Monitoring macroinvertebrates and diatom populations in East Stoke, Dorset

As part of a long term, collaborative research project between BU and the FBA, PhD researcher Tadhg Carrol and BU research assistant Jack Dazley have been assisting freshwater biologist John Davy-Bowker in sampling two rivers in East Stoke, Dorset for aquatic macroinvertebrates (such as insect larvae, aquatic worms and water beetles) and diatoms (microscopic plants with a glass-like ‘shell’). The research aims to understand how environmental changes, such as increased temperature and altered riverbed composition, affect the abundance and species diversity of these groups.

Samples were collected from 5 sites at each river – the Frome and the Piddle, where a square sampling area 10m wide was set up from each bank. Macroinvertebrates were collected using the kick sampling method (pictured), whereby the person sampling would rigorously kick the river bed, exposing mud and stones, and with them the invertebrates, which flow into the net. Environmental measurements were also taken, and included width and depth of the site, percentage cover of each species of aquatic plant, and substrate composition of the riverbed (i.e. what types of rocks/stones are present). Once collected, the samples were preserved to allow identification at a later date.

Diatoms were also collected from each site, and were done so by collecting 5 large stones (one from each corner of the site and one from the centre) which had clearly visible signs of algae growing on them, such as green mats on the surface. Using a toothbrush, a section of the green mat was scrubbed off into a plastic tray to collect the diatoms, and to work out the abundance the scrubbed area was traced onto acetate. The diatoms were preserved to be analysed at the lab.

Alongside collecting macroinvertebrates and diatoms, careful note was taken in the Piddle upon the capture and rerelease of protected species, including bullhead fish and white clawed crayfish. These native crayfish are particularly monitored as they are susceptible to diseases carried by the non-native signal crayfish. Infact, the Piddle is thought to be one of the only sites in Dorset where the white clawed crayfish is relatively abundant.

This project is incredibly important to understanding the future of river communities from a bottom up perspective – diatoms and macroinvertebrates form the basis of the food chain in river ecosystems, and so support larger freshwater organisms such as fish and birds.