الفهرس 
Introduction
Zooplankton definition and their impact on the ecosystemOnly 14 pages are availabe for public view
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Abstract
Plankton includes those organisms having limited power of locomotion and are under the mercy of the prevailing water movements. It is subdivided into phytoplankton, which comprises free-floating plants capable for photosynthesis, and zooplankton.
Zooplankton includes small animals that float freely in the water column of rivers, lakes and oceans and whose distribution is primarily determined by water currents and mixing. Zooplankton is among the most important components of the aquatic ecosystem, plays a major role in energy transfer between phytoplankton and the various economically important fish populations.
Zooplankton serves in the evaluation and productivity of the ecosystem since it is considered as essential food for other organisms. The importance of zooplankton communities in the ecology of their habitat is due to the fact that they are considered as primary consumers in the food chain. They also affect the fish production either directly or indirectly. Also, the study of the distribution of zooplankton is useful for the general monitoring of certain aspects of the environment such as hydrographic, eutrophication, pollution, warning trends and long-term changes which are signs of environmental disturbances. So, zooplankton search becoming increasingly important in recent years in both marine and freshwater ecosystems and it has occasionally been used as a tool to investigate the impact of pollution in river estuaries or in marine communities.
The present investigation was designed to carry out the following points:
1- Make a survey of the major zooplankton taxa inhabiting Al-Ibrahimiyah Canal at Assiut, Egypt: during one year (from January, 2011 till December, 2011).
2- Study the effects of some ecological factors including air and water temperature, pH, dissolved oxygen, turbidity and conductivity on the abundance and the distribution of the collected zooplankton taxa.
3- Study and compare the seasonal changes, diversity, distribution and the abundance of zooplankton taxa in the three investigated sites also in the two littoral zones and the pelagic zone of the studied sites.
4- Deduce the difference between the state of Cladocera that inhabited Al-Ibrahimiyah canal before 23 years and now.
5- Deduce the difference between the state of Copepoda that inhabited Al-Ibrahimiyah canal before 16 years and now.
6- Deduce the model equations which govern the density of the studied taxa.
To achieve these goals, monthly quantitative samples of zooplankton were collected during one year (extending from January 2011 till December 2011) from three sites in Al-Ibrahimiyah canal at Assiut governorate. These sites included polluted sites (site 2, Al-Qusiya: chemically polluted and site 3, in Dairut: organically polluted) and unpolluted site (site1, in Manqbad). For qualitative study another 14 sites were chosed for collecting. Each site includes three localities, two in the littoral zones ”A” and ”C” and one in the pelagic zone ”B” of the canal. Also, some ecological factors including air and water temperature, pH, dissolved oxygen, light permeability, and conductivity were measured during collecting period.
The study revealed the following results:
• Zooplankton communities in Al-Ibrahimiyah Canal at Assiut, during the period of collection comprised 73 taxa including 5 groups. Rotifera was the most important group (23 taxa belonging to, at least, 16 genera), Cladocera (18 species), Copepoda (10 adult species, Nauplius larvae and Copepodite stages), the group of the ”other groups” (12 taxa: 10 taxa of insects belonging to 7 orders, Nematoda and the” aquatic spiders and mites”) and Ostracoda (8 species).
• It is worthy to mention that, in the present work new genera, species and orders have been identified for the first time in freshwater of Assiut Governorate, Egypt and they are as follows:
16 genera of Rotifera; 11 of them have been identified for the first time in Assiut.
10 species of the 16th genera of the rotifers have been identified, 9 of them have been identified for the first time in Assiut and only one species (Platyias patulus), was previously identified by El-Shimy and Obuid-Allah (1992).
A new order of insects (Plecoptera) was recorded for the first time in freshwater of Assiut.
Aquatic spiders were recorded for the first time in Assiut.
Thus, the present work represents a first detailed report of freshwater rotifers in Assiut since 23 taxa of Rotifera were identified, 17 taxa of them were recorded for the first time in Assiut. So, Rotifera was the most divers group in the canal.
