Shipping problems: Alien invaders
Ballast water is loaded with thousands of marine species, including plankton, algae, fish, jellyfish, and other invertebrates.
Most of the stowaways are not able to survive in their new environment when released from the ship. But some can - and only too well. These aliens can become invasive, rapidly out-competing local fauna or flora. They can alter the entire local ecology, leading to the collapse of fisheries and threatening endangered species. Exotic algal species can also pose a risk to human health by contaminating seafood.
Indeed, alien invasive species can be as damaging as oil spills, and their effects much more persistent.
With no enemies in their new home, the jellies propagated at an alarming rate. By the mid-1990s, they accounted for 90% of the total biomass in the Black Sea - a biomass more than the total annual fish catch around the world. The species quickly spread into the neighbouring Azov Sea too.
The invasion contributed to the near collapse of Black Sea commercial fisheries within a few years. The once quite prosperous seafood industry has lost about US$1 billion since the jellies were released. Anchovy fisheries in the Azov Sea, already under stress from pollution and overfishing, have completely collapsed.
Dolphin numbers in the Black and Azov Seas also dropped dramatically, as the fish they used to feed on disappeared. The entire ecosystem has been disrupted - the jellies have even reduced the amount of oxygen in the Black Sea.
They've now entered the Caspian Sea, where they are similarly wreaking havoc, and have been found in the Baltic Sea and along the Atlantic coast of Norway too.