The shallow Vrana (Vransko) Lake in Dalmatia, Croatia, is a brackish water (oligohaline) lake that was artificially connected to the Adriatic Sea by the Prosika Canal, built in the 18th century. The aim of this study was to provide an updated overview of macro-crustacean diversity (class Malacostraca) in the Vrana Lake Basin. This synthesis includes all available records, combining the author's field observations with data from the scientific literature, and focuses on macro-crustacean taxa within the orders Amphipoda, Decapoda, Isopoda, and Mysida. Benthic macroinvertebrates were sampled using a hand net between 2011 and 2022, while baited crayfish traps were deployed during a one-night sampling effort in May/June 2024. Specimens of the invasive blue crab were collected manually in 2023 and 2024. In total, 32 sites were surveyed, 29 with a hand net and three exclusively with baited traps. A total of 21 macro-crustacean taxa were recorded in the Vrana Lake Basin between 2011 and 2024, comprising 16 species and five genera. The order Amphipoda was the most taxonomically diverse, with 11 taxa, followed by Isopoda (4), Decapoda (4), and Mysida (2). The highest species richness (16 taxa) was observed at the mouth of the Prosika Canal into the Adriatic Sea. The macro-crustacean fauna of the Vrana Lake Basin represents a unique assemblage of freshwater/oligohaline and brackish/marine species. The freshwater/oligohaline species, including the isopod Proasellus coxalis, amphipod Niphargus dalmatinus, and decapods Palaemon antennarius and Austropotamobius fulcisianus, were more abundant and widely distributed in the tributaries, with P. coxalis and P. antennarius also occurring in the lake. Most of the brackish/marine species were recorded only at the mouth of the Prosika Canal into the Adriatic Sea. Amphipods Gammarus aequicauda and Pectenogammarus stocki, and the isopod Lekanesphaera hookeri, were dominant in the lake and the Prosika Canal during, and immediately after periods of increased salinity. A recent addition to the brackish/marine group is the invasive blue crab (Callinectes sapidus), whose continued spread may pose a serious threat to biodiversity in the Vrana Lake Basin. The endangered white-clawed crayfish (A. fulcisianus) was recorded only in the freshwater Lateral Canal. Its continued monitoring is essential to assess the effectiveness of conservation measures, especially in light of planned sediment and vegetation removal to maintain flow in the canal. Salinization remains the primary threat to aquatic biodiversity in the basin. Urgent implementation of active management strategies, such as construction of a movable gate on the Prosika Canal, is necessary to mitigate this risk. The data presented in this study are critical for understanding and anticipating future changes in the macro-crustacean assemblages of this ecologically sensitive ecosystem.
Žganec et al. (Thu,) studied this question.