BLUECRAB INTERREG: THE REPRODUCTIVE BIOLOGY OF CALLINECTES SAPIDUS IN CAORLE AND MARANO LAGOONS

The blue crab Callinectes sapidus (Rathbun, 1896) is an invasive alien species in the Mediterranean that in recent years, thanks to its adaptability, has threatened local biodiversity and traditional fishing activities, especially on the coasts of the northern Adriatic. This study is part of the Italian-Slovenian Interreg Bluecrab project, which aims to protect the areas of the upper Adriatic threatened by this species through a monitoring system and sustainable management involving institutions, fishing companies and local communities. Little is still known about its life cycle and reproduction at the local level. Understanding this is fundamental to taking effective management measures. The crabs were sampled monthly in the lagoons of Marano and Caorle at three stations with increasing salinity. In the Marano lagoon, a fyke net was used for the catch, while in Caorle two different types of traps were used: the traditional square trap and a round trap. In addition, a multi-parameter probe was placed at each station to measure environmental parameters such as temperature and salinity, which are known to influence the distribution and behaviour of the species. Carapace width (with and without spines), carapace length and weight were measured. A subsample of 20 crabs per lagoon (10 males and 10 females, if available) was taken for dissection to calculate the GSI (gonado-somatic index) and HSI (hepato-somatic index) and to analyse gonadal development. The tissues were embedded in epoxy resin for histological analysis to confirm the reproductive stage. All statistical analyses were performed using R. A total of 297 crabs were sampled, 70 from Marano and 227 from Caorle. The average size of the species is 147.8±28.8 mm and 152.6±19.7 mm for females and males, respectively, in Caorle and 171.5±9.8 mm and 176.2±13.8 mm in Marano; the average weight is 158.4±56.2 g for females and 229.8±84.7 g in Caorle, 229.0±51.8 g and 372.7±71.7 g in Marano. The M:F sex ratio is 1:0.79 for Marano and 1:0.82 for Caorle. The breeding season is between May and August, with the peak between June and August. The reproductive indices are currently being analysed to determine the timing and duration of ovarian development in order to determine reproductive migrations. This is the first study of the reproductive biology of this invasive alien species in the high latitudes of the Mediterranean, and our preliminary data suggest particular physiological responses.