FRESHWATER ALGAE
P.A. Gainey and P.E. Tompsett
The algae are an abundant and diverse group occurring in seas, oceans, river systems and standing water where they can be found attached, free-floating or loosely associated with hard surfaces or sediments. The freshwater and terrestrial algae have received far less attention than the marine algae (seaweeds) and are consequently relatively poorly understood and recorded. Gainey, in Spalding, A. (Ed.) 1997, has reviewed the status of the rarer species of charophyte (stoneworts) present in Cornwall and the Isles of Scilly. More recently two species of desmid (Chlorophyta: Brodie et al., 2007) and one species of red alga (Rhodophyta: Monaghan, 2009, pers. comm.) have been considered for potential Red Data Book listing in Cornwall. The authors are indebted to Professor Juliet Brodie, Natural History Museum, London, and Elaine Monaghan, Freshwater Biological Association, Cumbria, for their assistance in the preparation of this section.
1. Chlorophyta
1.1 Charales (Stoneworts)
Many species of stonewort, particularly those of the genus Chara, secrete calcium carbonate crystals onto their outer surfaces. The greatest diversity of charophyte species tend, therefore, to occur in highly calcareous sites such as are found on the coastal sand dunes on the north Cornish coast and in quarry and heathland pools on the Lizard Peninsula, where the water overlies the ultramafic serpentine rocks. Stewart (1996) lists south west Cornwall as one of the key areas in Britain for stoneworts, with 15 species having been recorded (some 40% of the British stonewort flora). More recently, Stewart (2004) cites the Lizard heathlands and quarries to be of National and European importance. The Red Data Book of Stoneworts (Stewart & Church, 1992), lists one RDB species and one Nationally Scarce species found in Cornwall since 1970. In a more recent review, Stewart (2004), lists one RDB species and two Nationally Scarce species to be present in Cornwall. A further four species, Bearded Stonewort Chara canescens (VC1), Slender Stonewort Nitella gracilis (VC1), Many-branched Stonewort Nitella hyalina (VC1) and Tassel Stonewort Tolypella intricata (Isles of Scilly), all RDB species, have not been recorded in the region since before 1970. Records for Chara baltica on the Lizard Peninsula and elsewhere in Cornwall, which appear in the Red Data Book (Stewart & Church, 1992) are now thought to be incorrect (Stewart, 2003).
Chara curta Lesser-bearded Stonewort
Chara fragifera Strawberry Stonewort