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1

How was ocean depth historically measured?

Lowering a rope on a steam winch

2

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

1872-6
Discovered over 4000 species

3

How is depth measured now?

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

4

Features of continental shelves

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

5

What are continental shelves important for?

-Fisheries
-Shipping
-Hydrocarbons
-Renewable energy
-Aquaculture
-Recreation

6

Types of continental shelf communities

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

7

Features of soft-bottomed benthic continental shelves

-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

8

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

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

9

Size of macrofauna

>0.5mm

10

Meiofauna size

0.065-0.05mm

11

Features of hard-bottomed benthic continental shelves

-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

12

Features of kelp forests

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

13

Zonation of kelps in kelp forest

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

14

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

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

15

Deep sea benthos

-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

16

Deep sea benthic meiofauna

Nematodes
Foraminifera
Copepods

17

Deep sea benthic macrofauna

Polychaetes
Amphipods
Bivalves

18

How does macrofaunal community structure change with depth?

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

19

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

Scavengers increase in size in relation to depth

20

What is a seamount?

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

21

How do seamounts affect oceanic organisms?

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

22

Problem with overfishing around seamounts

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

23

Features of hydrothermal vents

Found along fault lines
Discovered in 1977
Diverse and endemic faunas

24

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

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

25

Species found in hydrothermal vents

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

26

Other chemosynthesis-based systems

Whale falls
Hydrocarbon “cold” seeps

27

Features of whale falls

-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

28

Features of hydrocarbon “cold” seeps

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