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

Abstract

The main goal of this investigation was to characterize the population structure and shell occupancy of two sympatric hermit-crab species, Pagurus brevidactylus and Paguristes tortugae. The study was undertaken at Couves Island on the southeastern coast of Brazil, from March 2010 through February 2011, on subtidal rocky bottoms. Specimens were collected by SCUBA diving sessions. A total of 195 individuals of P. brevidactylus and 132 of P. tortugae were examined. Both populations showed unimodal size-frequency distributions, which were non-normal for P. brevidactylus and normal for P. tortugae. The median size of P. brevidactylus was significantly smaller than P. tortugae; in both species, males were significantly larger than females. For both, juveniles and ovigerous females were recorded in all size classes and in almost the entire sampling period. No significant departures from the 1:1 sex ratio were detected, although some size classes were skewed. Overlaps in shell occupation were recorded. Pagurus brevidactylus and P. tortugae showed similar population features; they reached sexual maturity at small sizes, and the nearly year-round presence of young and ovigerous females suggests continuous reproduction. These inter-specific interactions involving resource partitioning suggest a regulatory process that is probably part of the equilibrium strategy of these populations.

Shell use by sympatric hermit crab species in a seasonally open coastal lagoon in Northeastern Brazil

“…Thus, the availability of N. virginea and differential use of other species of shells appear to reveal resource partitioning (of shells) between the two study species and among their CSL classes to minimize intra-/inter-specific competition between populations, promoting their co-occurrence (Turra & Leite, 2001;Vance, 1972b Competition-relatedness hypothesis postulates the existence of mutual competition between evolutionarily related taxa (Cahill et al, 2008;Elton, 1946;Elton & Miller, 1954); however, the present study shows otherwise. In this case, sister group fixed characters that favored develop mechanisms minimizing competition, a pattern reported in portunids of the genus Achelous De Haan, 1833, in Ubatuba Bay (São Paulo, Southeastern Brazil) by Lima, Andrade, et al (2014) and Lima, Cobo, et al (2014).…”

“…All specimens were identified according to Melo (1999) and sexed according to the position of the gonopores (in the third or fifth pair of pereiopods in females and males, respectively) as in Bertini and Franzoso (1999). Subsequently to identification and sexing, hermit crab specimens were classified into three categories: males (M), non-ovigerous females (F) and ovigerous females (OF) (females with egg mass adhered to pleopods), according to Lima, Andrade, et al (2014) and Lima, Cobo, et al (2014).…”

Composition, density, and shell use of hermit crabs (Crustacea: Paguroidea) from subtidal boulder fields in southeastern Brazil

“…It is commonly believed that these species are part of the decapod fauna in southeastern Brazil, especially in the rocky sublittoral as described by Melo (1999) and observed by Mantelatto & Garcia (2002) and by Lima et al (2014) for the coast of São Paulo State. In contrast, for C. tibicen and D. venosus, low densities were recorded in this study.…”

Shell occupation as a limiting factor forPagurus brevidactylus(Stimpson, 1859) in the Marine State Park of Laje de Santos, Brazil

“…That said, our aim is to study the population aspects such as population structure, fecundity and reproductive output (RO) of Pagurus brevidactylus (Stimpson, 1859) and their relationship with shell availability at Marine State Park of Laje de Santos (MSPLS). Species inhabiting protected areas can have differences in development due to local environmental factors (Teschima et al 2016), and although several studies had been conducted with P. brevidactylus in the northern littoral of São Paulo State, Brazil (Negreiros-Fransozo et al 1991;Mantelatto and Meireles 2004;Iossi et al 2005;Mantelatto et al 2005;Lima et al 2014; among others), we are bringing the first information on its biology for the MSPLS, a conservation area located in the central region of São Paulo state, and for being a conservation area, we expect to find shells of optimal sizes for full development of the hermit crab. Comparative studies are always important to understand the full biology of a determined species and its relationships with the environment, especially in protected areas to assess the management status and to help the future of the management plans.…”