Basic characteristics of the Adriatic Sea as a production basin
Abstract
A series of hydro-physical and hydro-chemical properties of the Adriatic Sea are presented in this paper - elements that may be important for the understanding of the ecologic properties of the marine basin concerned, particularly as regards its production (P u c h e r - P e t k o v i ć & Z o r e - A r m a n d a); on the basis of trophic artificially created ones.
Here are the conspicuous parts of the paper:
1) About four fifths of the Adriatic basin belong to the continental shelf. This fact has a positive significance for the organic productivity in the basin;
2) The phenomenon of warming up of the entire mass of Adriatic waters by several degrees in some winters (during the periods of so called Adriatic ingressions - the intervals of intense entering in the Adriatic of high saline water Intermediary water of eastern Mediterranean origin may be an ecological factor of especially important significance;
3) Some new proofs are brought forward to confirm an earlier statement to the effect that the waters of the southern Adriatic pit are by about 1 mg P-PO4/t richer in phosphorus than the waters of the Middle Adriatic. The importance of one additional milligram of phosphorus for the bioproduction in the Adriatic basin has been stated in earlier papers;
4) The results of investigations, carried out in the Adriatic, show that the maximum quantity of phosphate is found in the Southern Adriatic basin, in the water layer lying between the depths of 50 and 100 metres, this fact being closely conncted with the inflow of waters belonging to the Intermediary Water entering
5) Considerable quantities of nitrates have lately been found in the deeper layers of the Adriatic pits. The distribution of nitrates, i. e. the fact that the nitrate form exceeds the ammonia (and nitrite) from, may be considered as a geochemical distinction of the Adriatic bottom waters while, on the contrary, the ammonia form prevails in shallow and surface waters over the nitrate (and nitrite) form of nitrogen salts. The conclusion has therefrom been drawn that the Southern Adriatic Pit may be considered as a nitrate reservoir of great importance for the bioproduction taking place in the Adriatic basin.
6) While the waters of the Northern Adriatic are considerably influenced by the River Po and other rivers discharging in that part of the Sea, the waters of the Middle and Southern Adriatic and consequently their bioproduction are in turn exposed to the beneficial influence of Ingressions (i.e. occasional intensive inflow of high saline Intermediary water, carrying nutrient salts from the Southern Mediterranean basin into the Adriatic).
7) The possibility has been discussed of a favourable influence of Upwelling on the bioproduction in some divergence areas belonging to limited parts of the eastern Adriatic shore (Blitvenica).
8) A series of new data has been given concerning the chemical composition of waters of the rivers discharging into the Adriatic. Significantly enough, these waters contain more phosphorus, more carbonic acid, and more silicate than the sea water. This fact reveals the significant contribution of fresh water streams carrying also organic matter and detritus to the marine bioproduction. The quantities of nitrogen components, on the other hand, found in the waters of rivers discharging into the Adriatic, are on an average smaller than those occurring in the sea water. This, however, hardly represents a significant insufficiency, since the whole of the Adriatic basin is not poor in nitrogen, while the N/P ratio makes evident an insufficiency of phosphate in the offshore waters.
9) The beneficial influence of afforestation in the littoral area upon bioproduction in the inshore waters has also been considered.
10) The discussion also involved artificial fertilization to be performed in marine bays. This factor can play a significant and useful part in the future, adding to the biologic production in the Adriatic basin. The metod of gradual extermination may serve the same purpose.
11) Process of sea water eutrophization, developing as a consequence of some forms of pollution has also been considered.
12) The interconnection of a series of abiotical and biological factors in the general bioproduction process in the Adriatic Sea is presented in the paper.
13) Four productivity zones in the Adriatic Sea have been discussed, and numerical values for each one are given to show the extent of the primary production (P u c h e r - P e t k o v i ć & Z o r e - A r m a n d a); on the basis of trophic steps and percentage of ecologic efficaciousness, the annual fish production has been calculated in terms of tons.
14) Papers published by some other authors have been consulted, and the values obtained by the C14 method as used by C v i i ć have been found rather high. The values obtained by T. V u č e t i ć, on the basis of fish egg density and the size of spawning grounds, are also quoted.
15) M. B u l j a n's bioproduction data for three basic degees of the food chain are also presented. A decrease of considerable extent has been found in the exploitation of the tide up energy from the first step: primary production (index 100) to the second step: secondary production - of zooplankton (index 0.1) and thence to the third step: fishes (index 0.02).
The utilization of the solar global radition by the sea surface near Stončica has been calculated, and the resulting value is 1‰ (or 0,39‰ respectively) annualy for the primary production. In the case of the secondary production, the utilization value is considerably lower, i.e. 1/1,000.000 of the total radiation energy. The utilization is still lower in the case of fish production.
16) The conclusion has been drawn that the bioproduction in marine basins is an inefficent process for the transformation of light energy in the sea water. Now it will be hardly acceptable the opinion that the light could be taken as a minimum factor as regards productivity in the shallow Adriatic sea.
17) The paper finally deals with the fluctuation in the field of fisheries in the Adriatic and the possibility of prognostication in this field is discussed.
