Abstract The aim of this study was to characterize the pattern of gastropod shell occupation in the field and selection of shell size and type under laboratory conditions by the hermit crab Pagurus criniticornis (Dana, 1852), inhabiting the infralittoral area of Anchieta Island, São Paulo, Brazil. Hermit crabs were obtained monthly during 1999 by SCUBA diving. For experiments under laboratory conditions, samplings were performed in 2002. The hermit crabs occupied 16 species of gastropods shells. Cerithium atratum (Born, 1778) was the most occupied shell (89.31%), followed by Morula nodulosa (4.73%) (Adams, 1845). No difference was observed in the pattern of occupation between males and females. The equations that best demonstrated the relationship between hermit crabs and their shells were those that involved Shell Wet Weight (SWW) and Shell Internal Volume (SIV). The laboratory experiments were in accordance to the pattern of occupation observed in the field; the mean value of SAI (Shell Adequacy Index) recorded to the population studied was 1.13 with a trend to increase this value in the last size classes. The results obtained corroborate with the hypothesis of the occupation process of shells governed not only by availability of shells, but also by its architecture. In addition, the shell stock in the area is one another important condition related to the exhibited pattern of shell occupation by P. criniticornis, and allows the stable coexistence among the island assemblage. The pattern of occupation observed promotes a high reproductive profile for the population studied, maximizing the populational growth.

Diverse reproductive strategies may be adopted by different species of Macrobrachium prawns, and even among different populations of the same species. The present study evaluated the influence of differences in the reproductive strategies of two geographically isolated populations of Macrobachium amazonicum, upon female fecundity, reproductive output and the chemical content of prawns and eggs. One prawn population from Pará only completes its life cycle in brackish water, whereas another from Mato Grosso do Sul only inhabits freshwater. Pará female prawns exhibited a larger average size and weight and produced more eggs than females from Mato Grosso do Sul. However, the Mato Grosso do Sul population produced eggs that were larger in volume than those of females from the other population. Furthermore, eggs produced by Pará prawns were composed primarily of water (56%), whereas those produced in Mato Grosso do Sul were composed mostly of organic matter (80%). This difference in the eggs' chemical compositions did not apply to the chemical compositions of the females, as individuals from both sites were composed primarily of water. Mato Grosso do Sul females invested a higher amount of energy in brood formation (14% of their wet weight) than individuals from Pará (only 10%). It is possible that M. amazonicum populations show a higher degree of plasticity in their reproductive activity due to habitat conditions and genetic differences. Although the brackish population produces larger individuals, and exhibits higher fecundity, the freshwater population exhibited a higher reproductive investment. These results suggest a high reproductive capacity to adapt to different environmental conditions for this species, which should be considered in the context of aquaculture activities.

Diversas estrategias reproductivas pueden ser adoptadas por distintas especies de camarones del género Macrobrachium, e incluso entre diferentes poblaciones de la misma especie. En el presente estudio se evaluó la influencia de las diferencias en las estrategias reproductivas de dos poblaciones de Macrobachium amazonicum, geográficamente aisladas, sobre la fecundidad, rendimiento reproductivo y composición química de los camarones y sus huevos. Una población de camarones de agua dulce de Pará sólo completa su ciclo de vida en agua salobre mientras, que otra de Mato Grosso do Sul sólo habita en aguas dulces. Las hembras de la población de Pará presentaron, en promedio, mayores tamaños y mayor peso y producen más huevos que las hembras de Mato Grosso do Sul. Sin embargo, la población de Mato Grosso do Sul produjo huevos que eran más grandes en volumen que aquellos de las hembras de la otra población. Aún más, los huevos producidos por hembras de la población de Pará contenían mayor cantidad de agua (56%), mientras que aquellos producidos por las hembras de Mato Grosso do Sul se componen sobre todo de materia orgánica (80%). Esta diferencia en la composición química de los huevos no se aplicaba a la composición química de las hembras, ya que individuos de ambos sitios estaban compuestos principalmente de agua. Las hembras de Mato Grosso do Sul invirtieron una mayor cantidad de energía en la puesta (14% de peso húmedo) que las hembras de Pará (solo 10%). Es posible que las poblaciones de M. amazonicum muestren un mayor grado de plasticidad en su actividad reproductiva debido a las condiciones del medio y a diferencias genéticas. Aun cuando la población estuarina produce individuos más grandes y presenta mayor fecundidad, la población de agua dulce presenta una inversión reproductiva mayor. Estos resultados sugieren una alta capacidad reproductiva de adaptación a diferentes condiciones ambientales para esta especie, que debe ser considerada en el contexto de las actividades de acuicultura.