• The total density of zooplankton taxa collected during the whole period of all 9 localities of the main three investigated sites in Al-Ibrahimiyah Canal was 171255 organisms. They included Cladocera, Copepoda, Rotifera, Ostracoda, and the group of ”other groups” which included (insects, Nematode and the” spiders and mites”).
Site (2) had the highest zooplankton density, which represented by 64889 individuals with a percentage of 37.89%, followed by site (3) which represented by 60162 individuals with a percentage of 35.13%, while site (1) represented by 46205 individuals with a percentage of 26.98%.
The density in the littoral zone (C and A) was higher than it was in the pelagic zone (B). Zone (C) had the highest zooplankton density, represented by 58701 individuals with a percentage of 34.28%, followed by zone (A) represented by 57820 individuals with a percentage of 33.76%, while zone (B) represented by 54735 individuals with a percentage of 31.96%.
The seasonal abundance of total zooplankton in the study area showed the highest peaks in Winter followed by Autumn.
• Rotifera was by far the most important group in the whole community at all 9 localities of the three investigated sites in the canal, both quantitatively and qualitatively, constituting 614713 individuals during the whole period of study with a percentage of 40% from the total zooplankton taxa. Rotifera is dominant in Winter and it was poor in Summer and Spring.
Site (1) was represented by 38.29% from the total zooplankton, while site (2) was represented by 42.56% from the total zooplankton and site (3) was represented by 42.68% from the total zooplankton.
In the littoral zones, zone (A) was represented by 40.49%, while zone (C) was represented by 40.90% from the total zooplankton taxa. Zone (B) was represented by 39.10% from the total zooplankton taxa.
The most abundant and common taxa of Rotifera were: Synchaeta sp., Brachionus calyciflorus and Keratella cochlearis which represented by 8.99%, 8.72% and 4.13; respectively of the total zooplankton taxa.
• Cladocera was the second dominant group of zooplankton throughout the period of study, forming 555077 individuals, constituting 36.12% from the total zooplankton taxa.
Site (1) was represented by 38.29%, while site (2) was represented by 35.35% from the total zooplankton taxa and site (3) was represented by 35.10% from the total zooplankton taxa.
In the littoral zones, zone (A) was represented by 35.43%, while zone (C) was represented by 33.88% from the total zooplankton taxa. Zone (B) was represented by 38.91% from the total zooplankton taxa.
Bosmina longirostris was the most abundant cladoceran species represented by 15.00% followed by Ceriodaphnia reticulata which was represented by 5.14% from total zooplankton taxa.
• Copepoda was the third zooplankton taxa in abundance and was represented by 275462 individuals constituting 17.93% from the total zooplankton taxa.
Site (1) was represented by 22.01%, while site (2) was represented by 16.24% from the total zooplankton taxa and site (3) was represented by 16.51% from the total zooplankton taxa.
In the littoral zones, zone (A) was represented by 18.37% while zone (C) was represented by 19.15% from the total zooplankton taxa. Zone (B) was represented by 15.97% from the total zooplankton taxa.
Copepodite stages were the most abundant copepods taxa represented by 5.30% from total zooplankton taxa.
*Cyclopoid copepods were more diverse than the other copepods and represented by (8 species). This group was dominated by Mesocyclops ogunnus and Thermocyclops consimilis constituted 2.66% and 2.04%; respectively from the total zooplankton taxa.
*Calanoid copepods were represented by (1 species): Thermodiaptomus galebi which constituted 1.58% from the total zooplankton taxa.
*Harpacticoid copepods were represented by (1 species): Schizopera nilotica, which constituted .53% from the total zooplankton taxa.
• The fourth zooplankton group in the abundance was the group of the ”other groups”which was represented by 50760 individuals with a percentage of 3.30% from the total zooplankton taxa.
Site (1) was represented by 2.92%, while site (2) was represented by 3.46% from the total zooplankton taxa and site (3) was represented by 3.05% from the total zooplankton taxa.
In the littoral zones, zone (A) was represented 3.28%, while zone (C) was represented by 2.75% from the total zooplankton taxa. Zone (B) was represented by 3.89% from the total zooplankton taxa.
