The most likely scenario is that the beautiful red lionfish spread into the sea off the coast of Florida when an aquarium was smashed by Hurricane Andrew thirty years ago, writes the US National Oceanic and Atmospheric Administration (NOAA). Today, the red lionfish is completely dominant along the US coast and is out-competing other species in the ecosystem.
That may well be how the red lionfish spread, but the usual way species spread is by being carried in the ballast water of cargo ships. Today, huge volumes of ballast water are transported between the world’s ports, with up to four billion tonnes of water dragged around the world in this way every year.
Ships that are not fully loaded have to be stabilised. In the past, stones or sand were used, but these days, ships take on water in their tanks to stabilise the vessel. The water is pumped in after unloading and then emptied in the next port when loading the next cargo.
The water comes with hitchhikers in the form of animals, plants, eggs, larvae and micro-organisms. Most of them die on the voyage in the dark, often toxic space, while others die as soon as they reach their new environment. However, some survive the journey and some of them become what is termed invasive. In other words, they cause a great deal of damage in the ecosystems into which they spread.
There is no really good system for stopping invasive species and problems are increasing at an alarming rate as a result. Currently, a new species establishes itself somewhere in the world every two months.
Trials have been conducted to train sharks to eat the invasive red lionfish. This did not turn out to be a feasible solution. In general, it has proved difficult to stop invasive species by introducing other species to kill or destroy them, simply because the consequences are too difficult to control. Things can work out well, but can also go very badly wrong.