Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.
Becky Trippier our Croaking Science reporter, looks at the impact of Crassula helmsii on our native UK newts.
Whilst carrying out some fieldwork I stumbled across a pond where the water’s surface was completely covered in this small thin-leaved plant and thought How am I going to survey this?! I waded through the blanket of plants and attempted to sweep my net through the dense material to take an invertebrate sample, before taking a small piece of the plant home with me to identify later. When searching through my copy of Francis Rose I was horrified to realise it was Crassula helmsii, the deadly and invasive ‘Pond-killing Plant’.
Crassula helmsii, also known as the New Zealand Pigmyweed or Australian Swamp Stonecrop is an aggressively invasive plant,having been present in the UK since 1911 (CAPM: CEH, 2004). The species is one of the biggest threats to ponds in the UK, completely blanketing the surface once established and dominating any available space. It is a pond owner’s nightmare, outcompeting native aquatic plants forming dense mats, shading the underwater environment and depleting the water’s oxygen supply (CAPM: CEH, 2004). The loss of native plants and dissolved-oxygen has been found to have detrimental impacts upon zooplankton and macro-invertebrates, causing knock-on trophic effects such as reducing fish populations (De Vries et al. 2012). The impact the species may be having upon the UK’s amphibians is still fairly unknown with studies suggesting contrasting views.
A study by Will Watson (1999) looked at the species’ impact upon wetland ecology in the UK finding reductions in the breeding success of the Great-crested newt, Triturus cristatus, which is a highly-protected priority species under the UK BAP and Wildlife and Countryside Act 1981. He also noticed large reductions in float grass and lesser spearwort, emergent plants which are regularly used by the newts for laying their eggs. The populations of palmate or smooth newt present at the pond however, he found to be unaffected, although suggested that the rapid plant growth and silt accumulation may impact upon these species with further Crassula helmsii expansion.
In contrast to this, a more recent study by Langdon et al. (2004) found that the development of Great-crested newts were unaffected by the presence of the invasive species. However, smooth newt eggs were found to hatch at a later development stage when the species was present, which may have detrimental effects on their subsequent development as adults. The most significant findings of the study were that six of the plant species they identified as being important egg-laying plants for newts failed to germinate in the presence of Crassula helmsii.
Although the direct impacts of the plant upon newts are unclear, the indirect effects it is having upon the environmental conditions within ponds and upon native flora do pose several threats to newt species. So what can be done? Well once Crassula helmsii is in a pond, it is very difficult to get it out again. Even the smallest fragments of the plant can grow back, further spreading its presence.
However the best way to manage its spread across the UK is by preventing its movement by:
- Making sure you know what it looks like, especially so you don’t pick it up and bring it home with you!
- Properly cleaning and drying all equipment, wellies, and clothing which has been in contact with a pond containing Crassula helmsii.
- Raising awareness of the detrimental impacts the species can have and why people shouldn’t introduce it into their pond.
Ironically it was previously sold as an ornamental “oxygenator” pond plant, however its effects have now been realised and its sale in the UK has now been banned as part of new DEFRA legislation being enforced April this year (Berwick 2009, NNSS 2014).
Berwick, H. (2009). Crassula helmsii at Lound Lakes Management Options. Broads Authority – The broads, a member of the National Park family. Essex and Suffolk Water.
De Vries, W., Rannap, R. and Briggs, L. 2012. Guidelines for eradication of invasive alien aquatic species. Project report: “Securing Leucorrhinia pectoralis and Pelobates fuscus in the northern distribution area in Estonia and Denmark”. LIFE08NAT/EE/000257.
NNSS 2013. Sale of invasive water plants banned to protect wildlife. Available from: http://www.nonnativespecies.org//news/index.cfm?id=107 [Accessed 29/05/14].
Langdon, S.J., Marrs, R.H., Hosie, C.A., McAllister, H.A., Norris, K.M. & Potter, J.A. 2004. Crassula helmsii in U.K. Ponds: Effects on Plant Biodiversity and Implications for Newt Conservation. Weed Technology 18, pp 1349-1352.
Shuker, L., Gurnell, A. & Cockel, C. 2014. Adult New Zealand (Crassula helmsii). Available from: http://beta.urbanriversurvey.org/?attachment_id=91 [Accessed 29/05/14].
Watson, W. 1999. Amphibians & Crassula helmsii. Froglog 31. Available from: http://www.amphibians.org/wp-content/uploads/2012/05/Froglog31.pdf [Accessed 29/05/14].