Cephalothoracic Shield Length Research Articles

Spatiotemporal distribution and population structure of Clibanariussymmetricus(Randall, 1840) (Crustacea, Diogenidae) in an Amazon estuary

Rocky outcrops in the intertidal zones of estuaries often contain a highly diverse microbenthic community which includes the hermit crab, Clibanarius symmetricus, an abundant species on the equatorial Amazon coast. However, the ecology of this anomuran is poorly understood. Given this, the present study investigated the spatiotemporal distribution and structure of the C. symmetricus populations that inhabit the rocky outcrops of the Marapanim estuary in northern Brazil. Samples were collected monthly over a yearly cycle covering both the dry and rainy seasons in the upper and lower midlittoral zones during low tide. The distribution and abundance of C. symmetricus were affected directly by environmental factors such as temperature, seasonality, the intertidal zone, and salinity. The population presented sexual dimorphism, with males being larger than females, a male-biased sex ratio (1.5:1), a nonnormal and unimodal distribution, continuous reproduction, and sexual maturation at a cephalothoracic shield length of 3.6 mm. Despite the unique characteristics of the Amazon coast and the study estuary, the spatiotemporal distribution and structure of the C. symmetricus population were similar to those recorded at higher latitudes.

Population structure and morphology of South African deep‐water parapagurid hermit crabs

AbstractThe parapagurid hermit crabs Sympagurus dimorphus (Studer, 1883) and Parapagurus bouvieri (Stebbing, 1910) form dominant components of South African deeper‐water benthic invertebrate communities and, as adults, forego the use of “traditional” gastropod shells in favour of symbiotically associated Epizoanthus carcinoecia. A total of 1,122 adult S. dimorphus and 549 adult P. bouvieri derived from demersal research trawl surveys were examined to investigate parameters of population structure, carcinoecia association and morphology. S. dimorphus had a female‐biased sex ratio of 1:1.5, and P. bouvieri an equal sex ratio of 1:1. The proportion of males of both species increased with cephalothoracic shield length (CL). The lengths of the major right chelipeds of both S. dimorphus males and females, and P. bouvieri males were positively allometric, and negatively allometric in P. bouvieri females. All P. bouvieri inhabited carcinoecia, while 3.39% (n = 38) of S. dimorphus specimens occupied gastropod shells. There was a positive relationship between S. dimorphus CL and rate of gastropod shell occupation (r2 = 0.96). In S. dimorphus, number of zoanthid polyps forming the carcinoecia pseudoshell increased with both total shell volume (R2 = 0.73) and colony height (R2 = 0.61), but no such relationships were found for P. bouvieri. Euspira napus was the most common original shell around which carcinoecia developed in both S. dimorphus (45.45%) and P. bouvieri (39.00%). We speculate that these hermit species exist along an evolutionary continuum of carcinoecia use. Sympagurus dimorphus retains the ability to occupy both gastropod shells and pseudoshells and, like most other hermit crabs, continue to use shells/carcinoecia as shelters to protect the entire body. In contrast, adult P. bouvieri appear to be totally reliant on carcinoecia, which they use more as a brood pouch covering only the abdomen, rather than as a shelter into which they can fully retract to escape predation.

Geographical variation in fecundity and reproductive investment of Loxopagurus loxochelis (Decapoda: Anomura: Diogenidae) along the south-eastern coast of Brazil

