Population dynamics of the burrowing shrimp Lepidophthalmus siriboia Felder and Rodrigues, 1993 (Reptantia: Axiidea: Callianassidae) on the Amazonian coast

Abstract

This study provides information on the population structure, reproductive biology, growth, and mortality of Lepidophthalmus siriboia Felder and Rodrigues, 1993 on Algodoal Island in northern Brazil. Each month between June 2007 and May 2008, approximately 100 specimens were collected from a sand-muddy beach. In the laboratory, the specimens were wet weighed, measured - carapace length (CL) - and length of the major chela (ChL) and sexed. The ovigerous females were classified according to the stage of embryonic development. A total of 1268 individuals were analyzed (753 males, 515 females). Females were significantly larger than males throughout most of the year. Males reached sexual maturity at 6 mm and females at 7 mm. The observed overall sex ratio (1.5 male:1 female) was significantly different to the expected sex ratio of 1:1 (chi(2) = 44.3; df = 1; p < 0.01; n = 1268). There was a significant female bias (0.7:1) in the specimens with a carapace length of over 10 mm (chi(2) = 7.9; df = 1; p < 0.01; n = 313). Ovigerous females occurred throughout the study period, peaking in July, January, and April. The smallest ovigerous female had a carapace length of 7.5 mm. Fecundity was positively and significantly related to carapace length and body weight. Females had a higher maximum asymptotic carapace length and longevity (females: L infinity = 15.3 mm carapace length, longevity = 1.4 years; males: L infinity = 14.9 mm carapace length, longevity = 1.3 years). Males grow faster (K = 0.009) than females (K = 0.007) before reaching sexual maturity, but as adults, growth rates are similar in both sexes. Estimates of mortality rates varied among methods, but were invariably higher for males.