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  1. #1

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    David Stocker of the Countryside Alliance sent me this info in an email. Does anyone know anything about it?

    "Is anyone out there aware of the fact that an insidious aquatic weed called Australian Swamp Stonecrop (crassula helmsii) appears to have taken hold in Britain? It appears that Bewl Water (Kent) has been 'infected', yet, given the propensity of this weed to spread like wildfire if its spores are transported elsewhere, no precautionary measures seem to be in operation (at least not at the time the person who tipped me off about it was there). Words like 'spreads like wildfire' and 'dominates all native waterplants' were used. I'm no freshwater biologist, but it might be worth a.) investigating and b.)broadcasting a warning."

  2. #2
    Phil Hackett Guest

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    I guess it’s down to me to answer this one mate!
    I have been aware of the problem of New Zealand Water Stonecrop Cressula helmsii (Also known as Australian Swamp Stonecrop) for some time. I have also been monitoring its progress for the SACG now SAA as it spreads across Britain.

    It is now a well established plant across the UK, with over 400 sites according to the last map I saw from the EA. Who it must be said, are doing their bit on it. I have spoken to their weedman David Holland who tells me that it’s dam near impossible to irradiate. It’s frost and to some extent herbicide resistant. One fronge (a piece) of it, and it can and generally does establish a new colony. It has the ability to grow to depths of 8 metres and when fully established can blanket out a whole lake. There are some known cases of where people have mistaken a fully colonised pond as being a firm weedy/grassy areas and got wet. As yet no one has to my knowledge, been drowned through it. It is, as you will realise, a public health & safety issue on places like country parks. It has for sometime now been prescribed as endemic weed, and illegal to sell, transfer and/or introduce to any waterbody in the UK. It was introduced into the UK by the aquarist trade as a pond plant back in the 1960-70s.
    All of this I know is no comfort to us as anglers, because of the likely potential that in the not too distant future, our favourite water may become infected with it.

    The only crumb of comfort I can offer is that it is being looked, but a solution to the problem is some way off yet.

    Believe me when I say this is the WEED FROM HELL.

    A more sobering thought is, "how many more WEEDS FROM HELL have been brought into the UK by the aquarist trade as they search for the perfect pond?"


  3. #3
    Phil Hackett Guest

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    Oops! should have read eradicate. Or perhaps that’s the answer to this bloody weed, irradiate it!

  4. #4
    Carp Angler Guest

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    Thanks for the input Phil.
    If this stuff can grow in depths upto 25 feet, then if it colonises any of our natural lakes, which are generally shallower than that, then can I assume that it will block out all sunlight and slowly kill the lake of all bottom dwelling invertabrae life?

    If it doesn't die down in the winter, then permanently weedy lakes will slowly suffocate, although if it doesn't die off then rotting vegetation on the bottom will be a thing of the past.
    Are there any pro's to this stuff or will it just kill off our fishing?

  5. #5
    Phil Hackett Guest

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    Carp Angler
    The answer to the first part of your post (If this stuff can grow in depths upto 25 feet, then if it colonises any of our natural lakes, which are generally shallower than that, then can I assume that it will block out all sunlight and slowly kill the lake of all bottom dwelling invertabrae life?),
    is a qualified yes! In theory it could conceivably colonise a whole natural lake such as the Meres if it takes hold.
    The qualification comes from the fact that it’s a rooting plant and large waters are prone to strong wave driven currents caused by gales. Such actions can rip the anchorage out and keep the more exposed areas free of it. The areas that are most likely to blanketing on such waters, are the sheltered bays and corners. Without doubt the most likely type of waters that could be totally blanketed out are small club pools and well-sheltered lakes.

    As to it killing all of the invertebrate life, the answer is no in the sort-term. The invertebrate trophic structure is such that some feed on decaying matter on and in the bed of the lake. It would however, kill over a far shorter time, all the animals that are dependent on alga for food due to blanketing. As alga growth and production is totally dependent on sunlight.
    In sort, there is most likely to be a marked decrease in the bioproduction of an infected water as it is totally blanketed out. The result of this would be less food availability to fish and other animals that depend on the water for food.

    On the worst affected waters (small club pools and well-sheltered lakes) the long-term situation could be that they suffer from accelerated succession. Succession is a natural process of shallowing through a build up of sediments through dead organic matter. The eventual outcome of this process is that the pool disappears and dries out. I know several ponds local to me that I fished as a kid 40 years ago that are no longer there due to this process.

    What I should have pointed out in the above post when I said it was frost resistant, was that frost doesn’t kill the plant, it only subdues its growth and it dies back in the winter as do many other aquatic plants. That said, some native and non-native aquatic plants can be eradicated by prolonged freezing.

    You asked are there any pros to this? There may be some short-term gains such as providing refuge for fish from predation from cormorants as the plant starts to colonise a water. On the lager more exposed waters there may be a temporary increase for a short time of some invertebrates that graze on plant. But it must be remembered that it is not a native plant, therefore its likely that few species have evolved to utilise its resource. In general terms most non-native plants both aquatic and terrestrial have few animals that feed on them.

    To the best of my knowledge no one has looked at the invertebrate fauna that utilise this plant.

    I hope these answers assist you in your understanding of this obnoxious plant.

    It does however illustrate the ecological damage we can do by innocently bring in Allen plants species, I think!

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