The document provides an overview of deep-sea ecology, including key definitions and concepts. It describes the deep-sea as the largest ecosystem on Earth, located below 200m depth where there is no light. Life exists through chemosynthesis or relying on organic matter from surface waters. Organisms have adaptations for high pressure, low food availability, and absence of light. Diversity is high despite low population densities. Hydrothermal vents and cold seeps also support unique ecosystems through chemosynthesis.

1. Geronimo R. Rosario

3.  Deep-sea Ecology- study of the marine organisms
living in the aphotic zone
 largest ecosystem on Earth, with approximately 50%
of the surface of the Earth covered by ocean more
than 3,000 meters deep
 Not lifeless as thought 200 years ago
 Shells first dredged from abyss in 1846
 Challenger expedition, 1873-1876
 Animals from 5500 m
 1967: first quantitative measure of deep sea diversity
by Hessler & Sanders
 2006: Venter sampling of microorganisms

5.  Deep sea - all environments below the
compensation depth (below Photic Zone)
 Up to 10,000 m
 Water column + Benthic habitats
 Some organisms are “depth specialists” but others
move > 1,000 m vertically

6.  Photic zone- lighted zone
 Disphotic Zone- the upper layer of the deep sea
which receives some light.
 Aphotic zone- dark zone


7.  Epipelagic - 0 – 200m
 Mesopelagic - 200- 1000m
 Bathypelagic - 1000-4000m
 Abyssalpelagic - 4000-6000m
 Hadalpelagic - 6000-10000m

9.  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.

11.  devoid of light
 no photosynthesis
 bioluminescence
 rely on other senses other than vision

12.  increase of pressure by 1 atm (14.7 lb/in2 or 1 kg/cm2) per 10 m
descend
 range from 20 to 1000 atm
 hard to get live specimens
 special pressure chamber is used to retrieved organisms
undamaged
 hydrostatic pressure plays a major role to adaptations in deep-
sea environment
 inefficient muscles enzymes
 lower metabolic rates and sluggish
 “float and wait” predators
 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

13.  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 oC at 1000m
 isothermal from 3000m to 4000m
 no seasonal temperature changes in the deep
 hydrothermal vents – 400oC but kept from boiling by
hydrostatic pressure


14.  supplied by oxygen-rich cold Antartic or Arctic oceans
 oxygen is no depleted in the depths by organisms due to low
density of organism and low metabolic rates
 above 20 m from the sea bottom the temperature declines
 oxygen minimum zone- a zone of low DO2 concentration
that occurs at a depth of 500 to 1000m. (0.5 mg/l)
 Due to respiration and water interchange
 Abundance of organisms in this layer
 Oxygen depletion does not occur above 500 m due to
constant replenishment from air and by autotrophs
 Likewise in the depth due to low number of animals
 The diffusion and sinking of cold, dense water masses are the
chief mechanisms of O2 transport into the deep sea.
 Dissolved O2 is slowly diminished by animals and bacteria,
leaving an O2 minimum zone at intermediate depths.
 Below this zone, dissolved O2 gradually increases to just
above the sea bottom

16.  no indigenous primary productivity
 potential food from the surface
 high probability of food from the surface to decay
and consumed
 small body of deep sea fishes
 food is very scarce, decreases with depth and
distance from land

18.  Decreasing densities of populations
◦ consequences for finding mates, sociality
 Decreasing availability of food for offspring
◦ migrations to surface waters, or . . .
◦ delayed reproduction & smaller repro effort
◦ more parental care
◦ slow embryological development

19.  Due to the absence of light, plants are generally
absent in the deep-sea. The deep-sea is
dominated by the animals.

20.  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

21. 
 Reproduction and Development
◦ Few eggs, large, yolk rich
◦ Slow gametogenesis
◦ Late reproductive maturity
◦ Reduced gonadal volume
◦ Slow embryological development
◦ Breed usually once (semelparous)

22.  Physiological
◦ low metabolic rate
◦ low activity level
◦ low enzyme concentration
◦ high water content
◦ low protein content
◦ small size

23.  Ecological
◦ slow, indeterminate growth
◦ high longevity
◦ slow colonization rate
◦ low population densities
◦ low mortality due to low predation pressure

25.  Color

 Mesopelagic
◦ Fishes are silvery gray or a deep black not counter
shaded
◦ Invertebrates are purple, bright red or orange
◦ Jellyfish dark purple
◦ Crustaceans brilliant red
◦ Why the red color?- since most bioluminescent color is
blue, the red pigmentation will protect these animals
from the revealing rays of the bioluminescent flashes
used by the predators

26.  Abyssal and Bathyal
◦ Most organisms are colorless or dirty white
◦ lack pigment
◦ fishes maybe black at all depths
◦ except anemones which are colorful

27.  Eyes
 Mesopelagic, Upper Bathypelagic
◦ Large eyes, this give maximum light-collecting abilities
◦ Enhanced twilight vision derived from pigment “rhodopsin”
 Abyssalpelagic, hadalpelagic
◦ small eyes or lack eyes
◦ fishes in depths 2000m and above have large eyes
◦ below 2000m eyes are small, degenerate or lost
◦ bottom dwellers have no eyes
◦ Tubular eyes- the eye is a short black cylinder topped with
a hemispherical translucent lens
◦ Others have one bigger eye while the one is smaller

28.  Mouth
◦ Large mouth
◦ Mouth and skull are hinged , open mouth wider than
their bodies
◦ Long teeth recurve toward the throat
 Mating
◦ Females are larger than males
◦ Males are parasitic to females

