Ectosymbionts of the non‐indigenous Asian shore crab,Hemigrapsus sanguineus (Decapoda: Varunidae), in the western north Atlantic,and a search for its parasites

Over 560 Asian shore crabs, Hemigrapsus sanguineus, collected mainly in the spring of 2005 and 2006 from rocky intertidal locations in southern New Jersey, were examined for epibionts. Small numbers of the sympatric green crab, Carcinus maenas, and the Atlantic mud crab, Panopeus herbstii, were examined for epifauna to compare with H. sanguineus. Blue mussel spat, Mytilus edulis, and the encrusting, cheilostome bryozoan, Conopeum tenuissimum, were the dominant ectosymbionts of the shore crab, with prevalences of 22.2 and 32.1%, respectively; ranges of intensity were 1–146 spat/crab and 1–31 colonies/crab. Both species are incidental symbionts. Larger crabs had higher prevalences and intensities of C. tenuissimum colonies, and these colonies displayed a distinct pattern of attachment to the carapace which seemed to be related to crab morphology and habitat. Much less common was the encrusting, ctenostome bryozoan Alcyonidium albescens, a facultative symbiont species with a prevalence of 3.4%. Other epibionts were the encrusting, cheilostome Membranipora tenuis, the tubicolous polychaetes Hydroides dianthus, Sabellaria vulgaris, and Spirorbis sp., the barnacles Balanus improvisus and Semibalanus balanoides, and unidentified thecate hydroids, all incidental symbionts with prevalences from 0.2 to 3.2%. The total number of known ectosymbionts of H. sanguineus, including additional species found previously in the USA and the western Pacific, is 13. Carcinus maenas and P. herbstii share some of the same symbionts. Rhizocephalan externae were not observed in any of the crab species used in this study, nor were gill parasites or internal parasites found among 248 specimens of H. sanguineus.     

Symbiotic associations between hermit crabs and bryozoans from the Otago region,southeastern New Zealand

Thirteen species of bryozoans (six cyclostomes and seven cheilostomes) occurring off the Otago Peninsula (southeastern New Zealand) form symbiotic, possibly mutualistic, associations with hermit crabs. For all but one of these bryozoan species, such an association has not been reported previously. At most only 3 of the 13 bryozoans are obligate symbionts of hermit crabs. Associations are apparently initiated when a bryozoan larva settles on a gastropod shell occupied by a juvenile hermit crab and develops to form a colony which encrusts the whole shell and then continues to grow out beyond the shell aperture in the form of a helicospiral tube. The tube-building bryozoan colony grows in step with the crab, and tube development appears to be controlled by crab morphology and activity. Of the six species of hermit crabs found occupying bryozoan tubes, four were regular tube occupants, although they could also be found in other shelter types. Hermit crabs occupying bryozoan tubes very rarely indulged in shell exchanges or shell fights. There appear to be no clear cut pairwise correlations between hermit crab species and tube-forming bryozoan species. The following bryozoan species are described for the first time: Heteropora parapelliculata, Borgiola otagoensis, Disporella gordoni, Osthimosia monilifera and O. socialis.     

Aspects of mangal ecology along the Red Sea coast of Saudi Arabia

Surveys of the mangal along the Red Sea coast of Saudi Arabia form the basis of this study. Both soft-bottomed mangals and the less well known hard-bottomed mangals are represented. The distribution of Avicennia marina, the dominant mangrove species, is discontinuous in the northern part of the Red Sea. Its development increases southwards, and mean height is inversely correlated both with latitude (P<0·05) and salinity (P<0·05). Another species, Rhizophora mucronata, was recorded in only five areas. Molluscs and crabs represent the principal faunal elements within the mangal. The density of Cerithidea cingulata, the dominant mollusc species, shows significant correlation (P<0·01) with the abundance of blue-green algae. Four species of fiddler crab (Uca) are included among the crab fauna of the mangal, one of which (U. urvillei) is here newly recorded for the Red Sea. Evidence is given for suggesting that the mangal biota in the region sampled may not be distinctive. Rather, it consists of many species found not only within the mangal but also in other habitats such as seagrass beds and even rock beaches. It is suggested that the mangal of the Red Sea represents a composite habitat, containing both hard and soft substrates and inhabited by species typical of each. This contrasts with the situation in most other mangals studied.     

