The impressive comeback of a seahorse colony off Halkidiki

In November 2007, scuba diver Vassilis Mentogiannis joined a dive team from the Ephorate of Underwater Antiquities on a mission to inspect the expansion of a port at Stratoni, Halkidiki, in northern Greece.

"As we finished our underwater inspection of the port, we thought to continue exploring a bit further, over to the mouth of the Argyro stream. Suddenly, a seahorse swam past me. I was excited, because even though I have been diving for years I had never seen a seahorse. Then we saw another, and another... the place was full of them. It was really quite special," remembers Mentogiannis.

Fascinated by the discovery, the diver returned to the location a few months later.

"Again, we came across a large number of seahorses in the area, where the water quality is not very good. Coming out of the sea, we asked the locals what they knew," says Mentogiannis. "At...