Low-cost DNA tests can reveal the range of wildlife living in our seas, according to a new study carried out off Cornwall.
Environmental DNA (eDNA) tests can identify genetic material left by organisms in the environment, such as cells and excrement.
Surveys of ocean wildlife can be difficult and expensive, and standard eDNA tests are also costly.
The University of Exeter study compared a standard method against a cheap, simple eDNA system called Metaprobe 2.0 - a plastic sphere with rolls of gauze inside, which is dropped in the sea and collects DNA to be tested.
While the expensive method performed slightly better, Metaprobes produced more consistent results and successfully identified the same species in Cornwall's waters: European anchovies, Atlantic mackerel and Blue sharks.
The other species targeted - the thresher shark - was not found by either method.
The study only looked for these four species, but a single eDNA sample can reveal a vast range of species - so Metaprobes could, for example, monitor UK waters for the arrival of the elusive great white shark.
"With marine biodiversity under increasing pressure from climate change, overfishing and habitat degradation, governments and conservation organisations are keen to use eDNA at scale," said Dr Molly Kressler, from the Centre for Ecology and Conservation at Exeter's Penryn Campus in Cornwall.
"Our study suggests that Metaprobe 2.0, which is cheap and easy to deploy, performs well against a standard eDNA method that costs significantly more.
"Metaprobes might widen the accessibility of eDNA monitoring in the future - allowing sampling in remote places, or when cost is a significant factor."
The study relied on help from Cornish tour operators and sailors.
Dr Kressler trained staff from Marine Discovery Penzance to deploy and recover Metaprobes, and joined Padstow Sea Safaris vessels to collect seawater samples and give science talks.
"I also enlisted a citizen-science sailor fleet who would go out and collect samples for me, as they travelled around the South West," Dr Kressler added.
"I recruited volunteers via local yacht clubs and social media. In one case, someone in New Zealand saw my post and they knew a sailor in Cornwall, who then took part - showing how online appeals can go around the world and back."
White sharks?
Commenting on great white sharks - which have never been positively identified in UK waters - Dr Kressler said: "With warming waters and seal populations increasing, it's likely that we will see a white shark here within a few decades.
"At present, any white shark coming here would have to be very large and very bold to make the journey from their current hot spots like the northwest Atlantic.
"Given the nature and behaviour of white sharks, eDNA would be the primary way of knowing they were here."
The study was funded by an Exeter Marine student project grant.
The paper, published in the journal Environmental DNA, is entitled: "Passive gauze-based eDNA sampler proves efficient and cost-effective in the marine environment." The instructions to print a Metaprobe 2.0 are open to the public, and can be found here.
