Growth of a living fossil: the lampshell Magellania venosa in the Chilean Patagonian fjord region
Already in the Cambrian 600 million years ago (bivalves didn't really get started for another 50 to 100 million years), the floors of the coastal seas were populated almost everywhere by lampshells (brachiopods) with over 30,000 known species and shell sizes of up to 30 cm. The end-Perm mass extinction saw the demise of the lampshells, which are now replaced almost everywhere by bivalves. Although, from a first sight bivalves and lampshells look pretty similar, evolutionary origin and shell arrangement are very different: left-right in bivalves and up-down in lampshells.
One of the rare environments where aggregations of living brachiopods are found is the northern Chilean fjord region, where the largest recent brachiopod Magellania venosa occurs in dense populations in spite of space-competing bivalves. The reasons why lampshells appear to thrive so well are so far unknown. To address this question, we assessed the population structure and growth performance of Magellania venosa in the fjords Pitipalena and Comau.
For this purpose, we tagged lampshell specimens in situ by SCUBA diving to be able to assess the shell size increments over the next twelve months (see figures). Together with knowledge on their abundance (i.g. number of individuals per area) and the size frequency distribution the data will allow us to calculate the production of lampshells and assess their ecological role in the cold-water habitats of the Chilean Patagonian fjord region.