The seas surrounding the UK - and the rivers that flow into them - are filled with animal and plant species that originate far from our shores.

While some of these non-native invaders will die out over time, others are thriving - and are becoming a huge threat to biodiversity.

Here, two experts - Jack Sewell and Philine zu Ermgassen - explain how these alien invaders are affecting our ecosystems.

Slideshow production by Paul Kerley.

The BBC is not responsible for the content of external internet sites