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This study describes biometric characteristics of the pea crab Pinnaxodes gigas, a symbiont of the geoduck clam Panopea globosa in the eastern-central Gulf of California. Differences were observed in the coefficient of allometry when length-weight relationships (LWR) were analysed under a multi-model approach. The winner model for LWR in females was that exhibiting two phases (”two-segments” and “broken-stick”), while in males the models cubic and quadratic, presenting a continuous change in coefficient of allometry along all sizes, were chosen as the best. The relationships of carapace width, length and height were also tested for females with the two-segment model and the breakpoint was found at 20 mm carapace width for these three relationships. It is concluded that the breakpoint must be related to the size-at-maturity reached by females, and that these changes in dimensions correspond to an adaptation in the female’s shape for carrying the egg clutch.

Fluctuations in abundance of dominant species can cause competitive release of resources with consequences on community structure and functioning. In the present study, changes in the intertidal macroinfauna community of an exposed sandy beach were evaluated during two contrasting periods characterized by low and high densities of the yellow clam Amarilladesma mactroides. The increase in clam abundance and biomass was associated with a significant decrease in abundance of the rest of the community. In particular, a decline was observed for the pea crab Austinixa patagoniensis, a commensal species that lives in the burrows of the shrimp Sergio mirim. Our study demonstrates that fluctuations in clam abundance lead to long-term changes in community structure, suggesting the presence of competitive interactions. The environmental stability over the two periods strengthens the hypothesis that the competition between species is crucial for shaping the ecological community. Stable isotope analysis allows discarding trophic competition as mechanism of exclusion. Image maps reveal complementary distribution of species, showing the relevance of the spatial competition, which is mediated by changes in abundance of a third species. Indeed, high densities of A. mactroides reduce the available area for the establishment of the S. mirim burrows, limiting the foraging behavior of its commensal, the pea crab. Such an interaction drives density-dependent exclusion of the pea crab from the intertidal zone following the establishment of the yellow clam population. This study illustrates that spatial competition triggered by the increase of a bed-forming species can have community-wide consequences in exposed sandy beaches. Fil: Carcedo, Maria Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina Fil: Fiori, Sandra Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina Fil: Scotti, Marco. Geomar-Helmholtz Centre for Ocean Research Kiel; Alemania Fil: Ito, Maysa. Geomar-Helmholtz Centre for Ocean Research Kiel; Alemania Fil: Dutto, María Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina Fil: Carbone, Maria Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geografía y Turismo; Argentina

The holotype of the pinnotherid, Pinnotheres socius Lanchester, 1902, is extant and deposited in the University Museum of Zoology, Cambridge. The taxonomy of this pea crab is treated in this note and the specimen is illustrated by photographs and line drawings of the third maxilliped and pereiopods. Although the ovigerous type specimen is damaged, it is sufficiently intact to identify the specimen and synonymize the species with Nepinnotheres cardii (Bürger, 1895), described from the Philippines.

The marine parasitic African pea crab Afropinnotheres monodi Manning, 1993 has well-established populations in the gulf of Cadiz, where it is invasive. In this study, its tolerance to temperature and salinity variation during larval development were studied in the laboratory. Larvae were reared in seawater (salinity 36) at different temperatures (5, 10, 15, 20, 25 and 30 °C). At 20 and 25 °C larval development was successfully completed, with the highest rate of survival to the megalopa stage occurring at 25 °C. At this optimal temperature larvae were reared at different salinities (15, 25, 36 and 45), and maximum survival to megalopa occurred at salinity 25. Additionally, the time required for larval developmental increased with salinity: the shortest (12 days) and the longest (25 days) development time occurred at salinities 25 and 45, respectively. In some of the treatments an extra stage (zoea V) was observed, but the only zoea V specimens that successfully moulted to megalopa were those reared at 25 °C and salinity 25. Temperature seems to be the main factor determining whether larval development is successfully completed, whereas salinity has an additional effect on duration of larval development under optimal temperature conditions. Our results suggest that A. monodi is well-adapted to withstand higher temperatures than currently present in Europe’s marine waters and, if temperatures keep increasing, this species may be able to expand successfully northward along the European Atlantic and Mediterranean coasts., This study was partially funded by the Spanish “Ministerio de Economía y Competitividad (MINECO), Plan Nacional I+D” and the European FEDER funds through project AFROBIV (CGL2014-53557-P). The MINECO also supported an FPI PhD contract to MPM (BES-2015-072703). We want to thank “Consejería de Agricultura, Pesca y Desarrollo Rural” and “Consejería de Medio Ambiente y Ordenación del Territorio” of Junta de Andalucía by supporting the development of AFROBIV project.

Oysters (Crassostrea virginica) provide multiple ecosystem services to coastal habitats. Due to their declines, numerous restoration efforts target oysters, making it critical to explore factors that might limit recovery. Biotic stressors, such as pea crabs and boring sponges, can negatively affect oysters, and may interact with abiotic stressors like tidal exposure. In this study, boring sponge and pea crab distribution patterns were explored across an intertidal gradient on oyster reefs in Georgia (32.002° N, − 080.920° W) in the summer of 2016, while considering the effects of both stressors on oyster condition. Boring sponges and pea crabs were both most abundant on the lower intertidal of reefs (15% and 6% prevalence, respectively) and decreased with increasing tidal exposure (~ 1% prevalence of both pests in the upper intertidal). Pea crabs had a more negative effect on oyster condition in the upper intertidal zone (27% difference), whereas boring sponges caused the greatest condition reduction in the lower intertidal zone (30% difference). Pea crabs were more abundant in sponge-infected oysters than uninfected oysters. An observed negative relationship between oyster density and sponges suggests that higher sponge prevalence may drive low oyster density in the lower intertidal zone. Since biotic stressors on oyster reefs can affect oyster population structure and reef function, understanding their distribution and interactions is important for management and restoration. While sponges and pea crabs are not likely to be eliminated by restoration efforts, careful attention to location within the tidal prism can minimize their impacts on restoration efforts, particularly in the southeastern USA.

Made available in DSpace on 2022-04-29T08:31:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Brachyuran crabs of the family Pinnotheridae De Haan are a classic example of symbiotic lifestyle. Here, we described the host-use pattern, relative growth and sexual dimorphism of Austinixa patagoniensis (Rathbun 1918), a symbiont of the ghost shrimp Callichirus major (Say 1818). We use these analyses to test the A. patagoniensis mating system considering that monogamous species inhabit their respective host as male–female pairs and have a low degree of sexual dimorphism. Austinixa patagoniensis showed a high social plasticity, with individuals inhabiting galleries in solitary, in pairs, in trios or in groups of up to eight crabs. While it is true that 38% of the burrows sampled harbored pairs of crabs, the body size of paired crabs from the opposite sex was poorly correlated. This suggests that heterosexual pairing is short term with frequent shifts among burrows by male and/or female crabs, as reported before for other symbiotic decapods in which the body size of paired crabs is poorly correlated. A considerable proportion of the ovigerous females (34%) were found living solitarily, which suggest that males abandon these females shortly after insemination. The sexual dimorphism in terms of body and cheliped size was evident in this species, a condition that argues in favor of male–male competition in A. patagoniensis. The observations above argue against the notion that A. patagoniensis is monogamous. Lastly, our results revealed that body size and chelipeds of males are not under sexual selection by females, thus reinforcing the idea that male–male competition is the mechanism behind sexual selection in A. patagoniensis. Universidade Estadual Paulista – UNESP Instituto de Biociências – IB Câmpus do Litoral Paulista – CLP Grupo de Pesquisa em Biologia de Crustáceos – CRUSTA Programa de Pós-Graduação em Ecologia Evolução e Biodiversidade Instituto de Biociências (IB) Campus de Rio Claro (RC) Universidade Estadual Paulista (UNESP) Facultad de Ciencias Centro de Estudios Marinos y Limnológicos Universidad de Tarapacá – UTA Universidade Estadual Paulista – UNESP Instituto de Biociências – IB Câmpus do Litoral Paulista – CLP Grupo de Pesquisa em Biologia de Crustáceos – CRUSTA Programa de Pós-Graduação em Ecologia Evolução e Biodiversidade Instituto de Biociências (IB) Campus de Rio Claro (RC) Universidade Estadual Paulista (UNESP)

