On a Marine Aquarium

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ON A MARINE

AQUARIUM.

BY D P . DUDLEY W . COLUNGS, M . B . ,

F.Z.S.

THE sea at Southwold is practically almost always opaque and it is only for a very few weeks in the summer that the water becomes clear. The reason is that the sea-bed, for some distance from the shore, consists chiefly of drift sand, part of which is very fine and kept in suspension by the movement of the water. There are few rocks and therefore no clear rocky pools and, except for the wooden pier and the concrete of the harbour, no homes for Anemones or Molluscs such as Musseis or Winkles or Limpets. As a result of these conditions the study of local marine-life is extremely difficult, and possible only in an aquarium where the water can be kept reasonably c'ear. I have such a one : a small tank with plate-glass sides, 24 inches long and 15 X 15 in section. This has enabled me to make the following brief notes on its varying inhabitants. The water is strained and the bottom covered with about two inches of washed sand and a few smooth stones. The Brown Shrimp (Crangon vulgaris), our commonest Crustacean, is a true sand-lover and spends most of its time buried in the sand. It " digs itself in " at an astonishing speed : with its swimmerets it first excavates a shallow trench in the soft sand ; then lifts up its body longitudinally and brings it down suddenly and forcibly, thus deepening the hole and raising a small ridge of sand on either side. It finishes its work, being by now almost covered, by sweeping the ridges of sand over its body by means of its long extended antennae, using them effectively as arms. Usually all that can be now seen are the stalked eyes, which are almost invisible. The whole process takes about two or three seconds. These Shrimps occasionally swim round the tank close to the surface of the water, especially at night. They appear to locate their food by smell entirely : a small piece of fish, dropped anywhere on the bottom, soon brings the Shrimps to their meal. On the other hand, I have watched a Shrimp scuttling about among attractive food, when it seemed only as a current of water conveyed the " odour " from a fragment that the Shrimp hurriedly seized it. Owing to fear of looting apparently, the successful Shrimp holds its portion under its thorax ; and rc-buries itself to enjoy its meal in safetv and comfort. Crangon vulgaris is very tenacious of life : it will live for hours in a dry basket and, when apparently dead, will revive in a few minutes when put into sea-water.


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On a Marine Aquarium by Suffolk Naturalists' Society - Issuu