Size distribution and proportion of stages of Cyrtograpsus species in Playa Cangrejales, Argentina

Abstract

Crabs are fundamental in coastal ecosystems due to their role in nutrient cycling, habitat structuring, population control and as indicators of environmental health. Investigating the size distribution and life stages of these species is crucial for understanding their ecology and designing effective conservation strategies. This study provides data on the distribution and stage ratios of two populations of local species of the genus Cyrtograpsus (Decapoda: Brachyura: Varunidae) in the Playa Cangrejales intertidal. These endemic species had not been previously described in the study area, highlighting the need for further research in the future. Three surveys were conducted from December 2019 to February 2020, following a transect perpendicular to the coast, obtaining two series of data (C-I and C-II). Specimens were identified, sexed and measured in situ for subsequent release. A total of 1099 individuals were counted, identifying Cyrtograpsus affinis (C-I = 278; C-II = 332) and Cyrtograpsus angulatus (C-I = 215; C-II = 277), with a higher proportion of C. affinis. The presence of these species at Playa Cangrejales coincides with the geographical distribution reported in the literature, although the proportions differ from those reported for other Argentinean beaches. The most frequent lengths were equal to or less than 10 mm cephalothorax length (±1 mm). The maximum lengths reported in the literature for each species were not recorded. For C. angulatus, juveniles always predominated over adults and recruits. C. affinis showed fluctuations between adult and juvenile proportions in the upper and middle zones, with adults predominating in the lower zone during December and February. Juveniles occupied all mesolittoral floors, whereas adults were more frequent in the middle and lower floors. This information is essential to develop management tools to protect these species and their environment. The division between stages was realized following criteria from the literature. Analyses and interpretations were made using data distribution and frequency graphs.