This study aimed to determine the shell choice pattern of the southern Atlantic endemic hermit crab Loxopagurus loxochelis from two different biogeographic provinces in Brazil and Argentina. Size and shell species preferences were determined for the two most occupied shell types (i.e., Olivancillaria urceus and Buccinanops gradatum) in Caraguatatuba region (Brazil) and in Mar del Plata (Argentina). Shell occupation was analyzed considering the biometric characteristics of shells, the occurrence of shell types, and the preference of the hermit crabs for the most frequently occupied shell species. Samples were taken using otter trawl in the infralittoral area of both regions and the animals captured were measured and weighed. Shells were identified, weighed, measured and their internal volume calculated. Experiments were accomplished in aquaria where the hermit crabs were allocated together with a sufficient number of adequate sized shells. In laboratory, L. loxochelis from Argentina presented no preference for any of the two offered shell species, while the specimens from Brazil significantly preferred B. gradatum shells. It was observed that the relation between shell dimensions and shell weight were the variables that best explained the association between hermit crabs and shells. Considering that Argentinean specimens are larger than the Brazilian ones we may infer that body size is a relevant factor to explain the observed differences found in relation to shell type preference

Este estudio tuvo por objetivo determinar la forma de elección de conchas de caracoles por el cangrejo ermitaño endémico del Atlántico sudoccidental Loxopagurus loxochelis proveniente de dos provincias biogeográficas de Brasil y Argentina. Se determinaron las tallas y las preferencias de conchas entre los dos tipos de caracoles más ocupados (Olivancillaria urceus y Buccinanops gradatum) en la región de Caraguatatuba (Brazil) y en Mar del Plata (Argentina). La composición de las conchas fue analizada por las características biométricas y ocurrencia de los tipos de conchas y la selección por la preferencia del cangrejo ermitaño en relación a la especie de concha más ocupada. Las muestras fueron tomadas usando redes de arrastre en las áreas infralitorales de ambas regiones y los animales capturados fueron medidos y pesados. Las conchas de caracoles fueron identificadas, pesadas, medidas y calculado el volumen interno. Las experiencias fueron realizadas en acuarios donde los cangrejos ermitaños fueron ubicados con un número suficiente y adecuado de conchas de caracoles. En el laboratorio, L. loxochelis de Argentina no presentaron diferencias entre las dos especies de conchas ofrecidas, mientras los especímenes de Brasil prefirieron conchas de B. gradatum en forma significativa. Se observó que las relaciones de las dimensiones y los pesos de las conchas fueron aquellas que mejor reflejaron la asociación con los cangrejos ermitaños. Teniendo en consideración que los especímenes de Argentina fueron más grandes, se puede inferir que ello puede ser uno de los factores influenciando en las diferencias por las preferencias de los tipos de conchas halladas

Os estudos sobre a biologia dos ermitões no Atlântico sul ocidental são escassos considerando-se a biodiversidade local. O presente trabalhou caracterizou a população do ermitão Paguristes calliopsis Forest and Saint Laurent, 1968 quanto à distribuição de freqüência de tamanho dos indivíduos, ao sex-ratio, e a ocupação das conchas no ambiente natural. Os exemplares foram coletados por mergulho autônomo na região infralitoral da Ilha Anchieta. Um total de 116 indivíduos foi analisado. O tamanho do comprimento do escudo cefalotorácico (mínimo; máximo; média ± sd, respectivamente) dos indivíduos variou de: 0.8; 4.5; 2.76 ± 0.79 mm para machos e 2.28 ± 0.36 mm para fêmeas. O sex-ratio foi de 1.47:1 em favor dos machos, sendo estes os que prevaleceram nas maiores classes de tamanho. Os ermitões ocuparam conchas de 11 espécies de gastrópodes sendo Cerithium atratum (Born 1778) significativamente a concha mais ocupada (75.86%). Não foram obtidas correlações significativas em todas as análises de regressão, demonstrando diferenças entre os grupos sexuais quanto a adequação das conchas ocupadas. Na área estudada a população de P. calliopsis pode ser considerada pequena quando comparada com as outras populações coexistentes. O padrão de utilização de conchas variou em função da disponibilidade destas e da competição interespecífica.