ABSTRACTWe aimed to study the fecundity and reproductive investment of Loxopagurus loxochelis under different environmental conditions. In total, 67 ovigerous females were analyzed, 20 from Macaé, 26 from Ubatuba and 21 from Cananéia. The cephalothoracic shield length, fecundity and reproductive investment (Ubatuba 10.2%, Macaé 8.9% and Cananéia 7.5%) were different among the regions (ANCOVA, p < 0.05), caused by different abiotic resources and environmental characteristics found in each sampling region. Cananéia had the smallest individuals and low availability of adequate shells to hermit crabs, a condition that may have affected the growth and reproduction of the animals. Macaé has a continuous transport of nutrients such as nitrogen and phosphorus to the surface promoted by the Cabo Frio Upwelling zone, which may be a favourable condition for plankton production and, consequently, the extended ‘match/mismatch’ adjustment of spawning females of L. loxochelis. We propose that the highest reproductive investment on the Ubatuba coast is a consequence of regional environmental scenarios of waters colder than the Cananéia region, i.e. females concentrate more energy to reproduce seasonally. Thus, we proved that patterns of L. loxochelis’ reproduction can change on a regional scale according to the local condition of shell supply and water temperature.

Gastropod shell utilisation pattern by the hermit crab Clibanarius symmetricus (Anomura: Diogenidae) in an Equatorial Amazon estuary

ABSTRACTClibanarius symmetricus is a diogenid hermit crab that is highly abundant in rocky intertidal environments, including the rock outcrops of Amazon estuaries. This study characterises the C. symmetricus shell utilisation pattern in the Marapanim River estuary, Pará, Equatorial Amazon, based on the hypothesis that occupancy patterns would differ, in relation to biometry and diversity of occupied shells, from those of other regions in the range of this species due to the distinct and unique environmental characteristics of equatorial estuaries. Monthly samplings were carried out from August 2006 to July 2007, in the upper and lower areas of the mid-littoral during low tides. A total of seven gastropod species were found as shells occupied by hermit crabs: 93.33% were Thaisella trinitatensis shells, 2.00% Nassarius vibex, 2.00% Neritina virginea, 1.33% Natica marochiensis, 0.67% Parvanachis obesa, and, occasionally, Littorina flava and Phalium granulatum shells, each with only one occurrence (0.33%). Juveniles [cephalothoracic shield length (CL) of less than 3.6 mm] occupied a higher variety of shells, while adults occupied shells with larger meristic variation. Males occupied larger shells. The length of the animal was influenced by shell measurements (total width, aperture width and weight). Clibanarius symmetricus showed occupancy patterns generally similar to those of specimens of the same species previously studied in the Brazilian subtropical region, and this occupancy is explained by shell availability, shell size and weight, and hermit size. However, this study showed lower occupied shell species diversity, and the species with highest occupancy frequency (T. trinitatensis) was not reported in any previous studies on this hermit crab. In addition, the studied population differed in occupancy patterns, with differences between males and females, and between juveniles and adults.

Shell occupation by the hermit crab Dardanus insignis (Decapoda, Diogenidae) from the north Coast of São Paulo state, Brazil

The pattern of shell occupation by the hermit crab Dardanus insignis (Saussure, 1858) from the subtropical region of southeastern coast of Brazil was investigated in the present study. The percentage of shell types that were occupied and the morphometric relationships between hermit crabs and occupied shells were analyzed from monthly collections conducted during two years (from January 1998 to December 1999). Individuals were categorized according to sex and gonadal maturation, weighed and measured with respect to their cephalothoracic shield length (CSL) and wet weight (CWW). Shells were measured regarding their aperture width (SAW), dry weight (SDW) and internal volume (SIV). A total of 1086 hermit crabs was collected, occupying shells of 11 gastropod species. Olivancillaria urceus (Roding, 1798) was most commonly used by the hermit crab D. insignis, followed by Buccinanops cochlidium (Dillwyn, 1817), and Stramonita haemastoma (Linnaeus, 1767). The highest determination coefficients (r2 > 0.50, p < 0.01) were recorded particularly in the morphometric relationships between CSL vs. CWW and SAW vs. SIV, which are important indication that in this D. insignis population the great majority the animals occupied adequate shells during the two years analysed. The high number of used shell species and relative plasticity in pattern of shell utilization by smaller individuals of D. insignis indicated that occupation is influenced by the shell availability, while larger individuals demonstrated more specialized occupation in Tonna galea (Linnaeus, 1758) shell.

