Assembleia de ermitões nas proximidades de ilhas costeiras do sudeste do Brasil

An assortment of environmental factors may limit the permanence of hermit crabs in the environment, and determination of certain ecological indices can reveal the current conditions of the assemblage. This study evaluated the assemblage of hermit crabs near two islands adjacent to areas with fishing activity. Hermit crabs were collected monthly near Couves and Mar Virado islands on the southeastern coast of Brazil, from January through December 1998. Environmental factors were also recorded monthly. Ecological indices including species richness, diversity, evenness and dominance were calculated. The environmental characteristics differed between the islands, which helps to explain the differences in the composition of hermit crabs between the locations. Hermit crabs were significantly more abundant near Couves Island, where, according to the canonical correspondence analysis (CCA), the environmental parameters varied less. The Monte Carlo test (P < 0.05) confirmed the CCA model, indicating a strong correlation between the species of hermit crabs, bottom and surface water temperatures, and sediment organic-matter content. The presence of ovigerous females throughout the year indicates that these areas are favorable for reproduction. These results indicate that the environmental heterogeneity allows the establishment of different species of hermit crabs, influencing species richness and abundance of individuals in the ecosystem. These conditions favor the establishment of diverse benthic communities near the studied islands.Keywords: Diogenidae, Paguridae, diversity, abundance, multivariate analysis, Dardanus insignis, Loxopagurus loxochelis.Uma variedade de fatores ambientais pode limitar a permanência de ermitões no ambiente, sendo que alguns índices ecológicos podem revelar as condições da assembleia. Este trabalho avalia a assembleia de ermitões em duas ilhas adjacentes a regiões com atividade pesqueira. Os ermitões foram coletados mensalmente nas ilhas das Couves e do Mar Virado, pertencentes ao litoral sudeste brasileiro, no período de janeiro a dezembro de 1998. Fatores ambientais também foram registrados mensalmente. Índices ecológicos como riqueza, diversidade, equidade e dominância foram calculados. As características ambientais foram diferentes entre as ilhas, o que pode explicar as diferenças na composição de espécies entre os locais. A abundância de indivíduos foi significativamente maior na ilha das Couves, a qual apresenta, segundo a análise de correspondência canônica (CCA), menores oscilações em suas variáveis ambientais. O teste de Monte Carlo (P < 0.05) confirmou a robustez da CCA, evidenciando uma forte correspondência entre as espécies de ermitões, temperatura de fundo e superfície e teor de matéria orgânica. A presença de fêmeas ovígeras ao longo do ano também aponta as áreas como propícias à reprodução. Desta maneira, os resultados permitem concluir que a heterogeneidade dos ambientes permite o estabelecimento de diferentes espécies de ermitões, influenciando a riqueza de espécies e a abundância de indivíduos no ecossistema local. Tal condição propicia o estabelecimento de comunidades bentônicas distintas nas ilhas estudadas.Palavras-chave: Diogenidae, Paguridae, diversidade, abundância, análise multivariada, Dardanus insignis, Loxopagurus loxochelis

Composição, distribuição batimétrica e estrutura da assembleia de ermitões (Crustacea, Anomura) em uma área do litoral sudeste brasileiro influênciada pelo fenômeno da ressurgência

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Biologia e ecologia de ermitões (Crustacea, Anomura) do sublitoral não consolidado do sudeste brasileiro

