No one quite knows what happened in the tropical aquarium of a German zoo two decades ago, but according to biologists, experiments with a tropical seaweed unleashed a hybrid algae which is now decimating marine life in the Mediterranean. It was in the late 1980s that Alexandre Meinesz, a professor of biology at France's University of Nice-Sophia Antipolis on the Mediterranean coast, first detected the spread of a new species of algae along the French coastline. Horizon follows Meinesz on a scientific detective story as he attempts to unravel the source of this alien algae, alert the authorities to the danger and find a solution. Meinesz quickly identified the invader as a gigantic version of an algae called caulerpa taxifolia. But what puzzled him was that this variety of algae normally grows thousands of miles away in the tropics and is a small, relatively rare, plant. The plant he'd found was bigger and denser than any member of the caulerpa family he'd ever seen before and was thriving in the cooler waters of the Mediterranean. As scientists studied the invader, they found that although it posed no threat to humans, it was so toxic many Mediterranean animals preferred to starve to death, rather than eat it. And it was growing so fast that it was swamping indigenous rivals; where it grew the seabed was becoming a green desert. But nobody in authority listened to Meinesz's warning and today the algae is causing the biggest upheaval in the Mediterranean's ecosystem.

Film Duration: 43 min .