Ocypodid Crabs Research Articles

Breeding cycle and mating behaviour of the tropical ocypodidIlyoplax gangetica(Kemp 1919) (Crustacea Brachyura)

The population structure, female breeding cycle, male courting activity and the mating behaviour of the tropical ocypodid crab, Ilyoplax gangetica (Kemp 1919) were studied on the mud flat of Phuket Island, southern Thailand. The smallest sized female carrying eggs and male performing the waving display were 3.70 and 3.55 mm in carapace width, respectively. Both the male courting activity and the female breeding exhibited semilunar cycles. Males performing waving occurred in all the months of the year and during the periods between new or full moon and the following half moon on the monthly basis. After enticement into a waving male's burrow, the female copulated, laid eggs and released zoea after ca 12 days incubation. The pair was separated when the male left his burrow after the female laid eggs or within 6 days after pair formation.

Earthen Structures Built by Ilyoplax dentimerosa (Crustacea, Brachyura, Ocypodidae)

AbstractUnder observation, the small ocypodid crab Ilyoplax dentimerosa was found to commonly build three types of earthen structures: a barricade near its neighbour's burrow, a fence at an intermediate position between the burrows of the builder and its neighbour, and a minishelter near the builder's burrow. The sex ratio of barricade builders was found to be close to 1:1, whereas most of the fence builders were found to be female. Crabs against which barricades and fences were built, were usually smaller than the builders. Both barricade builders and fence builders had, in most cases, minishelters at the side, facing the barricade or the fence. Removal and rebuilding experiments for barricades and fences demonstrated that both structures functioned to deter the approach of the builder's neighbour to the builder's activity site. Fences also had the effect of restraining the movement of the builder toward the fence site.

GENETIC DIFFERENTIATION IN TRANS-FLORIDIAN SPECIES COMPLEXES OF SESARMA AND UCA (DECAPODA: BRACHYURA)

ABSTRACT Most nearshore brachyuran crabs of the northern Gulf of Mexico have been treated as conspecifics of those in warm-temperate Carolinian waters on the southeastern Atlantic coast of North America. However, historical physiographic constraints appear to have periodically restricted gene flow between northern Gulf populations and sibling Atlantic coast populations, and contemporary disjuncture of ranges often persists across south Florida. The present examination of intertidal complexes has centered on grapsid crabs presently assigned to Sesarma reticulatum and ocypodid crabs assigned to Uca minax, 2 species in which we have observed marked variations in coloration over their distributional range. Genetic differentiation between populations has been assayed by allozyme electrophoresis, and resultant data have been evaluated with F-statistics and cluster analysis of genetic distance. Allozyme divergence between Gulf and Atlantic populations of the S. reticulatum complex is at levels previously reported for speciated populations, while that between trans-Floridian populations of U. minax is much less pronounced. In both species, minimal divergence can be measured between 2 widely separated Atlantic coast sample localities that were compared, while more complex grades of differentiation are evident between sample localities compared within the northern Gulf of Mexico. Trans-Floridian divergence of populations for both of these species is compatible with models for periods of contact and subsequent isolation of Gulf and Atlantic stocks during and since peak glacial advances in North America. Less conspicuous patterns of genetic differentiation between sample localities within the northern Gulf of Mexico may reflect a history of glacial and postglacial alluvial events which resulted in contemporary physiography of northern Gulf estuaries.

SPERM COMPETITION AND THE ASSURANCE OF UNDERGROUND COPULATION IN THE SAND-BUBBLER CRAB SCOPIMERA GLOBOSA (BRACHYURA: OCYPODIDAE)

Studies of sperm competition are necessary for understanding mating systems in species where two or more males copulate with a single female. We studied fertilization ratios of successive male mates in the sand-bubbler crab Scopimera globosa (de Haan) (family Ocypodidae). Males copulate on the surface or pair underground. The male pairing underground is the last to inseminate the female before she extrudes eggs, as is the case in most ocypodid crabs. In serial mating experiments using irradiated and normal males, the last male to mate fertilized over 90% of the eggs. Females forced to mate in the burrows of irradiated males extruded infertile eggs, indicating that sperm transfer occurred in the burrow.

Molting and Breeding Cycles of the Rock-Dwelling Ocypodid Crab Macrophthalmus Roteltobagoe (Sakai, 1939) (Decapoda, Brachyura)

Temporal relationships between molting and breeding cycles of the rock-dwelling ocypodid crab, Macrophthalmus boteltobagoe, were studied at Horikawa reef flat, Okinawa Island, southern Japan. Daily sampling of exuviae and female crabs were carried out to investigate molting and breeding cycles in the wild. Female crabs were reared in the laboratory to study the temporal combination between molting and breeding events. Most females of the field population were found to oviposite around the new moon, to hatch larvae on the day immediately prior to the following full moon, and to molt a few days after larval release. In captivity, however, consecutive brooding without intervenient molting was also observed. In mature-sized males, two peaks of molting occurred per month, in contrast with the females which showed only one peak of molting per month.

