Hydrology and Hydrobiological Studies of the Iranian Waters in the Persian Gulf ( Khuzestan, Bushehr & Hormozgan Provinces)

Abstract

The comprehensive hydrobiological studies in the northern part of the Persian Gulf within the Iranian waters were conducted during 2001 2002. The project was implemented using Ferdous research vessel and with the cooperation of Hormuzgan, Bushehr and Khuzestan Fisheries Research Centers. The sampling area included the whole stretch of the Iranian waters along the northern part of the Persian Gulf from the northwest of the Iranian marine border of Khuzestan province to the mouth of the Hormuz Strait in Houmuzgan province. Along this stretch 15 equally distributed transects at a distance of 30 miles from one another were designated. 3 main sampling stations at a distance of 10 miles from one another were fixed at each transect. 1 to 3 secondary station depending on the distance of the third main station to the international waterway was also selected on each transects so as to cover as much Iranian waters as possible. Sampling was conducted seasonally from Feb. 2001 to Feb. 2002. Physicochemical parameters of water such as temperature, salinity, density, dissolved Oxygen, PH, EC and chlorophyll-a were recorded at stations using CTD multi parameter probe. Nutrients were measured by spectophotometric method. Plankton samples were collected by Niskin sampling bottles from 5 different depth layers in the water column. Bottom sediment for grain size and benthic analysis were collected using a Peterson bottom samples. Petroleum hydrocarbons and heavy metals concentration in water, sediment and demersal fish species were measured by GC-MS and ICP-MS respectively. According to the results a seasonal thermocline appears in the Iranian waters during spring, extended with its maximum formation in summer performing a temperature differences between surface and bottom waters as much as 10 C. The thermocline diminishes in autumn and gradually eliminate during winter season. The density of nutrients decreases from northeast (Hormuz Strait) towards northwest in the Khuzestan province, whereas the annual average of phytoplankton abundance was maximum in Khuzestan province and minimum in Hormuz province. The reasons for these differences within the survey area are discussed in detail in the report. Concerning zooplankton, the comparison of present data with other previous documents clearly shows that Cyclopoida which have less ecological value in the marine food chain has become the dominant group instead replacing Calanoids. The total of 146 families of macro benthic fauna were identified in this study, out of which Polycheats and Gastropods with 46 and 45 families were most diverse groups. Average biomass of macro fauna in the whole study area was estimated as 8.700 g/m2 wet weight. Concentrations of Cd, Pb and Ni in the sediments were considerably higher than global baseline values. The mean concentration of these elements in muscle of 3 selected demersal fish species from the study area clearly indicates that nearly in all cases the values were markedly below the permissible amounts for human consumption. The highest and lowest concentration of petroleum hydrocarbon in coastal waters was measured as 1.52 and 36.1 µg/l respectively. The general distribution pattern of petroleum hydrocarbon in waters and sediments shows an increase in concentration towards the northwest of the survey area in the Khuzestan province.