Hemigrapsus sanguineus (de Haan, 1835) – A new alien crab for the Bulgarian Black Sea coast (Decapoda: Brachyura: Varunidae)

In the summer of 2024 and 2025, the fishing port of the town of Balchik (Northern Black Sea coast) was surveyed by snorkeling and as a result, several specimens of the invasive Asian shore crab Hemigrapsus sanguineus have been found for the first time along the Bulgarian Black Sea coast. This finding represents also a new record of this genus for the Bulgarian Black Sea decapod fauna (Suppl. material 1). At a depth of 0.20–0.60 m, in crevices between piled-up stones on the periphery of the fishing port, two males and two females (one ovigerous), were collected. Two more males were spotted, but were not captured. This crab is native to the northwestern Pacific and has been introduced to several other regions, and is now regarded an invasive species in North America and Europe (Klassen 2012, Saborowski et al. 2023). Previously, the species has only been reported for the Romanian Black Sea coast (Constanța area), where a single male was found in 2008 (Micu et al. 2010). The discovery of breading Asian shore crab specimens 16 years later along the Bulgarian coast is of significant biological and ecological interest. Therefore, the aims of the present study were to: report on this new finding of an alien decapod species, describe the collected specimens, and present preliminary information about its diet. report on this new finding of an alien decapod species, describe the collected specimens, and present preliminary information about its diet. The specimen measurement ranges were as follows: ♂ carapace width (CW) 37.64–43.05 mm, ♂ carapace length (CL) 32.53–36.57 mm, ♀ CW 34.47–38.73 mm, ♀ CL 29.17–33.29 mm; ♂ cheliped propodus length (CPL) 25.67–33.28 mm, ♂ cheliped propodus width (CPW) 16.2–21.01 mm; ♀ CPL 16.6–18.6 mm, ♀ CPW 8.8–9.2 mm. According to literature data (Fukui 1988), the size of these crabs correspond to an age of over 2 years. The Asian shore crab is a generalist predator and an opportunistic omnivore. The collected specimens were dissected to examine their stomach contents and morphology of the ossicles. Diatoms, parts of algae-talus ( Cladophora ), particles of Zostera leaves, Porifera spicules, Polychaeta setae, shell-fragments of juvenile Mediterranean mussels, exoskeleton fragments from small crustaceans, and detritus were found among the stomach contents. The present observations confirm and complement our knowledge about the trophology of this species (Klassen 2012). For now, it is still difficult to predict the development of H. sanguineus populations along the Bulgarian coast and how they will affect native species in the Black Sea ecosystems, but this find should sharpen our attention towards targeted monitoring for early detection of a potential invasion in the area.