Wednesday, 17 April 2013
The heron and the fast flatworm
January’s blog highlighted the striking ability of pondweeds to get to unexpected places, considering that they can neither fly, walk nor swim under their own power (12th and 19th Jan). Here is another neat example of colonisation from Hauxley Nature Reserve. A few weeks ago we dug out some brand new ponds amongst the older experimental ponds from which I’ve recorded the invertebrates since 1994. The new ponds look raw: in the left hand photograph you can appreciate the unlovely bare mud, sheer sided and often clouded with muddy water. But look closely in the bottom left and there are the elegant prints of a heron which has deigned to wade through, and, amongst the heron’s tracks the dark, gliding oblongs of flatworms (right hand picture). They are species of Polycelis, either tenuis or nigra but hard to tell which without dissecting their reproductive organs and this is not that sort of blog. Polycelis are hunters, which suggests that there is something to hunt. Small Hydroporus water beetles and Crangonyx freshwater shrimps were also evident. All these creatures and numerous in the pools around about and have moved into this new home readily. The original ponds from 1994 also colonised very quickly but with a slightly different fauna of pea shrimps and water fleas. This new round of ecological succession may be different because the adjacent older ponds, spring boards for colonisation, harbour a more varied fauna.