Effects of temperature on the survival of the pea crab Afropinnotheres monodi, and on its realized fecundity (number of eggs) and actual fecundity (number of zoeas) were experimentally estimated on individuals from the Gulf of Cadiz (Huelva and Cadiz) at Southwestern Spain. The adult crabs of different demographic categories (soft females, hard females, and males) were cultured in seawater (salinity of 36) at six different temperatures: 5, 10, 15, 20, 25, 30 °C. After 42 days of culture, the three demographic categories survive at a wide range of temperatures (10 to 30 °C), although survival was high (88.5% to 98.8%, on average) for adults cultured at temperatures between 15 and 30 °C and moderate (69.4%, on average) for those cultured at 10 °C. When ovigerous females collected in winter (field temperature: 15 °C) were cultured at the four temperatures at which survival rates were high (15, 20, 25 and 30 °C), the actual fecundity average of the first brood decreased from 95.9% for females maintained at 15 °C to 3.2% for those maintained at 30 °C; whereas when females were collected in summer (field temperature: 23 °C) this actual fecundity average only displayed a moderate decrease from of 98.3% at 30 °C to 88.3% at 15 °C. Irrespective of the temperature, the number of eggs of the second brood of each female was on average smaller than that of the first brood. The duration of embryonic development was temperature dependent, becoming shorter as the temperatures increased between 15 °C and 30 °C. The embryonic plus larval development times in the Bay of Cadiz, estimated with a temperature dependent model, lasts from 105 days in winter to 43 days in summer. Besides, the effect of temperature on fecundity in the natural environment was estimated on ovigerous females seasonally collected from Cadiz and Huelva. The realized fecundity of A. monodi is higher than in most brachyurans and increases potentially with the size of the female; within females of the same size, there were no significant differences between seasons or locations, except in Huelva in autumn, when a decrease in fecundity was observed. Adult survivals and development time, expected for this species at the current seawater temperatures in the north of the Iberian Peninsula, suggest that northward expansion of A. monodi constitutes a potential risk to the mussel cultures and bivalve shellfishery catch in that area., This work was supported by the “Ministerio de Economía y Competitividad (MINECO) (Spain), Plan Nacional I + D” (Spain) and the European FEDER funds through project AFROBIV (CGL2014–53557-P), (Europe). The MINECO also supported a FPI Posdoctoral contract to MPM (BES-2015-072703). We want to thank to “Consejería de Agricultura, Ganadería, Pesca y Desarrollo Sostenible de la Junta de Andalucía“ and “Consejería de Medio Ambiente y Ordenación del Territorio of Junta de Andalucía” by supporting the development of AFROBIV project.

The eastern oyster Crassostrea virginica provides a number of ecosystem services and is an important commercial fishery species along the US East and Gulf Coasts. Oyster populations have declined dramatically due to overharvesting, habitat loss, and disease. As restoration efforts and aquaculture of oysters continue to increase throughout their range, it is important to consider the impacts of a number of potential oyster pests, including the boring sponge Cliona spp. and the pea crab Zaops (Pinnotheres) ostreum, on oyster populations. Both of these have been demonstrated to reduce oyster growth, condition, and in some instances, reproductive output. Boring sponges in particular are a major concern for oyster growers and managers. Our monitoring efforts have suggested that pea crabs might be more prevalent in sponge-infested oysters; we therefore conducted an observational study to determine if there was any relationship between pea crab prevalence and sponge presence, and to examine whether the presence of both pests had synergistic effects on oyster condition. At 2 very different sample sites, North Carolina and New Jersey, oysters with 1 pest (i.e. boring sponge) were significantly more likely to have the second pest (i.e. pea crab) than the background population. Furthermore, sponge presence negatively affected oyster condition in North Carolina only, while pea crabs significantly reduced condition at both locations. When sponges and pea crabs were present together, the effects on oyster condition were additive. This study provides further evidence that interactions between an individual and a fouling/pest organism can alter oyster susceptibility to other parasites.

Some pea crabs are parasite of bivalves and may cause a significant effect on the host's condition. In this study, the prevalence of the pea crab Afropinnotheres monodi and its effect on host condition are assessed for two commercially important bivalves (the mussel Mytilus galloprovincialis and the cockle Cerastoderma edule) from three natural beds of the Gulf of Cadiz (SW of Iberian Peninsula). The average prevalence of A. monodi ranged from 4.0% (Bay of Cadiz) to 51.4% (Carreras River) for cockles and from 30.5% (Bay of Cadiz) to 45.4% (Carreras River) for mussels. For both hosts, most bivalves were infested by a single pea crab (96.0% of cockles and 92.4% of mussels); among multiple infestations, one male and one female was the dominant combination (72.7% of cockles and 77.8% of mussels). Infested mussels showed a significantly decreased condition index (14.7%, on average), whereas crab infestation did not significantly affect the condition index of cockles (2.2%, on average). When the wet weight of the pea crab represented >5% of the wet weight of the host, an average condition loss of 12.7% and 15.9% were observed for cockles and mussels, respectively. As the relative condition loss of both mussels and cockles was negatively correlated with the relative size of the pea crab, the mentioned interspecific differences in the pea crab effects may be mainly due to the higher prevalence of soft females (larger size and obligatory parasitism) in mussels (70.6%, on average) and of hard females and males (smaller size and facultative parasitism) in cockles (81.1%, on average). This study highlights the importance of knowing the life cycle and host use of the pea crab A. monodi to ascertain the possible negative effect of this parasite on mussel farms and exploited cockle beds., This work was supported by the “Ministerio de Economía y Competitividad (MINECO), Plan Nacional I+D” and the European FEDER funds through project AFROBIV (CGL2014–53557-P). The MINECO also supported a FPI PhD contract to MPM (BES-2015-072703). We want to thank “Consejería de Agricultura, Pesca y Desarrollo Rural” and “Consejería de Medio Ambiente y Ordenación del Territorio of Junta de Andalucía” by supporting the development of AFROBIV project.

The pea crab Pinnotheres pisum was described by Linnaeus in 1767 as Cancer pisum and is the type species of the genus Pinnotheres Bosc, 1801, that at present contains 64 species (Palacios-Theil et al., 2016). This species has been so far studied due to its peculiar lifestyle as a symbiont of invertebrates (Orton, 1920; Atkins, 1958; Christiansen, 1959). Schmitt et al. (1973) provided a detailed list of hosts for P. pisum, mainly consisting of bivalves and in addition the ascidians Ascidiella aspersa (Muller, 1776) [as Ascidia aspersa Mueller, 1776], and Ascidia mentula Muller, 1776. However, after their detailed study of the pinnotherids along Europe’s coastal waters, Becker & Turkay (2017) concluded that P. pisum is, like other pinnotherids, not host-specific but still an associate only of bivalves. According to those authors, previous records in ascidians must be misidentifications of P. pisum that must have, on those occasions, been confused with Nepinnotheres pinnotheres (Linnaeus, 1758).

