Chesil Beach is one of the three major shingle structures in Britain and is of international importance for coastal geomorphology. Along about half its length it encloses the Fleet, the largest tidal lagoon in Britain. This, together with the Beach and associated habitats, incorporates a site that is of international importance to wildlife. The fossil-rich and stratigraphically important sequence of Jurassic strata exposed along the landward side of the Fleet adds further value to the site.

Special Areas of Conservation (SACs) are strictly protected sites designated under the EC Habitats Directive.

The primary reasons for selecting the Fleet as a SAC are its habitats listed in Annex 1.

1150 – Coastal Lagoons (priority feature)
The Fleet, is the largest example of a lagoonal habitat in England and has features of both lagoonal inlets and percolation lagoons. It is bordered by the fossil shingle barrier beach structure of Chesil Beach, through which sea water percolates into the lagoon, but most of its water exchange occurs through the narrow channel that links it to Portland Harbour. A low freshwater input produces fully saline conditions throughout most of the Fleet, with reduced salinity occurring only in the west. The lagoon is extremely sheltered from wave action and has weak tidal streams, except in the eastern narrows and entrance channel. The tidal range is much smaller and temperature range far greater than on the open coast. The lagoon supports extensive populations of two species of eelgrass Zostera and three species of tasselweed Ruppia, including the rare spiral tasselweed R. cirrhosa, and a diverse fauna that includes a number of nationally rare and scarce species.

1210 – Annual vegetation of drift lines
Chesil Beach is a large (28 km-long), relatively undisturbed shingle bar, and is one of two representatives of Annual vegetation of drift lines on the south coast of England. The inner shore of the beach supports extensive drift-line vegetation dominated by sea beet Beta vulgaris ssp. maritima and orache Atriplex spp. This community exists in a dynamic equilibrium with the perennial shrubby sea-blite Suaeda vera community typical of 1420 Mediterranean and thermo-Atlantic halophilous scrubs (Sarcocornetea fruticosi), for which this site has also been selected.

1220 – Perennial vegetation of stony banks
The shingle bar of Chesil Beach, including Portland Harbour shore, is an extensive representative of Perennial vegetation of stony banks on the south coast of England, and most of it is relatively undisturbed by human activities. Much of the shingle bar is subject to wash-over and percolation in storm conditions and is therefore sparsely vegetated. It supports the most extensive occurrences of the rare sea-kale Crambe maritima and sea pea Lathyrus japonicus in the UK, together with other grassland and lichen-rich shingle plant communities typical of more stable conditions, especially towards the eastern end of the site.

1420 – Mediterranean and thermo-Atlantic halophilous scrubs
Chesil and the Fleet contains a major concentration of Mediterranean and thermo-Atlantic halophilous scrubs in the UK. A band of shrubby sea-blite Suaeda vera and sea-purslane Atriplex portulacoides lines much of the 13 km length of the seaward margin of the Fleet. The community forms a clear zone between the Fleet and the shingle vegetation of Chesil Bank. It appears to exist in a dynamic equilibrium with Annex I type 1210 Annual vegetation of drift lines dominated by sea beet Beta vulgaris ssp. maritima, for which the site is also selected. This replaces the scrub in areas subject to disturbance, and is in turn displaced by the scrub after disturbance ceases.

1330 Atlantic salt meadows (Glauco-Puccinellietalia maritimae)
Atlantic salt meadows develop when halophytic vegetation colonises soft intertidal sediments of mud and sand in areas protected from strong wave action. This vegetation forms the middle and upper reaches of saltmarshes, where tidal inundation still occurs but with decreasing frequency and duration.

As this marine area has been designated as a SAC and the SPA, it is referred to as a ‘European Marine Site’ (EMS), which are protected under the EC Habitats and Bird Directives.