الفهرس 
chapter 1Only 14 pages are availabe for public view
 |  | from | 196 |  |  |
| | | from | 196 | | |
Abstract
In the oceans, ubiquitous microscopic photoautotrophs (phytoplankton) are responsible for approximately half the production of organic matter on Earth. They play a fundamental role in the marine food web and considered as a water quality indicator. The present study is carried out to follow up the phytoplankton species composition, abundance and biomass (chlorophyll a) off Hurghada Egyptian Red Sea coast, in relation to the monthly fluctuations of some physicochemical parameters. Also, to photo and identify as much as phytoplankton species using scanning electron microscope (SEM) technique. Water and phytoplankton samples were monthly collected from 12 stations representing different habitats during August 2014 to July 2015 off Hurghada, Red Sea coast between latitudes 27°14.362ˊ N and 27° 8.371ˊN, and longitudes 33 ° 51.235ˊE and 33 ° 51.46ˊE. Different hydrographic conditions were determined namely; temperature, salinity, pH, dissolved oxygen, nitrate, nitrite, ammonia, phosphate, silicate and chlorophyll a as a term for phytoplankton biomass. Phytoplankton samples were collected using net with 20μm mesh size, fixed in 4% formaldehyde and examined using an inverted microscope for identification and calculate standing crop.
The present study revealed that surface water temperature fluctuated between 30.9 and 20.4°C, salinity level between 39.7 and 40‰, with annunal pH value expressing water alkalinity 8.15 and well oxygenated water with annual value 7.3mg/L. Concentrations of nitrate, nitrite, ammonia, phosphate and silicate ranged during
English Summery
133
different months between; (1.08±0.23-0.49±0.06μM/L), (0.08±0.01-0.04±0.01μM/L), (0.95±0.13-0.44±0.03μM/L), (0.08±0.03-0.26±0.05μM/L) and (1.09±0.1-0.3±0.01μM/L), respectively. The low nutrients expressed oligotrophic nature of the Red Sea and influenced the chlorophyll a (0.03±0.01-1.32±0.00mg/m3). A total of 138 species and varieties belong to 58 genera was recorded and classified into five divisions. Bacillariophyceae (diatoms) and Dinophyceae (dinoflagellates) contained relatively close number of species (64 and 67 species, respectively), while other three divisions; Cyanophyceae (cyanobacteria), Ochrophta (silicoflagellates) and Chlorophyceae (chlorophytes) were collectively represented by a very low number of species (7 species). The most diverse genera were Tripos, Protopridinium with 28 and 7 species, respectively. The highest number of phytoplankton species was in August (74 species) while the lowest number was in September (39 species). Diatom species numbers was higher than dinflagellates only in winter from Novmber to Feburary. However, number of dinoflagellate species was higher than diatoms except at stations 1 and 4. Some species was recoreded for the first time such as Emiliania huxleyi (type A) and Coronosphaera mediterranea.
The standing crop of phytoplankton was characterized by low density in the area of study, with an annual average of 117 individual/L. Dinoflagellates were the most dominant group, constituting 67% of the total phytoplankton standing crop, followed by diatoms (30%). The contributions of other phytoplankton groups were either very low as in cyanobacteria (3%) or negligible as in coccolithophores, silicoflagellates and chlorophytes (less than
English Summery
134
0.1%). Spring and summer months exhibited high counts, with peaks in April (107.1 individual/L) and July (98.7), In addition to third but lower peak was appeared in December (69.6 individual/L). Otherwise, phytoplankton standing crop displayed low values in autumn with the minimum density in October (26.08 individual/L). Except for Januray and February, dinoflagellates were ahead in terms of their density than diatoms. The distribution of phytoplankton density among stations varied between 76.9 individual/L at station 3 and 45.8 individual/L at stations 8. Density of dinoflagellates showed obvious decrease southward but they increased seaward. The correlation and regression confirmed the influence of temperature, nitrate, ammonia and silicate on structure pattern of phytoplankton biomass and densities in the study area. Similarity analysis confirmed differences among monthes and stations depending on phytoplankton densities.
Although the previous studies, the strategy of collection in the present study based on may stations covering one area monthly lead to recognizing phytoplankton community and structure better. Some of the recorded species in the present study were either not detected before off Hurghada or detected in other regions in the northern Red Sea. Phytoplankton biomass had clear patterns at stations and zones of the study. Further similar studies are needed to cover the whole Egyptian Red Sea coast and with introducing molecular techniques to identify eukaryotic and prokaryotic phytoplankton.