Dardanus insignis is the most abundant hermit crab on sublittoral of soft bottoms along the southeastern coast of Brazil. It is among the Decapoda species that structure the macrobenthic community, from shallow regions to deeper areas up to 100 m. This study evaluated the distribution of D. insignis in a tropical-subtropical transition zone. In three bays (Ubatumirim, Ubatuba and Mar Virado), sampling was conducted monthly for two years, on four transects parallel to the coastline (at depths of 5, 10, 15, and 20 m), as well as one transect sheltered from wave action, and another in a more exposed area. Environmental variables were monitored in each sampling. The study sites differed in water temperature, salinity, organic-matter content and substrate composition. The size fractions of coarse, medium and fine sand were correlated mainly with Ubatumirim and Ubatuba bays, on transects 15 and 20 m deep. The distribution of demographic groups showed a positive relationship with these variables, with large numbers of individuals found in Ubatuba and on the deepest transects. These results suggest that living farther from the coast might provide protection for D. insignis against the oscillation of environmental variables, especially those that are affected by rainfall regimes, such as the sedimentForam avaliadas as características da história de vida de Loxopagurus loxochelis provenientes de uma zona de transição tropical-subtropical com foco em sua distribuição espaço-temporal, estrutura populacional, maturidade sexual, período reprodutivo, razão sexual, crescimento, longevidade e relações com variáveis ambientais. Amostragens biológicas e ambientais foram realizadas mensalmente, por dois anos, em três ensedas. Quatro transectos paralelos à linha de costa (5, 10, 15 e 20 m de profundidade), um transecto protegido da ação de ondas e um em área mais exposta foram levados em consideração. Foram capturados 1823 indivíduos, 838 em Ubatuba, 704 em Mar Virado e 281 em Ubatumirim. A proporção entre os sexos favoreceu os machos. O período reprodutivo foi caracterizando como contínuo, com pico durante o inverno. A maturidade sexual foi estimada 3.1 mm para os machos e 3.0 mm para as fêmeas. As curvas de crescimento em comprimento e peso foram diferentes para machos e fêmeas, indicando uma longevidade de 38 meses para os machos e 26.8 meses para as fêmeas. Os locais de estudo diferiram em diversos fatores ambientais, e a análise de redundância revelou que tais características explicaram 87.4% da variação na abundância dos grupos demográficos de L. loxochelis. Composição do substrato e temperatura foram as variáveis determinantes para ocorrência da espécie, justificando a maior abundância durante o inverno, principalmente na profundidade dos 20 metros. Estes resultados permitem concluir que a abundância de L. loxochelis é decorrente de uma estratégia de vida diferenciada em relação aos demais ermitões coexistentes, abrangendo características que propiciam o estabelecimento e a continuidade das populações do ermitão endêmico do atlântico sul na região estudad

Dinâmica populacional do ermitão endêmico Pagurus exilis (Benedict, 1892) (Crustacea: Decapoda: Paguridae) na região de Ubatuba-SP

Resumo: O presente estudo avaliou alguns aspectos populacionais e a abundância espaço temporal do ermitão endêmico P. exilis (Benedict, 1892), na região de Ubatuba, litoral norte do Estado de São Paulo. Os ermitões foram coletados por um período de dois anos, com auxilio de um barco de pesca de camarão equipado com redes dou­ble-rig. Foram coletados 142 indivíduos, sendo 95 machos, 22 fêmeas e 25 fêmeas ovígeras. Os indivíduos foram encontrados principalmente, entre os transectos de 15 e 20m e durante o inverno, no entanto as fêmeas ovígeras foram encontradas em grande proporção na primavera. O tamanho dos animais (comprimento do escudo cefalo­torácico) variou de 2,1 a 6,5 mm, e os machos foram significativamente maiores, demonstrando um dimorfismo sexual. A distribuição de frequência de tamanho demonstrou um padrão unimodal com distribuição não-normal. A razão sexual foi favorável aos machos durante todas as estações do ano e também favorável na maioria dos tran­sectos. A presença de indivíduos principalmente em maiores profundidades bem como nos meses mais frios, pode ser devido à espécie apresentar uma maior tolerância a águas frias, característica de espécies subtropicais. O perfil como essa população está estruturada, nos permite caracterizar um dimorfismo sexual nessa espécie, com machos alcançando maiores tamanhos que as fêmeas. A diferença na razão sexual, sempre em favor dos machos nas dif­erentes estações do ano e nos diferentes transectos, pode ser explicada pela migração das fêmeas para maiores profundidades e pela competição por recurso biótico, no caso a disponibilidade de conchas para os ermitões.Palavras-chave: Pagurus, Dinâmica populacional; ermitão; distribuição

Comparative analysis of populational structure of the Hermit Crab Dardanus insignis BJAST

