of benthic and bentho-pelagic species present

Question 22

Problem with overfishing around seamounts

Answer 22

Many species are very long-lived and take many years to mature, so stocks cannot replenish quick enough
Trawling causes huge damage to seamount communities
Fishing banned around many seamounts

Question 23

Features of hydrothermal vents

Answer 23

Found along fault lines
Discovered in 1977
Diverse and endemic faunas

Question 24

What is the basis of metabolism of chemoautotrophic bacteria which live near hydrothermal vents?

Answer 24

Hydrogen sulphide
E.g. sulphur-oxidising bacteria Beggiatoa
2H2S + O2 -> 2H2O + 2S (white)

Question 25

Species found in hydrothermal vents

Answer 25

Vestimentiferans (polychaete) tube worm - no digestive tract, depends on symbiotic bacteria in trophosome tissue. Specialised haemoglobin to bind to H2S and transport it to bacteria.
Bathymodiolus thermophylus (vent mussel) - depend on symbiotic bacteria on gill filaments but can filter feed too. Must live close to sulphides.
Alvinella (heterotrophic polychaete) - Pompeii worm, up to 13cm, aggregates, hairy, feeds on filamentous chemoautotrophic bacteria

Question 26

Other chemosynthesis-based systems

Answer 26

Whale falls

Hydrocarbon “cold” seeps

Question 27

Features of whale falls

Answer 27

• Lipids in bones create anoxic high sulphide environments
• Mats of sulphur-oxidising bacteria
• Specialist vestimentiferans, mussels, etc. form food web
• Also bone feeding tube worms

Question 28

Features of hydrocarbon “cold” seeps

Answer 28

Places where hydrocarbons seep from sediment
Methane hydrate “ice” forms when gas escapes in low temperature conditions
Often seeps coincide with brine pools
Successional environment - initially bacterial mats, then Bathymodiolus, then tube worms, more mussels, soft corals