The endosymbiont-host relationship between a pea crab and its bivalve host has been studied previously using bivalve's multi-physiological parameters. The present study is first of its kind that uses hemocyte's immune functionality to evaluate the symbiotic relationship between bivalve Paphia malabarica and its symbiont crab, Pinnotheres vicajii. The sampling was carried out at two stations (differed in nutrient concentration, productivity, and bacterial abundance) located along the southwest coast of India. The results showed lower immunocompetence in the case of bivalves infested with pea crabs. The lowering of hemocyte population was the most prominent and perhaps the initial reaction in response to focal inflammation or wound inflicted by the pea crabs. A significant lowering of phagocytosis, lysozyme, and esterase activity was also observed, indicating the detrimental impact of crab infestation. Interestingly, no significant correlation was found between parasitism and condition index despite the lower immunocompetence, validating the effectiveness of using hematological parameters in comparison to other life-history traits. This indicates that the immune parameters being directly related to the organism's metabolic state can elucidate the early effect of stressors, therefore, proving to be a better proxy for understanding a host-pathogen relationship. Disparity found in bivalve's immunocompetence between the sampling sites could be linked to either variation in environmental parameters, the size of the symbiont or the infection level. Our preliminary results provide a direction towards examining immunodepression in parasitized bivalves by considering ex-situ controlled parasitism induction along with varying environmental conditions. In view of this, efforts must be directed towards minimizing pea crab's outbreaks, especially in cultivated shellfish farms. Future studies should elucidate molecular mechanisms involved in the immunocompetence of P. malabarica, hosting the parasitic pea crabs.

Currently, there are five species of pea crabs in European waters. In the context of the AFROBIV project, in which the effect of the African pea crab Afropinnotheres monodi on bivalve species of commercial interest is being studied, a sampling campaign has been carried out on bivalve species of the coasts of southwestern Europe. The results of this campaign are used in the present study to evaluate the current distribution of A. monodi and its degree of infestation in its various hosts, together with the distribution of native European pinnotherid species. Previously collected information has also been reviewed and included with the present results to establish a baseline so as to enable future changes in distribution and host use of European pinnotherid species to be compared and quantified. To enable the more accurate identification of species and detection of new species in the area, three genetic markers (16S, Cox1, and H3) for the current five European pinnotherid species have also been compiled from Genbank or obtained in the present work. The results showed the high abundance of A. monodi in a significant portion of the area studied. In contrast, few specimens of the native Pinnotheres pectunculi and P. pisum were collected. The northern limit of the current distribution of A. monodi extends to the Sado estuary (Portugal), and the species has been recorded for the first time in the Mediterranean (Alboran Sea). New records of P. pectunculi in the Alboran Sea confirm the presence of this species in the Mediterranean, and considerably expand the known distribution of the species, until now restricted to the coasts of Brittany., This study was partially funded by the Spanish “Ministerio de Economía y Competitividad (MINECO), Plan Nacional I+D” and the European FEDER funds through project AFROBIV (CGL2014–53557-P). The MINECO also supported a FPI PhD contract to MPM (BES-2015-072703). We want to thanks “Consejería de Agricultura, Pesca y Desarrollo Rural” and “Consejería de Medio Ambiente y Ordenación del Territorio” of Junta de Andalucía by supporting the development of AFROBIV project.

The identity of the pea crab, Arcotheres borradailei (Nobili, 1906) is clarified. The holotype female is re-diagnosed, figured and its recent generic assignment to Arcotheres Manning, 1993, is discussed. A second poorly known species from India and Sri Lanka that resembles A. borradailei, Pinnotheres ridgewayi Southwell, 1911, is redescribed and assigned to Arcotheres. In addition, Pinnotheres sinensis atrinae Sakai, 1939, and Pinnotheres cyclinus Shen, 1932, from East Asia are re-examined and also referred to Arcotheres.

12 pages, 9 figures, 2 tables, After the recent detection, by both morphology and DNA barcodes, of the larval stages of an unknown species of pea crab (Pinnotheres sp.) in European waters, adults of this crab are herein reported and described as a new species. The current known geographic distribution of the species comprises the Gulf of Cádiz in the eastern Atlantic and the adjacent Mediterranean waters of the south of the Iberian Peninsula (Alboran Sea), where this crab is well-established inside the anomiid bivalve Anomia ephippium. In the Gulf of Cádiz, the species displayed a relatively high prevalence: on average, 55.6-77.7%, in A. ephippium samples. The dominant demographic categories of the new species were soft females (61.8-77.0%) with fewer males (17.7-21.10%). Most of the host bivalves carried only one crab; in bivalves harbouring two crabs, heterosexual pairs were collected more frequently than expected by chance, which suggests that they could be mated pairs. A strong correlation between host size and soft female size was found (r = 0.73, P < 0.01) indicating that space availability within hosts seems to be relevant in determining the size of the sedentary phase of the new crab species, This study was partially funded by the Spanish ‘Ministerio de Economía y Competitividad (MINECO), Plan Nacional I + D’ and the European FEDER funds through project AFROBIV (CGL2014-53557-P), and the Project PB92-0415, supported by the Spanish M.E.C, DGICYT funds

XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019., Afropinnotheres monodi Manning, 1993 is one of the many African crustaceans that have been recorded on the coasts of the Iberian Peninsula. This crab belongs to the Pinnotheridae, a family that comprises 303 species of small marine brachyuran decapods. Pinnotherids live as symbionts in other invertebrates, very often in the paleal cavity of bivalve molluscs. The main objective of this project has been to determine the effect of A. monodi on bivalves of commercial interest in the Iberian Peninsula, especially mussels (Mytilus galloprovincialis) and cockles (Cerastoderma spp.), which are the two species presenting the highest degree of infestation by this crab. In this study the distribution of A. monodi has been researched in the Gulf of Cádiz, and beyond its known limits (the south of Portugal and Strait of Gibraltar) to monitor its process of geographic expansion. Relevant aspects of its biology, that affect its reproductive success and dispersive capacity, have been also studied experimentally in order to predict the potential evolution of this species in the Iberian Peninsula.

XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019., As many other Pinnotherid crabs, the African pea crab Afropinnotheres monodi live in association with the mantle cavity of different bivalve species. This pea crab causes a significant reduction of the condition index of the mussel Mytilus galloprovincialis. The greatest effects brought about for the infestation with soft females (larger size and obligatory parasitism) and/or multiple infestation (two or three pea crab inside the same host); whereas erosion of the gills and mantle of hosts have been also observed in mussels and cockles (Cerastoderma edule) infested by hard females and males which have smaller size than soft females and are facultative parasites (Perez-Miguel et al. 2018). To test the hypothesis that the prevalence of this pea crab in subtidal mussels depends on the degree of exposure/shallowness of their habitats and consequently of the coexistence of hosts of all crab demographic categories in a reduced area, in this study we assess the prevalence and demographic structure of A. monodi in the subtidal mussels attached to the submerged chains of the navigational buoys (lateral marks) of the Port Authority located along the navigable channel of the bay of Cadiz.

