Hydrology and hydrobiological study of the Persian Gulf in the Bushehr region

In order to investigate some ecological condition of the waters of Bushehr province in the Persian gulf between 50~'-01 E to 52~'-47 E and 26~'-39 N to 29~'-03 N, 18 major and 16 minor stations have been studied from Nayband bay to Kharg Island, using R.V. Ferdows 1. There have been a preliminary survey in winter 2001, 4 seasonal surveys in 2001-2 and a complementary one in summer 2002. During this period the seasonal environmental conditions, physico-chemical parameters, zoo and phytoplankton concentrations in water layers, macrobenthoses and sediments were studied. Sea bed swelling in the Motaf region has resulted in division of the area in two parts and in a such away that the climatic and chemico-physical conditions in the southeast area are different from the northwest area. In the southeast area the termocline, halocline, picnocline and oxycline are generated in spring, increased in summer, moved down to the deeper layers in fall and disappeared in the winter. In the Northwest area the clines are only formed in spring and summer but disappear in fall and winter due to almost perfect water column mixing resulted from climatological conditions. During survey period the water temperature ranged from 18 34.1~'C, salinity 37.9 41.3 ppt, conductivity 51.3 70.4 ms/cm, sigmaT 23.1 30.2 g/cm3, dissolved oxygen 0.2 8 ppm, and chlorophyll a 0.1 3.6 mg/m3. It is observed that salinity, conductivity and sigmaT have increased from surface to depeer layer, while oxygen and chlorophyll a had a pick in mean layers but temperature have decreased from surface to the depth. Temperature and conductivity decreased from southeast to the northwest and from costal to offshore. Salinity and sigmaT increased from southeast to the northwest. Dissolved oxygen and chlorophyll-a did not show any trend. The concentration of nutrients including ortho silicate (Si-SiO4- 4), ortho phosphosphate (P PO4-4), nitrate (N NO3- ) and nitrite (N NO2- ) varied between 0.4 13.3, 0.05 1.6, 0.1 12.3 and 0.1 1.4 ~kmol/l, respectively. The overall nutrient concentrations increased from surface to depth. 61 genuses of 5 phytoplankton groups and 8 branches, 12 classes of zooplankton were identified. The identified phytoplanktons included 42 Diatom, 16 Dinophyceae, 3 Cyanophyceae, one Chrysophyceae and one Euglenaphyceae geneses. The highest intensity of phytoplanktons was recorded in summer, while in the case of zooplankton, was recorded in spring. Diatoms had the highest variety in all seasons and the maximum abundance in fall and winter. Cyanophyceaes were predominant group in the spring and summer. On the contrary to zooplanktons, the intensity of phytoplanktons decreased from coastal to the offshore waters. The highest intensity of all planktons (zoo and phyto) was in 10-20 m layer. The intensity of phyto plankton increased from southeast towards northwest. The zooplankton concentration didn t follow any particular trend. The identified macrobenthoses were 69 families including 34 polychaets, 22 gastropods, 10 of bivalvs, 1 crustacean, 1 scaphopoda, 1 foraminifera, 5 classes and 6 orders of crustacea, 1 order of echinodermata, 1 fish larva and 6 branches of other benthoses. Intensity and biomass of all groups were determined. The polychaets and malacostraca had the most abundance in contrast to the other groups. Macrobenthosis intensity decreased from coast to the offshore in southeast of Motaf region, while the middle stations of northwest of Motaf had a better intensity. The mean abundance and biomass of total area decreased from coast to the offshore, and the slope of decrease in biomass was more than abundance. Seasonal minimum and maximum abundance ranged from 1457 to 1903 per square meter in spring and winter, and the biomass ranged between 7.8-10.8 g/m2 in summer and spring, respectively. In spite of high abundance of macrobenthose in the transect no: 13, the estimated biomass was lower than other transects. This might be due to prolonged exposition to more pollutant. The grain size of sediments was classified as gravel, sand, silt and clay. The organic matter of sediments ranged from 1.12 3.3% with annual average of 1.6%. The grain size of sediments in southeastern point was coarser than other areas. The middle stations of northwestern area had fine grain and more organic matter in contrast to the offshore and coastal stations