Abstract
The shelled pteropod (sea butterfly) Limacina helicina is currently recognised as a species complex comprising two sub-species and at least five “forma”. However, at the species level it is considered to be bipolar, occurring in both the Arctic and Antarctic oceans. Due to its aragonite shell and polar distribution L. helicina is particularly vulnerable to ocean acidification. As a key indicator of the acidification process, and a major component of polar ecosystems, L. helicina has become a focus for acidification research. New observations that taxonomic groups may respond quite differently to acidification prompted us to reassess the taxonomic status of this important species. We found a 33.56% (±0.09) difference in cytochrome c oxidase subunit I (COI) gene sequences between L. helicina collected from the Arctic and Antarctic oceans. This degree of separation is sufficient for ordinal level taxonomic separation in other organisms and provides strong evidence for the Arctic and Antarctic populations of L. helicina differing at least at the species level. Recent research has highlighted substantial physiological differences between the poles for another supposedly bipolar pteropod species, Clione limacina. Given the large genetic divergence between Arctic and Antarctic L. helicina populations shown here, similarly large physiological differences may exist between the poles for the L. helicina species group. Therefore, in addition to indicating that L. helicina is in fact not bipolar, our study demonstrates the need for acidification research to take into account the possibility that the L. helicina species group may not respond in the same way to ocean acidification in Arctic and Antarctic ecosystems.
Highlights
Over the past 200 years the world’s oceans have absorbed approximately one third of the total carbon dioxide (CO2) released into the atmosphere by human activities [1]
Because of its aragonite shell and polar distribution, L. helicina may be one of the first organisms affected by ocean acidification, and it is a key indicator species of this process [3]
This degree of separation is sufficient for ordinal level taxonomic separation in other organisms [13] and convincingly demonstrates that L. helicina is not bipolar, but that the Arctic and Antarctic populations differ at least at the species level
Summary
Over the past 200 years the world’s oceans have absorbed approximately one third of the total carbon dioxide (CO2) released into the atmosphere by human activities [1]. Because of its aragonite shell and polar distribution, L. helicina may be one of the first organisms affected by ocean acidification, and it is a key indicator species of this process [3]. Antarctica to quantify genetic distance within and between these regions with the specific aim to assess the bipolar status of the L. helicina species group.
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