Tuesday November 4, 2025
Earth —
Scientists used traces of genetic material in seawater to reveal hidden patterns of biodiversity, finding marine fish in places where records said they were missing.
The most significant finding is that known geographic ranges were underestimated for 93 percent of species.
The work pulled together nearly 1,000 water samples from polar seas to remote tropical islands. The research shows how a simple DNA test can correct blind spots in our maps of ocean life.
Marine DNA reveals biodiversity
Environmental DNA, or eDNA, refers to genetic traces that organisms shed into water, soil, or air.
By collecting eDNA, researchers can detect species without catching or photographing them.
The research was led by Loïc Sanchez, a researcher at the University of Montpellier (UM) and CNRS. His research focuses on marine biodiversity, conservation, and species distributions.
“Our eDNA surveys showed that known geographic ranges for 93% of species and ecological niches for 7% were underestimated,” noted Sanchez.
“A machine learning model predicted that just 10 eDNA samples could reveal about 24 new fish species on average, and up to 98 in unsampled tropical areas.”
Why surveys missed fish
Conventional databases reflect where scientists and citizen observers have worked most often, which is rarely the high Arctic, remote islands, or far offshore. That pattern leaves sparse records in many places where fish actually live.
The team compared eDNA detections with global repositories, including the Global Biodiversity Information Facility (GBIF), a worldwide portal for species occurrence records.
In addition, the Ocean Biodiversity Information System (OBIS) is a database for ocean life observations.
The researchers found that eDNA filled gaps both where no one had looked and where past surveys had missed small or elusive species.
What the new detections mean
One eDNA sample placed the shortfin mako shark near the Arctic circle, far north of where most records cluster. The species is listed as Endangered on the IUCN Red List.
The study also turned up more records for cryptobenthic, small bottom dwelling reef fishes that hide in crevices and are hard to see.
These fishes are often undercounted by divers and cameras, as highlighted in a comprehensive review.
The authors tested whether eDNA was simply adding more data or revealing real ecological extensions.
A null model showed that about half of the ecological niche expansions rose above what random sampling would produce.
Comparing old and new methods
Environmental DNA and eyes in the water do not always find the same species, and that difference matters.
There is growing evidence that combining the two methods can reveal a fuller picture, especially for tropical fishes at range edges.
The new work suggests a practical rule of thumb, and it is budget friendly. Ten local water samples often add two dozen fish species that monitoring programs would otherwise miss.
DNA extends marine species’ ranges
The global analysis found that eDNA extended known ranges for most species by adding verified occurrences in places without prior records.
The team also widened the documented temperature and oxygen limits for a smaller set of fishes, which reshapes their measured ecological niches.
Those changes feed into models that forecast where species can live as oceans warm. Small shifts in measured thermal tolerance can change risk assessments for fisheries and conservation plans.
Limits in marine biodiversity mapping
Environmental DNA reads what water carries at the sampling time, and signals can be faint or transient.
The approach relies on genetic reference libraries that are still incomplete in some regions, which can limit identification to genus or family.
The researchers addressed false positives by keeping only sequences with perfect species identity and by discarding detections in genera with thin regional coverage.
The team also separated gains that fix geographic undersampling from those that reflect method bias in already surveyed places.
Mapping marine biodiversity matters
Conservation tools rely on where species are recorded, not where they truly are. If records are clustered near busy coasts, threat categories and protected areas can miss important habitats elsewhere.
A low cost eDNA sweep can quickly test whether overlooked species are present in a marine reserve, a shipping corridor, or a polar shelf.
This method is especially useful where logistics limit dive time, boat time, or camera deployments.
The future of marine DNA surveys
Two steps would raise the ceiling on what eDNA can deliver. First, expand genetic reference libraries in the tropics and poles so more detections resolve to species.
Second, design joint campaigns that run eDNA alongside nets, cameras, and diver counts in the same places and seasons.
That gives managers both the sensitivity of molecules and the context of behavior and size classes.
Reading the results carefully
A range extension of a few miles might simply patch a missing piece on an old map. But when that extension stretches hundreds of miles, it calls for deeper scrutiny – of the species, the ocean currents, and the sampling history behind it.
By measuring distance along the sea and testing their findings with straightforward statistics, the researchers grounded discovery in rigor.
It’s this balance of curiosity and discipline that turns raw data into truly reliable maps of life in the ocean.
The study is published in the journal PLOS Biology.