Just before the trip to the Shetland Islands I wrote about in the previous post, I spent two days in the Lake District teaching a course on identifying macroalgae for the Freshwater Biological Association. It coincided with a period of gorgeous weather, showing Windermere at its absolute best (as the photo at top of the post shows). Only a month ago my wheels were spinning in the snow on Whinlatter Pass (see “How to make an ecosystem (2)”).
Looking up Windermere towards the high peaks of the Lake District’s volcanic centre, I find myself reflecting on how geology creates the diversity in landscapes and aquatic features that, in turn, creates variety in the microscopic flora and fauna (see “The Power of Rock”). A nuanced understanding of the aquatic world requires one to view the grand panorama at the same time as focussing on organisms that are scarcely visible with the naked eye.
One of the locations that we visited during the course was Cunsey Beck, which flows out from Esthwaite Water and, a few kilometres later, into Windermere. Esthwaite is one of the more productive of the lakes in this region and we usually find a healthy crop of algae in the beck. This year was no exception and, amongst the different forms we collected were some long straggly growths that had a slighty gelatinous feel. Back at the laboratory we put part of one of these growths under the microscope and saw a large number of individual cells set in a jelly matrix. This identified the alga as Tetraspora gelatinosa, a green alga that I have written about before (see “More from the Atma River …”) although not for some time.
Tetraspora gelatinosafrom Cunsey Beck, Cumbria, May 2019. The picture frame is about five centimetres wide.
The genus Tetraspora gets its name from a mode of division that leaves many of the daughter cells in groups of four (visible in the lower illustration). These, in turn, are embedded in mucilage, and repeated divisions can lead to growths becoming visible with the naked eye. Three species have been recorded from Britain and Ireland, of which the Cunsey Beck population is most likely to belong to T. gelatinosa. In the past, it might have been called Tetraspoa lubrica, which has a more tubular thallus; however, this is now thought to just be a growth form of T. gelatinosa that is associated particularly with fast-flowing rivers. As far as I can tell, no-one has performed any detailed molecular genetic studies on this genus to better understand the relationships between these different growth forms so we will have to go with current convention for now.
Tetraspora gelatinosaunder the microscope. Cells in the foreground are about ten micrometres in diameter. Photograph by Hannah Kemp.
I’ve seen Tetraspora in a wide range of habitats – on stones in fast-flowing, relatively soft water rivers in Norway and growing on plant stems in the littoral zone of hard water ponds in Ireland. Most of my records are from the spring, though I should add that spotting some of the smaller gelatinous colonies (barely more than near-transparent dots on the stone surface) does take some practice and I suspect that I have missed it on a few occasions too.
The microscopic image of Tetrasporawas taken during the course using a Carson Hookupz, a neat device which allows a smartphone to be attached to a microscope (or any other optical device). It takes a little fiddling to get the set-up right but, once this has been achieved, the quality of pictures we obtained was excellent. My microscope engineer tells me that he is selling large numbers of these to schools and colleges as it means that students can capture images during practical classes that they can subsequently use in reports or just (as was the case during our course) as an aide mémoire.
The Carson Hookupz 2.0 as it comes out of the box (left) and (right) in action during the Identifying Macroalgae course at the Freshwater Biological Association.
Looking north from Miller Ground towards the central Lake District peaks as the sun sets. The photograph at the top of the post was taken from nearby but shows the view in early morning.