Lecture 9 Flashcards
How was ocean depth historically measured?
Lowering a rope on a steam winch
When did the HMS Challenger go on a deep sea discovery?
1872-6
Discovered over 4000 species
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
Features of continental shelves
Underwater during interglacial periods
End at shelf break/edge
8% of sea surface area
What are continental shelves important for?
- Fisheries
- Shipping
- Hydrocarbons
- Renewable energy
- Aquaculture
- Recreation
Types of continental shelf communities
-Soft bottomed benthic
-Hard bottomed benthic
-Kelp forests
+seagrass, coral reefs, etc.
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
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
Size of macrofauna
> 0.5mm
Meiofauna size
0.065-0.05mm
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
Features of kelp forests
- Rapid growth
- Canopy forming
- Attached by holdfast (up to 40m deep)
- Cold water environment
- Unique biodiversity
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
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
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
Deep sea benthic meiofauna
Nematodes
Foraminifera
Copepods
Deep sea benthic macrofauna
Polychaetes
Amphipods
Bivalves
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
What is the exception to size of organisms decreasing with depth?
Scavengers increase in size in relation to depth
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
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
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
Features of hydrothermal vents
Found along fault lines
Discovered in 1977
Diverse and endemic faunas
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)
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
Other chemosynthesis-based systems
Whale falls
Hydrocarbon “cold” seeps
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
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