The western Pacific pinnotherid crab, Fabia obtusidentata Dai, Feng, Song and Chen, 1980, which lives in the saucer scallop, Amusium (Pectinidae), is found not to belong to Fabia Dana, 1851 s. str. or Pinnotheres Bosc, 1802. In contrast to these two genera, F. obtusidentata possesses a carapace not having longitudinal grooves, a third maxilliped in which the dactylus is slender and inserted one-third from the proximal end of the conical propodus, and a prominently elongated right third ambulatory leg with a long dactylus. It is here referred to its own genus, Amusiotheres gen. nov. Pinnotheres hanumantharaoi Devi and Shyamasundari, 1989, from India, is also transferred to the new genus.

The African parasitic pea crab Afropinnotheres monodi lives in association with a high number of different bivalve species, although in its reproductive phase (soft females) a high prevalence has been observed infesting mainly intertidal Mytilus galloprovincialis. In recent years this pea crab has been recorded in the south of Iberian Peninsula, with well-established populations in the Gulf of Cadiz, and it has been observed that infested mussels showed a decrease of their condition index of 14.7%, on average. Until now, a high prevalence of A. monodi has been observed only in intertidal mussels inhabiting sheltered and relatively shallow habitats, but it has not yet been found in aquaculture farms located offshore in the surrounding zone. Considering the commercially-important mussel farms located in the Galician Rias and Ebro Delta (sheltered systems), the aim of this study was to test whether the prevalence of this pea crab in subtidal mussels depends on the degree of exposure/shallowness of their habitats and consequently on the coexistence of the primary hosts of all crab demographic categories in a reduced area. For this, we have assessed the prevalence of A. monodi in mussels attached to the submerged chains of the navigational buoys of the navigable channel of the Bay of Cadiz. The results show that A. monodi prevalence is correlated with the distance of mussels from the nearest inshore areas, where bivalves host the initial phases of this species (r = −0.92, p < .01). On average, the highest prevalence corresponded to B10 (the nearest inshore buoy sampled), with 74.5% of mussels hosting crabs and the lowest to B2 (the furthest buoy sampled) where only 17.0% of mussels hosted crabs. These results confirm that A. monodi infects subtidal mussels, in a condition similar to the cultured mussels in rafts and long-lines. Therefore, if the pea crab reaches sheltered areas where mussels are cultivated (i.e. the Galician Rias and Ebro Delta bays), it could become successfully established, with negative commercial consequences for these aquaculture farms., This work was supported by the “Ministerio de Economía y Competitividad (MINECO) (Spain), Plan Nacional I + D” (Spain) and the European FEDER funds through project AFROBIV (CGL2014–53557-P), (Europe). The MINECO also supported a FPI Posdoctoral contract to MPM (BES-2015- 072703). We want to thank to the “Autoridad Portuaria de la Bahía de Cádiz” (Spain) by the permissions to take samples of mussels from the buoys of the navigable channel of the Bay of Cadiz and to “Consejería de Agricultura, Ganadería, Pesca y Desarrollo Sostenible de la Junta de Andalucía“ (Spain) by supporting the development of AFROBIV project.

Background Arcotheres purpureus, a species of pea crab has been reported from the Red Sea, Maldives and Andaman Sea with no description of the male. According to existing literature the single host for this species is Ostrea. Methods The specimens examined were obtained from the dredge hauls. Results In the present study we report Arcotheres purpureus for the first time from the coastal waters of mainland India. The specimens have been observed within the mantle cavity of a venerid bivalve Protapes gallus a new host record for this species. A description of the male specimen is also communicated herein for the first time. Conclusions Bivalve fisheries is an alternative livelihood option for the fishermen of this region. In this context the manifestation of Arcotheres purpureus, from a commercially viable species of bivalve such as Protapes gallus as well as its incidence in waters of mainland, India is a cause for concern necessitating further investigations.

The oyster pea crab Zaops ostreum (Say, 1817), is a parasite of the eastern oyster Crassostrea virginica Gmelin (1791). This study examined the frequency of occurrence and impact of pea crabs on adult (50–70 mm shell height [SH]) oysters from natural intertidal reefs in Hewletts Creek, Wilmington, NC and artificially created intertidal reefs from Jones Island, NC. The reefs at Hewletts Creek and Jones Island were also sampled in the fall of 2012 to quantify the presence of pea crabs in two cooccurring bivalve species, the scorched mussel Brachidontes exustus (Linneaus, 1758), and the ribbed mussel Geukensia demissa (Dillwyn, 1817). To evaluate the impact of pea crabs on juvenile oysters (mean SH 11.07 ± 0.16 mm), oysters were deployed in Hewletts Creek at three densities during July 2013 and then retrieved in October 2013. The percent occurrence of pea crabs in adult oysters was low on the natural reefs (1%–3.7%), greater on the created reefs (10%), whereas the percent occurrence in the deployed ...

Pinnixa valdiviensis Rathbun, 1907 inhabits burrows of the ghost shrimp Callichirus garthi (Retamal, 1975) in the south-eastern Pacific. We described the host-use pattern and sexual dimorphism of P. valdiviensis to test for monogamy considering that the few other studied species of Pinnixa White inhabit their respective hosts as male-female pairs. Against expectations, P. valdiviensis lived either solitarily, or in small groups of up to four individuals; only a few burrows were inhabited by two crabs (either male-female or female-female pairs). The observations above argue against the notion that P. valdiviensis is monogamous. Furthermore, that a high frequency of solitary females were found brooding embryos and that the population sex ratio was skewed toward females suggests that males might roam among hosts in search of receptive females. We argue in favour of additional long-term (seasonal, >1 year) descriptive and experimental studies to reveal the mating tactics used by both males and females of P. valdiviensis. We also examined individual-level reproductive parameters in the studied species as little is known about reproduction in symbiotic crabs. Fecundity varied between 383 and 1052 eggs crab−1 with a mean ± SD of 774 ± 160 eggs crab−1 and increased significantly with female body size. Embryo volume varied between 0.0169 and 0.0443 with a mean ± SD of 0.0222 ± 0.0063 mm3 and did not vary with female body size. Reproductive output (RO) represented a mean ± SD of 5.74% ± 0.86% of crab body dry weight and increased proportionally with crab body weight. The RO in P. valdiviensis is lower than that reported for other free-living and symbiotic crabs.

Parasitism is one of the most common interspecific interactions, but little information exists on the detailed relationships among hosts, parasites, and hyperparasites (secondary parasites) in marine ecosystems. Pea crabs parasitize a wide variety of marine animals, and the crabs themselves are often parasitized by other animals. The present study investigated the relationships among the oyster Saccostrea kegaki, its parasite, the pea crab Pinnotheres boninensis, and a hyperparasite, the isopod Onychocepon resupinum. Field sampling was conducted during the oyster’s reproductive season (June–September 2014 and 2015) to evaluate effects of the pea crab on the body weight, maturation, and sex of the oyster in western Japan (Banshozaki, Shirahama Town, Wakayama Pref.; 33.41°N, 135.20°E). The relationship between the pea crab and the isopod and indirect effects of the isopod on the oyster were also investigated. The pea crab reduced the oyster’s body weight and affected its reproduction: the proportion of mature individuals was lower in infested oysters (39.1%) than in non-infested ones (86.2%). The isopod affected the crab’s sexual characteristics: infested female crabs had poorly developed ovaries, and infested males showed degrees of feminization and increased body size. The prevalence of the isopod was much higher in male (47.1%) than female (6.4%) crabs inside the oyster shells, suggesting that the parasitized male crabs became larger and were forced to remain inside the shells. Therefore, the isopod appears to have an indirect negative impact on the oyster by changing the male crab’s traits.

