5 ECU Menorca Biosphere Reserve

The Consell Insular de Menorca — the island's autonomous governing council — issued this piece the same year UNESCO formally designated Menorca a Biosphere Reserve, a status the island had been pursuing since the early 1990s as a direct response to the overdevelopment that had consumed much of the Spanish Mediterranean coastline. The ECU denomination, technically a unit of the European Monetary System rather than a sovereign currency, was frequently adopted by regional and municipal authorities across Europe for commemorative issues precisely because it carried no legal tender obligations at the national level, allowing bodies like the Consell to issue coins without infringing on Spanish monetary authority.

Menorca's reserve designation covered the entire island and its surrounding marine environment — an unusually comprehensive scope for the program at that time.