What a Seawater Sample Can Tell Scientists About Ocean Health

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Biodiversity

UNESCO is growing its environmental DNA, or eDNA, expedition programme. This ambitious and cost-effective project can give usable ocean data in a couple of weeks using a small number of seawater samples collected by citizen scientists.

DAR ES SALAAM, Tanzania, Oct 22 2026 (IPS) - A fishing boat’s catch tells only part of the story of the waters around World Heritage sites. Species that escape the net, shelter inside reefs or pass through deeper channels can go unrecorded, leaving communities and conservation officials with an incomplete picture of the marine life supporting coastal livelihoods.

A sample of seawater could help fill those gaps. Fish and other organisms leave genetic material in their surroundings, allowing scientists to identify species that might otherwise go unnoticed.

More than that, monitoring marine species once required years of fieldwork and millions of dollars. Now just a few samples of seawater collected by citizen scientists can provide actionable ocean data in a matter of weeks.

UNESCO is expanding this approach through its environmental DNA, or eDNA, Expeditions programme, which was launched today at the UN Biodiversity Conference, COP17, currently underway in Yerevan, Armenia.

The technique can monitor marine biodiversity without removing organisms from their environment. According to UNESCO, a single litre of water may contain genetic material from hundreds of species, offering a way to assess biodiversity that conventional surveys might miss.

Through the global rollout of eDNA Expeditions, UNESCO aims to track the distribution of ocean species and investigate how climate change may affect them.

Sampling the Most Remote World Heritage Sites

Building on the pilot phase, the programme will expand to 30 marine protected areas worldwide, including five of the most remote World Heritage Sites on the planet.

Saara Suominen, Scientific Officer for Genetic Data at UNESCO’s Intergovernmental Oceanographic Commission, said the initiative was developing methods that could eventually be used more widely.

Repeated sampling can help establish which species occur around particular reefs or seagrass beds and reveal changes that warrant closer investigation. Combined with fishers’ observations, catch records and underwater surveys, the findings could help managers target monitoring and assess whether conservation measures are protecting the intended species.

The process uses relatively simple equipment: a syringe to collect seawater and a small filter to capture genetic material. The samples are analysed in a laboratory, where genetic sequences are compared with reference information to identify the organisms.

“So, to give an idea, from a single litre of filtered water, we can identify, on average, 100 species, and there’s no limitation on the type of species we can detect,” Suominen told the briefing.

During the pilot phase, sampling at 21 marine World Heritage sites identified more than 4,000 species from about 500 samples, she said. Participants included children as young as six.

The expanded programme aims to collect around 3,000 samples by 2028. It combines repeated sampling at the original marine sites over three years with expeditions to five other remote World Heritage sites, building records that can reveal changes over time rather than providing only isolated snapshots.

For protected areas, these records could raise an important question: are the species they were established to conserve still found within their boundaries?

Tales Carvalho Resende, of UNESCO’s World Heritage Marine Programme, described observations from Greenland, where fishers have reported encountering marine animals in areas where they were previously uncommon.

“And, for instance, this kind of information allows us to see and know whether conservation and protection are happening in the right place,” he said.

Among others, the programme is expected to:

• Uncover global biodiversity trends through repeated samplings, revealing how species are progressively forced away from their habitats.
• Generate first snapshots of wildlife in the planet’s most remote areas.
• Provide early, actionable detection systems against invasive species.
• Determine if the existing 18,000 marine protected areas still harbour the species they were created for, and where new ones may be needed.

Expansion Beyond Heritage Sites

Asked by IPS how eDNA could help protect Zanzibar’s fish populations, coral reefs, seagrass ecosystems and coastal livelihoods, UNESCO researchers pointed to its potential to track changes in species distribution. They acknowledged, however, that they had no specific results from Zanzibar to present.

For Tanzania, better information about marine ecosystems has implications beyond conservation. According to the World Bank, fishing and aquaculture directly employ around 430,000 people, while more than 4.5 million depend on related activities, including processing, marketing and sales.

Seaweed farming also supports a substantial coastal workforce, predominantly women. Around Zanzibar, eDNA could help researchers investigate changes in species associated with reefs and seagrass habitats, but detecting genetic material alone would not establish reef condition, explain declining catches or determine sustainable harvest levels.

Ocean currents, tides, temperature and other environmental conditions affect how genetic material disperses, according to research described by the US National Oceanic and Atmospheric Administration. Scientists must therefore interpret eDNA results alongside other environmental information.

“So conventional monitoring approaches are extremely good, of course, and eDNA is not there to replace them,” Suominen said.

A list of species cannot, on its own, restore a damaged reef or replace lost earnings. The technology’s practical value will depend on whether its findings help communities investigate changes they observe at sea and influence decisions about the waters on which their livelihoods depend.

IPS UN Bureau Report