The deep sea is a vast and mysterious realm, encompassing the darkest and most remote parts of the ocean. It begins at around 200 meters (656 feet) below the surface and extends to the ocean floor, which can reach depths of over 11,000 meters (36,000 feet) in places like the Mariana Trench. This environment is characterized by extreme conditions: immense pressure, frigid temperatures, and near-total darkness. Despite these harsh conditions, life thrives in the deep sea, showcasing remarkable adaptations to survive.

1. DEEP SEA ECOLOGY
Seminar presented by
Santanu Sahoo
department of Marine Biology
Vikrama Simhapuri University, Nellore

2. Introduction
Deep-Sea Ecology – is the study of the marine organisms living in the aphotic zone .
• Largest ecosystem on earth approximately 54% of the surface of the earth covered
by ocean more than 3000 meters deep.
• Not lifeless as thought 200 years ago
• Shells Frist dreged from deep sea in 1846
• 1967, first quantitative measure of deep sea diversity by Hessler & Sanders
• 2006 : venter sampling of microorganisms
• Freyastera tuberculata(NOAA, 2022) – a deep sea starfish a newly identified
species living in a hydrothermal seep in the deep Sea.

3. IMPORTANCE OF DEEP
SEA
• climate regulation
• waste absorption and detoxification
• Oil, gas, mineral and biomedical resources
• Help us fill gaps to better understand planetary-scale
processes including tectonics and marine hazards
• Biological resources

4. Ocean light zonation
• Photic Zone(0-200m) –Surface layer of the Ocean that receives Sunlight ,
also called euphotic Zone or lighted Zone.
• Disphotic Zone(200-1000m) – the upper layer of the deep sea which
receives some light
• Aphotic Zone(>1000m)– Only small amount of light Penetrates the water .
Plant do not grow due to insufficient of light. The darkness layer or Aphotic
Zone is entirely dark meaning there is no light. About 90% of the ocean is in
this layer.

5. Ocean Vertical Zonation
• Epipelagic – (0-200m) the part of the ocean where there is enough sunlight
for algae to utilize photosynthesis
• Mesopelagic – (200-1000m)is cold and its light is dim, but with flashes of
bioluminescence—light produced by living organisms.
• Bathypelagic – (1000-4000m)is characterized by darkness, cold, high
pressure and low biological activity. Seasonal variations are essentially nil.
• Abyssalpelagic – (4000-6000m) is characterized by darkness, high pressure
(200-1000 atmos.), cold (less than 4°Celsius) and low levels of dissolved
oxygen. Physical change or variation appears slight, if any
• Haldalpelagic – (6000-10,000m) The bottommost layer of the oceanic zone,
lying below the abyssopelagic zone at depths greater than about 6,000 m
(19,680 ft).
N.B- The deepest part of the ocean is called the Challenger Deep and is
located beneath the western Pacific Ocean in the southern end of the Mariana
Trench, which runs several hundred kilometres southwest of the U.S.
Territorial island of Guam. Challenger Deep is approximately 10,935 meters
(35,876 feet) deep.

6. Deep-sea Habitats
▸ Heterotrophic habitats, the faunal communities depend, ultimately, on
organic matter produced at the surface by photosynthesis and are therefore
dependent on solar energy.
▸ Chemosynthetic habitats, the biological communities are sustained by the
energy provided by inorganic reduced chemicals such as hydrogen sulphide
(H2S) or methane (CH4) from the Earth’s interior.

