A clean sweep of waders and divers

The binoculars wait on the window-sill these mornings, the better to scan the strand for promising-looking objects on the tideline. After weeks of great waves pushing in from the west, one has the right to hope for an interesting delivery: a giant squid would do, or a walrus; even a new shell, or a drift-seed.

To venture out early, in a wind still whipping up the sand in long, rustling skeins, is to expect reward for effort; something better than a drowned island sheep on a bier of kelp and seapinks, or a conger pecked to death in mid-squirm. But nature's lottery continues to disappoint. The dog comes back from her fruitless chases after seabirds, blinking through a mask of sand. We shrug and turn for home.

On a strand as dynamic and mobile as ours, it's amazing how quickly the latest driftline vanishes: long furls of laminaria, the sheep, the plastic bags and bottles turned into the maw of the sand with all the prompt efficiency of a modern garbage lorry. I imagine, somewhere beneath, the marbled strata of plastic working their way down to bedrock.

On less exposed shores, the flotsam and jetsam accumulates into a sort of linear compost-heap, a fairly constant, modest tangle at the tideline. And at some corners of a rocky coast, whole beaches can disappear in winter under a thick, slithery mattress of stipes and fronds torn up from the offshore kelp forest.

Since nature lets nothing go to waste, all this organic material is reprocessed. Some of the scavengers are obvious: the ravens and black-backed gulls cleaning up the sheep; the fox, out ahead of me, its footprints winding single-file among the crabshells.

Others animals are largely invisible, working away in what, for them, is a self-contained ecosystem at the interface of land and sea. The little amphipods called sandhoppers, for example, are often there in millions, but can't swim very well. They spend their days in burrows at high-water line, hiding from the birds, and emerge at night to scavenge omnivorously on rotting weed and other detritus.

In Britain, where house-proud tourist resorts like to keep their beaches "clean", many local councils have replaced their human litter-pickers by machines that rake away the entire tideline. In Cornwall, for example, more than 200 kilometres of beaches are scoured in this way.

Sandhoppers breed in the summer months and need their seaweed. And where amphipod numbers are high, local bird populations thrive. On machine-raked beaches in the bays of south Wales, the amphipod count is meagre and the number of wading birds visiting in winter has fallen off sharply. In sandy beaches in Scotland, regular beach-raking has been blamed for dune erosion, since a seaweedy tideline and the plants that take root beyond it are part of an ecosystem that keeps the sand stable.

Apart from the general ecological moral, this may not seem all that relevant to Ireland as we have known it, "pristine" beaches and all. But another aspect of beach hygiene, currently concerning ecologists in Britain, certainly has its parallels on this island.

The EU directives on coastal water quality and clean-beach standards have put great pressure on the Republic and the UK, long used to pumping sewage through outfall pipes or dumping it at sea. At Dublin, Cork and Galway, costly new treatment plants will cut off the flow of nutrients into the city bays - organic material that, for more than a century, has nourished marine worms, snails and shellfish and all the birds that feed on them.

In Britain, the results are already beginning to exercise ornithologists. The closure of a sewage outfall in the Mersey Estuary in the 1980s has been linked to the disappearance of some 20,000 waders from the usual winter flocks. The Northumbrian Water company is supposedly concerned that providing more sewage treatment could lead it to break EU directives which protect coastal areas important for waders.

In Ireland, too, the same effects are beginning to be noticed. At Dun Laoghaire harbour, a sewage outfall has been closed and the sewage piped into a treatment works. The result, say local birdwatchers, has been a great reduction in the interesting winter ducks and divers which used to turn up behind the West Pier.

Dublin Bay and Cork harbour are two of the Republic's most important winter wetlands for wildfowl and waders, and the capital's Bull Island, with its wheeling clouds of knot, dunlin and bar-tailed godwit, probably draws more birdwatchers than anywhere else. The waders and ducks harvest millions of the Hydrobia water snails that graze the surface skin of algae on the mudflats (one shelduck was found with 3,000 snails in its stomach), or probe the burrows of teeming colonies of sandhopper-like amphipods, Corophium.

Ecologist Roger Goodwillie, who has analysed the available prey of the birds, points out that the size of their flocks "indicates the prodigal nature of the ecosystem". Estuarial mud downstream from a city founded by the Vikings must always have been rich in nutrients, and, even when the raw flow ceases, the bay's sediment could go on releasing chemical nourishment for a considerable time.

Ultimately, however, the city bays seem certain to lose some thousands of winter birds, and a few PhDs and expert studies will monitor the process and its causes, all of which will be very educational. Artificially-enriched estuaries may well be compensating the bird populations for loss of habitat elsewhere, so that smaller flocks could come to be the norm.

Ultimately, also, we shall deal with the dung of our cities in ways that return its nutrients, safely, to the soil. This could mean more beetles and earthworms and so more songbirds to set against the loss of European waders. In a world packed with eight or ten billion people, the size of wildlife populations in general will be anything but "natural".