How would you go about determining if this introduced species is harmfully invasive?

One of my very first iNaturalist observations has been ID-ed as New Zealand mudsnail, a non-native species in California. You can see that it has the pink exclamation point marking it as such. You can also see that my photograph is actually a micrograph, as shown by the millimeter ruler. I don’t think they get any bigger than that; so you probably wouldn’t notice them unless you were sampling the substrate.

Now, I have three ecospheres, built at three different points along American Canyon Creek. The ecospheres are now four months old, and I have only seen New Zealand mudsnails in the one from the location furthest downstream. At that location, they are so abundant that I get several of them every time I sample any substrate, even if I am just picking out a leaf or stick to examine the algae.(Incidentally, I noticed the same pattern when surveying that same creek for Asian clam: many shells at the downstream site, but as I proceed upstream, I come to a point where I no longer see them.)

Now, suppose it was your job to determine whether New Zealand mudsnail was a benign naturalized species in this creek, or an ecologically harmful invader. What would you look for, given its tiny size?


A good place to start is to read up on what the species has done elsewhere in similar habitats. In this case, Potamopyrgus antipodarum has reached ridiculously high densities in some European and North American waterways, enough to detectably alter the functioning of the invaded ecosystems. See for a summary and references. Based on that, it becomes prudent, I expect, to do what is practical to prevent or slow it from spreading throughout your sites.

The alternative would be to monitor carefully and see what it’s impacts turn out to be, but by then it will be much more challenging to wind back the clock and remove them.

Having said that, I expect they’ll already going to be hard to stop, in which case carefully monitoring their effects will be important.


The problem as I see it is in defining the word “harmfully”.
One could say that any invasive that is occupying space that could be utilized by a native species is “harmfull”


And then the question becomes, is there/was there a native species that occupies that particular space?

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I think every introduced species gonna affect ecosystem like rabbits in Australia . In one way or another , like if you introduced a species in other habitat they will fight for their survival and if they are lucky enough then they will dominate or just get some position in food chain then it will affect a native species in that position and native species above and below, anyway it will affect. Our ecosystem will be sure affected by introduced species.


But not every introduced species can be termed as invasive, sometimes it can be termed as helpful. Let’s imagine a ecosystem consisting of a predator, prey , producers(plants) . If one of these components gets endangered or extinct what shall be our next step. Then we are forced to introduce some species of animals which can be very similar to one that got extinct.
for eg:- If lions in Asia are extinct then our next step can be to introduce African species of lion.

And don’t forget about crops (non native) we grow help the pollinators(native) to flourish .
Fact:- Dingo our native species of Australia, is an asian wild dog introduced in Australia over 4000 years ago. It also means that introduced can become native after some time .

Wow, that was a mind-blower:

“In introduced populations, most individuals are triploid clonal females.”
" A high proportion of P. antipodarum are able to survive the passage through the digestive tracts of fish such as rainbow trout."

And yes, they do impact the functioning of the entire ecosystem:
“[Their massive secondary production] allows P. antipodarum to alter the overall nitrogen fixation rate of an ecosystem by consuming a high proportion of green algae, which causes an increase of nitrogen-fixing diatoms.”

At the point where American Canyon Creek joins it, the Napa River is brackish; I have determined that by the presence of Ribbed Mussel (another non-native species) on a beach upriver from there. The source you linked said that in its introduced range (but not its native range), New Zealand mudsnail can adapt to brackish water. If there is a brackish-water population in the Napa River, contiguous with this one, it is unlikely anything can be done; but if it is restricted to the freshwater portion of American Canyon Creek, it might be possible to eliminate it, as this is a very small creek.

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(We have another species of Potamopyrgus in New Zealand that dominates in brackish waters, the appropriately named Potamopyrgus estuarinus. I expect this is the main reason why we don’t see Potamopyrgus antipodarum in brackish waters here.)

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“A native species is one that is found in a certain ecosystem due to natural processes, such as natural distribution and evolution… No human intervention brought a native species to the area or influenced its spread to that area.”

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That comment said that not every introduced species is invasive. Though it’s questionable, mostly we don’t know its effect on native populations.

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If one of these components gets endangered or extinct what shall be our next step
The next step is to preserve and restore the habitat until it can support the endangered species again. Captive breeding programs can also be beneficial in some instances.
If it’s fully extinct and there’s no way for it to recover letting the other species that constitute the ecosystem adapt to its absence is always better than introducing an allochthonous potential pest to replace it.


One thing to keep in mind is that the population in American Canyon is actually a sub-population. This same snail species is found in most of the creeks around here. They are absurdly numerous in Sonoma Creek, for example. Birds, fish, boats, etc. moving between these many water bodies move snails. So even if you could clean every snail out of American Canyon, they would be reintroduced quickly and repeatedly.


In India, cheetahs were extinct in 1952, and now are they being reintroduced to India in November, What do you think, will it affect the ecosystem, I doubt that because I think the ecosystem has sure made some changes in order to from cheetah extinction

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