7. Environmental characteristics
Characteristics of a Typical Abyssal plain Habitat at 3000m
Water pressure – 300atm
Water temperature – 1° to 2°c
Salinity – 34.5-35%
Dissolved oxygen – 5ppm
Light – Bioluminescence
Current slow - <1cm/s or 0.7km/day
Sediment
Type soft fine oozes or clay
Deposition rate <0.01mm/yr.
Organic Content – 0-0.5%
Data collected from Gage and tylet,1991

8. Pressure
• Increase of pressure by 1 atm (14.7 lb/in² or 1 kg/cm²) per 10 m descend
• Hydrostatic pressure plays a major role to adaptations in deep- sea
• environment inefficient muscles enzymes
• lower metabolic rates and sluggish
• Homeoviscous adaptation- an adaptation of organisms in the deep-sea
incorporating more fluid lipids into their membranes to withstand high
pressure.
• pressure increases and temperature decreases, the solubility of CaCo3
increases which means that shell-forming species decreases with deep.

9. Salinity and Temperature
Salinity
• remarkably constant
• not a limiting factor
Temperature
▸ thermocline (100-1000 meters in thickness)
▸ cold and homogenous below the thermocline
▸ thermoclines are strongest in the tropics drops by 5 to 6 °C at 1000m
▸ isothermal from 3000m to 4000m
▸ no seasonal temperature changes in the deep
‣ hydrothermal vents – 400°C but kept from boiling by hydrostatic
pressure

10. GENERAL BIOLOGICAL CHARACTERISTICS OF
DEEP-SEA ORGANISMS
Reproduction and development
• Few eggs, large, yolk rich
• Slow gametogenesis
• Late reproductive maturity
• Reduced gonadal volume Slow embryological development
• Breed usually once (semelparous)

11. GENERAL BIOLOGICAL
CHARACTERISTICS OF DEEP-SEA
ORGANISMS
Physiological
• low metabolic rate
• Low activity level
• low enzyme concentration
• high water content
• low protein content
• a small size

12. GENERAL BIOLOGICAL CHARACTERISTICS OF
DEEP-SEA ORGANISMS
Ecological
• Slow, indeterminate growth
• high longevity
• slow colonization rate
• low population densities
• low mortality due to low predation pressure

13. Epipelagic Mesopelagic
(vertical
migrators)
Mesopelagic
(Non migrators)
Deep pelagic Deep sea
pelagic
Size Wide size range
from tiny to
huge
Small Small Relatively small,
larger than
Mesopelagic
Relatively large
Shape Streamlined Relatively
elongated or
laterally
compressed
Relatively
elongated or
laterally
compressed
No streamlining
often globular in
shape
Very elongated
Musculature Strong muscles
fast swimming
Moderately
strong muscles
Week, flabby
muscles
Week, flabby
muscles
Strong muscles
Eye
characteristics
Large eyes Very large,
sensitive eye
Very large
sensitive eyes,
sometimes
tubular eyes
Eye small,
sometimes
absent
Small eyes
Colouration Typically
counter shaping
: dark and white
or silver belly
Black or black
with silver sides
and belly:
counter
illumination
Black or black
with silver sides
and belly:
counter
illumination
Black,
occasionally red,
often lack
Colouration at
greatest depths
Dark brown or
black
Bioluminescence Bioluminescence
relatively
Bioluminescence
common, often
Bioluminescence
common, often
Bioluminescence
common,often
Only a few
groups

14. PROBLEMS OF DEEP
LIVING
• PRESSURE – increases by 1 atmosphere per 10m in depth
• LIGHT – little light penetrates deeper than 200m
• TEMPERATURE – The coldest waters are found in the deepest
depths – only a few °C
• LACK OF NUTRIENTS – low densities of organisms and virtually
no producers (<5% of photic zone) However the seabed is rich
with decaying organisms

15. DEEP SEA ADAPTATION
HIDING IN THE DARK
TRANSPARENCY – what light there is passes through these organisms –
making them invisible
REFLECTIVE – mirror like scales reflect what light there is, so the fish
match the background – no silhouette
PHOTOPHORES – Light emitting organs on the ventral surface faintly
lights their underside –silhouette does not stand out
RED PIGMENTS – Red light is the first to disappear. Red pigmented
organisms appear black (camouflaged) in the deep ocean