The highest abundance of the ”other groups”was Diptera larvae (almost were chironomid larvae), represented by 1.96% from the total zooplankton taxa.
• Ostracoda occupied the least abundant taxa among zooplankton groups, forming 40615 individuals with percentage 2.64% during the period of investigation.
Site (1) was represented 2.98%, while site (2) was represented by 2.38% from the total zooplankton taxa and site (3) was represented by 2.65% from the total zooplankton taxa.
In the littoral zones, zone (A) was represented by 2.42%, while zone (C) was represented by 3.32% from the total zooplankton taxa. Zone (B) was represented by 2.12% from the total zooplankton taxa.
Potamocypris variegata, Cypridopsis vidua and Hemicypris dentatomarginata were the most abundant ostracod species represented by 1.25%, 0.52% and 0.38%; respectively from total zooplankton taxa.
• The comparison between the state of Cladocera that inhabited Al-Ibrahimiyah canal before 23 years and its state now (2011) showed that:
In the present study (year 2011) 18 taxa belonging to Cladocera in the canal while Obuid-Allah (1987) recorded the same taxa except two which were: Scapholeberis kingi and Leydigia quadrangularis.
In (2011), Bosmina longirostris was the most dominant species of Cladocera, followed by Ceriodaphnia reticulata. However, Obuid-Allah (1987) found the reverse where Ceriodaphnia reticulata was the most cladoceran dominant species followed by Bosmina longirostris, in two successive years.
In (2011), the least dominant species was Leydigia acanthocercoides and Obuid-Allah (1987) found the same result and indicated that this genus was scarce due to the fact that it is not true planktonic form.
The highest density of Cladocera in (2011) was in Winter followed by Autumn and it was poor in Spring while Obuid-Allah (1987) found the highest density in Autumn followed by Spring and the lowest density was in Summer.
• The comparison between the state of Copepoda that inhabited Al-Ibrahimiyah canal before 16 years and its state now (2011) showed that:
In the present work (year 2011) 10 species of Copepoda (included Cyclopoida, Calanoida, and Harpacticoida), were found while Mohammad (1990, 1994) nearly recorded the same species except two which were: Paracyclops fimbriatus and Eucyclops serrulatus. However, the previous author recorded Ectocyclops phaleratus in the canal in (1994) which was not found during (2011).
In (2011), Mesocyclops ogunnus was the most dominant species followed by Thermocyclops consimilis, Mohammad (1994) came to the same result.
In (2011), the least dominant species was Eucyclops serrulatus. The same result was also recorded by Mohammad (1994).
• Shannon diversity index (H ̀) revealed that the diversity value index is closely similar (either in sites or in zones) during the period of investigation. The increase in the diversity index of Al-Ibrahimiyah Canal as a whole is attributed to the presence of many taxa which are highly tolerant to pollution.
The community of site (1) with the highest (H ̀) was more stable than site (3) and (2). The diversity values in sites 1, 3 and 2 were: (3.34), (3.27) and (3.23); respectively.
The community of zone (C) with the highest (H ̀) should be more stable than zone (B) and (A), during the period of investigation. The diversity values in zones were: (3.30), (3.28) and (3.25); respectively.
• Concerning the ecological factors measured and their influences on the abundance of zooplankton taxa collected from all 9 localities of the three investigated sites in Al-Ibrahimiyah Canal, the following model equations were deduced:
Total density of Cladocera organisms/m³=
7290.034 - 55.371 Air temperature - 552.070 pH.
Total density of Copepoda organisms/m³=
2196.194 - 188.434 Dissolved oxygen - 34.999 Air temperature + 39.694 Water temperature.
Total density of Ostracoda organisms/m³=
- 854.171 + 13.696 Water temperature + 0.408 Conductivity + 70.345 pH.
Total density of Rotifera organisms/m³=
8566.272 - 244.444 Air temperature.
Total density of the group of ”other groups” organisms/m³=
324.922 - 6.178 Air temperature.
Total density of (Total zooplankton taxa) orgs./m³ =
25400.459 - 358.661 Air temperature - 418.383 Dissolved oxygen -1065.869 pH.