STUDYING THE health of ecosystems on dry land—a habitat that biologists share with the organisms they are looking at—is challenging enough. Studying marine ecosystems is far harder. Even discovering which species are there, let alone in what quantities, can be tricky. But an insight by Stefano Mariani of the University of Salford, in Britain, may make things easier. As he describes in Current Biology, he thinks that sponges growing on the sea floor may offer a short cut to such information.
One way of sampling marine life is to sample the seawater itself, looking for DNA shed by creatures as they go about their lives. This is known to work in principle, but in practice it means running huge amounts of water through filters, to extract things like shed skin and blood cells for analysis. That is awkward, meaning sampling tends to be patchy. And attempts to automate the process using drones are proving pricey.
Sponges, however, are natural filters. Indeed, they make their livings that way, sucking in thousands of litres of water a day and running it through intricate systems of channels that trap particles of organic matter, which they then digest. Taking samples from sponges, and checking the DNA therein, might thus, Dr Mariani reasoned, be an effective way to assess the diversity of species in the region surrounding a particular sponge.