Can invasive species really be driven back by foodies?

Today's Species Calendar features the Chinese mitten crab, and at the end we mentioned that Chinese mitten crabs have become a headache-inducinginvasive speciesin Europe and North America. You might be surprised that Chinese mitten crabs can be a headache? Send in a team of Chinese foodies, and wouldn't it be solved in no time?

In earlier years there were even widely circulated rumors like "818 the invasive species of the great eating empire":

Indeed, there are quite a few similar cases of organisms (read: delicacies) invading like the Chinese mitten crab and the red swamp crayfish. Can Chinese foodies actually send the invasive organisms that give other countries headaches to their graves and save the world?

The answer is: no.

Never mind whether we could wipe out invasive species in other countries; let's just look at China's invasive species. According to data from the China Invasive Alien Species Database and the Research Center for Prevention and Control of Invasive Alien Species of the Ministry of Agriculture,China has 754 recorded invasive organisms, and the estimated annual economic loss exceeds 120 billion. Foodies solving the invasive alien species problem? You're being far too naive.

What is an invasive species?

An invasive species is a subset of introduced species. If a species is introduced by humans into a region where it did not previously occur naturally, and it has the ability to develop a certain population size locally without further human intervention, to the point that itthreatens local biodiversityand becomes a local nuisance, it can be called an "invasive species."

A species is not invasive at all times. For tens of millions of years, the tragedy and comedy of species turnover have played out continuously in global ecosystems, but this process is slow and can only occur under natural conditions. Then humans changed all of that.

Cooked marbled crayfish sold for human consumption at a market in Madagascar. Image source: Ranja Andriantsoa

Humans have gained an unprecedented advantage in moving species:transportation. This allows certain species to easily hitch a ride with humans to strange corners they have never reached before. A large number of introduced species face environments they cannot adapt to in the short term. For those species that humans actively introduce from foreign lands for some economic purpose, people often have to actively create suitable habitats for them so they can survive.

But a small number of species,with the help of human power, arrive in what becomes their new continent. This new environment unexpectedly suits their survival, so they can live well without human help. If they escape human control, and the factors that once curbed their population growth in their native range are completely absent, then these species become like unbridled wild horses forming wild populations, or through potential survival advantages they seize the living space and resources of native species by sheer numbers, or they have broad feeding habits and eat anything, directly preying on native species, or they can secrete toxins and use other means to suppress the survival of native species.

"Asian carp" in the Murray River in Australia. Image: Vaderluck / wiki commons

At the same time, invasive species do not necessarily look like sharp-fanged, fully armed creatures wiping out all other organisms. A species whose population is effectively suppressed in one place can become an invasive species in places with different environmental factors.

Having become familiar with these basic concepts, let's analyze a few cases.

The beginning of invasion was because of foodies

First look atthe American bullfrog（Rana catesbeiana）、the golden apple snail(Pomacea canaliculata) andtilapia. The invasion of these organisms was precisely caused by blindly introducing alien species as food without considering market capacity.

Simply put, the reason these species became invasive alien organisms in China is precisely that the original introducersoverestimated the fighting power of Chinese foodies, combined with a lack of effective farming control and environmental isolation.

American bullfrogNative to North America, it is called bullfrog in the United States, named for its rough, low call during mating season that sounds like a bull bellowing. The bullfrog is not only the largest existing frog species in North America, but also has a fierce personality and a hearty appetite. Its diet goes far beyond the insects, snakes, rodents, fish, turtles and crayfish that ordinary frogs eat, including any living thing it can catch and even many kinds of birds. Even its tadpoles pose a threat to small fish in the water bodies where they live.

Large bullfrog tadpoles. Image: californiaherps.com

Because farming conditions were extensive and people in the early period had no awareness at all of controlling introduced animals, bullfrogs escaped into the wild very early in Asia, becoming wild species and then invasive organisms. The recorded time of bullfrog invasion into China is 1959, entering through Hong Kong, China, but the larger-scale invasion came after the economic opening of the 1980s and 1990s, when "specialty farming" sprang up across South China and large numbers of unfamiliar animals and plants were introduced into the country as golden keys to fortune, and the bullfrog was one of them. However, compared with China's native wild frogs such as the spiny-breasted frog, the Chinese tiger frog and the black-spotted frog, the bullfrog's meat is too coarse and tough, failing to catch the eye of gourmets, so its sales were initially poor. As a result, large numbers of farms were abandoned, and the escaped American bullfrogs replaced many native frog species.

Similar to this isthe golden apple snail. The golden apple snail comes from the Amazon River basin in South America. In the 1970s it was introduced to Taiwan, China as food for farming, and later because its meat was poor quality it was discarded in large numbers, leading to its spread out of control. After the 1980s the mainland did not learn the lesson, and the consequence of introduction was repeating the same mistake. Because of its extremely strong reproductive capacity, the golden apple snail is now found in almost all water bodies in South China.

Egg clusters of the golden apple snail. Image: floridatimeforgot.com

If poor taste can barely be accepted as an excuse to forgive foodies, then tilapia becoming an invasive species is more the result of cultural tradition and low acceptance.

