Lecture 10 Flashcards
What is the twilight zone of the ocean?
Mesopelagic zone (200-1000m)
What depth do shelf regions go down to?
200m
Depth-related oceanic conditions
- Deep water
- Low temperatures
- Oxygen-rich
- High pressure
- No light
What is the thermohaline conveyor belt?
Flow of water around the world’s oceans driven by temperature and density
How are the deep waters formed and what characteristics do they have?
Formed as sea ice freezes in polar regions
Dense, saline, cold and oxygen-rich
Where is the strongest temperature and density gradient?
Mesopelagic zone
Deep sea has typically stable temperature and density
Oxygen and depth
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
What type of system does the deep sea have to bring in nutrients?
Allochthonous system
Food brought in from outside
By how many kilopascals does oceanic pressure increase every 10m?
101.325
How does pressure affect marine organisms?
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
How have “pressure-loving” animals adapted to resist high deep sea pressures?
Barophilic
Pressure resistance proteins (evolved to be more efficient under pressure)
Why does the deep sea appear blue?
Long wavelengths (reds) and short wavelengths (UV) fall off more rapidly than blue
Diversity and depth
Diversity of most major groups of marine organisms declines with depth
What do Elasmobranchs have they allows them to survive depth changes better than Teleosts?
Lipid-filled swim bladders - lipids less compressible than gas
Mesopelagic species examples
Crustacean zooplankton (often red as red cannot be perceived in twilight zone) Squid (with photophores) Fish usually small, dominated by bristlemouths and lanternfishes
Features of deep pelagic and benthic species
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
Deep sea adaptations
- Vertical migrations
- Camouflage
- Bioluminescence
- Vision
- Trophic morphology (teeth, jaws)
What is the world’s biggest migration?
Diurnal vertical migration
Mesopelagic
Takes place daily in ocean
What are the benefits of a diurnal vertical migration?
Productivity and predator avoidance / predation
Difference between migrators and non-migrators
Migrators active predators, more athletic, swim bladders often lipid-filled, well-developed bones
Non-migrators sit-and-wait, weak bones, weak muscles
Deep pelagic camouflage
- 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)
Bioluminescence of deep pelagic species
Blue-shifted
Deep sea organisms have evolved to see dim flashes of light
Photophores produce the light
How does a photophore work?
May have reflectors, filters, lenses, etc.
Light emitting compounds (luciferins) oxidised by enzymes (luciferases) to make light
May be from symbiotic bacteria
Benefits of bioluminescence
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
Adaptations of mesopelagic species for prey handling
Big recurved teeth
Large eyes with upward and lateral visual field
Adaptations of deep pelagic species for prey handling
Smaller eyes
Reliant on sit-and-wait
