Variabilidade do ciclo de vida e avaliação da densidade e abundância do Caranguejo cardisoma guanhumi (Latreille, 1828), no Brasil

Abstract

The current study analyzes the average density and abundance of the blue land crab, Cardisoma guanhumi Latreille, 1828, in an estuarine region located in the county of Macau/RN, in Northeast Brazil. The study area was divided into North, Central and South regions. A total of 529 natural dens or burrows were observed in 16 months of sampling (April/ 2014 to July/2015), of which 71,7% were open and 22,1% were closed and 6,2% were cached by fisheries. The diameters of the open burrows ranged from 12 to 174 mm with an average value of 62.05 ± 3.012 mm. The density of open burrows (Dob) and closed burrows (Dcb) was observed, presenting negative tendencies.The average density of the crabswas very variable in each region. The abundance index (AI) was estimated by counting the burrows in 30 fixed quadrants of 2m², with AI = number of burrows/m², being the highest AI and highest activity of the species (open burrows) verified between April and January. The closed hole abundance index was lower throughout the period, probably indicating a continuous process of ecdyses during the year. The negative trend of abundance is probably associated with the synergy between the rainy season and anthropogenic actions (fishing activities). The life cycle of C. guanhumi presented fertilized eggs with an average value of 0.40 mm in diameter. The hatching of the zoeae larva occurred every 5 days, passing through 5 larval instars (Zoea1-5), and in the 40 days after birth metamorphosed into megalopa. Around 7.5 days later, the megalopa became juvenile instar (J1), and in 47.5 days after birth remained in shallow water for 222.5 days. The 13th juvenile instar (J13) was reached at the age of 270 days (nine months), performing successive changes until adulthood. It was estimated that C. guanhumi reached sexual maturity at approximately 3 years of age. The age and growth parameters for both genders of C. guanhumi were determined from the Von Bertalanffy model. The growth curve showed a high value of K (0.37), indicating a relatively high growth rate until 6 years of age, decreasing over the years, but with a high longevity (LC∞ = 123 mm), reaching maximum age between 15 and 20 years. Keywords: Cardisoma guanhumi, guaiamum, burrows, abundance, density.