Population structure and growth of the hermit crab Pagurus brevidacylus (Anomura : Paguridae) from the northern coast of São Paulo, Brazil

The hermit crab Paguras brevidactylus (Crustacea: Anomura: Paguridea) from the infralittoral area of Anchieta Island, Ubatuba, was characterized by population Structure (size, sex ratio, reproduction and recruitment) and growth. Animals were collected monthly during 1999 by SCUBA diving. A total of 1525 individuals was collected (633 males and 892 females), 695 of them were ovigerous females. Overall sex ratio was 0.7:1 in favour of females. The crabs showed a unimodal distribution with males significantly larger than females. Ovigerous females were collected during all months and in high percentages from 1.0 mm of shield length, demonstrating intense and Continuous reproduction. The longevity was approximately 24 months for males and 18 for females, which showed larger growth rate and reached sexual maturity earlier (two months) than males. The low number of males in this Population may be due to the longer life span. Moreover, the sexual dimorphism favours males during the intra- and interspecific fights by shell, food, reproduction and territory. Females demonstrated a short life cycle and intense reproduction.

Desenvolvimento pós-embrionário de Pagurus brevidactylus (Stimpson, 1858) (Decapoda, Paguridae), em laboratório

All the larval stages of the hermit crab Pagurus brevidactylus were studied in the laboratory, with special emphasis on external morphology and on the duration of each stage. The larvae were kept in individual containers, with water of 35 salinity and fed on nauplii of Artemia salina; room temperature was maintained at 24±1ºC. The post-embryonic development includes four stages of zoea and one of megalopa. All the larval stages are drawn and described in detail.

Are the preference and selection patterns of hermit crabs for gastropod shells species- or site-specific?

Experimental analyses of hermit crabs and their preferences for shells are essential to understand the intrinsic relationship of the crabs' dependence on shells, and may be useful to explain their shell use pattern in nature. The aim of this study was to evaluate the effect of crab species and site on the pattern of shell use, selection, and preference in the south-western Atlantic hermit crabs Pagurus brevidactylus and Pagurus criniticornis, comparing sympatric and allopatric populations. Differently from the traditional approach to evaluate shell preference by simply determining the shell selection pattern (i.e., the number of shells of each type selected), preference was defined (according to [Liszka, D., Underwood, AJ., 1990. An experimental design to determine preferences for gastropod shells by a hermit-crab. J. Exp. Mar. Biol. Ecol., 137(1), 47-62]) by the comparison of the number of crabs changing for a particular shell type when three options were given (Cerithium atratum, Morula nodulosa, and Tegula viridula) with the number of crabs changing for this same type when only this type was offered. The effect of crab species was tested at Cabelo Gordo Beach, where P. brevidacrylus was found occupying shells of C. atratum, M. nodulosa, and T viridula in similar frequencies, whereas P. criniticornis occupied predominantly shells of C atratum. In laboratory experiments the selection patterns of the two hermit-crab species for these three gastropods were different, with P criniticornis selecting mainly shells of C atratum, and R brevidactylus selecting more shells of M. nodulosa. The shell preference was also dependent on crab species, with P. criniticornis showing a clear preference for shells of C atratum, whereas P. brevidactylus did not show a preference for any of the tested shells. The effect of site was tested for the two species comparing data from Cabelo Gordo to Preta (P brevidactylus) and Araca beaches (P. criniticornis). The pattern of shell use, selection, and preference was demonstrated to be dependent on site only for P. brevidactylus. The results also showed that the shell use pattern of P criniticornis can be explained by its preference at both sites, whereas for P. brevidactylus it occurred only at Cabelo Gordo, where the absence of preference was correlated with the similar use of the three gastropod species studied. Finally, the results showed that the shell selection pattern cannot be considered as a measure of shell preference, since it overestimates crab selectivity. (C) 2009 Elsevier B.V. All rights reserved.

The population structure of two sympatric hermit-crab species on a subtidal rocky shore of an island in southeastern Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Ecologia e biologia populacional dos ermitões (Decapoda, Anomura) do litoral norte de Santa Catarina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)