Population structure and dynamics of the invasive crab Charybdis longicollis parasitised by the rhizocephalan Heterosaccus dollfusi along the Mediterranean coast of Turkey

The invasive crab Charybdis longicollis was first reported in Mersin Bay (Mediterranean Sea/Turkey) in 1954, and since the early 1990s, its populations have been heavily parasitised by the alien rhizocephalan Heterosaccus dollfusi. In Antalya Bay, 46.6% of the trawled catch is constituted by C. longicollis. Monthly biomass values fluctuated between 67 kg km−2 (June) and 704 kg km−2 (October), with a mean of 260 kg km−2. The percentage of change in females ranged from 29% in October to 53% in January. The mean carapace width of uninfected crabs was significantly larger in males (35.1 mm) than females (30.6 mm). Male crabs (34.3%) were more heavily parasitised than females (12.1%). The reduction in size of the chela and broadening of the abdomen are two characteristic modifications of infected males. The size at first maturity was estimated at CW = 24.7 mm. Ovigerous females were found all year-round but were more abundant in spring. Male and female individuals of C. longicollis displayed a maximum of three and one modal groups per year, respectively. Natural mortality (M) was estimated as 1.1 year−1 for male crabs.