The hermit crab Sympagurus dimorphus (Anomura: Parapaguridae) at the edge of its range in the south-western Atlantic Ocean: population and morphometry features

Sympagurus dimorphus is one of the 12 hermit crab species recorded for Argentinean waters. Despite the high abundance registered in some scallop fishing grounds, its biology remains little known. In the present study, we analysed some population features of S. dimorphus living in symbiosis with Epizoanthus paguricola from a series of samples taken in the Argentine Sea, south-western Atlantic Ocean. Our results showed that S. dimorphus was commonly found from 40ºS to lower latitudes, in a patchy distribution along the shelf-break front. The overall sex ratio was 1:1. The smallest ovigerous female measured 6 mm in cephalothoracic shield length and this size was used as parameter to define the size of juveniles. The sex ratio size class pattern corresponded to Type IV or anomalous curve. S. dimorphus is a dimorphic species, as evidenced by the larger size of the males and the positive allometric growth of the right cheliped. The species also showed asymmetry, with the left uropod always larger than the right one. To the best to our knowledge, this is the first report on population features and relative growth for a member of the genus, based on long-term sampling. This species presents a patchy distribution along the shelf-break of Argentina. Its density tended to decrease over the five-year sampling period regarding the recruitment of hermits associated with colonies of zoanthids. In addition, the relatively homogeneous nature of this refuge does not seem to influence the growth of the hermit crab, which presents sexual dimorphism in relation to the sex/size conditions.

Life-history traits of the red brocade hermit crab Dardanus insignis on the subtropical Brazilian coast

We evaluated the population characteristics of Dardanus insignis, focusing on the reproductive period, juvenile recruitment, sexual maturity, growth and longevity of the species. Samples were collected monthly over two years (1998 and 1999), by trawling, in a subtropical region of Brazil. The hermit crabs were counted by demographic group, weighed and measured for cephalothoracic shield length, and their gonadal stage was identified using a stereo microscope. A total of 3169 hermit crabs were captured (1838 males and 1331 females). Ovigerous females were found from September to March; juvenile recruitment occurred throughout the year, peaking in summer. Males reached sexual maturity at larger sizes than females (cephalothoracic shield length = 4.4 and 4.1 mm, respectively). Longevity was estimated at 6.9 years for males and 4.3 years for females. The seasonal reproductive strategy, sexual maturity at similar sizes for males and females, continuous recruitment and differential growth are basic factors in the establishment and maintenance of the high abundance of D. insignis compared with other hermit crab species in the same region.

Characterization of the occupied shells by the hermit crab Clibanarius vittatus (Decapoda, Diogenidae) at Baixio Mirim tideflat, Guaratuba Bay, southern Brazil

A characterization of the occupied shells by the hermit crab Clibanarius vittatus was carried out. Hermit crabs were collected in the intertidal zone, during the low spring tide monthly from April 2005 to March 2006. They were sexed and their cephalothoracic shield length (CL) was measured. Shells were identified, dried, weighed and the aperture length (AL) and width (AW) were measured. 1187 crabs were collected (949 males, 216 females and 22 intersexes), which occupied 12 species of gastropod shells. Stramonita haemastoma, Olivancillaria urceus and Dorsanum moniliferum made up 96.55% of the total shell species. Male hermit crabs attained significantly larger sizes than females; therefore, males occupied a wider spectrum of shells in size and weight. A stronger correlation ratio was obtained between CL and AW of S. haemastoma. Last whorl with a rounded shape and a spacious inner area is a common feature of all shell species most frequently occupied by this hermit crab where it occurs. The successful establishment of C. vittatus at Baixio Mirim is mainly due to the appropriately shaped and wide range of size of S. haemastoma shells that were most often occupied by the hermit crabs of the studied population.

