Relative growth in the Mediterranean endemic shore crab Brachynotus foresti Zariquiey Álvarez, 1968 (Decapoda: Brachyura: Varunidae)

Abstract

Abstract The relative growth of crustaceans has become a solid field of study since the early allometric studies undertaken during the first decades of the 20th century. The type of relative growth of brachyuran crabs mainly depends on the number of critical moults and growth phases, as well as on differences in the slopes of the relative growth of secondary sexual characters. We analysed for the first time the allometric growth of the brachyuran Brachynotus forestiZariquiey Álvarez, 1968 (Varunidae), a small Mediterranean endemic species, testing whether its small size might impede the manifestation of large allometries through ontogeny. We obtained 13 body measurements from 370 females and 269 males collected from the eastern Iberian Peninsula. Carapace width ranged between 2.9 and 13.9 mm. Despite the small size, large differences between males and females were observed in the relative growth of the pleon and chelipeds, as previously seen in many other Brachyura. Females followed a two-phase growth pattern, with a clear pubertal moult separating them, approximately matching an estimated size at maturity of 6.8 mm. Males also showed a pattern of development in two phases, with an increased slope in the relative growth of chelipeds during the second phase, the shift corresponding to a size at maturity of 8.0 mm. The main effect of small size in Brachynotus foresti is that immature and mature growth phases overlap so that both males and females reach maturity over a wide size range.