Scientists at the University of Wales, Bangor have found a specimen of the marine bivalve Arctica islandica that lived for over 500 years, and several more that lived in excess of 300 years. This amazing longevity makes these bivalves the longest-lived animals known on Earth.

Arctica islandica . Photograph courtesy of Prof James Scourse, University of Wales, Bangor.

The age of these animals was determined by counting growth lines in the shell. Although growth lines can be seen on the outside of the shells, most of the bands on long-lived animals are much too close together to count in this way. Instead, sections were taken through the shell and studied under a microscope to count the growth increments – like counting tree rings.

The extreme longevity of Arctica islandica has made this bivalve the focus of research aimed at finding out just how they manage to resist the ageing process.

Since all shells living in the same part of the sea bed grow in the same way, we can take any dead shell we happen to find and see if its growth patterns are similar to the patterns in shells from living animals. If they are, we can work out the dates when the dead shell was alive (this technique is called ‘crossdating’) and use the growth patterns in the dead shells to study marine climate before any of the living clams were alive. As Arctica islandica is so long lived, it is possible to compare a long series of growth patterns and work out precisedly the dates of shells that were alive up to 1350 years ago.

Section through a shell of Arctica islandica. Image courtesy of Prof James Scourse, University of Wales, Bangor.

The shells of Arctica islandica are providing information about past climates in the North Atlantic. The dark growth lines in the shell are caused by an annual period of slow growth, probably in late summer or autumn. It is possible to record the amount of growth during the year by measuring the distance between these growth lines. In a good year, a lot of shell is laid down, in a bad year very little. The isotopes of oxygen and carbon in the shell can give information about the sea temperature and salinity. Concentration of other elements in the shell (calcium, zinc, magnesium and others) can be measured and compared to investigate marine pollution and ocean acidification.

For more information about research into Arctica islandica, visit  http://www.sos.bangor.ac.uk/sclero