Distribuição temporal do ermitão Clibanarius vittatus (Anomura, Diogenidae) no litoral do Paraná

Um estudo sobre a flutuação temporal da estrutura populacional do ermitão Clibanarius vittatus (Bosc, 1802) foi realizado no Baixio Mirim, Baía de Guaratuba, Estado do Paraná, Brasil (25°52'S, 48°36'W). Clibanarius vittatus é uma espécie largamente estudada, entretanto estudos da biologia populacional desta em diferentes regiões são escassos. Coletas mensais foram realizadas na zona entremarés, de abril/2005 a março/2006. Foram obtidos 1187 ermitões, dos quais, 949 machos, 22 indivíduos intersexo, 204 fêmeas não ovígeras e 12 fêmeas ovígeras. O comprimento do escudo cefalotorácico (CEC) foi medido e agrupado em 10 classes de tamanho. Machos ocorreram em 10 classes de CEC, enquanto fêmeas e intersexos em apenas seis. A razão de sexos total e mensal foi a favor dos machos. Todas as categorias demográficas estiveram presentes o ano inteiro, com exceção dos intersexos e das fêmeas ovígeras. Estas foram pouco frequentes e ocorreram do final da primavera até o outono, e em agosto de 2005. O período reprodutivo foi considerado contínuo-sazonal, com maior intensidade nos meses mais quentes. A razão de sexos nesta população, que é diferente das demais estudadas, corrobora a teoria de migração proposta para esta espécie. O presente estudo constitui o primeiro registro do período reprodutivo desta espécie em águas rasas de clima subtropical quente.

Morphometric Relationships Between the Hermit Crab Isocheles sawayai (Forest &amp; Saint Laurent) (Crustacea Anomura Diogenidae) and its Shell from Southern Brazil

A study on morphometric relationships between the hermit crab Isocheles sawayai and its shell in a population from Parana-Santa Catarina States coast was carried out. Hermit crabs from the by-catch of shrimp fishing (4-15m depth) were collected. Cephalothoracic shield length (CL) and width (CW) from hermit crabs and total length (SL), aperture length (AL) and weight (SW) from shells were taken. A total of 266 hermit crabs occupying eight species of shell - Buc- cinanops lamarckii, Dorsanum moniliferum, Oliva reticularis, Olivancillaria steeriae, O. urceus, Polinices hepaticus, Semicassis granulatum and Stramonita haemastoma - were obtained. Males (N = 189) that dominated strongly (1M : 0.4 F) occupied eight shell species, while females (N = 76) occupied only six. There was only one intersex individual that oc- cupied a Stramonita shell. Contrarily to intertidal populations, O. urceus was the most frequently occupied shell by males (57.14%) and females (62.33%) in this studied area. Due to the smaller size of females (mean CL 5.19±0.84mm), these ones occupied shells of a smaller size than males (mean CL 6.49±1.14mm). The highest O. urceus shell frequency of oc- cupation is connected to the hermit crabs life style: it is a filter feeding species and its shell remains totally buried in the sandy substratum having only its cephalothoracic appendages free. The heavy shell of this gastropod (highest SW/SL) fa- vors the stability in strong current water conditions, as it functions as an anchorage for this semi-buried hermit crab.

Relative growth and sexual dimorphism of the South Atlantic hermit crab Loxopagurus loxochelis (Anomura, Diogenidae) from Ubatuba, Brazil

Some morphometric relationships and biometric aspects were studied in the hermit crab Loxopagurus loxochelis (Moreira, 1901) with the purpose of describing its relative growth and finding the size where sexual maturity is reached. Specimens were collected monthly from September 1995 to August 1997 in the Ubatuba region using double-rig trawl nets. A total of 1084 specimens (625 males and 459 females) was analysed. In this species, sexual dimorphism is particularly evident in chela dimensions. Differences between males and females were found in the left propodus length versus cephalothoracic shield length (CSL) and wet weight (WW) versus CSL relationships. Males showed a high positive allometry in chela growth, while females were close to isometry/negative allometry. The size at which a clear differentiation occurred in the growth of the propodus length and in the increase in weight of males and females was between 4.5 and 6.0mm CSL, suggesting that size at which sexual maturity is reached.

