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The stunning 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, according to a new study.
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.
While these beautiful creatures dying out is bad news in itself, their reduced population also impacts larger pteropods and other oceanic creatures that feed on them. The entire underwater food chain of the seas surrounding Antarctica may suffer as a ripple effect.
But not all the shelled sea snails are impacted uniformly, the study by the British Antarctic Survey found. This is because their life cycles are quite different, according to the report published in the journal Frontiers in Marine Science.
The scientists studied the shells of the two dominant pteropod species, Limacina rangii and Limacina retroversa. They found that the life cycles of the species are such that both juvenile and adult L. rangii were found during the winter months, while only adults of L. retroversa were observed in the cold season.
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.
But L. retroversa is at higher risk. The authors explain why:
The fact that L. rangii adults and juveniles coexist over winter may give them a survival advantage. If one cohort is vulnerable, the overall population stability is not at risk. With L. retroversa, however, if one cohort is removed, the whole population may be vulnerable.
But neither species is entirely safe from the phenomenon if exposed for a longer time, they added.
As emissions rise, acidification of oceans intensify and extends to spring when the species spawn and they’re in the larval stage, the report noted. This can diminish the population that would otherwise develop into healthy adults, the scientists warned.
The team will now study the habitats in Scotia Sea to understand how sea butterflies are affected there. The findings can also inform studies on the impacts of ocean acidification on the marine ecosystem in general, the authors added.