The Settlement of Ophelia Bicornis Savigny Larvae The 1952 Experiments

Abstract

Previous conclusions that it should be possible to forecast the intensity of settlements which will be obtained in fifty-fifty mixture of two sands, provided the relative attractiveness or repellence of each component is known, were fully confirmed. The results of these mixture experiments agree with the classification of sands as attractive, neutral or repellent.It is shown that an attractive factor is capable of transference, in sea water, from fresh Bullhill Bank sand to acid-cleaned quartz sands, to calcareous oolitic sand and to an artificial sand of fused alumina. The attractive factor is present in water in which fresh Bullhill Bank sand had been shaken.A similar transference of a repellent factor from fresh Salthouse Lake sand is not so clearly demonstrable. Water in which fresh Salthouse Lake sand has been shaken appears to contain the attractive factor. Thus both attractive and repellent factors may be present in Salthouse Lake sand.Activated charcoal stimulates larvae to settle and metamorphose, but needs to be in granular form, or associated with neutral grains, to exert its full influence. The charcoal contains copper in minute proportion, but whether this has any significance for metamorphosis is undetermined.The grade of a sand was again shown to be a settlement factor of some importance. The most attractive grain sizes appear to be those of which the bulk of the Bullhill Bank surface sand is composed.Analysis shows that the surface sand of Salthouse Lake (St. II) contains some three times the organic nitrogen content of the surface sand of the Bullhill Bank.