Lecture 10

Question 1

What is the twilight zone of the ocean?

Answer 1

Mesopelagic zone (200-1000m)

Question 2

What depth do shelf regions go down to?

Answer 2

200m

Question 3

Depth-related oceanic conditions

Answer 3

1. Deep water
2. Low temperatures
3. Oxygen-rich
4. High pressure
5. No light

Question 4

What is the thermohaline conveyor belt?

Answer 4

Flow of water around the world’s oceans driven by temperature and density

Question 5

How are the deep waters formed and what characteristics do they have?

Answer 5

Formed as sea ice freezes in polar regions

Dense, saline, cold and oxygen-rich

Question 6

Where is the strongest temperature and density gradient?

Answer 6

Mesopelagic zone

Deep sea has typically stable temperature and density

Question 7

Oxygen and depth

Answer 7

Oxygen concentration high at surface due to atmosphere and photosynthesis
Organic decomposition depletes O2 forming “oxygen minimum zone” in mesopelagic zone
Little organic matter in deep sea, so little use of oxygen

Question 8

What type of system does the deep sea have to bring in nutrients?

Answer 8

Allochthonous system

Food brought in from outside

Question 9

By how many kilopascals does oceanic pressure increase every 10m?

Answer 9

101.325

Question 10

How does pressure affect marine organisms?

Answer 10

Gases are compressible
Pressure therefore affects gas-filled structures
Compression is less of a problem than decompression
Many deep sea species have gas-filled swim bladders
Pressure changes affect protein structure which can cause metabolic disturbance and lead to death

Question 11

How have “pressure-loving” animals adapted to resist high deep sea pressures?

Answer 11

Barophilic

Pressure resistance proteins (evolved to be more efficient under pressure)

Question 12

Why does the deep sea appear blue?

Answer 12

Long wavelengths (reds) and short wavelengths (UV) fall off more rapidly than blue

Question 13

Diversity and depth

Answer 13

Diversity of most major groups of marine organisms declines with depth

Question 14

What do Elasmobranchs have they allows them to survive depth changes better than Teleosts?

Answer 14

Lipid-filled swim bladders - lipids less compressible than gas

Question 15

Mesopelagic species examples

Answer 15

Crustacean zooplankton (often red as red cannot be perceived in twilight zone)
Squid (with photophores)
Fish usually small, dominated by bristlemouths and lanternfishes

Question 16

Features of deep pelagic and benthic species

Answer 16

Specialised for low energy lifestyle
Density reduction of all tissues (low bone density)
Most benthopelagic so use both habitats
Active scavengers
Brain olfactory regions highly developed
Some sit-and-wait predators

Question 17

Deep sea adaptations

Answer 17

• Vertical migrations
• Camouflage
• Bioluminescence
• Vision
• Trophic morphology (teeth, jaws)

Question 18

What is the world’s biggest migration?

Answer 18

Diurnal vertical migration
Mesopelagic
Takes place daily in ocean

Question 19

What are the benefits of a diurnal vertical migration?

Answer 19

Productivity and predator avoidance / predation

Question 20

Difference between migrators and non-migrators

Answer 20

Migrators active predators, more athletic, swim bladders often lipid-filled, well-developed bones
Non-migrators sit-and-wait, weak bones, weak muscles

Question 21

Deep pelagic camouflage

Answer 21

• Red cannot be perceived so appears dark
• Black contrasts with bioluminescence
• Transparency is common (although hard to achieve as body structure and chemicals must be transparent, and refractive index of tissue must match that of water)

Question 22

Bioluminescence of deep pelagic species

Answer 22

Blue-shifted
Deep sea organisms have evolved to see dim flashes of light
Photophores produce the light

Question 23

How does a photophore work?

Answer 23

May have reflectors, filters, lenses, etc.
Light emitting compounds (luciferins) oxidised by enzymes (luciferases) to make light
May be from symbiotic bacteria

Question 24

Benefits of bioluminescence

Answer 24

Most mesopelagic animals are bioluminescent
Ventral bioluminescence hides silhouette from below - match light output to ambient light
Startle predators
Escape from predators
Lures
Species recognition, intraspecific communication
Sexual selection

Question 25

Adaptations of mesopelagic species for prey handling

Answer 25

Big recurved teeth

Large eyes with upward and lateral visual field

Question 26

Adaptations of deep pelagic species for prey handling

Answer 26

Smaller eyes

Reliant on sit-and-wait