Relative growth and sexual maturity of the spider crab, mithrax tortugae rathbun, 1920 (brachyura, mithracidae) on a continental island off the southeastern brazilian coast

Abstract

Relative growth can be understood as a morphometric relationship of body parts with the body as a whole, described by a mathematic equation. This study provides information on the patterns of relative growth of Mithrax tortugae from Vitoria Island, southeastern Brazilian coast (23 degrees 44'04 '' S 45 degrees 01'35 '' W). Crabs were obtained from monthly collections by hand during SCUBA diving, between January 2004 and February 2007. A total of 168 crabs was obtained, 64 males and 104 females. Regression analysis was performed among carapace width (CW), as the independent variable, and carapace length (CL), abdomen width (AW), height high and length of the propodus (PH and PL), and gonopod length (GL) as dependent variables, using the power function y = ax(b). Young males showed positive allometry with regard to gonopod growth. Abdomen growth of juvenile females was also positively allometric. The growth patterns recorded for M. tortugae are associated with the species reproductive strategy, i.e., preparation of body parts involved in gamete transfer and egg clutch storage, like the male gonopods and the female abdomen. According to the results obtained, morphological maturity is attained at 12.95 mm CW for males and at 22.40 mm CW for females. The general patterns shown by M. tortugae are similar to the model adopted for Brachyura in general.