16. ADAPTATIONS TO DEEP LIVING
•ENLARGED AND SPECIALISED EYES – many low light sensitive rod
cells to detect what little light there is (but colour blind)
Mesopelagic – minute amounts of light from the surface
Bathypelagic – light from bioluminescence
•TELESCOPE EYES – As in Gigantura – to give better binocular
vision for hunting
•UPWARD POINTING EYES – Looking towards the surface – to see
the silhouette of fish swimming above against the faint light of
the surface

17. BIOLUMINESENCE
•Light emitting organs have a variety of uses:
•HEADLIGHTS – producing light to see prey
•LURES-to attract prey
•MATE ATTRACTION
•COMMUNICATION – especially in squid
•DECOYS and SMOKESCREENS – squid squirt luminous ink to startle predators & hide
their escape
Jellyfish, starfish, crustaceans, squid, sharks are some of the marine organisms that
exhibit bioluminescence

18. ECOLOGY OF THE BENTHOS
Faunal Composition
•Crustaceans (isopods, amphipods, tanaids and
cumaceans)-30-50%
•Polychaete worms-40-80%
•Sea cucumbers (Holothuroidae)- 30-80%, deposit
feeders, abyssal oozes are excellent food source
•Starfish (Asteroidea), sea lilies (Crinoidea), sea
urchins (Echinodea)- minimal
•Glass sponges (Hexactinellida)
•Sea anemones (Anthozoa)
•Rat tails (Macrouidae), cusk eels, bythidids (brotulas),
liparids (snaifishes) and certain eels

19. ANIMALS IN THE
DEEP-SEA
• Annelida (segmented worm)- sandworms. Clamworms
• Arthropoda (segmented body)- crustaceans
• Mollusca- Snails, octopus
• Echinodermata- sea stars, sea cucumber
• Cnidaria- corals, jelly fish ▸ Pogonophora- beard worm
• Sipuncula- peanut worm
• Echiura- spoon worm Nemertea- ribbon worm
• Hemichordata- acorn worm
• Priapulida- penis worm
• Brachiopoda- lamp shell
• Ectoprocta- moss animals
• Chordata- fishes

20. DESTROY DEEP SEA ECOLOGY
• Anthropogenic disturbance
• with new and direct threats from mineral mining increasing with
technological advances
• Ghost fishing ( various types of waste gears dropped under the deep
sea and this is destroy the deep sea organisms )
• Annual whale slaughter tradition in Denmark turns sea red over 100
whales killed . The natives of the faroe Islands in Denmark had been
practicing this tradition for centuries dating back to 1584 ( data
collected from wekipedia )

22. DEEP SEA RESEARCH PROJECT NAME
1. India launch a project “Samudrayaan” under research
centre National Institute of Ocean Technology (NIOT) 2022
2. Deep Oceanic Observing Strategy (DOOS) under various
deep sea project-
• Deep pelagic Nekton Dynamics of the Gulf of Mexico
• The ocean Twilight zone project
• Deep Ocean-Stewardship Initiative (DOSI)
3. The Deep Sea Drilling Project (DSDP) an Ocean drilling
project from 1968-1983
The program was Co-ordinated by the Scripps Institution of
Oceanography at the University of California, San Diego.

23. REFERENCE
• Book- Deep Sea Biology, J.D Gage &P.A Tyler
• Electronic media –
https://en.wikipedia.org/wiki/Deep_sea_community#Zones
https://www.slideshare.net/DrShaleeshaAStanley/deep-sea-
adaptationsppt
https://www.slideshare.net/GeronimoRosario/deep-sea-ecology-
207590903

24. ACKNOWLEDGEMENT
I would like to express my special thanks and gratitude to my
teachers as well as our faculty mam who gave me the golden
opportunity to do this wonderful project on the topic Deep Sea
Ecology which also helped me in doing a lot of research and I
came to know about so many new things.
I am really thankful to them.
It really helped me increase my knowledge and skills.
THANKS TO EVERYONE WHO HELPED.

25. Thank you