Getting swamped: Australian swamp stonecrop (Crassula helmsii) in the UK

In January this year, large parts of southern Australia were ablaze with fierce bush fires, while most of the UK was covered in snow. Half a world away from each other, and at one point nearly 40ºC apart, there aren’t too many similarities to be drawn between the two locations. And yet, there is a water weed, Crassula helmsii, that survives happily in both extremes – and in the UK, where it has been introduced, this adaptability is proving extremely problematic.

 Crassula helmsii, also known as Australian swamp stonecrop or New Zealand pygmyweed, is a small semi-aquatic plant in the Crassulaceae family. As its common name implies, this low-growing succulent originates from the antipodes, but was introduced to Britain from Tasmania almost 100 years ago. Initially sold by garden and aquatic centres as an oxygenating plant, by the 1950s it had established in the wild, and from there it has spread to numerous ponds, lakes and waterways throughout the UK.

A mat of Crassula helmsii in flower

Invasive species catch a wave

Over two years have now passed since the Tohoku earthquake rent the seafloor 40 miles off the coast of Japan. The 9.03 magnitude quake – the largest in Japan’s history – triggered a staggeringly destructive tsunami which cost the lives of over 15,000 people.

Aside from the human tragedy of the disaster, the tsunami has had another, quite unexpected, effect: the transport of invasive species across the globe.  Plants and animals from the north-west Pacific are now washing up over 8000 miles away on North American beaches, sparking fears that a wave of ecological invasions could be threatening coastal environments the length of the continent.

How have these organisms managed to travel so far? Such was the force of the tsunami as it tore into docks, boats and buildings on the Japanese coast that an estimated 1.5 million tons of debris was washed out to sea. This was not just the usual plastic waste that pollutes the Pacific Ocean; individual blocks of steel and concrete weighing over 100 tons have been sighted drifting off the coast of Hawaii and North America. Flotsam this large provides a substrate for sedentary coastal life and can shield species from the worst of oceanic conditions. Individual species regularly make similar transits attached to the hulls of boats.

However, what has surprised ecologists in this instance is the number of species that are washing up after 15 months adrift. Whilst whole communities are not turning up on American shores – larger and more mobile animals in particular have long since been washed away – species are certainly arriving en masse in North America. For example, a pier from Misawa port in Japan was harbouring over 100 species when it beached in Oregon in June 2012.

A pier from Misawa port, covered in non-native kelp, that washed up in Oregon in June 2012.
Source: Oregon Parks and Recreation Department

Asian longhorn beetle – A clear case for early eradication

It was confirmed last month that the first population of the forestry pest, the Asian longhorn beetle (ALB), was found in Kent, UK. Forest Research scientists discovered this damaging native of Japan and China infesting around 20 trees, and are now surveying the area to find out the full extent of the infestation. The establishment of this beetle in the UK could be extremely damaging, costing the timber industry millions of pounds, not to mention habitat loss for native species; there is no question that this pest should be eradicated as soon as possible.

Asian long horn beetle. Copyright Kyle Ramirez

Lantana – a battle not yet over!

I’m really pleased to see a more sensible discussion going on about the realities of invasive species management thanks to the article in Invasive plant News which involved one of our regional Coordinators for Invasives Arne Witt from our CABI Africa Centre.  The crux of the issue was the naïve use of the word eradication when speaking of efforts to control one of the worst weeds in the world, Lantana camara, which no one in their right mind would consider achievable, even in the early days.  More worrying is the emerging trend of publishing negative pieces on invasive management, leaving us with the feeling we should give up and accept what opportunist ecologists now call “novel ecosystems” and their increased productivity.  Little mention is made of the biodiversity reduction which is inherent in such invaded ecosystems and even more frustratingly for me, classical biological control is frequently overlooked.  The acceptance that the situation is unmanageable and we need to move on is not valid as long as biocontrol remains untried.  This echoes the excellent response in Science by our very own Harry Evans and his Brazilian colleague Robert Baretto, to the original “embracing invasives” article where they point out that doing nothing is not an option and the integration of biocontrol in areas of high conservation value such as the Galapagos is crucial.  True, in the case of Lantana, which has been the subject of biocontrol research for over a century, success is not a given.  Mankind and nature’s propensity for creating new forms of the weed has resulted in varieties that are not susceptible to some of our most promising biocontrol agents.  However, on the Galapagos a fungal agent looks likely to be able to provide control without harming the native Lantana sp. but remains unexploited.  When this was proposed, the decision was made to spend most of the flood of available money shooting goats from helicopters. A case of sour grapes on my part or perhaps an opportunity missed?  Either way before anyone declares a lost cause when speaking about invasive species they should first check that sensible goals have been set and secondly that all approaches have been explored. 

