This reports a 1991 repeat survey of that done in 1985, which followed a more extensive survey in 1983. All were carried out during August. Ruppia cirrhosa, Zostera noltii and Z. angustifolia were all thriving in the Fleet in very similar proportions to those reported in previous surveys. The nationally rare alga Lamprothamnium papulosum had extended its range and abundance.

The west-east and north-south zonation of species reported from previous surveys was confirmed. Ruppia cirrhosa was very dominant west of Rodden Hive Point, but then gives way gradually to Zostera eastwards down the Fleet. Z. noltii thrives best along the northern coves, whilst Z. angustifolia dominates along the shore in the shadow of Chesil and the main body of the Fleet. The decline of Ruppia cirrhosa recorded in 1985 has been shown by the 1991 surveys to be a temporary phenomenon. Lamprothamnium papulosum was found to be thriving better in 1991 than it had on previous surveys. In all surveys, this plant was always found associated with coarse sandy/gravel substrata where minimal amounts of organic matter were present.

[NB. Z. angustifolia is thought by other workers (den Hartog 1989, Brenchley & Probert 1997) to be an ecological/environmental variation of Zostera marina.]

The various recent potential threats to the seagrasses of the Fleet (invasion by Japanese seaweed Sargassum muticum, changes as a result of realignment of Smallmouth [in 1984?], and storms in 1989) do not appear to have had any adverse effect on Ruppia, Zostera and Lamprothamnium papulosum in the Fleet.

Whilst not directly mentioned in the text, records for % cover of algae Cladophora agg., Enteromorpha and Ulva are given for each of the 100+ quadrats surveyed in 1991.

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