We've recently been hearing about how scientists can tell which creatures are present in an aquatic environment, by detecting their cast-off DNA in the water. A new study suggests that doing so may soon become easier, thanks to natural DNA-trapping sponges.

Presently, researchers must filter large quantities of water in order to find the diluted "environmental DNA" (or eDNA) that animals expel as they slough off skin or defecate. According to Stefano Mariani – a marine ecologist at Britain's University of Salford – doing so is a lot of work, plus the results may be skewed by contamination from off-site DNA present in the filtration equipment. Additionally, DNA in stored water samples may degrade before those samples are processed.

With that in mind, he instead looked to the sponges that are already growing in both marine and freshwater environments. These organisms reportedly filter up to 10,000 liters (2,642 US gal) of water daily, capturing and concentrating eDNA in their tissue as they do so.

When Mariani and his team analyzed sponge samples gathered in the Antarctic and Mediterranean, they found the DNA of 31 taxa. These were mostly species of fish, although one sponge sample from Antarctica contained the DNA of Weddell seals and chinstrap penguins – this made sense, as the sample had been gathered near a penguin breeding colony.

Additionally, in order to avoid interference from the host material, the scientists utilized a DNA primer (a short sequence of nucleic acid) that amplified the DNA of vertebrates, but had no effect on the DNA of the sponge itself.

"Sponges are ideal sampling units because you find them everywhere and in every aquatic habitat," says Mariani. "Also, they're not very selective filter-feeders, they don't run away, and they don't get hurt by sampling – you can just grab a piece, and they will regenerate nicely."

That said, the gathering of sponge samples isn't always practical, such as when they're located in deep water. To that end, the researchers are now looking into gathering eDNA from other water-filtering organisms such as jellyfish or salps.

A paper on the study was recently published in the journal Current Biology.