Territorial behavior, and sizes of home range and territory, in relation to sex and body size in Ilyoplax pusilla (Crustacea: Brachyura: Ocypodidae)

In the ocypodid crab Ilyoplax pusilla (De Haan) observed in Shirahama, Japan between 1982 and 1989, three types of territorial behavior effective in repelling neighbors are reported here in addition to barricade-building and neighbor burrow-plugging previously reported by Wada (1984, 1987). These territorial behaviors were performed by crabs larger than ca. 3.5 mm in carapace width (CW). Juvenile crabs ( ca. 5 mm CW). Larger crabs of either sex had larger home ranges and territories. The size of the home range did not differ between males and females, but the size of territory was larger in males than in females. Thus, territorial behavior develops highly in larger males having a larger territory.

Context-Sensitivity in Crab Foraging Studies

Initial work examining crab foraging from optimality premises explored fundamental foraging scope (the capacity of animals to graze), often within an abstract experimental context. An emergent theme involves explicit consideration of biological constraints ( e.g. , predation risk) and environmental factors ( e.g. , substrate type) which, by modulating grazing capacity, determine the realized foraging pattern seen in nature. We briefly review two studies that illustrate the contemporary focus on realized foraging pattern. One defines field grow-out techniques for bivalves (raised in mariculture and resource enhancement programs) that minimize losses from predators such as the portunid crab, Ovalipes ocellatus . By focusing on marginal regions of predator: prey interaction (in this case, foraging on low densities of clams planted in heterogenous substrates), the study yielded novel insight into limits on portunid crab foraging on infaunal clams. The second study analyses the foraging performance of a deposit feeding ocypodid crab, Scopimera inflata , over different temporal and spatial scales. We demonstrate that whereas S. inflata performs sub-optimally at micro-scales (seconds to minutes; mm to cm), the crabs nearly optimize performance over macro-scales (days to years; cm to m). Continued research on the fundamental foraging scope of crabs is warranted, but should be explicitly referenced to natural historical context and, in particular, to the forager's ontogenetic stage. We also perceive a need for collaborative research incorporating behavioral, physiological, and biochemical facets in an integrated experimental setting. This would ensure that context does not bias information, as can occur in studies that emphasise a particular research perspective, methodological approach, or scale at which foraging is analysed.

チゴガニとハラグクレチゴガニの分布

Geographic distributions of two ocypodid crabs of the genus Ilyoplax : I. pusilla and I. deschampsi are summarized from the occurrence records in literatures and unpublished data. I. pusilla is distributed along the coast of mainland Japan and Okinawa, while I. deschampsi ranged along the continental coast of Bo Hai (Gulf of Chihle), Yellow Sea and northern East China Sea. The distributions of the two spesies overlap only at the southern coast of Korea and a part of northern Kyushu of Japan, and both species do not extend into the Japan Sea coast. Along the coast of Ariake Bay in Kyushu, Japan, where both species occurred, their distributions were investigated in detail. I. deschampsi was distributed on the innermost coast, while I. pusilla was on the coast of outer part of the bay, showing clear segregated distributions between them. In habitat conditions, there were some differences between the two species : soil hardness and coarseness of substratum, and salt content of underground water were, on the average, higher in the habitat of I. pusilla than in that of I, deschampsi.

The use of open burrows to estimate abundances of intertidal estuarine crabs

AbstractEstimation of absolute (or true) abundances of intertidal burrowing crabs is a difficult problem in some estuarine habitats because the nature of the substratum and behaviour of crabs can restrict researchers to the use of sampling methods which at best estimate only apparent, or relative, abundances. One method that has been used is to count open burrows to estimate population densities. This paper discusses the results of a test examining the validity of using burrows to estimate apparent abundances of a temperate ocypodid crab, Heloecius cordiformis. inhabiting mangrove forests of south‐eastern Australia. Under appropriate circumstances, this method may provide a quick and reliable estimate of abundance of crabs.

Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

AbstractMortality of eggs during incubation was estimated for three ocypodid crabs, Scopimera globosa, Ilyoplax pusillus and Macrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide. S. globosa and I. pusillus inhabited the upper intertidal sandflats, whereas M. japonicus inhabited the lower intertidal mudflats. Females of both S. globosa and I. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females of M. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. In S. globosa and I. pusillus, the ovaries of ovigerous females were small until egg‐hatching, whereas in M. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.

