Reproductive biology of invasive female Carcinus maenas (Linnaeus, 1758) (Decapoda: Brachyura: Carcinidae) in southern Australia

Invasive marine species pose significant threats to marine ecosystems, with reproduction often facilitating their establishment and spread. The European green shore crab, Carcinus maenas (Linnaeus, 1758), is a global marine invader, but its reproduction has rarely been studied in the Southern Hemisphere. We assessed ovarian development, size at sexual maturity, fecundity, and reproductive period of invasive female C. maenas in Gulf St Vincent, South Australia. We compared these reproductive traits with published data of C. maenas from native and invasive populations worldwide. Female crabs were collected monthly from March to November 2018, and their ovaries staged macroscopically and histologically to determine sexual maturity and reproductive period. Fecundity was measured in gravid crabs collected from 2018 and earlier surveys. Population structure analyses indicated a male-biased sex ratio and size-dependent patterns of ovarian development. Female C. maenas reached morphometric maturity at 30.2 mm carapace width (CW) and gonadal maturity at 29.8 mm CW, consistent with estimates from other regions. Mean fecundity (210,847 eggs per clutch, range 29,048–526,521) was higher than previously reported for the species. The reproductive period spanned eight months (April to November), coinciding with water temperatures below 20°C. Our findings characterise the reproductive biology of C. maenas in its invasive range in southern Australia, contributing to our understanding of the mechanisms driving global establishment and spread of the species.