Some dynamic and biological characteristics in the Adriatic and other basins of the eastern Mediterranean Sea

Abstract

      A model to predict secondary production in the Adriatic and its possible application to the other basins of the Eastern Mediterranean has been dis­cussed.

      It has been shown how some climatic factors, such as air pressure gradients and ice conditions in the North Atlantic influence some oceanographic para­meters in the Adriatic. An important parameter is the uneven advection of the Eastern intermediate water into the Adriatic which brings into this sea an important quantity of nutrients and thus influencing the rate of primary production. Some assumptions on the current velocities and their distribution permit the calculation of the average annual income and exit of water in the Otranto Strait in three different layers. This provided a basis for the calcu­lation of the annual nutrient budget and to make an estimation for the rate of increase of nutrients if water exchange in the Otranto Strait is more rapid. It has been shown that such an increase of nutrients is of the same order as the river input. The calculated water renewal for the whole Adriatic takes five years, but renewal may be over a longer period.

       Some observations show that coccolithophores could be considered as an indicating group of the Eastern intermediate water and that their percent within the phytoplankton population could indicate a specific relationship between silicate, nitrate and phosphate in the sea. At the same time, a high level of primary production is found. Statistical analyses show that the changes in the climatic factors and in the level of primary production could be related to secondary production but with a delay of three years. The total annual catch of fish has been analyzed for the entire Eastern Mediterranean showing that it could be related to the same climatic factors. The climatic factors are of great importance in that they regulate intensity of horizontal and vertical water exchange and the nutrient enrichment.