The goal of this paper was the comparison of the population structure and the reproductive period of Dardanus insignis from two sites in a subtropical area of the Brazilian coast. A total of 795 hermit crabs were obtained at Couves Island, being 56.4% males, 27.3% non-ovigerous females, 3.8% ovigerous females, and 12.5% juveniles; at Mar Virado Island a total of 336 specimens were captured, being 59.5% males, 31.8% non-ovigerous females, 4.7% ovigerous females, and 4.5% juveniles. The sex-ratio was statistically different from 1:1 in favor of males all study period in both sites. The reproductive period is seasonal in both sites and the juveniles’ recruitment occurred at first two winter months. Only males were found in the largest size classes. Despite of the distance and environmental and biological features of each site, both populations of D. insignis showed similar characteristics.The goal of this paper was the comparison of the population structure and the reproductive period of Dardanus insignis from two sites in a subtropical area of the Brazilian coast. A total of 795 hermit crabs were obtained at Couves Island, being 56.4% males, 27.3% non-ovigerous females, 3.8% ovigerous females, and 12.5% juveniles; at Mar Virado Island a total of 336 specimens were captured, being 59.5% males, 31.8% non-ovigerous females, 4.7% ovigerous females, and 4.5% juveniles. The sex-ratio was statistically different from 1:1 in favor of males all study period in both sites. The reproductive period is seasonal in both sites and the juveniles’ recruitment occurred at first two winter months. Only males were found in the largest size classes. Despite of the distance and environmental and biological features of each site, both populations of D. insignis showed similar characteristics

Shell occupation by the South Atlantic endemic hermit crab Loxopagurus loxochelis (Moreira, 1901) (Anomura: Diogenidae)

The evaluation of population characteristics, particularly those of endemic species, aids in population preservation and management. Hermit crabs present an innate behavior of occupying shells, which tends to individual needs and limits their distribution. This study characterized the pattern of occupation of gastropod shells by the hermit Loxopagurus loxochelis in three bays of the southwestern coast of Brazil. Monthly collections were made from January/1998 to December/1999 in the bays Ubatumirim (UBM), Ubatuba (UBA) and Mar Virado (MV) with a shrimping boat. Overall, ten species of gastropod shells were occupied by L. loxochelis. The shell of Olivancillaria urceus represented 66.8% of those occupied. Morphometric relationships demonstrated a differential occupation of the more abundant shells among demographic groups, where most of the males occupied O. urceus, non-ovigerous females occupied O. urceus and Buccinanops cochlidium, and ovigerous females occupied B. cochlidium and Stramonita haemastoma. Most of the individuals occupied the more abundant shells, considered adequate for the morphology of this hermit crab species. Thus, the studied bays seem to be stable and propitious environments for population perpetuation and the settlement of new individuals

GASTROPOD SHELLS USED BY Dardanus insignis (Decapoda, Anomura) NEAR ISLANDS IN THE UBATUBA REGION, SAO PAULO, BRAZIL

The use of gastropod shells by hermit crabs is determined by the availability of shells in the environment or through selection for size and volume. This study analyzed patterns in the use of shells by Dardanus insignis (Saussure, 1858). From January 1998 to December 1999, 386 individuals were collected from two islands at Ubatuba, Sao Paulo. The crabs were measured for cephalothoracic shield length (CSL) and wet weight (CWW). The gastropod shells occupied by hermit crabs were identified, and the shell aperture width (SAW), dry weight (SDW) and internal volume (STY) were measured. The relationships between the dimensions of the gastropod shell and the hermit crabs were evaluated by linear regression analysis. Among the 11 species of gastropod shells used by D. insignis, the most often used was Olivancillaria urceus (31%), followed by Strombus pugilis (22%) and Siratus tenuivaricosus (18%). The shell of O. urceus was used most probably due to its high availability on Couves and Mar Virado islands. The most significant biometric parameter was shell aperture width (F=18.231; p<0.0001), highlighting the importance of this variable for the shell choice by D. insignis at both sites

Ecological distribution and population features of Hexapanopeus paulensis Rathbun, 1930 (Crustacea: Decapoda: Xanthoidea) caught by bottom trawling in the southeastern coast of Brazil: implications for its population structure

ABSTRACT We analyzed the spatio-temporal variations of the abundance, distribution and the population structure of Hexapanopeus paulensis Rathbun, 1930 from the southeastern Brazilian coast. Monthly samples were taken from January 1998 to December 1999 at Ubatumirim, Ubatuba and Mar Virado bays. A total of 1084 individuals were obtained, 76 specimens at Mar Virado, 322 at Ubatuba and 686 at Ubatumirim. It was possible to verify an association between the abundance of H. paulensis and bottom temperature (positive correlation), grain size of sediment and organic matter content (both negatively). This explains the higher number of individuals in the stations nearest to the continent (with higher temperature values and heterogeneous substrate). Juveniles were recorded throughout the study period, constituting 39.5% of the sampled population, which highlights the importance of the region (especially Ubatumirim Bay, due the highest abundance) for the establishment of the species. Only females occupied the largest size classes, which could mean differential mortality between the sexes or growth rate. Nevertheless, further studies should be accomplished to a better comprehension of such difference