Pondnet diary day 2

Continuing the Pondnet survey that began about a week ago, having done a preliminary survey of the main environmental features and whichever species could be spotted from the side, this time a net and white tray were required.

My wife/field-assistant doing some pond-netting.

the first thing we notcied was the great increase in frog tadpoles - not only in number (from a couple of hundred to at least a thousand as a rough estimate) but in size. A week previously the ones we saw were newly hatched - these had developed their typical fat-headed shape. They hadn't all hatched in the last week, so many must have been well hidden. The net also meant that we could confirm the species of the numerous small fish seen previously - they looked like sticklebacks but it's always worth checking, and all the ones we caught (and yes re-released) were indeed three-spined sticklebacks (Gasterosteus aculeatus).

A three-spined stickleback Gasterosteus aculeatus - the dorsal spines are just visible

Of course, it wouldn't be a proper sampling day (for me) if there weren't invertebrates involved. The netting meant we could see beyond the larger surface-dwelling species and maybe find some that, even if common, are less immediately familiar.

The water-slater or hog-louse Asellus aquaticus

The water-slater or hog-louse Asellus aquaticus is an isopod crustacean i.e. related to woodlice, and is common and widespread in Britain. It can be found in a very wide range of water bodies and qualities, but especially under aquatic foliage, stones and wood (Gregory, 2009), so is rarely seen by the casual observer without a net. It can be separated from the similar Proasellus meridianus by the head pattern although the photo doesn't show it as clearly as could be seen on the live specimen.

Another common-but-overlooked species is Plea minutissima, the 'least water-boatman'. It is broadly similar to other water-boatmen seen 'rowing' beneath the water's surface, but is tiny (around 1.8 - 2.8mm long) and its domed shape means that it is initially more likely to look like a small beetle than a water bug at a glance (Denton, 2007) - it certainly did to me when seen among the debris and other small species from the net. However, under the microscope (or even a squinted eye) it is quite different and the pointed mouthparts can be seen.

The least water-boatman Plea minutissima is the sole British species in the family Pleidae.

Lastly, I'd like to keep moving down the size scale to look at the water mites - arachnids of the suborder Hydracarina. These are mostly bulbous and the body in not separated into separate sections (cephalothorax and abdomen) as would be seen in the suborder Oribatei. Identification is tricky, but Hopkins (1961) can be downloaded from free here and is very useful for those beginning to study this tricky, and again often-overlooked, group. I won't go into detail about the identification here, but the water mite I investigated was Piona coccinea - a red species around 2-3mm long, red and globose in form.

That's where I'll leave pond-related matters for today - more soon!

The water mite Piona coccinea.

References

Denton, J. (2007). Water Bugs and Water Beetles of Surrey. SWT, Woking.
Gregory, S. (2009). Woodlice and Waterlice (Isopoda: Oniscidea & Asellota) in Britain and Ireland. NERC/BRC, Wallingford.
Hopkins, C.L. (1961). A key to the water mites (Hydracarina) of the Flatford area. Field Studies 1(3): 45-64.