Friday, 26 July 2013

Gatwick's Alien Invaders

A battle is being fought all around Gatwick Airport... Aliens landed here quite some time ago, but together JS Agriculture and Gatwick Greenspace Partnership have plans for defeating these invasive species!

American Signal Crayfish (Pacifastacus leniusculus)

Signal Crayfish burrows in the bank and Himalayan Balsam growing along
 a section of the River Mole at Povey Cross

An important part of our Biodiversity Action Plan is to monitor the presence of non-native species occurring on Gatwick's land and to come up with plans to tackle them. As they have been established in our countryside for quite some time they are virtually impossible to eliminate, so instead we aim to control them as best as possible, reducing their impact on our native flora and fauna.

Bucket 'o' crays:  They have reached plague proportions in our part of the River Mole.
We humanely euthanise them under instruction from the Environment Agency

Tiny wee Signal Crayfish from the River Mole

The American Signal Crayfish (Pacifastacus leniusculuswas introduced to Britain in the 1970's and escaped from fish farms into our waterways. Having witnessed the size and quantity of their tiny larvae I'm not surprised they did! They are tough little pioneers and easily colonised our waterways; unfortunately they carry a disease which our native White-Clawed Crayfish (Austropotamobius pallipes) is vulnerable to. As a result White-Clawed Crayfish are now pretty rare and highly protected in areas where they still remain.

Our licensed crayfish traps with fish bait. 

Signal Crayfish have a voracious appetite and eat whatever they can get their claws on, be it aquatic plants, fish fry or invertebrates. They also burrow deep into river banks which causes destabilisation, erosion and eventually bank collapse. By trapping them on a section of the river and reducing the number of large, voracious adults I hope to see a positive effect on the aquatic biodiversity.


Gatwick Greenspace volunteers Adrian and James removing Himalayan Balsam; 
waders are not such a bad job on a hot summers day

Another problem alien here is Himalayan Balsam, which was introduced to Britain in 1839 as an attractive ornamental garden plant. It is a rapid coloniser, spreading along our waterways, growing very tall and quickly out competing our native flora. It has impressive pink flowers which are a good nectar source for bees and other pollinators, but perhaps at some cost to our own native wildflowers.

Himalayan balsam (Impatiens glandulifera) in flower

The root of the problem: the fleshy roots die back each winter, meaning the soil is left loose and exposed. This however does mean it is easy to pull up. 

The seed pods are pressurized, popping open at the lightest touch, scattering seeds into waterways which are then carried far and wide. The roots of this plant are weak and die back each winter, resulting in exposed mud which then erodes easily away .


Gatwick Greenspace volunteers are all-weather people with the correct gear, precautions and an ample supply of refreshments (I can testify to their high-standard biscuit selection!) On one of the hottest days of the year, they tackled a good length of the River Mole around Povey Cross, pulling up every individual balsam plant they could find.

Balsam is heaped into piles to rot down before it has flowered and seeded

Volunteer Georgina with a near full-grown Signal Crayfish

Gatwick Greenspace Partnership conservation volunteers at Povey Cross, North West Zone

The JS Agriculture team, balsam-bashing in the southern part of Horleyland Wood,
 Land East of the Railway Line

We are continuing the fight against Gatwick's invaders for the next few weeks. If you interested in volunteering and conservation around Gatwick then check out the website for Gatwick Greenspace Partnership, part of the Sussex Wildlife Trust.