The mating systems of symbiotic crustaceans vary broadly, ranging from monogamy to polygamy to promiscuity. This disparity in mating systems coupled with wide differences in host ecology provides opportunities to study the effect of environmental conditions on the social behavior of marine organisms. In this study, we tested the prediction that symbiotic crustaceans inhabiting relatively large and abundant host species are promiscuous rather than monogamous. The host traits above constraint host monopolization and favor host-switching behaviors by males individuals and, thus, ultimately drive promiscuity as a mating system in symbiotic crustaceans. As a model system we used Dissodactylus crinitichelis, a small ‘pea-crab’ that inhabits the relatively large and abundant sand dollar Encope emarginata. We described the population distribution of D. crinitichelis at two intertidal localities in Sergipe, Brazil, and conducted laboratory experiments to infer the mating system of this species. Dissodactylus crinitichelis inhabit sand dollars as adult heterosexual pairs more frequently than expected by chance alone, but these heterosexual pairs did not exhibit size-assortative pairing. Sexual dimorphism was reversed in D. crinitichelis, with males attaining smaller average body sizes than females but exhibiting more elaborated weaponry (male > female claws). These findings disagree with expectations for monogamous symbiotic crustaceans. Laboratory experiments demonstrated that male and female crabs switch among host individuals rather frequently and heterosexual pairs retrieved from the field did not remain together for long times. Our results argue against social monogamy and in favor of promiscuity in D. crinitichelis. Our study supports the notion that host abundance and large body size (relative to that of symbiotic guests) favor promiscuity in symbiotic crustaceans.

The symbiotic crab Pinnaxodes mutuensis Sakai, 1939 was found in the mantle cavity of the mud-burrowing bivalve Mya arenaria Linnaeus, 1758 (the family Myidae) in Busse Lagoon at southern Sakhalin Island. Along the Russian coasts, this species has been previously found in the mantle cavity of epifaunal bivalves of the family Mytilidae [Modiolus difficilis (Deshayes in Maillard, 1863), Modiolus modiolus (Linnaeus, 1758), Mytilus edulis Linnaeus, 1758, Crenomytilus grayanus (Dunker, 1853)] and the family Ostreidae [Crassostrea gigas (Thunberg, 1793)]. New data on the morphology and ecology of this crab are presented.

The successful settlement of the African pea crab Afropinnotheres monodi in the Bay of Cadiz was analysed to gain new insights into the evolution of pea crab parasite life history traits. The pea crab lives symbiotically and with high prevalence in the bivalves Cerastoderma glaucum and Mytilus galloprovincialis, and with low prevalence in Scrobicularia plana. A remarkable monopolisation of the host (1 crab per bivalve) occurred irrespective of host species and crab demographic categories (males, hard females, soft females), probably as an optimisation of resources in small hosts. However, there was a clear asymmetry in host use by the different crab categories. A 1:1 sex ratio was found in crabs harboured by C. glaucum and S. plana, with most of the female crabs being small and hard specimens, whereas crabs inhabiting M. galloprovincialis were primarily large reproductive females. Ovigerous females were found throughout the year in M. galloprovincialis, and there was a strong correlation between female size and fecundity, suggesting that the females harboured by this host were the major contributors to the reproductive effort of the studied population. Conversely, most of the new crabs recruiting to the population were harboured by the remaining 2 host species. We hypothesise that such a generalist but asymmetrical usage of bivalve hosts by pea crabs may have clear benefits for species such as A. monodi, that are undergoing geographical expansion, facilitating their dispersal to new locations and their successful settlement in sheltered systems, such as the Bay of Cadiz. © Inter-Research 2014., This research work was funded by remnant funds of the PAI RNM108 research group.

9 pages; International audience; In some long-living symbiotic species, movements between hosts are not limited to offspring since adult parasites can move from one individual host to another one. Host-switching may be driven by different parameters such as (1) mating strategies of symbionts, (2) foraging for resources or (3) avoiding overcrowded or diseased/dead host. Symbiotic marine crustaceans are suitable models to understand what underlies host-switching behavior. In this study, we investigated host desertion by the parasitic pea crab Dissodactylus primitivus associated with the echinoid host Meoma ventricosa. Mark-recapture field experiments, during which crabs were almost always found on their host in heterosexual combinations, suggest that host desertion occurs less frequently when 2 crabs (compared to 3) share the same host. During laboratory experiments with high crab density, the proportion of crabs leaving an echinoid was low when the 2 genders of crabs were present on the host, compared to 1 gender only (males or females). This suggests that host desertion is mostly driven by intersex selection and the search for a mate and, to a lesser extent, by competition between crabs. However, both field and laboratory experiments showed evidence that when they switch host, most crabs remained for a while in the sediment underneath their host. We propose that this behavior, associated with the aggregative behavior of their hosts, would allow the crabs to solve the trade-off between staying on their hosts (therefore suffering overcrowding and sub-optimal mate search) and moving too far from the host (therefore suffering loss of food source and high predation risk).

In organisms using a wide variety of refuges, both the cost and benefits to the users might be refuge-specific. Under these circumstances, users using mechanisms (e.g., behavioral preference) that allow them to find and colonize refuges in which net benefits are maximized are expected to be selected by the environment. Herein, we tested the hypothesis that resource generalists display strong preferences for resources that provide the greatest reproductive benefits using Calyptraeotheres garthi, a crab that inhabits the limpets Crepidula cachimilla and Bostrycapulus odites in the south-western Atlantic. In the field, female crabs inhabiting C. cachimilla featured larger average body size, and subsequently, larger average fecundity and brood weight than those inhabiting B. odites. Thus, C. cachimilla is a higher quality host for C. garthi compared to B. odites. In contrast to expectations, host selection experiments revealed that female crabs were attracted to the host species from which they were collected and not to the host species that provided the greatest reproductive benefits (C. cachimilla). Host chemical and/or visual cues imprinted in crabs early during ontogeny (soon after colonization of their first host), rather than genetic differences, may explain the source-host fidelity of C. garthi. In the two hosts, females of C. garthi lead a solitary lifestyle and appear to inhabit the same host individual for long periods of time as indicated by the close relationship between female crab and host body size. The frequency of male–female pairs within host individuals was lower than expected by chance alone. Also, males were, on average, smaller than females and did not appear to inhabit the same host individual for long periods of time. The above suggests that males might be using a pure‐search mating strategy, continuously roaming among host individuals in search of receptive females. The details of the mating system of C. garthi need to be further investigated.

Austinixa aidaeinhabits burrows of the ghost shrimpCallichirus majorat Perequê-açu beach, Ubatuba, Brazil. We described the host-use pattern and sexual dimorphism ofA. aidaeto test for monogamy given the generality of this mating system in the subfamily Pinnothereliinae (family Pinnotheridae) to whichA. aidaebelongs. Against expectations,A. aidaelives as solitary individuals within burrows more frequently than expected by chance alone. Additional observations suggested thatA. aidaeexhibits a polygynandrous mating system with males moving among burrows in search of receptive females. First, only 21% of the burrows harboured heterosexual pairs of crabs and the body size of paired crabs was poorly correlated. This suggests pair instability and frequent shifts among burrows by male and/or female crabs, as reported before for other symbiotic crustaceans in which the body size of paired crabs is poorly correlated. Second, males paired with females that were sexually receptive (without embryos) or that have been receptive recently (carrying early embryos) were found more frequently than expected by chance alone. The above agrees with that reported for species in which sexual pairing does not last long. Third, sexual dimorphism in terms of claw size and coloration was evident. Claws were larger in males than in females, a condition that argues in favour of male–male competition inA. aidae. In addition, the body coloration of males was more similar to the sand grains of the beach than that of females. This sex-specific coloration suggests that males are ‘better adapted' than females to roam on the surface of the beach in search of burrows because their coloration should diminish the risk of detection by predators. Experiments are needed to reveal the details of the polygynandrous mating system herein inferred forA. aidaeand to understand those conditions favouring particular reproductive strategies in symbiotic decapod crustaceans.

