WATER­SIDE WILDLIFE

Even with ice on the canals, there’s still life to be found if you know where to look for it, Pip Web­ster ex­plains...

Canal Boat - - This Month -

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…

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