Morphological reproductive aspects of males ofDiogenes pugilator(Roux, 1829) (Crustacea, Decapoda, Anomura) from southern Spain

Abstract The morphological reproductive aspects of male of the hermit crab Diogenes pugilator have been studied. The different germ cell development stages have been reported. In addition, the zones of the vas deferens, according to their anatomy and the spermatophore formation, and the gonopore zone have been described. The histological data obtained have shown that males with a cephalothoracic shield length higher than 1 mm are mature. The minor size had a cephalothoracic shield length of 0.57 mm

Shell occupancy of the intertidal hermit crab Clibanarius erythropus (Decapoda, Diogenidae) on São Miguel (Azores)

The intertidal hermit crab Clibanarius erythropus was collected at three sites on Sao Miguel (Azores) during low spring tides. Shells occupied were identified and measured. Crab sizes ranged from 1.78 to 13.67 mm (cephalothoracic shield length), with an average size of 4.40 ± 1.44 mm. Of the 19 different shells utilised, the most frequent were Littorina striata (23.8%), Nassarius incrassatus (22.5%) and Mitra sp. (22.0%). At Fenais da Luz, L. striata was most frequently occupied, while at Agua de Alto it was N. incrassatus and, at Caloura, Mitra sp. shells were most frequently used. Shell selection appears to be determined by respective sizes of hermit crab and shell species. Small size-class crabs occupy more shell species than larger crabs. The smallest crab was found at Fenais da Luz occupying a small Bittium sp., whereas the largest crab was found at Caloura inhabiting Stramonita haemastoma.

Population Structure and Growth of the Hermit Crab Diogenes pugilator (Decapoda: Anomura: Diogenidae) from the Northeastern Atlantic

ABSTRACT A population of the hermit crab Diogenes pugilator from the northeastern Atlantic (Barbate, Straits of Gilbraltar, Spain) was studied. The results show continuous recruitment throughout the year, within a size range from 0.4-1.02 mm in cephalothoracic shield length, as a consequence of the prevalence of ovigerous females throughout the year. The sex ratio was in favor of females. Results of size-frequency distributions from different locations show that there was no clear segregation of sizes by sexes or depths. Five cohorts can coexist, although a decrease in the number of specimens was observed in the second year studied, perhaps induced by human influences in the area (the building of a new harbor and the restoration of the beach). The values of the Von Bertalanffy parameters (K and Loo) showed slight differences between sexes and between years within sexes, as is shown in the φ' index analysis. The estimated maximum longevity of the individuals in the population studied was about 2 years, but normally the cohorts lived in the study area for approximately 1 year.

POPULATION STRUCTURE AND GROWTH OF THE HERMIT CRAB DIOGENES PUGILATOR (DECAPODA: ANOMURA: DIOGENIDAE) FROM THE NORTHEASTERN ATLANTIC

A population of the hermit crab Diogenes pugilator from the northeastern Atlantic (Barbate, Straits of Gilbraltar, Spain) was studied. The results show continuous recruitment throughout the year, within a size range from 0.4-1.02 mm in cephalothoracic shield length, as a consequence of the prevalence of ovigerous females throughout the year. The sex ratio was in favor of females. Results of size-frequency distributions from different locations show that there was no clear segregation of sizes by sexes or depths. Five cohorts can coexist, although a decrease in the number of specimens was observed in the second year studied, perhaps induced by human influences in the area (the building of a new harbor and the restoration of the beach). The values of the Von Bertalanffy parameters (K and Loo) showed slight differences between sexes and between years within sexes, as is shown in the φ' index analysis. The estimated maximum longevity of the individuals in the population studied was about 2 years, but normally the cohorts lived in the study area for approximately 1 year.