An Oceans Abcdarium created by the University of Applied Sciences in Mainz, Germany

Killer Algae

Carolin Nonnenmacher

The undulating green on the Mediterranean seabed seems thriving and peaceful, but appearances can be deceptive; what looks like a healthy seagrass meadow often turns out to be a virtual desert, overgrown with Caulerpa taxifolia. This invasive alga from the Pacific and Indian Ocean and the Caribbean Sea was probably introduced in the Mediterranean in 1984. It is thought to have been accidentally released from a public aquarium in Monaco. From there it spread rapidly throughout the Mediterranean Sea in subsequent years, dispersed by anchors and fishing gear. Due to its toxicity, Caulerpa taxifolia is of no value to local herbivores, and was considered a major threat to Mediterranean ecosystems, especially by displacing seagrass meadows. Many methods of eradication have therefore been tested, with varying degrees of success. However regardless of the human efforts, the so-called killer algae mysteriously declined drastically across the whole of the Mediterranean between 1997 and 2009.

Sources: Žuljević, Ante et al., “Decline of Caulerpa Taxifolia in the Adriatic Sea”, Proceedings of the 1st Mediterranean Symposium on the Non-Indigenous Species, Split, (2019).