Adaptive Features of the Marine Organisms Living In the Oceanic Trenches


Adaptation is an evolutionary process whereby an organism becomes increasingly well suited to living in a particular habitat.

Different types of adaptation

  • Behavioural adaptations
  • Physiological adaptation
  • Structural adaptation

What are the oceanic trenches

Ocean trenches are steep depressions in the deepest parts of the ocean where old ocean crust from one tectonic plate is pushed beneath another plate, raising mountains, causing earthquakes & forming volcanoes on the seafloor and on land.

With depths exceeding 6000 meters (nearly 20000 feet) trenches make up the world’s “hadal zone”.

Why are they important?

  • By studying ocean trenches, scientists can better understand the physical process of subduction & the causes of these devastating natural diseases.
  • This study also gives researchers insight into the novel & diverse adaptations of deep-sea organisms to their surroundings.
  • Studying the way the hadal organisms have adapted to life in their harsh surroundings could help understanding in understanding in many different areas of research.
  • These may also hold a key to understand the origins of the ocean life.

Marine animals which live in ocean trenches


Amphipods are soft-shelled crustaceans, which have been found as deep as 9100 meters below the ocean surface.


Foraminifera or forams are free-living single cell organisms. They have very unusual processes for acquiring nutrition & reproducing.


Although starfish are commonly seen on beaches, as a species they are quite adaptable & found in the deep water of trenches which use sea water to pump food through their bodies.


Primarily they are lobsters, crabs & prawns. These creatures were spotted at around 7000 meters by the scientist.

Rat-tail fish

Rat-tails have large mouths & a tapering tail which makes them look like giant tadpoles which were found 7000 meters.                           They have a well-developed sense of smell. They move slowly along the ocean floor to conserve energy as they hunt.


Liparid or snailfish which was found at 7000 meters. The Liparid has an elongated body similar to the ratfish. These fish have well developed, prominent sensory pores on their heads to assist in locating food.

Giant tubeworms

Giant tubeworms can grow 8 feet or more and do not have mouths or digestive tracts. They survive on the symbiotic relationship.


The Cusk-eels live in the deepest water & is a species of fish. Most commonly these fish are elongated & look very similar to eels.

Physical characteristics of the ocean trench

    1.Abiotic factors

  • Light,
  • Temperature, Pressure,
  • Current,
  • Oxygen,
  •  Nutrient.

    2.Biotic factors

  • Predators,
  • Foods,
  • Mates,
  • Competitors or Symbionts.

Adaptation to light


Many fish species have adapted to life in these dark ocean trenches. Some use bioluminescence, meaning they produce their own living light.

In the deep sea, scientists estimate that about 90% of organisms have the ability to produce bioluminescence.

Organisms that bioluminesce in the deep sea include:

  • Marine hatchet fish
  • Anglerfish
  • Flashlight fish
  • Pineconfish
  • Gulper eels
  • Rat-tails
  • Colossal squid
  • Sparkling enope squid

    Adaptation to light

Scientists think bioluminescence has different functions :

  • Special signals for attracting mates.
  • To attack curious prey.
  • Making the fish invisible to predators.
  • Confuse predators or prey such as bright flashes that some squid make to stun their prey. There are two general categories of bioluminescent light: Blue & Red.

Headings such as the forward-facing light organs

  • The blue light is used primarily for long-range communication. It can also be used for predatory purposes by attracting prey items. An example of this is deep-sea anglerfishes.
  • The second category is red light which is used primarily as a prey detection device. This device is very effective to the predators because the prey is unable to detect light, but the predator is able to locate its quarry.

Adaptation to pressure

Considering the volume of water above the deepest parts of the ocean, it’s no wonder that hydrostatic pressure is one of the most important environmental factors affecting the deep sea life.

Life appears to cope with pressure effects on two ways:

  • Firstly, Their membranes and proteins have pressure-resistant structures that work by mechanisms.
  • Second, some organisms may use “piezolytes”. These are small organic molecules recently discovered yhat prevent pressure from distorting large biomolecules, One of these piezolytes is trymethylamine oxide (TMAO).

Adaptation to pressure

Swim bladder :

  • Most fishes use swim bladders to maintain buoyancy.
  • Their gas-filled swim bladder adapted to resist high pressure.
  • The swim bladder are inflated with gases to maintain buoyancy.
  • Fish at this depth fill their bladders with lipids and wax esters to maintain close to neutral buoyancy.

