THE SEA OVER WALCHEREN
By C. M. YONGE
THE Netherlands exist in parlous equilibrium with the sea against which the Hollanders have long waged defensive war- fare. From time to time they have taken the offensive and wrested great areas from beneath its surface. Their supreme achievement was the successful completion in 1932 of the Great Zuider Zee dyke with the prospect of eventual reclamation of the major part of the wide area of shallow water so enclosed. At the crises of their history the Dutch have not hesitated to seek aid from this enemy to repel the incursions of other invaders. By alliance with the sea the sieges of Alkmaar and of Leiden were raised and the power of the United Provinces erected upon the ruins of Spanish domination. History repeated itself in October, 1944, when, through great breaches in the surrounding dykes blasted by Allied bombers, the sea poured over the Island of Walcheren. Again the Dutch hailed the sea as deliverer from a no less terrible invader.
While the Zuider Zee dyke was in construction marine biologists in Holland made careful study of tht. animal and plant life of the brackish waters. They knew that when the dyke was completed and contact with the open sea broken, great changes must over- take these waters and their inhabitants, as what had been an arm of the sea slowly changed into a fresh-water lake. Then, when the dyke, was finished, they followed the effect of lowering salinity on the population. Marine animals and plants died out, and gradu- ally fresh-water species spread down from the rivers and out into the wide waters of what was now the Yssel Lake. Just a few of the former inhabitants remained and may be perpetuated to remind future dwellers around its contracted margins that the Yssel Lake was once the Zuider Zee. Knowledge of how the contained life slowly changed from marine to fresh-water species as the sea was driven back was gained by the routine observations of naturalists in the quiet days of Dutch life before the war. Recently, in such very different days, there came to me from my friend Dr. W. S. S. Van Bentham Jutting of the Zoological Museum, Amsterdam, an account of "'Marine Organisms in the Island of Walcheren (Netherlands)
during the Inundation, October, 1944-October, 1945." By the pen of an experienced naturalist there is here described how the inhabitants of the sea, during that brief period of invasion, began to swarm again over the land so hardly won from them in earlier days.
The result of the bombing between October 3rd and October nth, 1944, was the blasting of four passages, ranging in width from 350 to 900 metres, in the dykes surrounding the island of Walcheren. The forward and backward rush ot tidal waters through them widened these passages and excavated them to depths of up to 25 metres. The sea poured over the flat land which was everywhere covered except for, the dunes, for two small areas of the polder to the north and east and for the cities of Middelburg, Vlissingen and Veere with villages that lay on slight elevations. The German plans were as effectively frustrated as were those of the Spaniards in the sixteenth century but at an equal cost of devastation. "Every tree, shrub and herb which came in contact with the sea-water perished and so did the animal population of land and fresh-water." With help in material and men from this country, the gaps in the dykes were closed about a year later, the water then pumped out and the land reclaimed. What had been a richly fertile countryside was now revealed as a barren waste so utterly devoid of life as to recall, in the impressive words of Dr. Van Bentham Jutting, "the earth in the beginning of the Creation : 'And the earth was without form and void '."
Like their German counterparts the inhabitants of the sea settled quickly to exploit the conquered land. In the waters which rose and fell with the tides there swam shoals of fish with prawns and jellyfish. Porpoises and seals are said to have followed. Within a few months of the inundation there settled from these waters the spores and freely swimming larval stages of seaweeds and of animals. Trees, walls, fences, houses and even pavements were covered with amazing quickness by filaments of green weed, by the conical shells of barnacles, by clusters of mussels and by irregular masses of tea mats. The barnacles, as is their habit, settled near high-tide mark, so leaving a zone of innumerable white points exposed on the trunks and branches of trees or on walls and fences when the tide fed. Some had attained an inch in breadth before the sea was driven back. Attached by their tough byssus threads, mussels clustered densely on walls, hung like strange fruit from the branches of trees and carpeted the ground. Within six months of settlement many were already over two inches long. Between and upon them there clustered a varied population of worms with crabs and smaller crustaceans and other creatures. Within the year of their domination, this population grew dense enough in places for the original settlers to be suffocated under the overlying layers of their successors. These massive beds of mussels had at least the virtue of protecting in some measure houses and pavements from the wash and occasional fury of the seai. Scattered more sparsely on trees and sometimes attached to earlier settled barnacles were thin-shelled oysters up to one and a half inches wide. With the invading sea there also came the motile young of animals which burrow in the bottom mud. The early stages of both cockles and clams must have been thus carried throdgh the gaps in the dykes. These animals move little in adult life, and yet were found in abundance on the barren land which lay exposed when the sea had been pumped out. The rare animals were those that could not swim in actively, like fish and prawns, or be carried in passively during early life but could only move slowly along the bottom. For this reason marine snails, usually amongst the commonest of marine animals, were seldom found.
Thus within the short space of one year the inhabitants of the sea had already to a great extent established themselves far and wide over the surface of what had been, and again became, the Island of Walcheren. Another year or so and its fauna and flora would have been indistinguishable from that of the surrounding shallow seas. The Dutch have a proud saying that "God made the sea but the Hollander made the land." At what cost of ceaseless vigilance their conquests must needs be maintained and how pre- carious is their hold is revealed in this tragic story of the utter obliteration of the fauna and flora of the land by the alien medium of the sea and its replacement, with such impressive speed, by marine animals and plants.
Previous page
