Nine shopping trolleys are now seahorse housing on the floor of the Tagus
WWF Portugal and MARDIVE have staked nine salvaged trolleys across three spots in Trafaria bay, Almada, after divers found seahorses already clinging to abandoned ones. Monitoring runs to 2028.
Nine supermarket trolleys are sitting on the bed of Trafaria bay, in Almada, and nobody is going to haul them out. They were put there deliberately, pinned to the sediment across three separate spots. They are shelters.
The idea did not come out of a meeting. It came from underwater, when divers from MARDIVE, the association doing the science behind WWF Portugal’s D-EVOLUÇÃO work in the Tagus estuary, went to look at what was left of the seabed off the town. They found what you would expect: lost fishing gear, plastic, rubble. They also found abandoned shopping trolleys with seahorses holding on to them.
A population nobody expected to be there
Two species occupy the bay: the short-snouted seahorse, Hippocampus hippocampus, and the long-snouted seahorse, Hippocampus guttulatus. The population was identified in 2019 and, by the standards of these animals, it is dense. Gonçalo Silva, the biologist and scientific diver at MARDIVE who leads the underwater work, puts the contrast simply: elsewhere a dive turns up one or two individuals, and the first dive here turned up ten or twelve. The greater pipefish, Syngnathus acus, from the same family, shows up often enough that this counts as a community rather than a curiosity.
The trouble is everything around them. The estuarine habitat there has been worn down by marine litter, pollution, underwater noise and dredging, and a seahorse needs something to wrap its tail around. When the vegetation goes, it takes whatever is left.
Two metalworkers and a simple idea
Rather than remove the trolleys, the team decided to build on what was already working. Two local metalworkers took them in hand, stripping out plastics, welding on pieces and preparing each frame to be staked to the bottom so it would not roll about with the tide. The community joined the project through a workshop door.
The intervention brings together WWF Portugal and MARDIVE with support from Lidl Portugal, Solvena and Pastéis de Belém. Monitoring runs from 2026 to 2028 and will track three things: whether the target species actually take up the shelters, what biological communities settle around them, and how the treated area develops.
The Tagus is Portugal’s largest estuary and one of Europe’s most important wetlands, and its south bank has been taking hits from every direction — Almada’s water alert one summer, two new river crossings promised over ten years the next. That part of the bay’s recovery now runs through welded shopping trolleys says something about the state of the seabed, and something about the people who refused to write it off.
Image: Olivier Dugornay / Ifremer, via Wikimedia Commons (CC BY 4.0)