Pea crabs are a common parasite of bivalves around the world and frequently cause problems for bivalve aquaculture through end-consumer complaints and rejections of consignments at international borders due to biosecurity concerns. However, the financial impact of pea crabs on aquaculture production has never been quantified for any bivalve species. A large scale systematic sampling of a typical green-lipped mussel farm in New Zealand revealed that pea crabs were present in 5.3% (± 0.062 SE) of the mussels. The abundance of crabs increased gradually with decreasing water depth beneath the farm and greater distance from the shoreline. Mussels infected with pea crabs were 30% smaller in total wet weight [F1, 2573 = 669, p = 0.00], had a 29% lower meat yield [F1, 2573 = 355, p = 0.00], and shell dimensions were also significantly affected. A total production loss on the 1.71 ha farm was estimated at 803 kg at harvest. When this measured loss is extrapolated to current total mussel aquaculture production in New Zealand, pea crab infection represents an estimated loss to the industry of US$2.16 million annually. Our results indicate that parasitic pea crabs are producing a significant loss of production in shellfish farming aquaculture operations, even at low levels of infection, and therefore warrant a great deal more attention in terms of developing effective control measures.

The arrival and spread of the introduced western pea crab Pinnixa occidentalis Rathbun 1894 in South Africa is documented. The crab originates from the Pacific coast of North America and was first recorded in Saldanha Bay in 2004, although its identification was only confirmed in 2010. Subsequent surveys have shown the crab population to be increasing rapidly in both distribution and density, although it remains confined to the Saldanha Bay–Langebaan Lagoon system. The ecological impacts of the invasion are yet to be determined.

Calyptraeotheres garthi (Fenucci, 1975) is one of nine species of Pinnotheridae occurring in Argentina and the only species of that genus located in this region. This species can be found from the San Matias Gulf, Argentina to Rio Grande do Sul, Brazil where it lives in symbiotic association with limpets of the family Calyptraeidae. Currently, two species of limpets have been reported as hosts of this species: Crepidula protea (d’Orbigny, 1841) and Crepidula argentina Simone, Pastorino & Penchaszadeh, 2000. We report here four more species of limpets serving as hosts of C. garthi, namely Bostrycapulus odites Collin, 2005, Crepidula cachimilla Cledon, Simone & Penchaszadeh, 2004, Crepidula plana Say, 1822 and Trochita pileus (Lamarck, 1822). Thus, this pinnotherid appears to be, as others members of the family, a generalist symbiotic species since it dwells on almost all the potential limpet species reported for Argentina. However, there are notable differences in prevalence of C. garthi on each host, which suggest that the symbiont might prefer species of Crepidula over the others genera (Trochita and Bostrycapulus). Additionally, there exists an apparent relationship between host size and prevalence (e.g., Crepidula cachimilla, the limpet with the highest prevalence, is clearly larger than the others hosts). Perhaps it is premature to conclude that the size of the host might be of benefit for the symbiont, but it is a hypothesis worthy of being explored.

Pinna nobilis and its guests Pontonia pinnophylax and Nepinnotheres pinnotheres were sampled from Posidonia oceanica meadows invaded and non-invaded by the red alga Lophocladia lallemandii . Understanding the interactions among native and invasive species was the primary aim. Therefore, the effects of the invasive L. lallemandii on the percentage contribution of the food sources of P. nobilis and its guests and their trophic associations were investigated by applying mixing models to the δ 13 C and δ 15 N stable isotopes. Isotopic analyses revealed that the guests of P. nobilis occupied a higher trophic level than their host due to their capacity for food selection. The invasion of L. lallemandii altered the percentage contribution of the food sources to the consumers’ diet. Whereas the percentage contribution of the food sources to the δ 13 C signatures did not really change, L. lallemandii produced variations in the percentage contribution to the δ 15 N signatures. This red macroalga represented one of the main food sources for P. nobilis , with a real contribution of 19.4% in the invaded meadows. Moreover, L. lallemandii slightly decreased the trophic level of the consumers. This study provides the first isotopic and trophic data for the pea crab N. pinnotheres .

Introduced species are often thought to do well because of an escape from natural enemies. However, once established, they can acquire a modest assemblage of enemies, including parasites, in their new range. Here we quantified prevalence and effects of infection with copepods (family Myicolidae) and pea crabs (Pinnotheres novaezelandiae), in three mussel species, the non‐native Musculista senhousia, and two native mussels, Perna canaliculus and Xenostrobus pulex, at Bucklands Beach, Auckland, New Zealand. Copepod prevalence was highest in X. pulex (17.9%), whereas pea crab prevalence was highest in P. canaliculus (33.6%). Both parasites infected M. senhousia, but at a much lower prevalence. Dry tissue weight was significantly lower in P. canaliculus infected with pea crabs. In addition, we experimentally investigated host species selection by pea crabs. In an experimental apparatus, pea crabs showed a significant attraction to P. canaliculus, but not so for X. pulex or M. senhousia. When the muss...

Available information on the larval release rhythms of brachyurans is biased to temperate estuarine species and outcomes resulting from some sort of artificial manipulation of ovigerous females. In this study we applied field methods to describe the larval release rhythms of an assemblage of tropical rocky shore crabs. Sampling the broods of ovigerous females of Pachygrapsus transversus at two different shores indicated a spatially consistent semilunar pattern, with larval release maxima around the full and new moon. Yet, synchronism between populations varied considerably, with the pattern obtained at the site exposed to a lower wave action far more apparent. Breeding cohorts at one of the sampled shores apparently belonged to actual age groups composing the ovigerous population. The data suggest that these breeding groups release their larvae in alternate syzygy periods, responding to a lunar cycle instead of the semilunar pattern observed for the whole population. For the description of shorter-term rhythms, temporal series at hour intervals were obtained by sampling the plankton and confinement boxes where ovigerous females were held. Unexpectedly, diurnal release activity prevailed over nocturnal hatching. Yet, only grapsids living higher on the shore exhibited strong preferences over the diel cycle, with P. transversus releasing their larvae during the day and Geograpsus lividus during the night. The pea crab Dissodactylus crinitichelis, the spider crab Epialtus brasiliensis and a suite of xanthoids undertook considerable releasing activity in both periods. Apart from the commensal pea crab D. crinitichelis, all other taxa revealed tide-related rhythms of larval release, with average estimates of the time of maximum hatching always around the time of high tides; usually during the flooding and slack, rather than the ebbing tide. Data obtained for P. transversus females held in confinement boxes indicated that early larval release is mostly due to nocturnal hatching, while zoeal release in diurnal groups took place at the time of high tide. Since nocturnal high tides at the study area occurred late, sometimes close to dusk, early release would allow more time for offshore transport of larvae when the action of potential predators is reduced.

