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Biodiversity restoration in Lake Dianchi, China - Part 3: Alien invaders both hold back and support recovery

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Red-eared Sliders, one of the invasive alien species in Lake Dianchi. See full photogallery.
Another notable achievement of the ‘Restoration of Freshwater Biodiversity in Lake Dianchi’ project (see previous entries--part 1 and part 2) was the discovery and action taken against a number of invasive alien species which had not been recorded from the lake before the surveys initiated by the project. These include the Golden Apple Snail, Louisiana Crayfish, Red-eared Slider (the turtle or terrapin commonly found in pet shops the world over), and Muskrat. Their introduction to the area, as with many alien invasives, “seemed a good idea at the time” but they all have – or likely will have – serious negative economic and ecological impacts. The Golden Apple Snail has a predilection for young rice plants, the Louisiana Crayfish burrows into bunds, and the Red-eared Slider predates on fish.

Perhaps the lake’s most famous invasive alien is the pretty, purple-flowered Water Hyacinth from Brazil which once covered vast areas of the lake and which the authorities worked hard to (almost entirely) eradicate. Interestingly, the project team found that the roots hanging beneath these floating plants are major resting and feeding places for aquatic invertebrates (aka fish food) which would normally graze on the algae found on the surface of submerged macrophytes.  The conclusion must be that totally eradicating the Water Hyacinth before restoring the native macrophytes could cause problems of its own.

The Grass Carp, a herbivore whose grazing habits are probably a major reason that Lake Dianchi has lost most of its macrophytes. See full photogallery.
The project team has also been able to get some traction from the Governor and relevant authorities on the problems caused by the popular (and meaty) Grass Carp. This large fish is herbivorous and its grazing habits are probably a major reason that the lake has lost most of its macrophytes.  Luckily the species cannot breed in the relatively cool Lake Dianchi and so can be maintained only by restocking. The damage done to the lake ecosystem by this fish is becoming better known, but it will realistically take some time before all restocking will cease and even longer before all the grass carp will be caught or simply die. Nothing is simple. 

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