The value of costing nature in the fight against invasive species

Increasingly we are seeing the terms ‘ecosystem services’, ‘ecosystem functioning’ and ‘ecosystem processes’ in the media and the scientific literature, to highlight the benefits the natural environment provides to our wellbeing.  Invasive species, from bivalves to balsams, have the potential to impact on ecosystem services, though it is widely accepted that there are gaps in our understanding within this field.

Ecosystem services can be defined as the ecosystem processes that we as humans benefit from and they can be categorised into four groups:

Provisioning: The ecosystem provides products essential for our everyday needs including timber, fuel, food, genetic resources and medicine.

Regulating: We gain from natural services including pollination of wild plants and crops by bees, by rivers and floodplains providing natural flood management, and climatic regulation.

Cultural: We benefit from natural spaces for recreation and social activity.  We find harmony in natural areas that are aesthetically pleasing.

Supporting: These services underpin all of those mentioned above.  Biological diversity promotes stability and a healthy ecosystem, nutrient acquisition and flow through the ecosystem by fungal and invertebrate decomposers, and primary production.

The north American beaver, Castor canadensis has had a catastrophic impact on Chile’s sub-Antarctic forests impacting on provisional services (picture courtesy of http://www.martinezbeavers.org)

Rusty Solutions for a Prickly Problem

The state of Queensland has got an alien thorny invader: Prickly acacia, or in scientific terms Acacia nilotica subspecies nilotica.

Prickly acacia invasion, north Queensland, Australia, Photo: Kunjithapatham Dhileepan, DEEDI, Australia

Prickly acacia is a shrub or small tree which belongs to the plant family Leguminosae, subfamily Mimosoideae, a family which also accommodates the sensitive plant Mimosa pudica, well-known as a curiosity house plant. The prickly invader A. nilotica is native to Africa, the Middle East and the Indian subcontinent and was introduced from India into Australia in the late 1890s. Originally imported as an ornamental, A. nilotica ssp. indica was later widely used as a shade and fodder tree for sheep. But what was initially a valued addition to the Australian flora soon became a menace. When the grazing regime in Australia changed from predominantly sheep to cows and the country also experienced a number of successive wet years, the balance swung in the favour of prickly acacia. The thorny shrub spread quickly and has now invaded around six million hectares of arid and semi-arid land in the State of Queensland. Acacia nilotica ssp. indica is also present in the Northern Territory as well as in Western Australia. Due to its substantial impact on the environment as well as on the economy, particularly on the livestock industry, prickly acacia was initially declared a noxious weed in Queensland in 1957. Subsequently the plant has also been listed as a “Weed of National Significance” for the whole of Australia. And Australians have every reason to be worried, as the prickly invader has got the potential to spread throughout the arid regions of the whole of northern Australia.

Alien Battlefield

Recent articles in Science, the NY Times and Nature have suggested that we should embrace invasive species and the resultant “novel ecosystems” and that those that do battle with such species are verging on xenophobic. This is a common cycle in many fields and I’m told that a discussion thread is considered closed once a poster has been described as xeonophobic or worse, if so this discussion could be over before it even begins. Nevertheless, a group of scientists and practitioners wrote a response which can be found on the ISSG website. The issues are certainly complex. It is true that preserving pristine ecosystems is a lost goal and there are probably none in existence anymore, but to do nothing and indeed to try to argue that the new system is one worth accepting suggests that the authors have either given up in the face of too difficult a task, or have seen an opportunity to publish something controversial. There are certainly “profits” of doom to be had on both sides. In order to get your invasive management project funded it is necessary to take the public with you and when engaging with the media evocative negative language can appear in print. On the other side it is easier to stand out from fellow authors if you challenge an accepted paradigm. In the case of weeds, it is generally understood that monocultures of the new plant are less biodiverse but more productive than the flora they replace and depending on your priorities their arrival could be a good or a bad thing. If we accept that biodiversity is a priority there are few arguments to be had for introducing new invasive exotic species except for biocontrol where the excellent paper by Van Driesche and many co-authors shows the potential benefits. It is this tool that was notably overlooked in the discussions despite choosing the Galapagos as a case study where there are excellent targets for weed biocontrol yet no funding has materialised despite the vast sums spent on vertebrate eradications.

Lantana on the Galápagos - a major invasive for which all hope is not lost