Contribution a la connaissance d'une Poussee extraordinaire d' algues unicellulaires (Adriatique Septentrionale)

Abstract

The phenomenon known as "sea-water bloom" ("mare sporco", "Meeresbliite") was observed in the northern Adriatic in summer 1983. It appears as a gelatinous, dense mass floating at the sea surface. Samples from Crikvenica (July) and Lopar, Rab Island (August) were analysed. A total of 58 diatoms, of which 32 benthic species, 25 dinoflagellates and 10 coccolithophorids were identified by microscopy. A recently described genus, Spatulodinium Cachon & Cachon, represented by the type species S. pseudonoctiluca (Pouchet) Cachon & Cachon, was also found. With respect to the known ecology of individual algal groups it may be concluded that benthic diatoms had reproduced intensively at the sea bottom a long while before the phenomenon became visible at the sea surface. Reproduction is also the period of the most intensive secretion of mucus. Release of the gelatinous mass from the sea bottom at summer temperatures which are unfavourable for diatoms, is actually the end of the bloom. A gelatinous mass full of gases released by bacterial degradation begins to ascend and on its way towards the sea surface, it embeds plankton organisms. In the final stage torn mucus descends to the bottom where it is gradually completely degraded.