A comparative study of the larval development of Monodaeus couchi (Couch), Xantho incisus Leach and Pilumnus hirtellus (Linnaeus) (Crustacea: Brachyura: Xanthidae)

Summary

Comparative accounts are given of the larval and first crab stages of three crab species belonging to the family Xanthidae: Monodaeus couchi (Couch), Xantho incisus Leach and Pilumnus hirtellus (Linnaeus). Features are discussed that distinguish the larvae of these species from those of other N.E. Atlantic brachyrhynch crabs.     

Aggressive,omnivorous, invasive: the Erythraean moon crab Matuta victor (Fabricius, 1781) (Crustacea: Decapoda: Matutidae) in the eastern Mediterranean sea

Since its first sighting in 2012 in Haifa Bay, Israel, the population of the Indo-Pacific moon crab, Matuta victor, has increased greatly along the Israeli littoral and spread to Lebanon and the Mediterranean coast of Turkey. To examine possible interactions with the Levantine nearshore psammophilic community, the crab’s feeding behaviour was observed in situ and the foregut contents of 69 specimens collected in December 2015 and June 2016 were analysed. Its omnivorous diet was confirmed and previously unknown intraspecific competitive feeding behaviour is reported. The agonistic behaviour may denote behavioural flexibility that enables the crabs to colonize and persist in a depauperate novel habitat. Site-specific disturbance regimen related to human activities seems to have had a critical role in driving the rapid population increase.     

Aspects of the biology of the jonah crab,Cancer borealis Stimpson, 1859 in the mid-Atlantic Bight

Summary

Jonah crabs, Cancer borealis, were collected in October 1971, June 1973, and March and April 1974 during trawl surveys of the continental shelf of the mid-Atlantic Bight and the shelf and slope east of Beaufort, North Carolina. In 171 trawls made from the M/V Blesk, R/V Columbus Iselin, R/V Albatross IV and R/V Eastward, 1626 jonah crabs were captured. Crabs were contagiously distributed within a depth range of 20–400 m. Maximum abundance occurred within 150–400 m and 8–13·9°C.

Male crabs ranged from 12 to 175 mm in carapace width; females from 13 to 152 mm. Three modal size groups for males and females were recognized: 13–40 mm, 41–80 mm and 81–110 mm. There was a fourth group of male crabs over 110 mm width. Crabs 40 mm were most abundant at depths of 75–150 m; crabs 41–80 mm were not captured in depths < 150 m, but were the dominant group in strata > 150 m. Larger crabs (81–110 mm) occurred from 40 to 400 m and reached maximum numbers at 150–400 m. Male crabs ≥ 111 mm were found only in 150–400 m.

Male crabs predominated in June. Sex ratios (M:F) ranged from 1·1:1 to 17:1. In October the ratios ranged from 1:16 to 2·4:1. In March and April the ratios were 2·9:1 and 1·9:1, respectively. In most cases the ratios were significantly different from 1:1.

The species was actively moulting in June, but recent or incipient ecdysis was not observed in October. Only one recently moulted crab was noted in March.

Gonad development in June was related to size. Most crabs ? 80 mm width were undeveloped or only slightly developed. Mature gonads were seen only in crabs ≥ 100 mm width. Testes and vasa deferentia of most males ≥ 150 mm were well to very well developed. No ripe ovaries were seen and no ovigerous individuals were taken in June. One berried female was observed in March.

The incidence of fouling organisms on crabs reflected the moulting history of the crabs. Sixty per cent of crabs in anecdysis and 14% of those in postecdysis were fouled. The predominant organism was the lepadid barnacle, Poecilasma inaequilaterale Pilsbry, which was attached to the gills in the branchial chamber.     

