8–33.3 PSU) for most zooplankton groups and species. Only 2 of the 21 copepod species recorded in the study area (Paracalanus crassirostris and Oithona nana) formed the main bulk of the copepods, in addition to 3 other species (Centropages kroyeri, Euterpina acutifrons and Paracalanus parvus) that were frequently captured. These

species are the major constituents of the zooplankton population along the Egyptian Mediterranean coast ( Abdel-Aziz & Dorgham 2002, Abdel-Aziz 2004). Paracalanus crassirostris was the most dominant copepod in Lake Timsah (6241 individuals m−3; 36.4 and 28.3% of the total copepod and total zooplankton population respectively). Its densities peaked in summer, and there was an increase in autumn. This finding is in agreement selleck chemicals llc with that reported by Abou-Zeid (1990) in Lake Timsah, by El-Serehy et al. (2001) in the Suez Canal area and by Michel et al. (1986) in the Arabian Gulf. Also, this small paracalanid copepod is a major constituent AG-14699 of plankton communities in the tropics ( McKinnon & Thorrold 1993, McKinnon & Klumpp 1998). Widely distributed in estuaries, neritic and oceanic waters, O. nana, the second most abundant species, is cosmopolitan; it seems to prefer deeper shelf and coastal waters ( Paffenhöfer 1993, Bradford-Grieve et al. 1999, Vieira et

al. 2003, Abdel-Aziz et al. 2007). It is also a eurytopic species, tolerating a wide range of temperature and salinity ( Dowidar 1965); it was abundant in the eastern Mediterranean ( Hussein 1977). Maximum standing crops of this species were recorded in summer in the Egyptian Mediterranean ( Dowidar & El-Maghraby 1970, Hussein & Abdel-Aziz 1997), Lake Timsah ( Abou-Zeid 1990) and the Gulf of Suez ( Abdel-Rahman 1993). Oithona nana was the most important species in Doha Harbour (Arabian Gulf), comprising 34% of the total copepods, with the highest density in summer ( Dorgham & Hussein 1997). It is distributed in the tropical and subtropical waters of the Pacific and Indian Oceans, with a high density in tropical waters ( Nishida 1985).

It has frequently been recorded in the tropical and subtropical Atlantic ( Grice 1960, Gonzalez & Bowman 1965). Temperature, pH and total phytoplankton count were Oxalosuccinic acid the most important and significant factors controlling the densities of these species (r = 0.717, 0.583, 0.469 and 0.443, 0.499, 0.314 respectively). Rotifers are known to be excellent indicators of organic pollution as they thrive better in organically rich environments (Karabin 1985, Paleolog et al. 1997). A comparative investigation of Egyptian lagoons showed that cleaner environments have smaller standing crops and are not so species-rich, whereas eutrophic areas sustain the greatest number of both individuals and species, though only up to a certain level (Guerguess 1992). Rotifers constituted the second most important group, representing 9.