BIO3021 Lecture Notes - Lecture 21: Deep Scattering Layer, Pelagic Fish, Oxygen Minimum Zone
25 May 2018
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Lecture 21 – The Deep Sea
Deep Sea
• Definitions vary
• 85% of area and 90% of volume of oceans
• Largest habitat on earth
• Least known and explored habitat
• Has unique characteristics that limit life
• Thermocline
o Colder → warmer
• Fish don’t like thermocline
• Th
Characteristics
• Light, pressure, salinity, temperature, oxygen,
food
Light
• Below mesopelagic – no light at all
o No photosynthesis possible
o Only self-generated light below
mesopelagic
• Aphotic – no light present
Pressure
• Increases by 1atm each 10 m of depth
• Biochemical adaptations necessary
• Enzyme kinetics pressure sensitive as pressure increases
• Calcium carbonate solubility and dissociation changes
• Membrane lipid solubility changes
• Adaptations to pressure limit vertical mobility of species
• Inverse relationship between pressure and volume
• If pressure increases, volume of space will decrease
• Animals need adaptations to survive pressures
• Snorkelling is only inhaling atmosphere at 1 pressure
• Graph
o 1 bar = 1 atm of pressure
o As pressure increases → 200: more bacteria
present
o Stay high level until 600 atm then declines
o To survive different depths: requires biochemical changes to body
Salinity
• Epipelagic variable salinity, 33-37%
• Due to river outfall and rainfall (the freshwater)
• Deep sea very constant 35%
• Salty water denser and contributes to great ocean conveyor
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Temperature
• Thermocline is transition zone
• Below thermocline temp. is fairly constant at 1-4˚c
• Cold water denser
Oxygen
• Surface water can exchange oxygen with atmosphere → oxygen rich
• Deep water needs to be oxygenated
• Deep sea distant from atmospheric oxygen
o Deep sea water originates at poles
• Great ocean conveyer
o Cold water at the poles sinks down continental shelf into deep sea →
forms conveyer across ocean and Gulf stream
o Responsible for ocean currents like Gulf stream
o And getting oxygen into the stream
o Oxygen minimum zone at 500-1000m – lots of animals live there
o Oxygen consumption low in deep sea because not a lot of animals live
there
o Therefore deep sea has a lot of available oxygen due to conveyer belt
• Cold waters settle out over sea floor
Food
• No photosynthesis – no base to food web
• Organic debris sinks from above and may decay or be consumed on the way
• Less food and poorer quality at depth
• Only low density of life supported
Inhabitants of the Mesopelagic
• No phytoplankton
• Midwater animals include
o Krill and small crustaceans
o Copepods
o Ostracods
o Squid (planktonic and nektonic)
• Lots of vertebrates
• Abundant mesopelagic fish
o Vary in size
o Usually grey-black
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o Flabby long bodies – not good swimmers and don’t migrate
vertically/swim far
o Large eyes to see small amount of present
o Big teeth and big mouth
▪ Advantage of large mouth: Can swallow anything (as big as
itself) and bag like stomach will expand and hold it
o Two types
▪ Those that migrate vertically and those that don’t
▪ Vertical migrators (1)
▪ Non-migrators (2)
• Deep scattering layer
o Common for mesopelagic organisms to migrate vertically at night
o Vertically moving layer of midwater animals
o Primarily lantern fish, krill, shrimp, copepods, jellyfish and squids
o Migrate up to epipelagic at night to feed
o Important import of nutrients to mesopelagic
Inhabitants of Bathypelagic
• Jellyfish and ctenophores
• Crustaceans
• Squid
• Typically don’t migrate vertically
o Energy required to migrate from deep sea to surface is too much so not
worth the effort (too far0
Benthic organisms (very bottom of sea)
• Few suspension feeders
• Deposit feeders dominate (e.g. polychaete worms, crustaceans, molluscs, sea
cucumbers)
• Predators include sea spiders, brittle stars and crabs
• Many lift themselves slightly above sediment
• Bethnic fish: slow moving or sedentary
• Ectothermic animals – surround environment very cold
o Everything occurs very slowly
Adaptations of Deep Sea Animals
• Morphological
o Mesopelagic, bathypelagic and benthic differ
▪ Capacity to swim – highly modified structures to increase
chance of catching prey
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Deep sea: definitions vary, 85% of area and 90% of volume of oceans, largest habitat on earth, least known and explored habitat, has unique characteristics that limit life, thermocline, colder warmer, fish don"t like thermocline, th. Characteristics: light, pressure, salinity, temperature, oxygen, food. Light: below mesopelagic no light at all, no photosynthesis possible, only self-generated light below mesopelagic, aphotic no light present. Salinity: epipelagic variable salinity, 33-37, due to river outfall and rainfall (the freshwater, deep sea very constant 35, salty water denser and contributes to great ocean conveyor. Temperature: thermocline is transition zone, below thermocline temp. is fairly constant at 1-4 c, cold water denser. Food: no photosynthesis no base to food web, organic debris sinks from above and may decay or be consumed on the way, less food and poorer quality at depth, only low density of life supported.
