IAS Gyan

Daily News Analysis


17th May, 2023 Environment

Disclaimer: Copyright infringement not intended.


  • It has been observed that Ocean acidification is not only more dangerous for shelled, smaller sea butterflies but can impact entire ocean food web.  


  • The sea butterflies, a suborder of sea snails, are tiny creatures that play a big role in the marine ecosystem.
  • But the smallest species in this group found in the Southern Ocean are extremely vulnerable to climate change and their population is shrinking in a warming world.
  • The shelled pteropods (group of free-swimming sea snails) live at or very close to the ocean surface.
  • Like snails, they have muscular feet that they use as flappers to swim around in water, instead of glide on solid surface.
  • As the sea absorbs an increasing quantity of carbon dioxide (CO2) that turns the water more acidic, the thin outer casing, or the ‘homes’ of these small sea butterflies, dissolve.
  • This leaves them exposed, making it difficult for these delicate species to survive.


  • Pteropods are among the marine creatures most vulnerable to ocean acidification.
  • Ocean acidification lowers the availability of the mineral aragonite that pteropods use to form their shell, hindering this snail from building its protective armor.
  • The decline of these key organisms would result in dramatic impacts for the entire marine food web.

About Sea butterflies

  • Scientific name: Thecosomata
  • They are a taxonomic suborder of small pelagic swimming sea snails.
  • They have some form of calcified shell, although it is often very light and / or transparent.
  • The sea butterflies include some of the world's most abundant gastropod species, and because of their large numbers are an essential part of the food chain, and a significant contributor to the oceanic carbon cycle.
  • The sea butterflies are included in the Pteropoda order, and are also included in the informal group Opisthobranchia.


  • Sea butterflies float and swim freely in the water, and are carried along with the currents.
  • This has led to a number of adaptations in their bodies.

Importance in the food chain

  • These creatures, which range from lentil- to orange-sized, are eaten by various marine species, including a wide variety of fish that are, in turn, consumed by penguins and polar bears.
  • The sea butterflies form the sole food source of their relatives, the Gymnosomata.
  • They are also consumed by sea birds, whales, and commercially important fish.
  • However, if sea butterflies are consumed in large quantities fish can get "black gut", which makes them unsellable.


Q) Which of the following statements with reference to Sea butterflies is/are incorrect?

1. Because of their large numbers are an essential part of the food chain, and a significant contributor to the oceanic carbon cycle..

2. Like sea snails, they use flappers to glide on solid surface.

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2

Correct Answer: 2