15-Jan Hidden Activity Below the Surface

Summary

We take a fascinating dive into the vibrant world of pondlife during winter on 15th January. From the tiny water fleas and copepods to the captivating flatworms and algae, this article will reveal the surprising abundance of life in London's ponds and rivers. Learn about the unique adaptations and behaviors of these small but mighty creatures that thrive even in the coldest months. Don't miss out on this intriguing exploration of nature's hidden winter wonders!

Article

Pondlife

In January, when there is such an absence of animal activity on the ground, it is a surprise to see how much is going on below the surface of a pond. There is always a proliferation of life where land meets water and even in the depths of winter at the edge of a London pond the same is true.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

Although in much smaller numbers than later in the year, there are still a whole host of tiny active animals and plants to be seen. In the water itself there are water fleas Daphnia spp. and copepods e.g. Cyclops which are easily visible with the naked eye.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

Under the microscope the beating heart of the former can be quite clearly seen. In among dead vegetation water lice Asellus aquaticus are often abundant as are lesser numbers of water mites, molluscs and mayfly, damselfly and caddis fly larvae.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

The surface of the muddy ooze is the best place to take samples, using a pipette to catch amoebae, flagellates, ciliates, rotifers, oligochaetes and nematode worms. On the surface meniscus of spring fed ponds such as those on Keston Common there are often large numbers of springtails looking a little like dancing soot. The edges of rivers have an equally rich assemblage of animals and plants which even in January usually include some water shrimps Gammarus pulex, sticklebacks as well as some molluscs and leeches.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

Many of the most surprising and captivating creatures in a pond are a mere hundredth or a thousandth of a centimetre long. With a microscope needed to see them they were unknown to almost anyone until the eighteenth century and are still largely unknown to most Londoners today. The variety of shape, form and mobility of these tiny creatures is truly immense. With a little practice, even amoebas can be seen with the naked eye moving across the surface of a glass sampling jar.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

Often thought of as the simplest form of life, it is quite mesmerising to watch under a microscope these colourless dots of protoplasm gently flowing across a surface, and then engulfing any prey in their path with their arm-like pseudopodia.

Other than the surface of the mud it is also worth taking samples from semi-decayed pieces of submerged vegetation. The variety of algal flora in such situations can be immense. It is particularly worth looking for diatoms, which have many different sculptural shapes but are also noted for the beautiful and patterns on their silica cell walls.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

Other algae with interesting shapes include the desmids and in mild winters blooms of the desmid Stephanodiscus astraea occur in London’s reservoirs. Other common algae such as Spirogyra with its spiral chloroplasts are filamentous and immobile, whereas species such as Chlamydomonas can be seen moving rapidly around mud particles using their small whip-like threads to project themselves. Darwin recorded 537 different species in a single cup of mud.

Flatworms

There are eight species of free-living flatworm to be found in London’s ponds and rivers. The one most likely to be seen is Polycelis nigra. This is a black flattened worm with a wedge-shaped head which is usually first noticed gliding along the surface of a glass sampling jar. This gliding motion is achieved by vast numbers of tiny moving threads called cilia which cover its surface. Polycelis nigra, unlike some of the other species, is typically deep black and so its internal organs cannot be seen although its eye spots can. There are up to thirty of these ‘eyes’ along its front edge and others continuing down the side of its body.

15-Jan Hidden Activity Below the Surface Section Image

15-Jan Hidden Activity Below the Surface Section Image

These odd-looking worms have a number of other unusual features. If a worm that has learnt how to locate a particular food is killed and then fed to another, the worm that ate it acquires the same skill. To eat, these worms extrude their pharynx from their mouth at first to sample a piece of carrion, then draw the food back into their body to digest it.

In pale species such as Dendrocaelum lacteum the patterned multi-branched gut is quite visible. This may be different colours depending on what the worm has recently eaten. Dendrocaelum lacteum is one of four different species that can be found in the ponds on Bookham Common. Flatworms are also famous for their powers of regeneration. When cut into several pieces each piece will regrow into a new worm.

Some are even known to tear themselves apart as a method of reproducing themselves. Other species such as Dugesia tigrina and D. polychroa are found under stones in London’s rivers. It is their shiny, round flattened egg discs attached to stones that are usually noticed first.