Occurrence of the lessepsian species Portunus segnis (Crustacea: Decapoda) in the Gulf of Gabes (Tunisia): first record and new information on its biology and ecology

The alien blue swimming crab, Portunus segnis (Forskal, 1775), an Indo-Pacific species has been recorded in the Southern Mediterranean Sea since decades, even if its occurrence along the Tunisian coasts was not recorded yet. This paper reports the first record of P. segnis in the Gulf of Gabes, south-eastern Tunisia, with few observations on its biology and ecology. Twenty-four females of P. segnis were accidentally caught by local fishermen in October 2014 in shallow sandy areas covered mostly by seagrass and algal beds. Among these 24 individuals, 14 specimens (58.33%) were ovigerous. The mean carapace length (CL) and width (CW) of ovigerous females were 143.0 +/- 5.8 mm and 67.8 +/- 3.6 mm respectively, whereas in non ovigerous females these were 127.3 +/- 6.8 mm and 58.9 +/- 4.2 mm, respectively. The relationships between the size (CW and CL) and weight (TW) for ovigerous and non ovigerous females were also examined with non-linear equations. In addition, the mean number of eggs (fecundity) of 12 ovigerous females (whose mean CW = 143.3 +/- 6.2 mm) was 777642 +/- 80684. The correlations between fecundity and both CW and TW were found to be statistically significant