Marine Biology
The Zones
 The Ocean Zones are:
 Sunlit Zone (Epipelagic)
Photic
 Twilight Zone (Mesopelagic)
 Dark Zone (Bathypelagic)
 Abyssal Zone (Abyssopelagic)
 Hadal Zone (Hadopelagic)
Aphotic
Conditions of the Ocean
 Vary with depth
 Light and temperature changes occur quickly
 Pressure increases incrementally
 Each zone produces very different conditions
for living things
Life in these
zones are
linked to
the amount
of plankton
and light
intensity
Deep Sea Exploring
The Surface Layer
 The top one meter of the ocean (part of sunlit zone)
 Richest in nutrients
 Amino acids, fatty acids, and proteins excreted by
plants and animals float, as do oils from
decomposing bodies of dead animals
The Surface Layer
 Gas exchange takes place between the ocean and
atmosphere
 Phytoplankton gather here in daylight, as do the
animals that feed on them
 Highly susceptible to chemical pollution and floating
litter, which can be deadly for marine life
The Sunlit Zone (0~200m)
 Seawater rapidly absorbs sunlight, so only 1% of light
reaches 200m below the surface
 Phytoplankton use the light to photosynthesize, forming
the base of food chains
 This zone drives all ocean life
 More than 90% of all marine
life lives here
The Sunlit Zone
 Nearly all red light is absorbed within 10 meters, so red
animals look black below this depth
 Green light penetrates much deeper in clear water, to
around 100 meters, and blue light to 200 meters
 Due to presence of chlorophyll, phytoplankton
preferentially absorb red and blue portions of the light
spectrum for photosynthesis and reflect green light
Sunlit Zone (in cloudy water)
 In cloudy water, the sunlit zone is shallower
because light is absorbed more quickly
 Accumulation of phyto- and zooplankton in fertile
waters absorb sunlight, reducing the depth of the
sunlit zone
 Phytoplankton must stay here during the day to
photosynthesize, zooplankton follow them to feed,
along with animals that feed on zooplankton
Nocturnal and Diurnal
Distribution
 The sunlit zone is dangerous for animals because they
become conspicuous to hunters, so many stay in the
twilight zone by day and only go up at night
Living in the Sunlit Zone
 Phytoplankton need to remain in the sunlit zone to
photosynthesize, but don’t want to expend huge
amounts of energy to stay afloat
 They may use/be:
 buoyancy bubbles, droplets of oil, or stores of light fats to
keep afloat
 covered in spines to increase surface area and buoy
them up
 In colonial chains to produce more drag in water and slow
sinking rate
 threadlike flagella to swim weakly
Adaptations of vertical migrators like Lanternfish on left
as opposed to non-migrators like Dragonfish on right
 Well developed muscles and bones
 Swim bladder of air or fat
 Withstand extreme temperature changes
The Twilight Zone (200~1000m)
 Too dark for photosynthesis, but just light enough for
animals to see…and be seen
 Many species are almost totally translucent or
camouflaged with countershading to avoid casting even
a faint shadow (dark on top, light on bottom)
 Others are reflective to disguise themselves against the
light from above
 To cope with dim light, many
have large eyes
Midwater Trawl to Collect
Mesopelagic Organisms
Remote-controlled net opens only at certain depths
“Invisible” Octopus at Night
The Twilight Zone
 Main source of food is detritus (organic matter from
dead organisms)
 Many animals migrate up into the sunlit zone where
food is plentiful at night, and return to twilight zone as
the sun rises
 30% of the total marine biomass make this daily trek
(the largest migration of life on Earth)
 Some planktonic animals less that 1mm long may
migrate 20m, but larger shrimp travel 600m each way,
every day
Spookfish
 Found at depths up to
1,000m, on boundary of
dark zone
 Bones are so thin its
almost transparent, and
large eyes look up to spot
predators attacking from
above
Typical Mesopelagic Fish
The Dark Zone (1000~4000m)
 Almost no light penetrates
 No plants can grow and virtually only food source is




“snow” of waste from above
Temperatures are 35~39°F (2~4°C)
Extreme pressure so only adapted animals can survive
Liquid filled bodies are almost incompressible
compared to gas-filled bodies of surface-living birds and
mammals
Only light comes from bioluminescent animals
Typical Deep Sea Fish
Bioluminescence
 Living light is used for:
 Counter-illumination to mask silhouette
 Escape from predators with confusing light
 Attract or see prey
 Communication and courtship
Vampire Squid
Abyssal Zone (4000~6000m)
 Beyond the continental slope
 Around 30% of total seabed area lies here
 Animals are typically slow-moving (to save energy), slow-
growing, and long-lived (up to 100 years)
 Conserve energy by waiting for food to come to them,
many therefore have massive mouths and powerful
teeth
 Use tricks to catch prey- bioluminescent lures and other
glowing structures
Viperfish
 Accomodates
large prey with
large, hinged
jaw
Aliens of the Deep Sea
Hadal Zone (6000m~)
 Only in few deep ocean trenches
 Less than 2% of total seafloor area
 Only three human beings have ever visited this zone
(James Cameron who directed Titanic is the third)
 Pressures are so high (14,700psi) only a few unmanned submersibles are able to operate here
 We know very little about what lives here, but few have
been photographed
 Tough to visit and bring fish back alive
Fangtooth Fish
 Has been recorded at depths of
4,992m
 Like many deep-water fish, has
a large head and massive
teeth.
 Sensory organs along its body
detect prey movement in dark
 Has to grab food in short
time they float past