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 environmentalhealth. Investigating the size distribution and life stages of these speciesis crucial for understanding their ecology and designing effective conservationstrategies. This study provides data on the distribution and stage ratios of twopopulations of local species of the genus Cyrtograpsus (Decapoda: Brachyura:Varunidae) in the Playa Cangrejales intertidal. These endemic species had notbeen previously described in the study area, highlighting the need for furtherresearch in the future. Three surveys were conducted from December 2019 toFebruary 2020, following a transect perpendicular to the coast, obtaining twoseries of data (C-Iand C-II).Specimens were identified, sexed and measuredin situ for subsequent release. A total of 1099 individuals were counted, identifyingCyrtograpsus 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 ofthese species at Playa Cangrejales coincides with the geographical distributionreported in the literature, although the proportions differ from those reported forother Argentinean beaches. The most frequent lengths were equal to or lessthan 10 mm cephalothorax length (±1 mm). The maximum lengths reported inthe literature for each species were not recorded. For C. angulatus, juvenilesalways predominated over adults and recruits. C. affinis showed fluctuations betweenadult and juvenile proportions in the upper and middle zones, with adultspredominating in the lower zone during December and February. Juveniles occupiedall mesolittoral floors, whereas adults were more frequent in the middleand lower floors. This information is essential to develop management tools toprotect these species and their environment. The division between stages wasrealized following criteria from the literature. Analyses and interpretations weremade using data distribution and frequency graphs.