Tilapiais actually not just one kind of fish, but a collective term for multiple species of introduced farmed fish in the genus Oreochromis and the genus Tilapia of the family Cichlidae. Their meat is tender and fresh, and they have broad feeding habits. They are a protein source recommended by the United Nations World Food Programme, and institutions in the United States, Israel and India all do farming and breeding work on them.

Tilapia. Image: fishbase.se

But in China, its problem lies in acceptance. Because its appearance is completely different from the traditional four major Chinese carps raised for food, and because tilapia grows quickly, some people who do not accept it view it as "raised in dung water." This view (perhaps better called prejudice) not only caused farming failures and species escapes in some places, but also prevented people from catching tilapia that flowed into the wild, causing wider invasion.

Some rumored invasion cases

Thecoypu(Myocastor coypus) invasion has little to do with foodies. They were initially introduced from the Soviet Union to China as fur animals, and likewise formed a specialty farming boom after the 1980s, then escaped into the wild and became invasive species. At present, the coypu meat and processed products we can see in markets or restaurants all come from farming, because the cost of farming coypu is lower than the cost of catching them in the wild, and the wild population of coypu in China has not yet grown large enough to be easily caught by people. Their invasive harm mainly lies in damaging dikes and crops.

Coypu. Image: Alpsdake / wiki commons

Yellow chamomile (Anthemis tinctoria), garland chrysanthemum (Chrysanthemum coronarium) and wild garland chrysanthemum (Gynura crepidioides) also appear on the list of invasive alien species, but none are on the list of serious harm. In fact, some flowers we know well, such as marigold, Cosmos and cornflower, are on this list, meaning there is evidence that they have established wild populations, but they have not yet caused serious economic and ecological harm.

Interestingly, many people's concept of invasive species was formed through two so-called"piranha incidents"and the panic and media attention they triggered, all of which were later proven and regarded asa farce. "Piranha" generally refers to various fish under the subfamily Serrasalminae of the family Characidae in the order Characiformes, which have sharp teeth, live in groups and have carnivorous habits. One point that can now be made clear is that there is no definite information showing that any kind of "piranha" has established a population in the wild in China, and no kind of "piranha" has been included in China's list of invasive alien species. A very simple fact is that "piranhas" are very sensitive to temperature. Even if some "piranhas" escaped into China's freshwater bodies, first they could not establish a population, and second they could not survive the winter.

For example, this Weibo post.

Under the order Characiformes, some fish have indeed been introduced for farming. They all belong to the genus Piaractus, and their market name is generally freshwater pomfret. One of them,the small-scaled pacu(Piaractus mesopotamicus), entered China's invasive alien species database and often becomes the object of mistaken reports of "piranhas" in various places. In any case, they are omnivorous fish, tasty and non-aggressive. Their environmental impact is another matter, but foodies really might as well give them a try.

Rumors are not limited to China

There is also a rumor about mussels invading Western Europe and North America. The statement about the invasion is roughly accurate, but the invasive species is not the mussel, butthe zebra mussel（Dreissena polymorpha）。

The zebra mussel is native to the Caspian Sea and the Black Sea. As human ships traveled, it was brought in the first half of the 19th century to ports in Western European countries such as the United Kingdom, Ireland and Spain. Because of its extremely strong attachment ability and reproductive capacity, it caused damage to local port facilities and kept invading as far as the Netherlands, Czechia and Sweden, reaching Italy in 1973. In 1988, it was first discovered in Windsor, Canada and Detroit, United States, and over several decades the zebra mussel spread wildly throughout the entire Great Lakes region. Their ecological harm mainly lies in reproducing so rapidly that they cannot be controlled, which is enough to change the energy flow of ecosystems. And because of their potential to accumulate toxins and pollutants, experts do not recommend eating zebra mussels (although they can be eaten). The United States spends 500 million dollars each year to control the spread of zebra mussels.

Zebra mussels in the Netherlands. Image: Bj.schoenmakers / wiki commons

What we call mussels, however, are multiple species of the family Mytilidae living along the coast of East Asia. Although they can also sometimes cause damage to harbor facilities, because they are native species whose numbers are effectively controlled by other organisms, they do not cause serious problems.

Unfortunately, foodies cannot save the world

At this point, the errors in theclassic cases of "foodies saving invasive species"that you may have heard of have all been analyzed. However, in a broader sense, invasive species are far from being a problem that can be solved simply by people "eating" them.

Taking China's situation as an example, among the 754 recorded invasive organisms, 134 are various microbial plant diseases, the vast majority of the animals are insects, and most of the plants are not fit to eat.As human "foodies" we are so useless, but we can use this to broaden our thinking and use the "foodies" among other species to help us solve the problem, which is so-called "biological control."

While developing the economy, striving to maintain the current environmental condition is currently humanity's best strategy for continuing civilization. Therefore,doing our best to control the number and types of invasive species, together with environmental protection, should all be means for the continuation of civilization.

This article was first published on Guokr, from Species Calendar author @Zhong Shushu.

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