Pea crab species are globally ubiquitous parasites of marine bivalves including several major aquaculture species. However, little is known about the environmental factors that affect their recruitment into aquacultured mussels. The effect of depth and distance from shore on the recruitment of the parasitic pea crab Nepinnotheres novaezelandiae into New Zealand green-lipped mussels Perna canaliculus was examined with a field experiment. The incidence of pea crab infection of mussels over 295 d was nearly double when deployed at 5-10 m depth (1.97%) compared to 20-30 m depth (0.96%), although it was not significantly different due to the overall low period prevalence in the experimental population. The sex ratio of crabs recovered was significantly skewed towards females with a ratio of 1:14 (χ = 11.3, p < 0.001). Infection with pea crabs was found to significantly reduce final mussel shell height on average by 28% (21.0 mm) over 295 d (Mann-Whitney U = 6.0, p < 0.0001). This study confirms that parasitism of green-lipped mussels by pea crabs has a significant impact on the growth of the mussels and suggests that the incidence of pea crabs will be higher in shallower water and when mussels are in closer proximity to the shore. With no control methods available for preventing pea crab infection, these results suggest that moving mussel farms offshore has the potential to reduce the incidence of pea crabs in mussels and warrants larger-scale assessment.

The aim of this study was to assess the effect of temperature on the survival and duration of larval development in the African pea crab Afropinnotheres monodi, as well as to describe its larval stages. We studied larvae reared in the laboratory and also specimens collected from plankton from the Gulf of Cádiz at two different temperatures. According to the results of this study, larval development of A. monodi involves four zoea stages and one megalopa and lasts around 25 days at 25°C, and longer than 40 days at 19°C. Such a temperature-related duration of this dispersive phase may be causing a higher recruitment to parental populations during the summer, but a higher dispersal to new locations during the rest of the year, a seasonal pattern of dispersion which could favour the successful expansion of this non-native species into European waters. The identification of both larval phases from plankton samples and adult specimens was carried out using morphological characters and molecular techniques. Both the 16S mtDNA sequences of this species, now available in GenBank, and the larval descriptions provided by this study could help to establish an early alert for the detection of this African species in its northward expansion., The research was carried out within the framework of the projects MEGALOPADN [CGL2009-11225], ‘Transporte y reclutamiento larvario de crustáceos bentónicos litorales: importancia de los agentes forzadores costeros y regimen mareal’ [CTM2005-00024/MAR] and AFROBIV [CGL2014-53557-P], co-financed by the ‘Ministerio de Economía y Competividad (MINECO)’ Spanish Plan R+D+I and ERDF, European Union. Elena Marco-Herrero acknowledges a pre-doctoral FPI Fellowship supported by MINECO [BES-2010-033297].

The pea crab Orthotheres barbatus is one of seven species of the family Pinnotheridae reported from Venezuelan marine waters. Larval life histories are not known for any species of the genus Orthotheres. Ten ovigerous females of O. barbatus were obtained from their host gastropod, Cittarium pica, at Los Roques Archipelago, Venezuela. Larvae of O. barbatus were reared in the laboratory from hatching to the first crab stage. This species exhibits abbreviated development in both the number of larval stages (two zoeal stages preceding a megalopa) and the duration of development (minimum of four days from hatching to first crab). The number of zoeal stages for pinnotherid species described to date ranges from 3 to 5, with only Tunicotheres moseri, Pinnotheres taylori, and Nepinnotheres pinnotheres known to also have only two zoeal stages. Morphology of the larval stages of O. barbatus is described, illustrated and compared to that previously described for larvae of the Pinnotherinae. Selected larval c...

The condition index (CI) is a tool that has been used to estimate the effect that different environmental factors have on oyster meat quality. The CI of oysters in five beds in Sapelo Island and the Doboy Sound (Georgia, United States) were calculated using three different methodologies. Values from each site were used to: (1) compare two sites located in relatively large systems (river/sound) and three sites in a small creek to test for differences due to system size and related nutrient availability; (2) determine the effect of a parasite, the pea crab (Pinnotheres spp.), on oyster CI; and (3) determine the effect of differential position of oysters on a bed, with respect to CI (oysters were collected from areas of the bed that are permanently submerged and areas with the longest dry periods between tidal cycles). With respect to the three analyses mentioned earlier, it was found that oyster CIs for sites in larger systems (river and sound sites) were significantly higher than those in sites wi...

Diel, lunar, and seasonal abundance, as well as population structure, of the free-swimming stage of the pea crab Pinnotheres bidentatus Sakai, 1939, from tidal waters off the west coast of central Taiwan were examined. A total 5,123 specimens were collected from tidal waters of the Kaomei coastal flat. These crabs were found year-round but mostly during fall to early winter (October to December 1994 and September 1995), with a peak in early December 1994. Numbers of crabs dropped sharply in mid-December 1994 and remained low during the months of January to April 1995, with slightly increasing numbers during mid-May to September of the same year. Daily abundance of the crab appeared to be related to new and full moon phases, indicating a semilunar pattern of swimming activity. Moreover, pea crabs were only collected during nighttime flooding tides, suggesting a nocturnal swimming activity which may have advantages for avoiding fish predators. Size structure of the crab indicates that P. bidentatus has life-history characteristics of which males die in the hard stage and females subsequently lose their swimming hairs and become commensal with their host. The overall sex ratio was 1:1.3 (2,206 males and 2,917 females) and varied according to month and size. The continuous occurrence of small individuals (1-mm size class) year-round indicates a long period of recruitment which may be a consequence of the long reproductive period of P. bidentatus.

A new species of pea crab, Pinnotheres halingi sp. nov. (Pinnotheridae), found encysted in the right respiratory tree of the sea cucumber, Holothuria scabra (Holothuridea), from Solomon Islands, is described. The reproduction, infestation and pairing behaviour of the crabs were investigated through field observations and experiments. Infestation frequency in 8 monthly samplings of 25–30 holothurians was 98.6±2.6% in Kogu Halingi bay and 0% in two nearby sites. Of 403 pea crabs, 91.4% were found in pairs of opposite sex, 7.9% were single females and

Pinnotherid crabs are typically found associated with many benthic invertebrates. On sandy beaches of southern Brazil, Pinnixa patagoniensis Rathbun, 1918 inhabits burrows of the ghost shrimp Sergio mirim Rodrigues, 1971. The population dynamics of this crab were studied from monthly samples taken between March 1989 and November 1991 near the Patos Lagoon outlet, southern Brazil ca. 32°13'S; 52°15'W. There was no correlation between the number and size of the crabs and the size of their respective hosts. Mean densities and incidence reached 3.1 indiv. opening-1 range: 0 to 29 and 83.9%. respectively. Sex-ratios were not significantly different from 1:1 for the different size classes and sampling dates. Ovigerous females were found between October and March, showing an average fecundity of 1529 eggs per female. The annual recruitment pattern was bimodal, with a minor peak in summer and a fall peak that accounted for almost 70% of the population maintenance. Males and females both reached a maximum carapace width of 11.5 mm and had a life span of nearly two years as estimated from fitted von Bertalanffy growth curve parameters.

The pea crab, Pinnotheres tsingtaoensis, symbiotic with the bivalve mollusk, Sanguinolaria acuta, was collected in the estuary of Bazhan Stream on the west coast of Taiwan from May, 1992 to November, 1993. More than 90% of the bivalves were infested and most infested specimens (90-97%) hosted one crab. Two cohorts, i.e., year classes, of the bivalves were observed in May, but only one was seen between July and November; the life span of the crab is less than 2 years at the site. Recruitment of both the bivalves and the crabs apparently occurred between November and May next year. Positive size correlation between hosts and symbionts was found in larger sized females, but was not consistent in smaller sized males. All females had a soft carapace whereas most males had a hard carapace; females were less likely to leave the hosts than males upon collection of the host bivalves. Females accompanied by males were more likely to carry eggs. Mating probably took place inside the hosts where female crabs remained stationary, with males visiting different bivalves and spending much time outside the bivalves.