Genetic diversity of freshwater crabs (Brachyura: Sesarmidae) from central Jamaica with description of a new species

Jamaica is the only island of the Greater Antilles where freshwater streams are not populated by representatives of the old lineage of freshwater crabs, the Pseudothelphusidae. Instead, a very diverse fauna of endemic sesarmid crabs inhabits freshwater and terrestrial habitats throughout the island, thereby showing complete independence from the sea. They have been reported thriving in bromeliad leaf axils, rock rubble, empty snail shells, caves and mountain streams. Otherwise, the Sesarmidae are typical inhabitants of soft‐sediment littoral habitats like marshes and mangroves. For many years, crabs from Jamaican mountains streams had been considered to belong to a single species, Sesarma bidentatum Benedict . However, recent morphological and molecular studies have shown that crabs from mountain streams of different regions of the island belong to different species. Consequently, four new crab species have been described over the last 10 years. In this study, we give evidence that freshwater streams in central Jamaica also host two different species of crabs. In streams draining to the north we exclusively found the species S. windsor Türkay and Diesel, , while streams draining to the south were inhabited by a closely related but undescribed species of crab. The southern species is here described as new and is referred to as Sesarma meridies sp. n. Morphological and molecular (12S and 16S mtDNA) evidence is provided that allows these two species of freshwater crabs from central Jamaica to be distinguished. The species richness of Jamaican endemic sesarmids thereby increases to 10, which makes the island unique in terms of its diversity of land‐dwelling crabs.     

Larval development and emigration behaviour during sea-to-land transition of the land hermit crab Coenobita brevimanus Dana, 1852 (Crustacea: Decapoda: Anomura: Coenobitidae) under laboratory conditions

To determine the early life history of the land hermit crab Coenobita brevimanus Dana, 1852, larvae were cultured individually in the laboratory. The zoeal and the megalopal stages are described and illustrated. The larvae developed through four planktonic zoeal stages to the megalopal stage. The major differences in the zoeal characters between C. brevimanus and other described Coenobita species were found in the armature of the pleomeres, whereas the character of pleomeres of C. brevimanus zoeae is the same as that of the coconut crab Birgus latro, a different genus in the same family. Morphological similarity was also found in segmentations of antennules and antennae in megalopae between C. brevimanus and the coconut crab. Megalopae of C. brevimanus were cultured in containers holding seawater and a hard substrate. These crabs migrate from the sea to land after developing a habit of acquiring gastropod shells.     

Hypersymbioses in the pinnotherid crabs (Decapoda: Brachyura: Pinnotheridae): a review

Members of the brachyuran family Pinnotheridae are nearly all symbionts of other invertebrates; some crabs are parasitic and others are commensal. Most live inside bivalve molluscs or in the tubes or burrows of polychaetes and other marine organisms. Animals living on or in pinnotherid crabs are considered to be hypersymbiotic and are reviewed here. Hypersymbionts are poorly represented within only 26 members (～8.6%) of the Pinnotheridae (20 species in the subfamily Pinnotherinae and six species in the Pinnothereliinae). Parasitic hypersymbionts are as follows: three species of fungi; one cestode larva (undescribed procercoid of Trypanorhynchida); one trematode metacercaria (undescribed Microphallidae); nematode cysts (undescribed); three species of Nemertea (Carcinonemertidae, two undescribed); two species of rhizocephalan Cirripedia (Sacculinidae; plus five or more undescribed potential sacculinid species); epicaridean Isopoda [13 species of Bopyridae (one undescribed) and four species of entoniscids (Entoniscidae, three undescribed)]. Preliminary biological information on undescribed entoniscids is presented. Several mainly incidental hypersymbioses involving ectosymbionts are known primarily from Pinnixa chaetopterana, a symbiont of polychaete burrows. The ctenostome bryozoan Triticella elongata is the only known obligate ectosymbiont in P. chaetopterana, but it also infests five other species of pinnotherids. Some of the other ectosymbionts (all incidental) on P. chaetopterana are stalked ciliates, hydroids, juvenile polychaetes, bivalve molluscs, balanomorph barnacles, harpacticoid copepods and urochordates. Species of ectosymbionts including an ectoproct bryozoan have been reported from other pinnotherid species. Factors influencing our meagre knowledge of hypersymbioses in the Pinnotheridae are discussed, among them the inaccessibility of crab hosts and research emphasis on taxonomy within the family.     

