Dan Thornhill, Conservation Scientist
There’s a tiny sea anemone – known to scientists as Aiptasia – found worldwide throughout tropical oceans. This little animal is infamous among aquarium enthusiasts as a reef tank pest that is quite difficult to remove from a home aquarium. But Aiptasia isn’t all bad; in fact, this anemone is helping scientists like me understand how coral reefs will respond to climate change and ocean acidification , problems that threaten the very existence of this ancient and vulnerable ecosystem. Now it is time to add a third quality this versatile little anemone’s résumé: introduced species.
When my colleagues and I set out to study the effects of climate change on coral reefs, we took samples of species living on many different reefs in different regions. We were surprised to discover that Aiptasia has recently been spread all over the world! Although this anemone is found on coral reefs all across the globe today, DNA evidence shows that this was not always the case. When we looked at the genetic material of Aiptasia and their algal symbionts, we encountered identical clones on reefs across the Pacific Ocean, from Mexico to Hawaii to Japan, as well as the movement of anemones throughout other parts of the world. It appears that these anemones have commonly and recently spread over tremendous distances, much further than they should be capable of moving on their own.
So how are these small, mostly sedentary anemones moving from one side of the Pacific Ocean to the other? Unfortunately it looks like people are to blame. Although we cannot be sure who is responsible, there are several likely causes. The first is ballast water from ships, which is well known for moving around marine life and introducing animals and plants to places where they don’t belong. It is possible that Aiptasia has been hitching a ride with ships all around the world and hopping off at different ports along the way.
Another suspicion is that Aiptasia spread via the aquarium trade. We know that trade introduced lionfish , for example, to the waters of Caribbean were they are rapidly gobbling up many other fish and disrupting the ecosystem. It is feasible that anemones were introduced to reefs around the world in a similar manner.
Finally, the perpetrator could be marine farms raising oysters, or some combination of all of the above possibilities. Whatever the source, Aiptasia are now abundant and they are likely here to stay. It’s just another example of the ways, both big and small, that humans are changing the way plants and animals live on Earth.
For a more in-depth look at the spread of Aiptasia, you can read the full study here, recently published in Molecular Ecology.