In this article we will discuss about the Deep Sea Adaptation:- 1. Introduction to Deep Sea Adaptation 2. Characteristics of Deep Sea 3. Adaptive Characters 4. Examples.
Introduction to Deep Sea Adaptation:
Usually lightless sea bottom is referred to as deep sea, i.e., from lower limit of littoral zone (200 metres deep) to the ocean floor.
The benthic division includes Bathyal (200 m – 400 m), Abyssal .(4000 m – 6000 m), and Hadal (from 6000 m and below) zones, Pelagic division includes Mesopelagic (200 m – 1000 m), Bathypelagic (1000 m – 4000 m) and Abyssopelagic (4000 m and below) zones. The physical characterization of deep sea conveys the nature of adaptation of animals.
Extent of Deep Sea:
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According to geologists, extension of deep sea is marked as one half of the entire globe.
Physical Characteristics:
Environmental factors in deep sea are uniform from ocean to ocean and from season to season. Sea bottom is smooth in physical characters. Therefore, deep-sea creatures of different oceans have a convergent type of adaptation. The remarkable characteristic of deep sea may be discussed as follows.
Characteristics of Deep Sea:
i. Temperature:
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Below 3000 ft. the temperature in about 37° F or less. In the great ‘deeps’ the water is ice cold, averaging about 32° F. There is no diurnal and seasonal fluctuation.
ii. Quiescence:
Below the limit of disturbance caused by the storm wave, i.e., about 600 ft. and below the average depth of the tidal action all movements of sea wave are exceedingly slow.
iii. Darkness:
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The distance to which light penetrates varies with the angles of the sun rays and the clarity of the water. Generally below 1200 ft. light does not penetrate. So there is endless darkness in deep-sea.
iv. Pressure:
The atmospheric pressure at sea level is about 7 kg/sq inch. This increases enormously to about 1 ton/sq inch for every 6000 ft. Therefore, in greater depth, the pressure is unbelievably high.
v. Green Plants:
Beyond the light zone green plants are totally absent, i.e., ecologically, no producer is present in deep-sea.
vi. Other Characters:
Deep-sea water possesses uniform salinity (3.5 – 3.7%), as no external factors can affect its water qualities. Oxygen content is comparatively low (3.29 – 5.9 c.c/litre of water), because there are no producers, which generally contribute oxygen during day-time.
vii. Sea Floor:
The ocean floor generally is a vast undulating plain with occasional volcanic and other elevations. The floor of the sea is usually carpeted with mass of land material and organic materials. Organic materials are either excretory and secretory products or carcasses of the upper inhabitants. The organic remains are known collectively as oozes. The oozes are of following types.
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(a) Pteropod Ooze:
This layer consists of lime shells of pteropod mixed with other organic remains ranging at a depth of 3000 – 9000 ft.
(b) Globigerina Ooze:
This layer includes shells of foraminifera’s and other organic material and ranging from 9000 – 15000 ft. Beyond 12000 ft Radiolarian and Diatom oozes are evident.
(c) Red Clay:
Beyond 15000 ft. red clay is found.
viii. Food Supply:
Oozes constitute the sole food supply to the depth, i.e., dead organisms of upper level, when die, come down to the deep sea and provide food for the deep-sea organisms. Sometimes decomposers, like bacteria and fungus are also used as food. So deep-sea animals are either oozivorous or carnivorous due to lack of vegetation.
Origin of Deep-sea Fauna:
All phyla of animals are represented in the deep-sea fauna. None of the deep-sea form is the product of the locally evolved race, but they are simply adapted migrants from the lesser depth. In response to physical conditions of deep sea, modifications have occurred in such fauna. Ancient zoological forms are rare in deep-sea and this indicates that deep-sea fauna includes recent forms only.
Adaptive Characters of Deep-sea Animals:
i. Consistency of Animals:
The animals are frail and weak and their body is thin and flabby. Vertebrates possess un-calcified or weakly calcified skeleton. It is due to inability to accumulate calcium within the tissues in absence of sunlight. Totally un-calcified skeleton is found in Chimaera.
ii. Body Contour:
Deep-sea fishes are slender and delicate. In many species, tail becomes a long whip like caudal filament, e.g., Chimaera, Macro pharynx etc. Body is compressed either laterally or dorsoventrally, giving the body a ribbon like shape. In case of dorsoventrally compressed body, both eyes comes to lie side by side. It is supposed that dorsoventrally compressed body appears due to high pressure on the body surface.
iii. Colour:
As a rule there are simplified colours among deep-sea animals. Usual colours found are red, brown, gray or black. Standard aquatic colouration is black back and silvery belly. Black back hides the deep-sea animal from its upper predators.
Because upper predators cannot see a black animal in black background. Similarly, silvery belly helps the animal to escape from the eyes of underwater preys. Macrurus filicanda exhibits a black belly and silvery top; which is exception to the standard coloration.
iv. Vision:
In a completely dark atmosphere, eye has no function. So some deep-sea fishes are blind. Others have either telescopic eyes or bear eyes like concave mirrors.
v. Tactile Organs:
As vision becomes nil, tactile organs are highly developed. Long feelers and slender attenuations of the fins act as a tactile organ.
vi. Luminescence:
The light producing function or luminescence is a common, phenomenon in almost all deep-sea fauna. Luminescent bodies may be round or elliptical in shape, shining mother of pearl coloured body, embedded in the skin at the side of the body and tail.
vii. Weak Jaws:
Many deep-sea fishes live on decaying oozes and they generally loose their powers of mastication.
viii. Reproduction and Care of Young:
There are various ways of carrying the young’s among deep-sea fauna. These animals lay fewer eggs with much yolk, and hatch at an advanced stage of development. In ice cold water, time for embryonic development increases.
So eggs are laid with much yolk. Some are even viviparous and produce young ones in large number. Uncared eggs in water results in predation, which forces some of the deep-sea animals to become viviparous.
Care for young is very common. Deep-sea environment exhibits changelessness or to some extent change occur very slowly. There is nothing to mark the day and night, there is no sequence of seasons and same condition prevails throughout the year.
Actually, environmental factors in deep seas are uniform from ocean to ocean. Sea bottom is so uniform in physical conditions that virtually there are no environmental barriers. Therefore, less competition in deep-sea and prevalence of similar environmental conditions resulted in very slow rate of evolution. Convergent type of evolution is only evident due to specific ecological condition.
Examples of Deep-sea Vertebrates:
(i) Swallower (Snccopharynx):
They have very long slender body with enor- (v) mous jaws (Fig. 4.31b).
(ii) Linophryne:
In this animal pelvic fins and scales are absent, colour is black, the fin rays are tipped with luminous organs to attract the pray.
(iii) Silver Sharks:
They have huge eyes, long body and tail.
(iv) Ipnops:
They have no eyes but two large luminescent organs are present on the head.
(v) Cryptosaras:
They have fusiform shape with elongated luminescent organ on the head region while the broadest trunk region bears another luminescent organ.
(vi) Raffish (Chimaera):
It is also called as ‘king of Herrings’. It possess short nose and elongated shark-like body (Fig. 4.31g).