Of the 33 charophyte species recorded from the UK and Ireland, 4 (Chara baltica, Chara canescens, Lamprothamnium papulosum, and Tolypella nidifica) have a strong affinity for brackish water habitats (Stewart and Church 1992). All four species are considered rare and threatened (UKBG 1999).

The most frequently recorded species in saline lagoons is the foxtail stonewort (Lamprothamnium papulosum) and it is considered a lagoonal specialist. It usually grows on sand, gravel or pebbles in less than 2 metres water depth, and is intolerant of strong water currents or wave action. Previous British and Irish work indicates that Lamprothamnium papulosum occurs within a salinity range of 10 ppt to 30 ppt, but studies elsewhere have found viable populations in up to 40 ppt whilst recent work in Britain has found the species in sites as low as 5 ppt (Martin 1999). It is often found where there is some disturbance from birds or animals, or in shallow water where fluctuations of water level result in more open vegetation (UK Biodiversity Group 1999). It usually occurs with tasselweed Ruppia spp., but does not compete well with dense vascular plant growth (Li 1997). It is a summer annual, germinating in spring, with oospores produced between July and September.

Charophytes such as Lamprothamnium papulosum are associated with clean, unpolluted water because most species cannot tolerate high levels of phosphates and nitrates (Bingham 1997), probably due to their inability to successfully compete with dense growths of filamentous algae such as Cladophora spp. Nutrient enrichment has been implicated in the decline of brackish charophyte species (Martin 1999). In Denmark, Sweden and Norway, Lamprothamnium papulosum populations have been severely reduced, with anthropogenic induced eutrophication and consequent competition for light and space suggested as the probable cause (Blindow and Langangen 1995, in Martin 1999) similar evidence has been found in the Netherlands (Coops and Doef 1996, in Martin 1999).

More recent research has found Lamprothamnium papulosum to be absent where soluble reactive phosphate (SRP) levels exceed 30 g/l in the water column and total phosphates (TP) are about 100 g/l (Martin 1999). These maximum values both come from the Fleet (at Herbury). Based on survey of 40 potential and known sites, Lamprothamnium papulosum most frequently occurs at sites with SRP of less than 10 g/l and TP less than 50 g/l (Martin 1999).

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