The tale of the founder flounder

Have you ever wondered where the flounder found in Iceland has come from?

It is well known that alien European flounder has been officially documented in Icelandic waters in 1999. For a long time, the question remained where the flounder came from. Over the years, people have debated whether the flounder came from the Faroe Islands or from the coasts of western Europe. Now Theresa Henke and colleagues have published a study where they took a closer look at the origin of flounder. To do this, they followed the methods used in a study from 2007 that had shown a genetic difference between flounder in the Faroe Islands and other European populations. In the summers of 2020 and 2021, Theresa collected flounder samples all around Iceland. Comparing them to the data from the earlier study showed: European flounder found in Iceland likely arrived from the Faroe Islands.

One answer and many new questions

This study has answered a big question in the case of flounder in Iceland. But as it often is the case in research, it has also opened up many new ones. Even though we now know where the flounder came from, we still don‘t know how it arrived from the Faroe Islands (400 km from southeast Iceland): Did the flounder swim to Icelad? Was the flounder accidentally brought over to Iceland by boats? And does this even matter?

It does. Right now, European flounder in Iceland is classified as a potentially invasive, alien species in Iceland. The definition of an alien species, according to the recent IPBES report (read more here), is a species that was introduced because of human activity. If the flounder arrived in Iceland by itself without the help of humans,it would not be an alien species based on this definition.There is no definite answer to this question yet, but we hope future research will provide one. Read more about this discussion in the paper!

For now, Theresa and her co-authors suggest to keep the classification with a little addition. By adding the term “polyvectic” the classification points out that there are more than one potential ways how the flounder has arrived and that it is still unsure which one is correct.

What about the hybrids?

This study did not only find out where the flounder came from, it also showed that there are hybrids between flounder and the native European plaice. When, in this case, two different fish species produce an offspring, it is called a hybrid. When flounder and plaice live in the same area, you can often find hybrids, such as in the Baltic Sea. But this is the first time that these hybrids have been officially documented in Iceland.

Read the full study on the tale of the founder flounder here.