ANABAENA, A TOXIC BLUE-GREEN ALGA CONTAMINATING LAKES IN EAST ANGLIA

G . D.HEATHCOTE

During the summer droughts of 1989 and 1990 several reservoirs and lakes in East Anglia were 'attacked' by a mysterious blue-green slime which was eventually shown to be growth of a toxic blue-green alga. It first caused trouble at Rutland Water and 18 sheep and 12 dogs died after drinking the water. Some soldiers who swam in affected water also became severely ill (pers. comm. Mr. Ian Hill of the National Rivers Authority). The public was assured that normal filtration was sufficient to render infected water harmless but it was necessary to prevent people from swimming or sailing on those waters and to keep animals away. The alga thrived in the hot weather, especially where there was a high phosphate content to the water from fertilizers and other agricultural chemicals. Anglian Water spent £2 million applying ferric sulphate to diminish the growth of the alga.

My nearest affected stretch of water was a large flooded gravel pit at Flempton near Bury St. Edmunds, used by Flempton Sailing Club. On 20th August 1990 the Environmental Health Department of St. Edmundsbury Borough Council posted a notice informing the public that the National Rivers Authority had found the blue-green alga Anabaena in the lake and warning everybody to keep away from the water. The alga has been known to cause a skin rash, eye irritation, vomiting, diarrhoea, fever and pains in muscles and joints. Few would wish to swim in the lake after such a warning! Of course the Sailing Club closed the lake temporarily.

When I visited the lake in September 1990 there was a band of blue-green scum a metre or so wide in patches round the edge of the water, and pale brown scum extending over the mud at the edge of the lake. The scum had the consistency of emulsion paint (thick enough to retain the footprints of the water birds for some time) and it had a foul smell, more like pig slurry than stagnant mud. It could be described as 'moss coloured', but with a trace of blue when it dried. Nearby waters were unaffected.

It is not surprising that the identity of this unwelcome addition to the freshwater flora was not immediately obvious. The blue-green algae (Schizo-phyceae, or Cyanophyceae in an earlier classification) are a group of microscopic plants with uncertain affinities. They are today considered closer to the bacteria than to other green algae (Chlorophyceae). They can occur as individual roundish cells or linked together in chains of many cells. Individ-ual cells are very small but they can occur in quite large gelatinous masses. Peter Wanstall and I found Nostoc forming dark brown gelatinous masses the size of plums in fast-flowing streams in the Pyrenees. Blue-green algae are common on damp mud and the trunks of trees.

Anabaena belongs to the Chroococceae group of blue-green algae, simple roundish cells consisting of a cell wall of cellulose and pectic substances containing a hollow, blue-green sphere (chromoplasm) with colourless tissue (centroplasm) inside. There are no chloroplasts, vacuoles or true nuclei.

Trans. Suffolk Nat. Soc. 27 (1991)

ANABAENA, A TOXIC BLUE-GREEN ALGA 35

Sexual reproduction is unknown and asexual reproduction is by simple fission.

The cells contain not only chlorophyll and carotin but also pigments (phycocyan and phycoerythrin) which respond to light, changing from green to red. It is these pigments in blue-green algae which can cause 'sea bloom' in warm seas. One such toxic alga, Trichodesmium erythraceum, probably gave rise to the name of the 'Red Sea' between Africa and Arabia, and was the cause of one of the seven plagues of Egypt; 'when the Nile turned into blood, and the fish died, and the river stank, so that the Egyptians couldn't stand to drink the river' (Exodus, 7, 20). Toxic blue-green algae can occasionally make shellfish dangerous to eat, but seldom in Britain.

Many of these algae are free-living but some live in close association with other plants. The most well-known association is with fungi (mostly Ascomycetes) to form lichens; green algae may be associated with fungi in the same way. Blue-green algae can make a major contribution to the nutrition of lichens as some have the ability to 'fix' nitrogen in the air in the same way as nodule bacteria do in the roots of Leguminosae.

Anabaena has a particularly interesting association with Water Fern, Azolla filiculoides Lam., (Pteridophyta, Azollaceae), which I found on a pond at Barrow, in west Suffolk, some 5 miles from Flempton (Trans. Suffolk Nat. Soc., 18, 298). This year I found Azolla in the River Stour at Rodbridge picnic site, south of Long Melford. It appears to be spreading in the west of the County. A. filiculoides is an introduction from America but has become naturalised in some areas. The fern is free-floating and consists of overlapping lobes from which hang numerous roots. Anabaena can always be found within cavities in the fronds. A note with the record of Azolla from Southwold (Trans. Suffolk Nat. Soc. 18, 233) comments: 'the plants had turned red over a whole dyke in May, 1989, possibly as a result of late frost. ' I have seen Azolla bright red not only at Barrow but also at Lewes Levels in Sussex, and I suggest it is more the quality of the light affecting the Anabaena (i.e. changing it from green to red) than an affect of temperature on the fern.

Although blue-green algae are extremely widespread they are also ex-tremely small and therefore difficult to study. They will probably only be

Blue-green alga greatly magnified Azolla filiculoides

Trans. Suffolk Nat. Soc. 27 (1991)

36 Suffolk Natural History, Vol. 27

thought of interest to most of us when they are infecting our fresh water. They should cause little harm in cooler, wetter conditions. Anabaena is normally common only in late summer, disappearing as lake water is mixed by gales and drop in temperature during the winter. In spring its growth is restricted by competition with diatoms and other algae.

Dr G . D. Heathcote, 2, St. Mary's Square, Bury St. Edmunds, IP33 2AJ

Trans. Suffolk Nat. Soc. 27 (1991)