Carpospore release in a species of Polysiphonia

Intertidal algae from rockpools at different tidal heights, along with Laminaria holdfasts and samples of sublittoral algae were collected from both the sheltered and exposed side of Filey Brigg, North Yorkshire. Samples of sediments were also collected from MLWS on the sheltered shore. A total of 1091 individual ostracods, consisting of 32 species, from 20 genera and 12 families, were identified from 15 sites along the Brigg in July 1996. The current study lists the occurrence of thirteen species previously unrecorded for the Yorkshire coast, and confirms presence of three species that were thought to have a general distribution around the British Isles. The seven Paradoxostoma species showed distinct zonation patterns on both the sheltered and exposed shore. Paradoxostoma ensiforme and P. variabile were only found intertidally, P. hibernicum decreased numerically down shore, and P. bradyi and P. abbreviatum were only found in low shore, Laminaria holdfast or sublittoral samples. This pattern was also seen in many other species, e.g. Xestoleberis aurantia, which only occurred in the intertidal phytal samples, whereas others were only found sublittorally, e.g. Sclerochilus truncatus. Cytherois fischeri, Paradoxostoma robinhoodi, Hemicytherura cellulosa, Leptocythere psammophila, Semicytherura sella and Sclerochilus gewermuelleri were found on the exposed shore only and Cuneocythere semipunctata only occurred on the sheltered shore. Apart from these differences in distribution, the other species occurred on both sides of the Brigg, with only minor differences in density. Some species were more numerous on the sheltered shore (e.g. Heterocythereis albomaculata), whereas others occurred in higher frequencies on the exposed shore (e.g. P. hibernicum). However, there was no marked difference in assemblage structure between the sheltered and exposed side of Filey Brigg. The intertidal phytal assemblages then showed a high degree of similarity. However the sublittoral assemblages were markedly dissimilar from the high-shore assemblages and there was little similarity between the intertidal phytal and sediment assemblages. Although some species occurred in both habitats, e.g. Cythere lutea, others were only found in either one or the other. The phytal assemblages had a higher species richness of ostracods and were more diverse than the sediment assemblages. However, there was no correlation between phytal ostracod species diversity and tidal height, or between diversity and sediment content of the algae. The Yorkshire coast ostracod fauna is compared and contrasted with that previously described by other workers from southern and western Britain.     

The diets of juvenile horseshoe crabs,Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), from nursery beaches proposed for conservation in Hong Kong

Once common as a fishery resource, adult horseshoe crabs of two species occur in Hong Kong. A third, Tachypleus gigas, can no longer be found. Once common too were breeding and nursery beaches for horseshoe crabs in Hong Kong but overfishing of adults, pollution and coastal reclamation have reduced these to but three identified sandy mudflats and only one where juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda are sympatric. Nothing is known, however, of the conservation requirements of these two species locally and this study of the diets of these juvenile horseshoe crabs on two such nursery beaches aimed at providing information on this most elementary aspect of their biology. Gut contents of juvenile horseshoe crabs, i.e. nine Tachypleus tridentatus (8.5–67?mm prosoma width) and two Carcinoscorpius rotundicauda (50 and 52?mm prosoma width), were analysed and compared with the composition of the ambient assemblage of meiobenthos on a nursery beach at Pak Nai, Hong Kong. The obtained data suggest that juvenile horseshoe crabs of both species are selective benthic feeders and subsist mainly on insect larvae, polychaetes, oligochaetes, small crabs and thin-shelled bivalves. A strong, positive, preference for insect larvae (Chironomous sp.: Diptera: Chironomidae) was recorded, but with no preference for meiofauna over macrofauna.     

The prey and predators of Homalopsine snakes

The diets of all South-East Asian water snakes of the subfamily Homalopsinae are reviewed. New diet observations for 10 species of homalopsine snakes are presented. The data on four of these, Cantoria violacea, Enhydris doriea, E. longicauda and Gerarda prevostina represent the first published diet records for these species. The observations for Fordonia leucobalia, Myron richardsonii andEnhydris enhydris represent the first taxonomically detailed diet records for these three species. The records provided for Cerberus rynchops, Enhydris plumbea and Homalopsis buccata add new taxonomic categories to previous records. The records provided for Cerberus rynchops, E. plumbea and Homalopsis buccata add new taxonomic categories to previous records. Four generalities emerge from our findings: (1) freshwater homalopsines feed primarily on fish and the adults and larvae of amphibians; (2) at least four of the eight estuarial species specialize on crustaceans while two primarily prey on fish; (3) feeding on crustaceans appears to have evolved independently at least twice; (4) prey are usually less than 10% of the predator's mass. The known predators of homalopsines are summarized and include both invertebrates and vertebrates. The microhabitats of the estuarial species are discussed and related to prey and habitat preferences.     

