Variation in the Adult Sex Ratio and Morphological Traits of <i>Cardisoma guanhumi</i> (Latreille, 1828) in Contrasting Habitats in the Southwest of the Gulf of Mexico

The habitat and its environmental conditions, when optimal, influence the reproduction and survival of organisms, since they can have an impact on demographic parameters such as adult sex ratio (ASR), density, and functional traits (morphological, physiological). Few studies evaluate these factors as a whole in contrasting habitats (such as mangroves and pastures), especially in crab species such as <i>Cardisoma guanhumi</i>. We hypothesized that mangroves would be a favorable habitat for <i>C. guanhumi</i> at a local and regional scale because the environmental conditions (lower temperature, soft and clayey substrate) would have a positive effect on its population dynamics and morphological traits. In order to test this hypothesis, we selected 12 sites on the coasts of the Gulf of Mexico. We found an effect of habitat on ASR, which was male-biased in the mangrove and female-biased in the pasture at a local (by site) and regional scale. Furthermore, crab density was higher in the mangrove and decreased in both habitats as soil hardness increased. In addition, females were heavier and larger (quela, carapace, ventral plate) in the mangrove, and these traits were positively related to burrow temperature in this habitat. Our results support the hypothesis that mangroves are the optimal environment for the development of <i>C. guanhumi</i>. However, although this threatened species has been able to adapt to modified habitats such as pastures, its vulnerability is increased by the surrounding environmental conditions, predation, and commercial exploitation, and the viability of its populations may be affected if it persists in these modified environments.