Gelatinous material :

organisms many related to sea stars or jellies are made of mostly water and gelatinous material that can not be crushed.

Adaptation to temperature

  • In most parts of the deep sea, the water temperature is more uniform and constant. Fish in cold environment tend to move & reproduce very slowly.
  • Life in the deep is thought to adapt to this intense cold is by having “loose” flexible proteins & unsaturated membranes which do not stiffen up in the cold.
  • Membrane is made of fats and somewhat flexible to work well.

Feeding Adaptation

Deep-sea creatures have evolved some fascinating feeding mechanisms because the food is scarce in these zones.

  • Deep sea pelagic fish such as gulper eels have very large mouths, huge hinged jaws & large & expandable stomachs to engulf large quantities of scarce food.
  • Many deep-sea pelagic fish have extremely long fang-like teeth that point inward.
  • Anglerfish & the viperfish are also equipped with a long, thin modified dorsal fin on their heads tipped with a photophore lit with bioluminescence used to lure prey.
  • Many deeper pelagic species also save energy by having watery, gelatinous muscles & other tissues with low nutritive content.
  • Many deeper pelagic species also save energy by having watery, gelatinous muscles & other tissues with low nutritive content.
  • A deep pelagic blacksmelt or viperfish they can achieve a larger body size with much less maintenance cost.

Adaptation to oxygen

The dark, cold waters of much of the deep sea have adequate oxygen. This is because cold water can dissolve more oxygen than warm water.In certain places, oxygen-rich waters cool off so much that they become dense enough to sink to the bottom of the sea.

Low Biomass:

Descending through the water column, the biomass decreases to a very small amount. The small biomass stays relatively constant until reaching the ocean floor where the number of organisms increases again.

The accumulation of dead organisms is greatly responsible for the spike in biomass here.

Constant condition:

Constancy is a unique characteristic of the deep sea that has shaped the evolution of many deep-sea animals. There are no diurnal or seasonal changes; the day is night and summer is winter in the deep sea.


Animals at these depths tend to move very slowly, have bulky and unstreamlined bodies & require little oxygen.

Energy conservation:

While the majority of the adaptations that have been discussed conserve energy there are a wide variety of morphological trends that free up the energy to be used in other areas.

Examples of this include underdeveloped muscles & reduced skeletal structures.

By not developing these structures the conserved energy can be used for functions necessary for life in the deep-sea.

Other adaptations of oceanic trench animals

Many of unique adaptations that animals of the ocean trench have evolved to cope with their harsh environment. Let’s look at some others :

  • Body color
  • Reproduction
  • Gigantism
  • Long Lives

Body color :

In the deep sea animals’ bodies are often transparent (such as many jellies & squids), black (such as blacksmelt fish), or even red (such as many shrimps and other squids).

Some fish such as hatchetfish have silvery sides that reflect the faint sunlight, making them hard to see.


  • Unique light patterns may aid in this.
  • Deep-sea anglerfish may use such light patterns as well as scents to find mates, but they also have another interesting reproductive adaptation.
  • Males are tiny in comparison to females & attach themselves to their mate using hooked teeth, establishing a parasitic-like relationship for life. The blood vessels of the male merge with the females so that he receives nourishment from her.

Gigantism :

  • Another possible adaptation that is not fully understood is called deep-sea gigantism.
  • This is the tendency for certain types of animals to become truly enormous in size. A well-known example is the giant squid, but there are many others such as the colossal squid, the giant isopod, the king-of-herrings oarfish & the recently captured giant amphipod from 7000m.

Long lives :

  • Long-lived fishes include rattails or grenadiers & the orange roughy which are of special concern they are targets of deep-sea fisheries. These species reproduce & grow to maturity very slowly, such that populations may take decades to recover after being overfished.

References :

  • Marine Biology, an Ecological Approach, J.W. Nybakken, Benjamin  Cummings,1994. Chapter 4: Deep Sea Biology.
  • Deep-Sea Biology, J.D.Gage&P.A.Taylor, Cambridge Univ.Press,1992.
  • Deep-Sea Fishes , D.J. Randall & A.P. Farrell, Academic Press, 1997.
  • The Biology of the Deep ocean, P. Herring, Oxford Univ. Press, 2001.
  • The Silent Deep: The Discovery, Ecology, &Cnservation of the Deep Sea, T. Koslow, Univ. Chicago Press, 2009.
  • Deep Sea Biodiversity : Pattern and scale by M.A. Rex &R.J.etter, Harvard Univ. Press, 2010.

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