Welsh Journals

Marine Biology in Swansea Docks by E. Naylor. QUEEN'S DOCK MIGHT SEEM TO BE an unrewarding place for marine biologists, for its sides are choked with oil and ship's garbage ebbs to-and-fro on the surface. Yet the dock is of immense interest, partly because it is hardly affected by tides, but mainly because it is so warm. The dock is heated by a warm water effluent from the Tir John power station (Fig. 1, inset) which raises its temperature by as much as ten degrees Centigrade above that of the sea outside. King's Dock and even Prince of Wales' Dock are also warmed to some extent. In winter the temperature near the warm water outfall in Queen's Dock is about 14°C., which is not much below normal summer sea temperatures along the Gower coast nearby. Whilst in summer the temperature may rise to more than 25°C., which is extremely pleasant for bathing. Local boys know this of course and occasionally bathe in the dock, apparently oblivious to the oil. But for the more fastidious a rubber suit is recommended, together with a face mask, aqualung and flippers, if one wants to see the dock fauna at leisure. Below the surface, visibility is poor, often only a few feet, owing to the heavy traffic in the dock which continually stirs up detritus from the muddy bottom. In additon planktonic plants and animals swarm amongst the suspended detritus, contributing to the warm soup in which one is bathed. This soup forms the basis of the food chains in the dock and it is continuously sieved for nourishment by sessile, filter-feeding animals. In summer these are plastered thickly upon submerged timber and concrete supports, and upon each other. Sea squirts, tube worms, barnacles and even amphipod crustaceans all sieve the soup in various ways. Higher up the food chain are the slightly less obtrusive free- swimming or walking species which feed largely amongst the sessile forms. Shrimps and crabs come into this category as also do species of fish such as sand smelt, (Fig. ID), black goby (Fig. 1e) and grey mullet. The commonest species of crab in the docks is Carcinus, the familiar green shore crab (Fig. IA), which can occasionally be seen feeding. They pluck somewhat indiscriminately at the mat of sessile animals, pass food to the mouth by means of their claws and grind it with their numerous mouthparts. As the crab eats so a steady rain of detritus falls downwards,-crumbs from the crab's table which are readily eaten by small sand smelts and bottom living gobies which accumulate below. From the dock side grey mullet are perhaps the most obvious of the fish. If one approaches quietly shoals of quite large specimens