Original paper

The freshwater-algal flora of the Kent and Sussex Weald, UK: 160 years of change

Pentecost, Allan


The freshwater algal flora of a small area of southern England undertaken in 1842–1845 is compared with a survey undertaken in 1999–2002. In the first survey, 72 sites returned 592 records of algae and comprised 208 currently recognisable taxa. In the recent survey, only 45 % of these taxa were re-found. Taxonomic groups that fared particularly badly were the Chlorophyta (55 % loss) and the Charophyta (80 %). Losses were also apparent in the Cyanobacteria (60 %), Bacillariophyta (48 %) and Xanthophyta (50 %). All of the freshwater Rhodophyta were found extant though few species had been recorded. The most significant losses were within sub-orders of the Chlorophyta. The Desmidiineae fared worse (62 % loss) while most of the Closteriineae were re-found (27 % loss). Losses within other sub-orders of the Zygnemataceae and the Oedogoniales appeared significant but may instead indicate reduced fertility.The selective loss of algal taxa within particular phyla/families reflect both the ecological preferences of the phyla/families and biased recording of the larger, more conspicuous algae. The significant change in the flora within the period is attributed to seven factors, the three most important being changes in farming practice, site drainage and eutrophication. The remaining factors are air pollution, lake- and stream bank modifications, fish-farming and climate change.While some dramatic losses have occurred since the 1840s, many new taxa were recorded during the recent surveys, indicating a shift in community structure. Locally rich habitats still exist but are threatened by further human interference.