29.  Body size
◦ Generally have smaller body size
◦ Abyssal gigantism- a phenomenon in the depths
where some organisms have unusual bigger body size
as compared to other organisms
◦ Archieteuthis – giant squid, 18 m long, the largest
aquatic invertebrate, prey of sperm whale

30.  Two theories of gigantism
◦ peculiarities of metabolism under conditions of high
pressure
◦ low temperature and scarce food reduces growth rates
and increase longevity, longer time to reach sexual
maturity

◦ as one goes deeper, the anatomical organization of
the animals are simplified
◦ oxygen uptake on the deep sea floor ranges from 0.02
to 0.1 ml of O2 per m2 per hour or more than 100
times less than that measured in shallow water.

31.  Bioluminescence
◦ Refers to the production of light by living organisms
 Photophores
◦ light-producing organs

32. 
 food capture
 defense against predators
 finding mates
 finding and attacking prey
 ensuring survival
 recognition

33.  Early sampling limited by technology
◦ Suggested low density
◦ Suggested low diversity
 Increasing sampling intensity & with less
damage
◦ Low density generally was correct
 But High Diversity

34.  Epifauna- benthic organisms that live on or are
otherwise associated with the surface of the bottom.
 Infauna- are organisms that live within the substrate

 Dominated by “macrofauna”
◦ Defined by size (> 300 μm but too small to be identified by
photographs)
◦ Include polychaetes, molluscs, crustaceans, echinoderms
 Estimated to include between 500,000 and
10,000,000 species
◦ Program to inventory under way (CeDAMar or “Census of
Diversity of Marine Life”)

35.  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
(Synaphobranchus)

36.  Deep-sea fauna is highly diverse in the sense that
each deep-sea species is commonly represented
by only a few individuals.


37. 
 Stability-time hypothesis- states that high diversity
occurs because highly stable environmental conditions
have persisted over long periods of time and have
allowed species to evolve that are highly specialized
for a particular microhabitat or food source.
 Cropper or Disturbance theory- states that
organisms increase in number until a time the
resource is least in abundance causing competition
and resulting to high predation, allowing large number
of species to persist. In here, the species are
generalist as opposed to specialist.
 Area hypothesis- states that diversity increases with
depths

38.  young stages are spent in the surface waters and
then the animals migrate to the deep sea as they
mature or metamorphose
 no migration occurs and the young stages are
spent in the same area as adults


39.  The three main sources of energy and nutrients
for deep sea communities are
 marine snow
 whale falls
 chemosynthesis at hydrothermal vents and cold
seeps.

40.  Deep-sea organisms acquire chemical energy from falling
particulate organic carbon (POC) derived from primary
production in the euphotic (1-200 meters) zone, which
represents a minimal amount (~1%) of surface production.
 Given this severe energy constraint, the deep sea provides
an exceptionally good system to explore how
fluctuations/limitations in energetics impact species,
populations, communities, and ecosystem
 Because there is no light, there can be no photosynthesis.
Instead, bacteria and other single celled organisms
produce their own food using the energy found in the
chemicals and minerals coming out of the deep sea vent.
This process is called chemosynthesis

41.  Hydrothermal vent- a spot in the mid-ocean
ridge where heated water forces its way up
through the crust.
◦ A spring of hot water in the deep ocean floor
◦ Oases of the deep ocean
◦ 8 – 10oC
◦ Usually found at the ridges
 Vent water is anoxic

42.  Black Smoker- a hydrothermal vent on the ocean
floor that emits a black cloud of hot water filled
with dissolved metal particles.

43.  Arthropoda – (crabs) 35%
 Mollusca- 34% ( clams, snails, mussels)
 Annelida- 23%
 Cnidaria- 3%
 Pogonophora – 3%( vestimeniferan worms)
 Archaea- simple bacteria-like form organisms
(chemosynthesis)

45.  Chemosynthesis- a process by which bacteria or
achaea synthesize organic molecules from
inorganic nutrients using chemical energy
released from the bonds of a chemical compound
by oxidation.
 6H2S + 6H2O + 6CO2 + 6O2
 C6H12O6 + 6H2SO4

46.  Primary productivity depends on
chemoliautothrophic bacteria.
 Productivity is high – 19 ug C/g’/h
 Symbiotic relationship- bacteria and the organisms
 Vents have life span of years or decade while
seeps maybe longer
 When vents are inactive the animals recede and
look for another place or die

48.  Seep- an area where water of various temperatures
trickles out of the sea floor.
 Seep communities are more dispersed in areas where
hydrocarbons, particularly methane or other natural
gases, are percolating up through deep-sea sediments
 Hypersaline seep- 46.2% ppt
◦ 3000 m depth
◦ White microbial growth (mats) performs chemo
 Hydrocarbon seep
◦ 2200 m
◦ Microbial oxidation of methane produces CaCO3
 Subduction Zone seep
◦ 2036m
◦ 0.3oC warmer than seawater at that depth
◦ methane

49.  Cold seeps are characterised by the seepage of
cold fluid with a high concentration of methane.
 This methane may have a biological origin, from
the decomposition of organic matter by microbial
activity in anoxic sediments, or a thermogenic
origin, from the fast transformation of organic
matter caused by high temperatures
 Cold seeps also have high concentrations of H2S
in sediments, produced by the bacterial reduction
of sulphates using methane