Population biology and growth of the hermit crab Dardanus insignis at Armação do Itapocoroy, southern Brazil

Abstract

Brazil. Monthly samples were carried out in the morning, afternoon, and evening using two over-trawls with 6 m at the opening, 3.0-cm mesh at the outer part and 2.0-cm mesh in the bag. Dardanus insignis was collected year round but with higher densities in September and October. The hermit crabs were more abundant during the evening than the afternoon but no di¡erences were recorded between morning and both evening and afternoon. Females were slightly more abundant than males but the sex ratio did not di¡er from 1:1. Females were more abundant in the smallest size-classes (51.8 cm) while males outnumbered females in the largest ones (42.2 cm). The individuals of this population of D. insignis have a mean cephalothoracic length of 1.89 AE0.40 cm (range 1.00 to 3.90 cm) and a mean weight of 40.26 AE27.06 g. The size distribution showed an unimodal pattern, with males being larger than ovigerous females, which, in turn, were larger than non-ovigerous females. Dardanus insignis showed a seasonal reproductive pattern with a peak from September to November and complete absence of ovigerous females from April to August. The von Bertalan¡y growth function (VBGF) with temporal oscillation ¢tted for this population of D. insignis had the following parameters: L 1 ¼4.40 cm, K¼0.60, C¼0.95, WP¼0.35. Recruitment was estimated to start in September and was extended to the following months. Estimates of longevity ranged from 20 to 62 months. A mortality rate of 2.21 was estimated based on the length converted catch curve. The cephalothoracic length of males and females showed, respectively, positive and negative allometry with both cephalothoracic width and crab weight.

Population biology of the hermit crab Petrochirus diogenes (Linnaeus) (Crustacea, Decapoda) in Southern Brazil

“…However, a sympatric population of D. insignis at Arma~ao of Itapocoroy showed pos iti ve allometry between cephalothoracic length and width (BRANCO et al 2002). Variati on in the all ometri c patterns was also recorded fo r the relationship between cephalothoracic length and crab weight.…”

“…Variati on in the all ometri c patterns was also recorded fo r the relationship between cephalothoracic length and crab weight. Isometry was recorded in the study populati on and for D. insignis (s hield length vs. shell weight -FERNANDES-G6ES & FRANSOZO 2000) in Ubatuba region, while BRANCO et al (2002) recorded a negative all ometry between these variab les fo r D. insignis at Arma<;:ao of Itapocoroy. T his variability in allometric patterns between species and populations reinfo rce th e plasticity of crab dimensions proposed by BLACKSTONE (1985).…”

Use of pleopod morphology to determine sexual dimorphism and maturity in hermit crabs: Isocheles sawayai as a model

“…Such diVerences are potentially important, both in determining the nature of population regulation within a species, and in determining the nature of interactions between species (Abrams 1988). Sexual dimorphism has been extensively reported for many hermit crabs; almost all studies have focused on the propodus chelipeds and/or these appendages in relation to resource use (Fotheringham 1976;Bertness 1980;Abrams 1988;Manjón-Cabeza and García Raso 1996;Gherardi and Nardone 1997;Fransozo and Mantelatto 1998;Mantelatto and Sousa 2000;Garcia and Mantelatto 2001;Branco et al 2002;Martinelli et al 2002;Litulo 2005;Mantelatto et al 2005). Recently, we demonstrated that the pleopods may be an important aspect to be considered in such studies .…”

Habitat heterogeneity in the assemblages and shell use by the most abundant hermit crabs (Anomura: Diogenidae and Paguridae): does the occupied shell species differ according to gender and species?

“…This is because the sexes have different sizes, with males being larger than females, which has already been described in several studies on hermit crabs (Branco et al, 2002). In general, two hypotheses have been proposed for the size difference (see references below): males invest more energy in growth to reach larger sizes than females, allowing them to use larger and heavier shells, whereas females direct energy into the production of eggs and incubation, resulting in less somatic growth and therefore, they occupy lighter shells that require less energy to carry (Bertness, 1981a).…”

“…In general, two hypotheses have been proposed for the size difference (see references below): males invest more energy in growth to reach larger sizes than females, allowing them to use larger and heavier shells, whereas females direct energy into the production of eggs and incubation, resulting in less somatic growth and therefore, they occupy lighter shells that require less energy to carry (Bertness, 1981a). Alternatively, the difference in body size might be the result of an evolutionary selection of reproduction prowess, where hermit crabs compete for reproductive partners and the largest individuals tend to win intraspecific combats, which might represent a selective factor over generations (Bertness, 1981a;Abrams, 1988, Mantelatto andSousa, 2000;Garcia and Mantelatto, 2001;Branco et al, 2002;Martinelli et al, 2002;Mantelatto et al, 2005;Biagi et al, 2006;.…”