Population dynamics of Armases rubripes in southwestern Atlantic salt marshes: seasonality, abiotic influence and reproductive biology

Abstract

The knowledge about reproductive biology and influence of seasonality and abiotic factors over crabs improves the understanding of their role in salt marsh ecosystems. Focusing on Armases rubripes, we analyzed of 2,206 individuals in terms of abundance, sex ratio, morphometry and egg count, monthly sampled along two years. Through Generalized Linear Mixed-effects Models we found a continuous presence of A. rubripes at Patos Lagoon Estuary (PLE), Brazil, with seasonal peaks of males and non-ovigerous females mostly during cold autumn–winter. The opposite pattern was found to ovigerous females, when they were prevalent during warm spring–summer and early autumn. The overall sex ratio indicated a predominance of males over females (1.2♂: 1♀), but male peaks during summer months (mainly ≥2♂: 1♀) could be due the migration of females to spawning grounds. The first maturation size based on the carapace width (CW) was estimated at 7.9 mm for males and 7.0 mm for females. The highest gain in fecundity (79.2%) occurred in the width class immediately after the transitional maturation stage (10.1–11.0 mm CW), suggesting that size influences in the ability of ovigerous females in the transitional maturation stage to reach the maximum reproductive outputs. The fecundity of 2,880 (± 1,964) eggs shown a low fecundity for A. rubripes along the sampled region. Our results bring a new information about the occurrence and reproductive biology of this species in salt marshes from medium latitudes, opening the discussion about our findings.