Increasing CO2 in the atmosphere is causing ocean acidification (OA) at unprecedent rates and affecting the way marine organisms produce their calcified shells and skeletons. This impact is due to a decrease of calcium carbonate in seawater, which is their shells and skeletons’ main ingredient.
Shelled holoplanktonic snails, known as sea butterflies and sea elephants, are among the most vulnerable marine animals to OA because they live in the open ocean and build thin shells of calcium carbonate. Sea butterflies have received considerable attention and are reported to decrease calcification and experience shell dissolution under high CO2 conditions. Sea elephants have received much less attention over the years, but are expected to be equally vulnerable. Both groups of planktonic snails are important in marine ecosystems. They are intermediaries in the ocean food webs. Sea butterflies are mucus web feeders, feeding primarily on algae throughout their life. Sea elephants feed on algae in their early life stages and become predators when metamorphosing into adults, feeding on sea butterflies and other zooplankton. Sea butterflies, in particular, are also highly abundant in the oceans being important contributors to the overall ocean’s carbon biomass.
The aim of the EPIC action “Evolution of planktonic gastropod calcification” was to study how sea butterflies and sea elephants build their calcified shells and to assess how this process will cope with the ongoing ocean changes, namely, ocean acidification.
Similar to other molluscs, holoplanktonic gastropods build shells through a process called biomineralization, that is genetically controlled, but the genes involved this process were unknown.
Using molecular techniques, shell proteomics combined with transcriptomics, Dr. Ramos-Silva was able to identify for the first time the genetic toolkit involved in biomineralization in three species of sea butterflies, representing three major lineages with distinct shell wall architectures. The discovery of these genes provides new understanding on how the thin shells of sea butterflies are made and sheds light on the evolution of their biomineralization over the past 140 million years. These biomineralization genes are fast-evolving and suggest high adaptive potential of sea butterflies to respond to environmental changes.
Dr. Ramos-Silva has also studied the response of sea butterflies and sea elephants to conditions mimicking the past, present and future CO2 concentrations in the oceans. By measuring the gene expression at different life stages, she found that juveniles are more vulnerable to OA than adults and may constitute the major bottleneck in the adaptability to ocean changes.
In sum, EPIC enabled to shed light on the evolution of calcification in holoplanktonic gastropods and to make more realistic predictions of the impacts of ocean acidification on this process.
