GS Paper III

News Excerpt: 

Diel Vertical Migration (DVM) has been recently in the news due to its role in carbon sequestration.

What is DVM?

Every day, billions and billions of animals, mostly zooplankton (e.g., smallish animals, including fish, various shrimp, and jellies), migrate up and down in the ocean all over the planet. This movement is referred to as Diel Vertical Migration.

• Diel means that it occurs on a daily, 24-hour cycle. 
• Vertical refers to the direction of the movement up and down in the water column, generally between the surface layer (called the epipelagic layer) and the deeper, middle layer (called the mesopelagic layer). This journey of almost 1000m is quite impressive, especially for creatures of the size of zooplanktons.

• • Layers of Oceans: The surface layer of the open ocean is between 0 and 200 m deep. In this layer, there is enough light for phytoplankton to grow. The middle layer of the open ocean is between 200 and 1,000 m deep. Light rapidly declines in this layer and it is often called the “twilight zone.” All this movement consumes a great deal of energy.

History:

Daily migrations of aquatic animals were first noted by the great French naturalist Georges Cuvier in the early 1800s. DVM is like a circadian rhythm (in humans) which is associated with genetics.

Migration of Different Animals:

• Zooplankton cannot stay in dangerous waters during the day because of the presence of their predators on the surface. DVM allows them to come to the surface at night for their food (phytoplanktons) safely. Example: Copepods are a type of zooplankton and are a big part of the diel vertical migration
• Animals like dragonfish, Sharks, and glass squid, may also migrate to reduce ultraviolet damage to their DNA, to use the currents to move to areas with more food or to take advantage of the benefits of colder (deeper) waters to get more nourished or produce more eggs.

DVM plays an important role in Carbon Sequestration:

DVM is also more than just a survival strategy as it plays a pivotal role in sequestering carbon, a process vital for regulating the earth’s climate. 

• Animals dwelling in the mesopelagic layer actively remove substantial amounts of carbon from the upper ocean as they feed on surface-dwelling plankton. When these organisms return to deeper waters, they carry carbon with them.
• In the twilight zone, certain migratory species contribute to the food chain by passing on the carbon they eat to their predators. The predators' carbon-rich waste sinks to the ocean floor, which remains locked for centuries. This natural mechanism is a major carbon sink that aids in the regulation of carbon dioxide levels in the atmosphere.

Way Forward:

• During this current scenario of global climate change, any shift in the intensity of DVM behaviours could impact the carbon cycle of the earth.
• There is little knowledge about how this phenomenon is taking place in different parts of the world and in what way it is responding to climate change, so this remains to be explored in future research.