Sea butterflies are small, free-swimming sea snails that belong to the group of pteropods.
They have thin, delicate shells that are sensitive to ocean acidification, a process that lowers the pH and the availability of carbonate ions in seawater due to the absorption of carbon dioxide (CO2) from the atmosphere.
Sea butterflies are important components of the marine ecosystem, as they are food for many fish, birds, and whales, and they also play a role in the carbon cycle by transporting organic matter from the surface to the deep ocean.
However, sea butterflies are facing multiple threats from climate change, such as warming, acidification, deoxygenation, and changes in food availability.
These factors can affect their survival, growth, reproduction, and distribution, and have consequences for the whole Southern Ocean ecosystem.
In this article, we will focus on how climate change affects the life cycle of two dominant species of sea butterflies in the northeast Scotia Sea: Limacina rangii and Limacina retroversa.
Contrasting life cycles and vulnerabilities
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Researchers from the British Antarctic Survey have examined the life cycles, abundance and seasonal variability of these two species using sediment trap samples collected at 400 meters depth over a year, as per Phys.org.
They found that L. rangii and L. retroversa have different life cycles that make them more or less vulnerable to changing oceans.
L. rangii is a polar species that can be found as both adults and juveniles during the winter months. This means that they have two cohorts (groups of individuals born at the same time) coexisting over winter, which may give them a survival advantage if one cohort is more affected by environmental stress than the other.
L. rangii also has a faster growth rate and a shorter lifespan (about one year) than L. retroversa, as per Ocean Fauna.
L. retroversa is a subpolar species that appears to occur only as adults during the winter. This means that they have only one cohort over winter, which makes them more vulnerable to environmental stress as there is no backup population.
L. retroversa also has a slower growth rate and a longer lifespan (about two years) than L. rangii.
The researchers suggest that winter is a critical period for sea butterflies, as they are exposed to lower temperatures, higher CO2 levels, and lower food availability.
These conditions can affect their shell formation, metabolism, reproduction and survival.
The fact that L. rangii and L. retroversa have different life cycles implies that they may respond differently to climate change and have different impacts on the marine food web and carbon cycle.
Sea butterflies are key organisms in the Southern Ocean ecosystem, as they link primary producers (such as phytoplankton) with higher trophic levels (such as fish, birds, and whales).
They also contribute to the biological pump, a process that transfers carbon from the surface to the deep ocean through the sinking of organic matter, any changes in their abundance, distribution, or quality as food can have cascading effects on the whole ecosystem.
The researchers warn that climate change may cause a decline in Antarctic Ocean pteropod populations, which could affect their predators and prey, as well as their role in carbon sequestration.
They call for more studies on the life cycle of these keystone organisms to improve predictions of ocean acidification impacts on the Antarctic ecosystem.
