A PRELIMINARY SURVEY OF DIURNAL VERTICAL MIGRATION OF PLANKTONIC CRUSTACEANS IN THE XIAMEN HARBOUR

The diurnal vertical migration of planktonic crustaceans may be divided into two types:Type 1, species with marked diurnal vertical migration; Type 2, species without marked diurnal vertical migration. The former may be further grouped into three patterns:Pattern 1, sinking by day and rising by night; Pattern 2, rising by dawn and evening and sinking by day and midnight; Pattern 3, rising by day and sinking by night. The latter may be further grouped into the following three patterns:Pattern 1, surface layer distribution; Pattern 2, bottom layer distribution; Pattern 3, even distribution between the surface and bottom layers. Among these patterns the two most common ones appear to be the sinking by day and rising by night' and the surface layer distribution. Most of the females are no more marked in the diurnal vertical migration than males in the Xiamen Harbour. The diurnal vertical migration of the animal become more and more conspicuous with the increase of the ages and varies markedly with seasons.Among the environmental factors affecting the diurnal vcrtical migration, light appears to be the most important. Salinity discontinuity layers may restrict the upward or downward movements of the animals.