Trillions of Microscopic Creatures Are Revealing What Sargassum Is Really Doing to Puerto Morelos Waters

You can't see them. You can't feel them. But trillions of microscopic creatures living in the sand and water just off Puerto Morelos are telling scientists something important about what sargassum is really doing to our coast.

A new study funded by the Quintana Roo Council of Humanities, Sciences and Technologies (Coqcyt) is using a cutting-edge technique called environmental DNA (eDNA) to measure how sargassum affects the health of marine ecosystems right here along our shores.

What Is Environmental DNA?

Environmental DNA analysis works by collecting water or sediment samples and scanning them for genetic fragments left behind by living things. Think of it like a fingerprint kit for the ocean.

Researcher Arely Martínez Arce, who led the study, says the method can detect species ranging from tiny worms to whales, all without ever seeing the animal directly.

The technique can analyze millions of genetic fragments at once. That is a massive leap over older methods that could only study one organism at a time.

The Tiny Creatures That Tell the Whole Story

The study focuses on marine nematodes, microscopic worms that live in beach sediment and shallow seafloor areas. They recycle nutrients, feed larger animals, and sit at the very base of the food chain. When nematode populations change, the whole ecosystem feels it.

The findings are striking. Beaches without sargassum can host up to 200 different nematode species. Beaches buried under sargassum accumulation? That number drops to around 100. That is a 50 percent reduction in biodiversity.

The reason comes down to chemistry. Rotting sargassum strips oxygen from the water and releases hydrogen sulfide, the same gas responsible for that rotten-egg smell locals know all too well.

Those conditions are lethal to many bottom-dwelling organisms, including the tiny creatures that keep the ecosystem running.

Puerto Morelos Is Not Immune

Puerto Morelos has done better than most towns at managing sargassum. Offshore barriers, daily beach cleanups, and coordination between the mayor's office, the Navy, and the private sector have helped keep the worst of it at bay. In 2025, crews were collecting an average of 30 tons per day during peak season.

But the study is a reminder that even when the beach looks clean, the damage can already be happening below the surface. The reef, the fishing grounds, and the water quality that make Puerto Morelos what it is all depend on a healthy seafloor ecosystem.

The study also detected exotic species arriving with sargassum, organisms that have never been recorded in this region before. Scientists are not yet sure if those species have established permanent populations here.

Why This Matters for Daily Life

Martínez Arce put it plainly: when ecosystem quality drops, so does everything that depends on it. That means fishing, water clarity, and the overall health of the reef.

For a town where local fishermen still launch their boats from the beach every morning, and where the reef draws snorkelers and divers year-round, that is not an abstract concern.

The research is a call to pay attention to what cannot be seen. The ocean's health is written in its smallest inhabitants, and right now, they are sending a warning.