Bioinformatic approach to explain how Mg from seawater may be incorporated into coral skeletons

Corals have been used as geochemical proxies since the 1970s, playing a prominent role in paleoceanography. However, it has not been well elucidated how aqueous ions sourced from seawater are transported and precipitated in coral skeletons. There are limited foundational methods to differentiate and quantify biogenic and abiogenic effects during skeletal formation. Especially, Mg in coral skeletons show individual variations suggesting large biogenic effects. Here, we evaluated biological complexity by investigating how coral genes evolved over geologic time scales. We focused on Mg transporter and analysed five species from genus Acropora and three species from genus Porites. Mg transporter of Acropora digitifera, Acropora hyacinthus, Acropora millepora and Porites australiensis showed higher similarity to Mg transporter of vertebrates and were reported to appear on Earth during the Pleistocene. On the other hand, Acropora palmata, Acropora tenuis and Porites astreoides showed lower or no similarity to vertebrates, and they were reported to appear on Earth before the Pleistocene. We suggest such evolutional records can be evidence to demonstrate biological complexity of Mg transport from seawater. This might explain that Mg transport is subject to evolution and why Mg incorporated in coral skeletons tends to show strong biogenic effects compared with other elements.