In southern Atlantic studies on hermit crab biology are scanty considering the local biodiversity. In this way, some population features of Paguristes calliopsis Forest and Saint Laurent, 1968 such as size frequency distribution, sex ratio and shell occupation in the natural environment were studied. Specimens were collected by means of scuba methods in the infralittoral area of the Anchieta Island. A total of 116 individuals were analyzed. Size measurements (minimum; maximum; mean shield length ± sd, respectively) were 0.8; 4.5; 2.76 ± 0.79 mm for males and 2.28 ± 0.36 mm for females. The sex ratio was 1.47:1 in favor of males which prevailed in the largest size classes. The hermit crabs occupied shells from eleven gastropod species and Cerithium atratum (Born 1778) was significantly the most occupied one (75.86%). Significant correlations were not obtained in all regression analysis, demonstrating sexual differences on fitting of the occupied shells. In the studied area P. calliopsis population is small if compared with the other hermit crab populations. The shell utilization varies as a function of shell availability and hermit crabs interspecific competition, in relation to the other coexistent species.

This study aimed to assess the spatial and seasonal distribution of the hermit crab Pagurus exilis in Caraguatatuba region, characterizing the abundance and distribution of individuals seasonally and bathymetrically. The relationship between groups of individuals and environmental factors (temperature, salinity, depth, amount of organic matter and texture of sediment) was checked. Sampling was carried out monthly from July 2001 to June 2003, at seven depths (5, 10, 15, 20, 25, 30 and 35 m), with a shrimp fishery boat equipped with two double-rigged trawling nets. A total of 1960 specimens of P. exilis were collected, including 1369 (69.9%) males, 304 (15.5%) non-ovigerous females and 287 (14.6%) ovigerous females. The individuals were distributed between 15 and 35 m and were absent at 5 m. A large amount of individuals was collected (40.6%) during winter and 57.8% of ovigerous females were also captured in the same period. Pagurus exilis tended to occur in association with a group of factors composed by: higher depths (15 to 35 m), higher salinity (34 to 37 psu), lower temperature (18 to 24ºC), and sediment of organic matter varying from 1 to 9%.

Este estudio tuvo por objetivo determinar la distribución espacial y temporal del cangrejo ermitaño Pagurus exilis en la región de Caraguatatuba, caracterizando la abundancia y distribución en función de la estación del año y profundidad. Se determinaron las relaciones entre los individuos y algunos factores abióticos (temperatura, salinidad, profundidad, concentración de materia orgánica y textura del sedimento). Las capturas fueron realizadas mensualmente, entre julio de 2001 y junio de 2003, en siete profundidades (5, 10, 15, 20, 25, 30 y 35 m), utilizando dos redes de arrastres. Se obtuvo un total de 1960 individuos de P. exilis, incluyendo 1369 (69,9%) machos, 304 (15,5%) hembras no ovígeras y 287 (14,6%) hembras ovígeras. Los animales estuvieron distribuidos entre 15 y 35 m de profundidad y ausentes en 5 m. La mayor cantidad de individuos (40,6%) fue obtenida durante el invierno y así como 57,8% de las hembras ovígeras. La presencia de Pagurus exilis parece estar relacionada con la combinación de algunos factores abioticos tales como profundidad (15 y 35 m), alta salinidad (34 a 37 psu), temperatura baja (18 a 24ºC), y concentración de materia orgánica entre 1 y 9%.