Morphometric analyses of Mithraculus forceps (Brachyura: Mithracidae): linear and geometric approaches in a no-take marine reserve population

Mithraculus forceps is a common species on islands in Brazil, and investigations of their sexual and population structures provide insights into their life cycle. Our aim was to analyze relative growth, estimate morphological sexual maturity, and investigate sexual dimorphism in a population inhabiting the Alcatrazes Archipelago. Sampling was conducted using artificial refuge and active capture methods. Five body structures were analyzed for relative growth and morphological sexual maturity estimation: carapace and abdomen width, propodus length and height, and gonopod length in males. Sexual dimorphism was observed in carapace and propodus shape. Morphological sexual maturity was estimated at 10.12 mm carapace width for males and 10.66 mm carapace width for females. Some variations in morphometric aspects were observed in the analyzed population when compared to other populations of M. forceps inhabiting unprotected areas. Crabs from Alcatrazes may reach larger sizes due to their protected habitat. This underscores the crucial role of a marine conservation unit in preserving significant ecological processes and highlights the importance of management plans for other locations and environments facing anthropogenic pressures.