Deep Sea Ecosystems

Question 1

Oceanic Depth Zones

Answer 1

Euphotic (day-light zone): up too 200m

Twilight/Disphotic Zone: Mesopelagic zone (200-1000m), detectable light to 1000m but no photosynthesis

Midnight/Aphotic Zone: Devoid of light

Seafloor: Average depth of 3800m

Question 2

Components of deep-sea topography (4)

Answer 2

Abyssal plain: largest ecosystem on earth, deep basins between continental margins and mid-ocean ridges

Seamounts

Mid-ocean ridge

Trenches

Question 3

Factors affecting deep-sea life (6)

Answer 3

Light: no light below 1000m, animals of the deep sea exist in total darkness

Temperature is uniformly low and salinity is high

Oxygen is non-limiting except in specific areas

Predominantly soft-sediment habitat

Pressure is extremely high: increases by 1 atm per meter (average deep-sea pressure is 380 atm)

Food supply is low and unpredictable

Question 4

Food sources in the deep sea (3)

Answer 4

Particulate Organic Matter (POM) is generated by primary production at the surface

Chemosynthesis: sulphur based (hydrothermal vents) and hydrocarbons (methane creeps)

Food falls (carcasses): short term or long term (whale fall communities)

Question 5

What does the amount of POM reaching deep-sea depend on? (3)

Answer 5

The density of organisms (spring bloom vs summer)
Level of primary production
Bacterial activity in the water column

Question 6

Adaptions to low food availability

Answer 6

Conserve Energy: Watery muscles, fatty tissues, weak skeletons, no scales, poorly developed respiratory, circulatory and nervous systems, no vertical migration behaviour

Enormous/expandable mouths to swallow a variety of large prey

Expandable stomachs to hold large prey items

Question 7

Feeding Modes in the deep-sea(5)

Answer 7

Deposit Feeding: dominant method due to soft sediments

Suspension Feeding: less common due to food paucity
Sporadic but found in areas with abundant suspended particles

Mucous Nets: larvaceans

Predation: fish, tunicates

Scavenging

Question 8

Larvacean Mucous Nets

Answer 8

Giant Larvacean: feeds with large mucous nets, harness food in the deep sea, absorbs a wide range of organic matter down to colloidal material, clog in 1-2 days and discarded (sinkers)

Question 9

Sinkers

Answer 9

Important input of carbon to deep-sea
High in carbon
Contribute to the organic content of seafloor
Sink quickly (800m a day)
Con occur in substantial numbers

Question 10

Effects of limited food on abyssal ecology (

Answer 10

Reduced faunal densities
Deep-sea food supply cannot sustain large numbers
Compared to the epipelagic zone: 5-10 times fewer organisms in the mesopelagic zone and 50-100 times fewer organisms in the deep-sea

Size of deep fauna
Mesopelagic and deep-sea organisms are generally smaller compared to organisms of the epipelagic zone
Gigantism can occur

Question 11

Goals of ceDAMar (4)

Answer 11

Describe biodiversity in the abyss on a global scale
Describe new species
Investigate what regulates diversity
Collect baseline data for climate change

Question 12

CeDAMar major findings ()

Answer 12

Extreme is normal: wide range of organisms thrive, business as usual

Rare is common: nearly all abyssal species are rare, no one species dominates, density is low but biodiversity is higher than expected, lots of unique species found in the deep sea

Question 13

Threats to deep-sea

Answer 13

Polymetallic nodule mining and other forms of resource extraction
Climate change

Question 14

Effects of mining (3)

Answer 14

Chemical effects: toxicity and plume effects

Physical effects: habitat destruction

Major regulation challenges

Question 15

Climate change and the deep sea

Answer 15

As primary production decreases at the surface the productive layer decreases and there is weaker upwelling.

The supply of carbon to the deep-sea will decrease