Vertical migration patterns in phytoplankton of mixed species composition

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Abstract
The vertical distribution and migration of phytoplankton composed of seven organisms in a small eutrophic pool is described. Vertical migration during a 24 h period is shown to be exhibited by Pandorina morum, Mallomonas tonsurata, Chroomonas pusilla (Rhodomonas) and Ochromonas sp. in the epilimnion and Cryptomonas rufescens in the surface of the hypolimnion. The degree of horizontal variation in distribution of the organisms is discussed and found to be greatest for the microflagellates. Changes in vertical distribution are shown to be significant and result from active movement of the cells rather than from either water movement or the combined variation associated with patchiness in distribution and counting errors. Differences between the behaviour patterns of the different algae are evident and may be used to explain Hutchinson's “paradox of the plankton”.