Question

1. In the context of marine environments, provide a short (one sentence) definition of the thermocline, the oxygen minimum layer, and the epipelagic zone.

2. List, and provide a 1-3 sentence description, of at least three contercurrent exchangers in physiology. List an actual organism that has each one

3. List and describe at least three adaptations you would expect to see in a bathypelagic fish, including at least one life-history adaptation, and describe their significance. Give an example of a bathypelagic fish that has each adaptation.

Answer 1

• Thermocline: The abrupt temperature drop observed as we move down from the warm surface layer of a waterbody upto a certain depth after which the temperature gradient is not as steep, is the thermocline layer.
• Oxygen minimum layer: The oxygen minimum layer is that layer or zone of ocean where the concentration of dissolved oxygen or oxygen saturation is the lowest.
• Epipelagic Zone: The uppermost layer of ocean which receives sunlight and has the most biodiversity is called the epipelagic zone.

• There are 3 countercurrent exchange mechanisms:
  • Countercurrent oxygen exchange: This mechanism is present in the gills of fishes. The fishes can uptake oxygen only when thier blood comes in contact with oxygen rich water, so by the help of countercurrent exchange the deoxygenated blood is moved in the opposite direction of oxygen rich water. As the blood remains in contact with oxygen rich water for longer time period, there is more oxygen uptake.
  • Countercurrent heat exchange: This type of countercurrent exchange is present in legs of birds. In order to maintain body temperature, birds have countercurrent heat exchange mechanism through which the heat coming from body's core is lost at the periphery. The warm blood from the body's core moves to the legs through the artery beside which is vein coming from the periphery having cool blood, due to the temperature gradient arterial blood cools a little by conducting heat to the venous blood.
  • Countercurrent multiplication: This countercurrent exchange is found in the nephrons of mammals. Here active transport of NaCl takes place into the ascending loop of Henle resulting in the formation of a osmotic gradient. Now in the collecting tubules there is higher concentration of water, so it moves along the osmotic gradient resulting in the formation of concentrated urine.

• Adaptation in bathapelagic fishes:
  • Body color: Availability of light is very low in the bathapelagic zone of ocean, so to camouflage themselves the fishes of this zone have dark colors. Some are black like Blacksmelt fish and some have developed red color, as red light does not reach this zone, like Velvet whalefish.
  • Bioluminescent lures: Deep sea predatory fishes have developed the property of bioluminescent lures which allows them to lure their prey towards them. This can be seen in Dragonfish.
  • Reproduction: Larger females have more eggs and even a small male can produce large number of sperms. Due to the harsh environment this adaptation is necessary for the survival of species, the small male uses its energy to find and mate with female and then spends all its life attached to female and depends on her for nutrition. Example: Anglerfish