Discovery reports (1964) Discovery reports discoveryreports32inst Year: 1964 236 DISCOVERY REPORTS on the surface (p. 149), although perhaps of considerable lateral extent, are disposed in shallow rafts or plates no more perhaps than a metre or two thick in which the vertical nets, fishing only momen- tarily, capture far smaller numbers than they would obviously do if the swarms were densely disposed in depth. The orders of abundance of the Nauplii, Metanauplii and First Calyptopes taken at deeper levels are also (Fig. 49) inclined to be low, suggesting that from the outset the larvae are as
Discovery reports (1964) Discovery reports discoveryreports32inst Year: 1964 236 DISCOVERY REPORTS on the surface (p. 149), although perhaps of considerable lateral extent, are disposed in shallow rafts or plates no more perhaps than a metre or two thick in which the vertical nets, fishing only momen- tarily, capture far smaller numbers than they would obviously do if the swarms were densely disposed in depth. The orders of abundance of the Nauplii, Metanauplii and First Calyptopes taken at deeper levels are also (Fig. 49) inclined to be low, suggesting that from the outset the larvae are assembled in pockets of shallow draught. °/ '° DEPTH 100 • 7S- 1000 - 750 75- T 1 r 10-100 100-1000 1000-10000 lOOOO-IOOOOO Fig. 49. Orders of abundance of deeper living E. superba larvae and Ctenocalanus vanus expressed as percentages of the total samples from the Warm Deep current (see legend to Fig. 45). Further investigation, involving a comprehensive and elaborate programme of staging and measuring, may reveal that other plankton animals, like the krill, throughout much of their lives, are assembled discretely on or near the surface in swarms, and I believe that a great deal of the patchiness of the plankton as a whole will eventually be explained in terms of this phenomenon. In so far as our Discovery collections are concerned, one is struck by the frequency with which the surface (0-5 m.) nets produce enormously larger samples of certain species than are produced, for instance, by oblique nets hauled open to the surface or by horizontal or oblique closing nets fished at subsurface levels. One is struck, too, by how often these enormous surface samples are severally composed of individuals that to the eye at least appear to be all of much the same size and in much the same developmental Among the euphausians E. crystallorophias (p. 124) is a known surface swarmer, and Thysanoessa macrura may well prove to be another, the recent discovery by the Japanese (Nemo
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