Alien Species of the Week-Chinese Mitten Crab

Chinese Mitten Crab (Eriochier sinensis) 

The Chinese Mitten Crab originates from the Yellow Sea region, along the border with China and Korea. It was first recorded in Europe in the early XX century and is now common in Europe as well as in North America (Dittel and Epifanio 2009). Eriochier sinensis first appeared in the UK in 1935 (Thames river) but became firmly established in 1975 (Veilleux and de Lafontaine 2007).

Chinese Mitten Crab (Eriochier sinensis)

Its omnivorous nature makes the Chinese Mitten Crab a threat to local ecosystems due to its consumption of native species such as fish larvae, algae, detritus and a variety of macro invertebrates and aquatic plants.

As a result of its burrowing activity, the Eriochier sinensis is also a cause of river bank erosion and collapse. The economic impact of this alien specie in Germany, since its appearance in 1912, is estimated at around 80 billion euros (Global Invasive Species Database).

Cohen and Carlton (1997) (cited in Veilleux & de Lafontaine, 2007) identified 10 pathways that would account for the worldwide spread of the Chinese Mitten Crab:

• ƒ dispersal of larvae by currents 

• ƒ passive dispersal of adults or juveniles on floating material 

• ƒ transport of adults or juveniles by ship fouling 

• ƒ transport of adults or juveniles in cargo 

• ƒ transport of adults or juveniles on  semi-submersible drilling platforms, 

• barges and other long-distance slow-moving vessels 

• ƒ transport of larvae or juveniles in ballast water 

• ƒ transport of adults or juveniles in fisheries products 

• ƒ transport of larvae in water with shipments of live fish 

• ƒ escape or release from research, public, or private aquaria 

• ƒ intentional transfer to develop a food resource

General distribution of mitten crab Eriocheir sinensis populations in their native and invasive ranges.Circles correspond to established () and non established populations () in non-native range; () indicates distribution in the native range.

(from Dittel & Epifanio, 2009)

So far the eradication measures such as the physical trapping of the crabs has not proven successful.

Check out this video:

Philine zu Ermgassen, Freshwater Ecologist at the University of Cambridge, talks about its identification, impacts and management in Great Britain:

Further reading on the spread of Eriochier sinensis:

NOBANIS –Invasive Alien Species Fact Sheet

DAISIE - Species fact sheet

Natural History Museum - Chinese Mitten Crab page

Are we nearing a 6th Mass Extinction?

Having already looked at the impacts of several alien species on their invaded environment, I think is important to examine past and future extinction rates.

So I thought we should delve into the past and examine whether or not we are entering into the Sixth Mass Extinction?

What are Mass Extinctions?

Mass extinctions are defined as the loss of  at least 75% of Earth's species in a geologically short time frame (Jablonski and Chaloner 1994). Palaeontologists recognize five major extinction events ("Big Five") in the past 540 million years, with the most recent mass extinction event ending 65 million years ago-Cretaceous (Barnosky et al. 2011).  The "Big Five" mass extinctions took place near the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous Period . As the number of known species which have become extinct over the past thousand years has risen, biologists suggest that a sixth mass extinction may now be under way.  It is expected that if all species currently deemed "threatened" become extinct in the next century, then future extinction rates will be 10 times recent rates ( Pimm et al.1995)-astonishing!!

Mass Extinctions and CO2 Levels

What are the main causes?

Observations suggest that humans are the main cause of this sixth mass extinction, through habitat fragmentation/ modification, introduction of non-native species, spreading pathogens and killing species directly (Barnosky et al. 2011).  All of these human activities are associated with climate change through global warming due to increasing levels of carbon dioxide, increasing levels of volcanism and ocean acidification. According to the graph above,  all major extinctions occurred when CO2 levels exceeded a thousand parts per million (ppm). Highlighting the important role human's play in determining the speed at which we meet the sixth extinction. 

The graph below, produced by Barnosky et al. (2011), compares extinction rates versus extinction magnitude across different geological time periods. It shows that in the future, if current extinction rates over the last 500 years were to continue it would produce a "Big Five" style magnitude mass extinction. This means that current extinction rates for species are either faster or just as fast as all rates that would have produced the "Big Five" extinctions. 

However, I must point out that you should take CAUTION when comparing extinction rates, as the fossils used and quality of their preservation varies greatly. For example, many of the earlier mass extinctions rates were solely based on marine organisms.

Extinction rates versus extinction magnitude

Today, the current rate of species extinctions has most definitely been enhanced by human activities as CO2 concentration levels increase. Although, recent species loss is definitely serious and dramatic, we can't yet call it a mass extinction. However, the number of species now classed as "critically endangered" suggests that a sixth mass extinction is soon to become a reality.

This makes me question as to what the future holds for us humans and when will we potentially become "extinct"?!?

Power of the App!

 

So far I’ve spoken about some of the difficulties caused by invasive/alien species, but how as a member of the public can we help combat these invasions? 

Well the answer is simply “PlantTracker!"

The Environment Agency, the University of Bristol and the Centre for Ecology and Hydrology have teamed up and developed a FREE app allowing the public to identify some of the UK’s most problematic invasive, non-native plant species. 

The PlantTracker app allows users to very easily identify 14 invasive plant species (e.g. Rhododendron) with the help of an image gallery and a detailed description of each plant species. What is also great about this app is that it also includes a “Confusion Species” gallery, making it easier to distinguish non-native from similar looking indigenous plants. Furthermore, once you have identified one of the invasive plant species using the app, you can submit a geo-located photo of the specimen.

PlantTracker screenshot options

 

Why an app?

It is crucial to gather solid data to make important decisions on how to manage and deal with the problem of invasive plant species. However, it is usually very difficult collect verifiable and accurate data about the distribution of these invasive plant species. But by combining the smartphone application with the power of crowd-sourcing data collection, the app allows real time and verifiable data to be collected (see below).

Map showing the distribution of Rhododendron reports.
(The red dots indicates the number of verified Rhododendron records)

Where can I get the app?

PlantTracker is available free from the iTunes App Store and Android Market. So go on, why not give it a go and download the app? I’ve already downloaded mine!