ECOLOGY OF MUCILAGE PRODUCTION BY AMPHORA COFFEAEFORMIS VAR. PERPUSILLA BLOOMS OF ADRIATIC SEA MILENA BRUNO, ANNAMARIA COCCIA, and LAURA VOLTERRA* Laboratorio di Igiene Ambientale, Istituto Superiore di Sanit~ v. le Regina Elene 299 - 00161 - Roma, Italy (Received April 18, 1991; revised June 26, 1992) Abstract. Diatoms isolated from mucilage blooms which emerged in the Adriatic Sea during summer 1988, were put in culture and then later, identified as Amphora coffeaeformis vat. perpusilla (GRUN.) Cleve. Experiments of growth in orthophosphate and nitrate enrichment led to noticeable variations in the mucilage production. In this paper we propose a benthonic origin for the Adriatic mucilages, due to the presence of considerably more nitrates rather than phosphates. 1. Introduction In August 1988, large mucilaginous masses, clustered in extensive 'pillows', appeared in the northern Adriatic Sea, invading even the coastal bathing areas and following nycthemeral cycles and sea hydrodynamics. A microscopic examination of samples, collected along the coast of the Emilia Romagna region, showed the presence of many species of planktonic diatoms, a few dinoflagellates, pieces of macroalgae and exuviae of zooplankton. These organisms were probably trapped in the gelatinous matrix during the vertical and horizontal movements of the mucilages in the water. This invasion, although occurred previously, (Zanardini, 1873; Forti, 1906; Zanon, 1929), made a strong impression on the population mainly because of the exten- siveness of the area affected (along the northern and central Adriatic coasts from the Istrian peninsula in Yugoslavia as far as the Abruzzo Region) (Maley and Fagnaneli, 1988) as well as the fact that this occurred in the height of the holiday season. The blooms recurred in summer 1989 on a much wider scale, causing a serious drop in the numbers of tourists and considerable economic damage through the coastal area. The mucilage was arranged in floating 'pillows' 5 to 10 cm thick, and as long as a few metres up to as much as several kilometres; its color ranged from light ochre to dark brown which was probably a consequence of mucilage ageing. Materials together with degrading bacteria, were trapped in the matrix of mucilage during its wandering in the sea. According to Myklestad and Haugh (1972), Myklestad (1977) and Myklestad et al., (1989) these gelatinous masses are produced by several species of diatoms present in all the phases of cell growth, especially where there * Author for all correspondence Water, Air, and Soil Pollution 69: 201-207, 1993. 9 1993 Kluwer Academic Publishers. Printed in the Netherlands.