Long-term Monitoring of Carnivorous Gelatinous Macrozooplankton in the Area of Dubrovnik-Neretva County (Croatia)

Abstract

In the southern part the Adriatic, gelatinous macrozooplankton fauna is poorly known compared to the other taxa. Therefore, our goal was to collect and systematize all available phenological data and abundances of gelatinous organisms based on scientific surveys from 1996 to 2020 and a ”citizen science“ sighting program in the southern Croatian waters. The inter-annual variability and seasonality of planktonic Cnidaria and Ctenophora were described. A total of 590 reports was received from citizens, which summed up to result in 870 data together with the scientists’ records. In total, 15 species were recorded. Of these, scyphomedusa Pelagia noctiluca accounted for 34 %, followed by ctenophora Cestum veneris (19 %) and the scyphomedusa Cothylorhiza tuberculata (17 %). Mass occurrence was most frequently found in P. noctiluca and then in C. tuberculata and C. veneris. Isolated mass occurrence was recorded for the freshwater hydromedusa Craspedacusta sowerbii, found in Lake Kuti near the mouth of the Neretva River, and for the scyphomedusa Aurelia cf. solida. The three species A. solida, Mnemiopsis leidyi and C. sowerbii are not native to European waters. Considered that alien species are invading the Adriatic Sea and human impact and global warming are increasing, it is crucial to carefully monitor the occurrence of gelatinous zooplankton taxa and to conduct studies focused on deciphering their ecological impact in marine ecosystems. Therefore, our empirical analysis of 25 years of observations provides essential information on the variation of gelatinous zooplankton in the Southern Adriatic region.