Booterstown Marsh is the last remaining part of a saltmarsh which fringed most of the southern shore of Dublin Bay at one time. It is a most important educational resource for biology students and the teaching of ecology. Also it is one of the few areas in the Dublin area where a variety of birds can be easily seen. An ecological survey of the marsh was carried out in 1970 by Roger and Olivia Goodwillie and Erica Brandt. This survey forms the basis of this account.

Plants and flowers
A freshwater inflow complicates the situation at Booterstown. as it often does elsewhere, and gives rise to a good example of a marsh transitional between fresh and saltwater condition. Water entering the marsh from the culvert close to the road has the effect of driving the salt influence nearer the sea. It creates a small zone of freshwater marsh at the base of the roadside slope. The slope itself is covered by plants of disturbed soils - the weeds of our fields and gardens. Creeping thistle (Cirsium arvense) and the great willow herb (Epilobium hirsutum) are conspicuous. Early in the year the yellow flowers of coltsfoot (Tussilago farfara) may be seen pushing up through the ground on leafless stems. The leaves appear later - large and rounded with a felt of white hairs on the back. Bindweed (Calystegiasepium) twines around the other plants and produces its white trumpet-shaped flowers in July and August while another climber, traveller's joy (Clematis vitalba) clings by its twisted leaf stalks. Other woody species which soon spread to any open site are bramble (Rubus fruticosus), furze (Ulex europaeus) and a willow (Salix fragilis).

At the base of the slope the willow herb is still noticeable around the inflow with watercress (Nasturtium officinale) and fool's watercress (Alpium nodiflorum) - its green flowers in umbrella-shaped groups. The pond is the main feature here: it is shallow buy has a good depth of soft silt underneath. Along its edge and spreading seawards in large patches is the sea clubrush (scirpus maritimus) which is a bright green colour in growth but a pale brown in Winter. Look for its little black flower heads beside the railway station, in the corner of the marsh most frequently flooded. A close relative grows at the northern end of the pond, the grey clubrush (Scirpus tabernaemontami), but in this case the plant has no leaves and grows with its spiky blue-green stems. Here too and at intervals around the pond you can see the celery-leaved buttercup (Ranunculus sceleratus), a plant with pale green leaves and pale yellow flowers, and. with a bit of luck, the wild celery (Alpium graveolens). the original form of the cultivated type.
The largest area of ground on the marsh is covered by grasses. The fine-leaved red fescue (Festuca rubra) dominates the central section of the sea-side of the pond while creeping bent (Agrostis stolonifera) grows south, north and east of this. It has trailing stems and a head of minute brownish flowers. Species of dock (Rumex) occur among the grass with silverweed (Potentilla anserina). Tall fescue (Festuca arundinacea) is an imposing grass growing in clumps amongst this vegetation and you may also find the fox sedge (Carex otrubae) with spiky brush-like heads on sharply triangular stems. A prominent pile of soil is covered by scutch grass (Agropyron repens), and nettles (Urtica dioica).
Scattered through the other plants and forming distinct patches towards the southern end is the saltmarsh rush (Juncus gerardii). It is a low-growing plant no more than 30cm high and has black shining flowers. A number of parallel ridges (old potato beds) can be seen at the southern end of the marsh and the rush grows along most of the ditches between them. Two small pink-flowered plants are associated with the rush: sea milkwort (Glaux maritima) which bears its flowers among crowded leaves, and sea spurrey (Spergularia marina) with needle-like leaves. The lowest places in these ditches often have water in them. In summer this evaporates, leaving a whitish deposit of salt on the mud. A straggling spinach-like plant orache (Atriplex hastata) springs up in this situation and there is also a little samphire (Salicornia europaea). The most conspicuous plant on the saltmarsh, however, in August is the mauve sea aster (Aster tripolium) which brightens much of the seaward part, especially along the ditch beside the railway.

Birds and insects
The mud surface of the marsh is organic and very soft. The oligochaete worm (Tubifex) thrives here as it contains haemoglobin which allows full use of the little oxygen present in the mud. Two freshwater molluscs (Sphaerium corneum) and (Pisidium amnicum) together with another oligochaete worm (Eiseniella) also occur here together with (Asellus aquaticus). The rich diversity and abundance of the invertebrate populations plus the vegetation cover make the marsh an attractive habitat for birds. Mallard, moorhen, sedge warbler and reed bunting have been recorded breeding in the marsh while during the winter the area is important for snipe which can be seen standing by the edges of the ponds - Booterstown is one of the only marshes in the county where snipe can be seen in the open during the day. Redshank and oystercatchers are also frequent users of the marsh while black headed gulls and herons frequently roost in the marsh. During high tide conditions in the winter, the marsh is an important site for waders feeding in Dublin Bay - dunlin, knot, bar-tailed godwit, ringed plover, turnstone and sanderling. In summer, swallows and swifts are frequently seen over the marsh "hawking" for insects flying above the marsh. The best place to observe the birds is from the main road.

REFERENCES
GOODWILLIE, R. & O. and BRANDT, E. 1970 Ecological Survey of Bull Island mud flats and Booterstown marsh. Student thesis, Department of Botany, Trinity College, Dublin. Dublin.
AN FORAS FORBARTHA 1973 Areas of Scientific Inurest in County Dublin. AFF, Dublin

Used with permission from 'The Book of Dún Laoghaire' by John O'Sullivan and Seamus Cannon, 1987