Wednesday, 16 September 2015

Boring Bivalves

Bivalves and their borings in a coral skeleton
Bivalves are notoriously destructive organisms in ecological circles. While some species lead a relatively unobtrusive existence, others bore into the dead skeletons of corals in order to set up home. Yet they can end up destroying the foundations of entire reef systems.

Rock-boring bivalves are not uncommon and certain species have been known to opportunistically utilise driftwood. Organic detritus, such as the shells and bones of other marine organisms, also provide viable homesteads.  

A recent example of this was discovered by researchers from the University of Bristol led by Dr Imran Rahman. The team performed a CT scan of a specimen of the Miocene sea urchin Clypeaster and found that the shell was packed full of bivalves.

'The study confirms that the skeletons of dead animals, such as sea urchins, have been important island habitats for boring and encrusting organisms for tens of millions of years,' said Dr Zain Bela├║stegui from the University of Barcelona. 'This work also highlights how studying the traces left behind by animals, coupled with the processes that led to the formation of fossils in deep time, can provide new insights into the biology of ancient organisms and past environments.'

The sea urchin and its population of bivalves,
reconstructed from the CT scan data
Without sufficient protection, the bivalves would have been easy prey for larger creatures. The occasional sea urchin shell would have provided a safe haven even in the middle of shallow sandy sea beds with few other places to hide.

'We had no idea there would be so many bivalves inside the sea urchin,' said Dr Rahman. 'This goes to show the importance of CT scanning for understanding long-dead organisms and their ecosystems.' 

The CT scans showed that the bivalve species could be placed within the genus Rocellaria, whose modern counterparts still burrow into shells and rocks. Large scale ecological interactions - predators and prey, plants and herbivores - are easy to observe. It is only in recent decades that we have been able to probe more subtle interactions. This is partially due to a greater understanding of just what the fossil record can yield and advances in technology, allowing us to visualise previously invisible detail.