Unusual occurrence of Pelagia noctiluca in the Adriatic: I – Some notes on the biology of Pelagia noctiluca in the Gulf of Trieste

Abstract

       Large swarms of the jellyfish Pelagia noctiluca was noticed in the Gulf of Triest in the years 1977 - 80. Young stages - ephyrae (0.3 mm - 4.5 mm in diameter between tips of marginal lappets) were found from May to November in 1978 - 79. In the time of ephyrae occurence salinity ranged from 33‰ to 38‰ and temperature from 15°C to 24°C. Our findings tend to confirm that Pelagia noctiluca has a well - marked breeding period.

       Larger specimen were observed from March to December in the seawater of temperatures from 9°C - 25°C and salinities from 32‰ - 38‰.

        The food of the examined Pelagia noctiluca comprised Noctiluca scintilans, Hydromedusae, Siphonophora, Penilia avirostris, Evadne, Copepoda, Appendicularia, Doliolum, sardina and anchovy eggs.

       It is interesting to record that exceptionally aboundant Pelagia noctiluca during the summers 1977-79 was accompanied by swarms of Doliolum nationalis.