Effect of the Invasive Blue Crab (Callinectes sapidus Rathbun, 1896) in a Protected Coastal Lagoon

The potential threat posed by the invasive species Atlantic blue crab ( Callinectes sapidus ), through the foraging strategy based on stomach contents and reproductive ecology analysis, was investigated in the hypersaline Mar Menor lagoon (SE Spain). The main groups preyed upon by blue crab were mostly Penaeus kerathurus and Palaemon spp., accounting for 43.3% of their total weight (gravimetric index, %W), teleosts (19.7%W), brachyurans (14.7%W, mostly Carcinus aestuarii ), and bivalves (9.9%W, mostly Ruditapes decussatus and Cerastoderma edule ). Significant differences were found in feeding habits related to size but not sex. Size at first maturity (L 50 ) was 92 mm for males and 96 mm carapace width (CW) for females. Females showed a seasonal trend in the gonadosomatic index (GSI), which remained high between May and September and peaked in August. Ovigerous females appeared from May until October, peaking in September. The smallest ovigerous specimen found in the lagoon measured 73 mm CW. The number of eggs produced per individual ranged from 284 thousand to 2.2 million, showing a direct correlation with total length. Our results highlight that the blue crab constitutes a threat to the Mar Menor ecosystem, from both the economic and ecological points of view. The blue crab causes major economic damage to local fisheries shortening the average life of fishing gear. It also competes with the fishermen for economically valuable species such as striped prawn, rockpool shrimp, or Mediterranean green crab. We conclude that the blue crab behaves like a dangerous invasive species in the Mar Menor lagoon and further studies are required to design a proper management plan.