Even with ice on the canals, there’s still life to be found if you know where to look for it, Pip Webster explains...
Even if there’s ice on the canals, there’s still life to be found if you know where to look
Winter… when you feel the bone structure in a landscape – the loneliness of it – the dead feeling…” (Andrew Wyeth – 20th Century American artist). The bare branches of the deciduous trees and brown, decaying plant matter make midwinter feel very bleak, but there are still plants growing, including one that is purported to be the most abundant organism on the planet. The tiny green alga,
Pleurococcus, grows all year round – you may even find some established on your narrowboat (it certainly likes my drainpipes). A singlecelled alga, Pleurococcus thrives in moist situations and is commonly found on the bark of deciduous trees, more abundantly near the ground on the north side. It spreads upwards in the wan winter sunlight to dust the bare limbs with a thin emerald sheen. The more acidic surfaces of conifers are avoided, but you will also find it growing on stones, fences and lock gates. When a colonising
Pleurococcus lands on a surface, it releases a carbohydrate-rich slime that sticks the cell in place, then produces a new colony by cell division. The spherical cells have heavy cell walls that protect against excessive water loss – they would dry out in full sunlight. The closest relatives of
Pleurococcus live in freshwater, but there is fossil evidence of algal mats living on land from over half a billion years ago. Many organisms evolved once they had a foothold on land to give us the diversity of plants today, but the ancestor of Pleurococcus has changed very little.
These vertical pastures are welcome food for herbivorous invertebrates such as woodlice and millipedes that are active through the winter months. They ascend the trees, usually under cover of darkness, to scrape a living from the rich algal bloom on the bark.
Also active in the depths of winter are the so-called winter gnats that you can often see swarming in sheltered spots, especially when warmed by a shaft of winter sunlight. They emerge from larvae that live in rotting vegetation, such as drifts of decaying autumn leaves. The jigging clouds of dancers are exclusively male, trying to attract females to mate with – and no, they don’t bite! The females lay their eggs in decaying wood or on fungi and the larvae emerge in the spring before it gets too warm and dry.
‘Gnat’ is a term loosely applied to any small, twowinged fly that forms swarms. There are about nine different species of winter gnat and they resemble small daddylonglegs. They are actually flies in the genus Trichocera, about 6 to 8 mm long with long transparent wings. Abundant gnats can be an important winter food source for birds and spent gnats landing on water provide welcome snacks for hungry fish. Anglers use the pattern of the body shape of the gangly gnat when tying fishing lures.
There are very few plants floating on or near the surface of the canal in winter. Ice is potentially deadly for floating plants, and they survive by producing winter growth that sinks to the bottom of the water, out of harm’s way. Frogbit produces winter-buds (turions), consisting of tightly packed leaves rich in starch, on the creeping submerged stems. These dense buds drop off the dying parental plant and sink to the bottom where they remain dormant until spring growth starts. As the starch is used up, air spaces appear in the leaves and the now lighter buds float back up to the surface and daylight where they develop into a new plant.
Greater duckweed performs a similar clever trick – specialised purplish thalli (the name given to the small leaf-like structures of duckweed which combine the properties of leaf and stem) are produced in the autumn which become detached and sink to the relative safety of the warmer depths. In the smaller common duckweed (thalli bearing a single root), the whole plant fills up with starch and sinks from sight. It’s one way to survive the bleak midwinter…