Meet the aliens in UK waters

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.

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Slideshow production by Paul Kerley.

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