# Reading genomes from seawater

How shotgun reads become contigs and bins without reference genomes, why the value of a marine discovery now lives in a sequence rather than a sample, and why benefit-sharing for digital sequence information is contested rather than settled.

Metagenomics assembles genomes from fragments of DNA shed into the ocean, so prospecting no longer needs the organism — and because the valuable output is copyable data, the high seas needed a treaty to decide who benefits from a read.

Source: https://en.bioecon.ru/docs/blue-bioeconomy/marine-biotech/marine-genomic-prospecting-bbnj-treaty/
Updated: 2026-09-07



Prospecting the ocean once meant collecting organisms; today it largely means sequencing water. DNA shed by everything that swims, grazes and decomposes — environmental DNA — floats in seawater and sediment, and shotgun sequencing reads it without growing, seeing or naming most of the organisms it came from. The technique works, and its success is precisely what created the governance problem.

## Assembly from fragments

A metagenomic sample returns millions of short reads, and the computational task is to rebuild genomes from this shredded library. Reads that overlap are joined into contigs; contigs are grouped into bins using composition signatures and coverage patterns, ideally yielding draft genomes of organisms nobody has cultured. The difficulty scales with community complexity: strain variation shreds assemblies at repetitive regions, abundant organisms dominate reads while rare ones leave fragments too thin to assemble, and the deep sea is the hardest case because most of its lineages have no reference genome — annotation proceeds by distant homology, so a gene is labelled by its nearest cultured cousin, which may be very distant and wrong. The result is catalogs of hundreds of millions of gene sequences whose owners are unknown and whose functions are partly inferred. That is not a failure of the method but its definition: the power of metagenomics is reading without collecting, and the cost is that reading and understanding are not the same step.

## Why the value decoupled from the sample

The economics of prospecting changed when the valuable output became a sequence. A physical sample is scarce, perishable and enforceable; a sequence is none of those. Once a gene is read, it can be synthesized, expressed in a host organism and improved in a laboratory anywhere on Earth — the original organism is, from that point, unnecessary. A compound lead identified from a read or a specimen likewise enters chemistry, where it can be copied without returning to the sea. So the value of a high-seas discovery now travels as information, at near-zero marginal cost, across every border at once.

## Why the treaty question exists

Areas beyond national jurisdiction belong to no state, which by old convention meant their resources were free to whoever could reach them. Nagoya-type access rules cover genetic resources inside national waters; the high seas sat outside that logic — accessible to the few with deep-submergence fleets and sequencing budgets, closed to benefit claims by the rest. The BBNJ agreement extends access-and-benefit-sharing to those waters, and its hardest section is exactly the decoupling above: whether digital sequence information — the data, not the vial — triggers sharing obligations. Enforcement is genuinely unsolved, because sequences deposited in public databases are indistinguishable from any other data once downloaded; proposed mechanisms therefore lean on notification, database tracking and non-monetary benefits such as capacity building. The honest state of the question: the principle is settled — high-seas genetic wealth is not a free-for-all — while the machinery for tracing a copied string of letters back to the water it came from is still being invented. The molecular side of that bargain is described in the spine page of [marine biotechnology](../marine-biotechnology/).