Sea Butterflies | 18 May 2023

Why in News?

The population of the sea butterflies in the Southern Ocean is shrinking due to climate change, making them extremely vulnerable.

What are Sea Butterflies?

• About:
  • Sea butterflies, scientific name Thecosomata, are a suborder of sea snails known as shelled pteropods.
  • They have muscular feet that allow them to swim in water instead of gliding on solid surfaces.
  • Sea butterflies are holoplanktonic (organisms that pass their whole life floating, drifting, or swimming weakly in the water) and spend their entire life cycle in the water column.
  • They are found in all oceans but are more diverse and abundant in colder waters.
  • Sea butterflies have bilateral symmetry and a coiled or uncoiled shell of various shapes and sizes.
    • Their shell is mostly transparent and very fragile and can be easily dissolved by ocean acidification.
  • They have a pair of wing-like lobes or parapodia for propulsion and a head with eyes, tentacles, and a mouth with a long proboscis to capture prey.
  • They have a reduced or absent gill and rely on their body surface for gas exchange.

• Importance:
  • They are a major food source for many fish, seabirds, whales, and other marine animals.
  • They also play a key role in transporting carbon from the surface to the deep ocean through their shells and fecal pellets.

How does Climate Change Impact the Population of Sea Butterflies?

• Ocean Acidification:
  • Increased carbon dioxide absorption by the ocean leads to higher acidity.
  • Reduced availability of carbonate ions necessary for shell formation and maintenance.
  • The ocean is the most acidic in winter because cooler water absorbs more CO₂. This means, the winter months are the most dangerous for the shelled sea butterflies.
    • Sea butterflies' shells can dissolve, weaken, or deform.
    • Increased vulnerability to predators, infections, and stress.
    • Affects metabolism, growth, reproduction, and survival.
• Ocean Warming:
  • Rising ocean temperatures due to climate change.
  • Changes in distribution and abundance of sea butterflies.
  • Seek optimal thermal conditions for development and survival.
  • Alters food availability and quality.
  • Impacts ocean currents and mixing affecting sea butterfly transport.
• Ocean Deoxygenation:
  • Warmer and stratified ocean leads to decreased oxygen levels.
  • Affects sea butterflies' respiration and energy balance.
  • Alters vertical migration patterns.
  • Exacerbates effects of ocean acidification by increasing dissolved carbon dioxide concentrations.

How can this Reduced Population Impact Antarctic Marine Ecosystems?

• Reducing the Food Availability for Higher Trophic Levels:
  • Sea butterflies serve as a major food source for fish, seabirds, whales, and other marine animals.
    • Population decline of sea butterflies can lead to starvation, malnutrition, or reduced reproduction in their predators and prey.
• Disrupting the Balance of the Marine Food Web:
  • Sea butterflies play a crucial role in linking primary producers (phytoplankton) with secondary consumers (zooplankton) and higher trophic levels.
  • Decline in sea butterfly population can alter the structure and function of the marine food web.
  • Biodiversity and productivity of the Antarctic marine ecosystem may be affected.
• Decreasing the Carbon Sequestration Capacity of the Ocean:
  • Sea butterflies contribute to the "biological pump," transporting carbon from the surface to the deep ocean through their shells and fecal pellets.
  • Population decline reduces the amount of carbon sequestered (process of capturing and storing atmospheric carbon dioxide) in the ocean.
  • This results in increased carbon dioxide in the atmosphere and further ocean acidification.

Source: DTE