Sea Butterfly Life Cycle Threatened By Climate Change in the Southern Ocean
Although tiny, sea butterflies play a major role in the marine ecosystem. Sea butterflies are shelled pteropods (a group of free-swimming sea snails) which live close to the ocean surface. They use their muscular feet as flappers to swim across the surface. A new study suggests oceans and its populations are becoming severely affected by climate change (British Antarctic Survey, 2023). Oceans absorb about 25% of all the carbon dioxide emissions leading to the oceanic pH levels to fall known as ocean acidification. Ocean acidification also leads to lower carbon ion concentrations causing sea butterflies’ thin outer casing to dissolve. This thin outer casing is like a home for these creatures and so it leaves them exposed to harsh conditions when the layer dissolves (Gardner et al., 2023). Recent studies looked at life cycles, abundance and seasonal variability of sea butterflies in a region undergoing the fastest climate change in the Southern Ocean known as the north-east Scotia Sea.
Figure 1. Sea Butterfly, also known as shelled pteropods. (Peck, 2023).
Population Stability Essential for Species Survival
A team of researchers investigated the life cycles of two shelled pteropod species. The scientist began by collecting sea butterflies in an sediment trap (sampling device anchored at 400 meters in depth. The scientists observed different life cycles for the two dominant species collected: Limacina rangii and Limacina retroversa, which lead to different vulnerabilities to the ocean conditions (Down To Earth, n.d.).
The life cycles of L. rangii is that both juvenile and adult were found during the winter months, while only adults were seen for L. retroversa in the winter months. The ocean pH levels lowers even more in winter as cooler water is capable of observing more carbon dioxide, making the winter months more harsher for these creatures (British Antarctic Survey, 2023).
Figure 2. Summer population of L. rangii species from the Scotia Sea. Larger juveniles living alongside smaller, larval stages. (Peck, 2023).
L. retroversa is at more risk than L. rangii as L.rangii have a more survival advantage. L.rangii can exist as both adults and juvenile over winter months. If one cohort is at risk, the overall population stability is not at risk. However, for L.retroversa, if one cohort is at risk, the overall population is at risk (Gardner et al., 2023).
Prolonged Exposure is a Survival Challenge
Although there is a contrast in the way the species are affected, prolonged exposure to these harsh ocean ph conditions will harm both species.
As the ocean acidification intensity and length increases, it will interfere with the life stages of the sea butterflies. For instance, when the ocean acidification extends into spring, overlapping with the spawning events, the larvae (most vulnerable life stage) will be at most risk. This could lead to succeeding life stages to be affected, overall diminishing future populations (Gardner et al., 2023).
More studies are to be done including the investigations of habitats in Scotia Sea to further understand how sea butterflies are affected there (Down To Earth, n.d.).
Figure 3. The location of sediment trap mooring (Gardner, 2023).
Figure 4. An illustrating of the seasonal and monthly presence of veligar, juvenile and adult L. rangii and L. retroversa, as well as their spawning period (Gardner, 2023).
Gardner, J., Peck, V. L., Bakker, D. C. E., Tarling, G. A., & Manno, C. (2023, March 28).
Contrasting life cycles of Southern Ocean pteropods alter their vulnerability to climate
change. Frontiers. https://www.frontiersin.org/articles/10.3389/fmars.2023.1118570/full
Sea butterflies are threatened by climate change. here’s how this can impact Antarctic Marine
Ecosystems. Down To Earth. (n.d.).
Sea butterfly life cycle threatened by climate change. British Antarctic Survey. (2023, May 15).