The pea crab, Zaops ostreum, a symbiont in the mantle cavity of the American oyster (Crassostreavirginica), is itself a host to a symbiotic nemertean. Thisnemertean belongs to the genus Carcinonemertes, and issimilar to or possibly the same as C. pinnotheridophila,known from another sympatric pinnotherid crab, Pinnixachaetopterana. Living in mucous sheaths within the gillchambers of female crabs, the life cycle of the nemertean isintimately synchronized with and dependent on the crab's reproduction. A total of 138 pea crabs were collected andexamined for nemerteans during the summers of 1965 to 1967 atBeaufort, North Carolina, U.S.A.; of these 97 (70%) were mature(5th stage) female crabs. Mature females harbored thenemerteans, and had a prevalence of 39.2%. A maximum of 20worms was found in the gill chambers of a single crab, 9 ofwhich were the red, eyeless, mature female worms, along with 11colorless males. Worm egg sacs were attached to the pleopods ofovigorous crabs; a maximum of 293 sacs was recorded in anindividual crab with 7 mature females. At about 110 eggs persac, this translates to a potential production of >32 200nemertean larvae. Since female Z. ostreum may live for 2to 3 yr and produce two broods of eggs per year (beyond thefirst year), the reproductive potential of the symbionts may beeven greater. Gills of crabs with more than one mature femalewere usually covered by the worm sheaths, and were frequentlydamaged (gnarled, torn, silted, etc.). The sternum of infestedcrabs was often damaged due to the projection of worm sheathsthrough it to the subabdominal region. There the egg sacs weredeposited on the pleopods to develop along with the crabembryos.

The pinnotherid crab Dissodactylus primitivus lives parasitically on 2 burrowingechinoid species, Meoma ventricosa and Plagiobrissus grandis. The fecundity of female crabsvaries between hosts, and is higher when parasitizing P. grandis than M. ventricosa. Moreover, thehosts present great variations in morphology (size and density of spines). These characteristicssuggest the potential to differentiate crabs according to host species. We investigated the genetic(microsatellites) and morphometric (outline analysis) differentiation of this parasitic crab between2 host species at 1 Jamaican site (Western Lagoon, Discovery Bay), and compared it with geographicdifferentiation among 4 sites along the north coast of Jamaica. Greater genetic differencesbetween parasites of the 2 sympatric hosts than between parasites of a single host at different geographiclocations would indicate host differentiation. Genetic analyses (microsatellites) did notdetect spatial differentiation (probably due to local hydrography) or differentiation according tohost species. This lack of host differentiation could be explained by mobility of adult crabsbetween hosts. However, there was weak but significant morphological differentiation betweenfemale crabs from the 2 hosts. This morphological difference may reflect constraints due to hostmorphology., info:eu-repo/semantics/published

Pea crabs are commercially significant parasites in the aquaculture production of bivalves in many parts of the world. However, there is scant information available on the biology of these important parasites in aquaculture. The population structure, sex ratio, and breeding status were determined for the pea crab Nepinnotheres novaezelandiae residing in a typical green-lipped mussel Perna canaliculus farm in New Zealand. Of the 324 crabs randomly sampled, there were significantly more female (82.4%) than male (17.6%) crabs found. The vast majority of crabs (87.0%) were sexually mature and of these, females comprised 86.4% and males 13.6%. However, the sex ratio of immature crabs was relatively even, suggesting that male crabs may have higher mortality while searching for mates. Crab size was highly variable, indicating that recruitment to mussels in the farm was continuous. Carapace width ranged from 4.00 to 11.5 mm, with males tending to be smaller with a mean (±SE) carapace width of 6.31 ± 0.16 mm versus females with a carapace width of 8.03 ± 0.06 mm. The crabs did not show any preference for parasitizing mussels of different sexes. Despite the fact that the mussels were only 10 mo old, most female crabs were sexually mature (Stage V) and 89.3% were gravid. The mean (±SE) clutch size was 2592 ± 579 and clutch size was directly associated with female carapace width. The mussel farm pea crab population was estimated at 126390 ± 14144 individuals, including 93000 gravid females carrying a total of over 241 million eggs. Overall, the results show that pea crabs rapidly colonize farmed mussels and mature quickly to establish a significant breeding population within the mussel farm, with larval output capable of infecting nearby mussel farms as well as wild populations of bivalves.

Mechanisms of host detection and host choice are important for mobile parasites or symbionts that frequently move among host individuals. The parasitic pea crab Dissodactylus primitivus is an ectoparasite exploiting asymmetrically two spatangoid echinoid hosts, Meoma ventricosa and Plagiobrissus grandis. The entire life cycle takes place on M. ventricosa, while only adults colonize P. grandis, the host where female's fecundity is the greatest. Dissodactylus primitivus frequently exhibits host-switching, a behaviour that raises the question of host detection. To test if adult crabs are able to detect potential hosts and are attracted to the host where their fitness is greater, crab olfactory responses were investigated using a Y-tube. We first showed that D. primitivus are attracted by olfactory cues of M. ventricosa, versus those of a non-host echinoid species, Clypeaster rosaceus sharing the same habitat. This attractiveness was not due to a yellowish water-soluble substance secreted by the host. We then showed that the chemical attraction to the two hosts was different according to the origin of the crabs. Crabs coming from M. ventricosa were more attracted to this host than to P. grandis, a pattern compatible with an imprinting phenomenon. However, crabs collected from P. grandis were equally attracted to both host species, as if imprinting was lost after host change. We propose that the pattern of D. primitivus host detection could be intermediate between the behaviour of specialist and generalist symbionts.

Exploitation of more than one host species may increase fitness of parasites, but it also shapes their life cycle and evolution. During its post-metamorphic stages, the pea crab Dissodactylus primitivus parasitizes the echinoids Meoma ventricosa and Plagiobrissus grandis with high prevalence. However, the present study provides evidence that P. grandis is infected by adult crabs only, attesting to an unusual asymmetry in host exploitation. Because of its low population densities, P. grandis could be a secondarily acquired host, and its addition to the crab life cycle could be adaptive. The latter hypothesis is tested in this study. Choice experiments revealed that adult and juvenile crabs were equally attracted to and able to settle on the 2 hosts. Most adult crab characteristics were not significantly different between the host species, but females living on P. grandis had higher fecundity. This asymmetric life cycle, where adult parasites infecting the 2 hosts show different relative fitnesses, looks like a transitory stage as predicted in models which predict the evolution of parasitic complex life cycles. However, this parasite asymmetric exploitation may also be a stable state, which occurs due to insufficient differences in crab fitness between the 2 hosts and the absence of host preference.

The inter-relationship between the pea crab Pinnotheres sinensis and its bivalve host Septifer virgatus was studied from July 2002 to December 2004. The infested bivalve generally contained a single crab (72.4–94.7%), but multiple infestation was also observed in some cases (5.3–27.6%). Seasonal fluctuations in the prevalence rate, sex ratio and ovigerous rate were examined. The prevalence rate and sex ratio increased in autumn and decreased from spring to summer. By contrast, the rate of the ovigerous female increased in summer and decreased in autumn. The carapace width of females was larger than that of males, and seasonal fluctuation in the carapace width was observed in the female crabs. All the females had a soft carapace whereas most males had a hard carapace. No females were observed outside the host, though a small number of males were observed outside it. Mating probably took place inside the host where females remained stationary, with males visiting different bivalves as well as spending much time outside the bivalves.