Zooplankton of the Red Sea

Abstract

The Red Sea zooplankton distribution pattern is characterized by a decreasing gradient in species numbers from the south to north while biomass and abundance of small-sized copepods decrease from the epipelagic zone of the southern Red Sea to the central-northern area. In the northern Red Sea, the seasonal abundance of the total zooplankton standing crop showed two peaks. The highest peak was observed in autumn with a maximum of 4990 ind/m(3) in November, while the small peak was recorded during late spring-early summer, attaining a maximum (4300 ind/m(3)) in July. The diversity of oceanic zooplankton species in the Red Sea is relatively poor compared to other tropical seas and the number of oceanic species decreases with depth and toward the Gulfs of Suez and Aqaba. Species composition and abundance of demersal zooplankton differed considerably between the reef substrates. The highest mean density of zooplankton emerged from the living coral area (daily average: 4983 ind/m(2)), while the lowest mean density emerged from sand substrates (daily average: 938 ind/m(2)). The total number of demersal zooplankton that emerged from the coral patch was significantly higher than from sand or rubble areas. The emerged zooplankton was significantly higher in night-hours (2251 ind/m(2)) than in day-hours (286 ind/m(2)) over any substrate in the studied areas. Seasonally, the demersal zooplankton increased during summer with the maximum averages of 493 ind/m(2) and 3813 ind/m(2) during day and night, respectively. The minimum abundance of demersal zooplankton was recorded during autumn with the lowest values in October. Copepods were the most abundant group of all catches, accounting for 58.7% of the total demersal zooplankton abundance. The presence of copepod larval stages (nauplii and copepodites) all the year round indicated the continuous reproduction of copepods throughout the year. A total of 34 zooplankton species could be identified from the emergence trap fixed on different substrates (i.e., living corals, rubble and sand).