Amphibians and dry ditches

27th November 2010, Saturday

Continuing the theme of the results of the 2009 drought on ditch flora and fauna at East Guldeford I surveyed the ditches for amphibians in March.  By far the most abundant species was the marsh frog Pelophylax ridibundus which was present in all the ditches in good numbers.  This is far and away the most aquatic of the Marsh amphibians and will have evaded the worst effects of the drought, and the little egrets and grey herons, by hiding in damp crevices and hollows in the bottom of the ditches.  Although not of any conservation significance (because it is an introduced species) it does act as as a prey species for the medicinal leech that abound in these ditches.

Great crested newt egg on water-speedwell leaf

I would not say that newts abounded in the ditches.  There were moderate numbers of smooth newt Lissotriton vulgaris and no palmate newts L. helveticus.  This latter species is generally absent from Romney Marsh other than on the ditches bounding the edge of the higher ground.  This seems to be typical for many of the extensive grazing marshes in the south-east.  I was pleased, however, to find one great crested newt Triturus cristatus egg on a piece of pink water-speedwell Veronica catenata.  This was followed by a single large tadpole in july in the same ditch.

 This looks likely to be a small population of this species, and it was confined to just one ditch.  The likely reason was the presence in all of the other ditches of reasonable numbers of three and ten spined stickleback Gasterosteus aculeatus and Pungitius pungitius which had managed to recolonise rapidly through the inter-connecting ditch network.  These fish are effective predators of great crested newt tadpoles, though not smooth newts.  The former tend to swim in the mid water column whereas the latter tend to spend more time hiding in the cover of mats of weed and algae.  The occurence of this species in just one ditch was interesting.  Whereas all of the other ditches formed an interconnecting network the one with the great crested newts was isolated from the main ditch network, effectively becoming a linear pond.  Furthermore it is a very ephemeral ditch with a limited aquatic flora and fauna, largely dominated by mats of creeping bent grass Agrostis stolonifera.

So, for the great crested newt it appears that drought on grazing marsh habitats can be a blessing in disguise too, providing that predatory fish do not have an obvious recolonisation route when wet conditions return.