VERTICAL MIGRATION OF ZOOPLANKTON GROUPS IN AN EUTROPHIC BAY, DEKHAILA HARBOR, ALEXANDRIA, EGYPT

VERTICAL MIGRATION OF ZOOPLANKTON GROUPS IN AN
EUTROPHIC BAY, DEKHAILA HARBOR, ALEXANDRIA,
EGYPT
NAGWA EL-SAYED ABDEL AZIZ
National Institute of Oceanography and Fisheries, Alexandria, Egypt
Email: [email protected]
Keywords: Zooplankton, Vertical migration, Ecological factors, Diel migration,
Dekhaila Harbor
ABSTRACT
Diel vertical migration of different zooplankton groups in Dekhaila Harbor was studied
monthly from May 2003 to April 2004. Generally, more groups were found in the surface
layer (0-10 m.) than the deeper one (10-20 m.). Some zooplankton groups undergo
significant vertical migration at certain time of the year, others showed no clear differences
in distribution patterns and exhibited no directed movement patterns. Some species stayed a
part of the day within certain layer of the water column, others were randomly dispersed in
the whole water column during different hours. Responses appear to depend also on the life
stages of each zooplankton group, as well as other ecological conditions such as
temperature, light and amount of food. Population budget indicates that the abundance of
some groups was greater at the morning time, others at the sunset time. While the noon
time often showed lower density. The time of the day which showed the lowest count of
each group is known as the day deficit, which is probably due to diel horizontal migrations.