Ingression of the hydromedusa Neotima lucullana (delle chiaje, 1822) into the ecosystem of the Neretva river estuary (south-eastern Adriatic, Croatia

Abstract

Hydromedusa Neotima lucullana is an endemic species of the Mediterranean Sea. In this study we document the first numerous and permanent occurrence of N. lucullana in the estuary of the Neretva River, an unusual habitat for this typical marine species. We provide COI barcode sequence of this species, which is also first genetic sequence ever published of N. lucullana. Weekly data on the occurrence and abundance of N. lucullana were obtained from reports and records of autonomous divers and local fishermen in the area from Opuzen to Metković from mid-June to the end of October 2021. The individuals were always located in the layer above the bottom with salinity between 35.2 and 38.2. The diameters of the jellyfish bells ranged from 15 mm to 72 mm, most of them between 40 mm and 58 mm. Differential development of the gonads was observed in all specimens larger than 25 mm. In mid-June, the specimens were common but solitary. A week later, the jellyfish were more frequent and in smaller aggregations. From late June to mid-September, the jellyfish were constantly observed in larger aggregations. Toward the autumn, the number of individuals gradually decreased, and by the last week of October, only single individuals were observed. Our results indicate significant changes in the ecosystem of the Neretva estuary and confirm the observed composition of zooplankton communities dominated by marine species in summer and autumn.

First Record of the Alien Tintinnid Ciliate Rhizodomus tagatzi Strelkow and Wirketis 1950 in the Adriatic Sea

“…The non-indigenous copepod species Pseudodiaptomus marinus [54] and a very high proportion of non-indigenous macrozoobenthic species have already been found in this port [55]. Interestingly, P. marinus was also found upstream from the port of Ploče (S2 station in our study), confirming seawater intrusion into the upper reaches of the river [56]. According to the available data, a total of 1.035 × 10 6 m 3 of ballast water was discharged into the Port of Ploče since 2013, with the largest amount in 2021 [57].…”

The Distribution of Pseudodiaptomus marinus in European and Neighbouring Waters—A Rolling Review

“…The Neretva River is the largest watercourse on the eastern coast of the Adriatic Sea, and the Neretva Delta is one of the most important and fertile agricultural areas in Croatia. Following the first record of P. marinus in the delta [22], a further one was tallied in August 2021 during a one-time check of the zooplankton composition in the upper reaches of the Neretva River at the station Opuzen, with two separate vertical hauls from the bottom to the surface using a modified Nansen net with a 125 µm mesh size [37]. Three individuals (two males and one female) were recorded at this time.…”

“…n.a. Neretva River (HR) [37] 10.6-25.5 Vertically integrated values: §1 0-5 m; §2 0-50 m; §3 0-10 m; §4 0-90 m; §5 0-50 m; §6 0-4.5 m. # surface values.…”