Notes on Simulium ovazzae Grenier and Mouchet (Diptera: Simuliidae) and river crabs (Malacostraca: Potamidae) and their association

Summary

Collections of crabs in the forest zone of West Cameroon produced three species—Potamonautes africanus, P. orthostylis and P. pobeguini. The P. africanus carried populations of immature Simulium ovazzae.

Analysis of crabs collected by hand and those collected in traps indicates very little overlap in the sizes of the crabs obtained by the two techniques. This problem is discussed.

The infestation rates of S. ovazzae on P. africanus were found to be highest on medium-sized crabs. The attachment sites of the S. ovazzae on the crabs were found to vary with both the size of the crab and the size of the Simulium larva.

The size distributions of S. ovazzae larvae on small crabs were found to be different from those on medium and large crabs. The characteristic deficiency of smaller larvae on medium and large crabs reported for other crab-phoretic species was also found with S. ovazzae but the smaller crabs showed a deficiency of larger larvae. A hypothesis is put forward to explain the dearth of larger larvae on the smaller crabs and the higher infestation rate on medium crabs.

S. ovazzae are shown to arrive on their hosts as single larvae carried by the current.

Six adult S. ovazzae were reared from pupae in the laboratory. Small numbers of presumed S. ovazzae biting man in Cameroon are reported.     

Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.     

Singing and dancing in the ghost crab Ocypode platytarsus (Crustacea,Decapoda, Ocypodidae)

Male ghost crabs, Ocypode platytarsus, have the most elaborate visual and acoustic/vibrational display so far described in the genus. In common with other species, rapping as a result of hitting the ground with the major cheliped produces rap trains with a variable number of elements. Ocypode platytarsus also produces faster and longer rap trains by drumming with both chelipeds. Additionally, at the approach of a wandering crab, a dance display is also performed. The display begins with the crab rearing up on outstretched legs. Rapid stepping on the spot leads to swift sideways movements that increase in complexity with the longest ones being full circling movements around the wanderer. The display generates an auditory/vibrational sound that is distinct from that produced by the chelipeds. Longer rap trains and drumming events occur in close association with, or following dance displays, but usually when the wanderer is moving away. At other times, rap trains with fewer than ten elements are produced. These observations are discussed in relation to the possible interaction of the three communication channels that are available to the Ocypodinae.     

Intertidal distribution,symbiotic association and reproduction of Pinnotheres bidentatus (Brachyura: Pinnotheridae) from Taiwan

The intertidal distribution of the free-swimming stage of the pea crab Pinnotheres bidentatus Sakai, 1939 was examined on the Kaomei coastal flat of western central Taiwan. Most pea crabs were collected from tidal waters close to the shoreline regardless of the collecting treatments utilized. Results suggest that the pea crab population remains inshore during ebb tides. Many hard and post-hard stages of P. bidentatus were discovered, including ovigerous females. The host was found to be Laternula marilina (Valenciennes, 1860) (Mollusca: Bivalvia: Laternulidae). The infestation percentage of the bivalve was high (average 74.6%). However, this may be due to collections of the bivalve population in the present study being skewed towards large sizes. This biased size structure of the host population may be also responsible for lack of positive size correlation between number and size of male and female symbiotic crabs and the host. Multiple infestations of P. bidentatus appear to be uncommon for L. marilina. Single infestations might be a model for bivalves in tropical regions where the sea is relatively oligotrophic and food competition may be enhanced with multiple infestations. In comparison to other members of the genus Pinnotheres or related species (e.g. P. pisum (Linnaeus, 1767) and Zaops ostreum (Say, 1817)), the body size of sexually mature female P. bidentatus is relatively small, even though it produces similar size eggs (approximately 300 microns). The general rule for size correlation between fecundity and female size in brachyuran crabs holds for P. bidentatus.     

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

Clibanarius 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.