Factors influencing drove formation and foraging efficiency in Macrophthalmus japonicus (De Haan) (Crustacea : Ocypodidae)

Individuals of the intertidal ocypodid crab Macrophthalmus japonicus (De Haan) either feed near their burrows or they leave their burrows and wander to the water's edge where they feed in droves. The proportion of crabs that wandered to feed was highest when the water content of the substratum near burrows and the water-table in burrows was low. Differences in the amount of food as measured by the nitrogen content of the substratum near burrows and at the water's edge did not affect the proportion of crabs that wandered. Experimental addition of water to the substratum around burrows increased the feeding rate of large, but not small, residents. The weight of the hepatopancreas relative to body weight was lower in wanderers than in residents. Wandering to feed in wet areas may increase the feeding efficiency of large crabs. This study supports the hypothesis that wandering in M. japonicus is due to dry conditions in burrow areas.

Reproductive ecology of three ocypodid crabs I. The influence of activity differences on reproductive traits

AbstractReproductive traits of three ocypodid crabs, Scopimera globosa, Ilyoplax pusillus and Macrophthalmus japonicus, were compared. S. globosa and I. pusillus, inhabiting the upper‐middle intertidal zone, produced 1–2 large broods per year, whereas M. japonicus, inhabiting the lower intertidal zone, produced 4–5 small broods per year. In S. globosa and I. pusillus, ovigerous females remained in their plugged burrows without feeding until their eggs hatched. On the other hand, female M. japonicus fed actively on surface mud while incubating. We concluded that few large broods may be advantageous in crab species that incubate in burrows, whereas continuous small broods may be advantageous in species that feed actively while incubating.

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia.

Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m-2), although litter fall was high; 822 and 1022 g·m-2·y-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m-2·y-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m-2·y-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m-2) and crabs removed less litter; 173 g·m-2·y-1 or 33% of the annual litter fall of 519 g·m-2·y-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m-2·y-1 or 32% of annual litter fall), and tides exported 107 g·m-2·y-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.

Foraging on mangrove pneumatophores by ocypodid crabs

Seven species of ocypodid crabs living in mangrove swamps of Halmahera, Indonesia, were found to forage on pneumatophores of Sonneratia alba as well as on the substratum. The proportion of pneumatophore-foraging individuals among active crabs was highest in Macrophthalmus quadratus. The timetable of pneumatophore foraging by individuals of M. quadratus exhibited no clear tendency in relation to low tide. When the bark of pneumatophores was scraped off together with growing macroalgae, M. quadratus foraged less frequently on it, compared with intact pneumatophores. When comparing M. quadratus foraging on pneumatophores and those on the substratum, the former had bark of pneumatophores and macroalgae in their stomachs more frequently and in larger quantities than the latter. These findings suggest that bark and macroalgae are important food items of M. quadratus in pneumatophore foraging.

Hood construction as a spacing mechanism inCleistostoma kuwaitense (Crustacea: Ocypodidae)

The ocypodid crabCleistostoma kuwaitense inhabits the upper shores of the mudflats of Kuwait, where it constructs a semi-permanent mud hood over the entrance to its burrow. Between September and November 1986, data were collected on the distribution and orientation of the hoods and their openings to investigate the crab's social spacing system. Irrespective of density, the distribution of burrow hoods is non-random, tending towards a regular dispersion. A contributory factor for this dispersion pattern is that the surface hoods tend to increase the distance between adjacent burrows. The hood openings are randomly distributed with respect to compass direction but avoid directly facing those of nearest neighbours. In the absence of burrow plugging and eviction as used by other ocypodid crabs, construction of elongated hoods appears to be a good alternative for ensuring social spacing.

Neighbor burrow-plugging in Ilyoplax pusillus (Crustacea: Brachyura: Ocypodidae)

The burrow living ocypodid crab Ilyoplax pusillus (De Haan, 1835) sometimes plugs the burrow of neighbors situated from 1.0 to 8.3 cm away with surface mud, while the neighbor, termed the pluggee, is in the burrow. Most pluggers were large males, whereas pluggees were smaller than pluggers and had a sex ratio close to 1:1. After being plugged, most pluggees usually reemerged on the surface within 5 min, but occasionally took up to 77 min to do so. The plugger always foraged or performed waving displays around the burrow of the pluggee while the pluggee stayed inside the burrow. Although the activity site of the pluggee was originally directed toward the burrow of the plugger or the adjacent area, after reemergence its activity site was oriented toward another direction. From these observations, it is suggested that neighbor burrow-plugging is a behavior adopted mainly by large males as a means of maintaining the area of their surface activities against smaller neighbors. My observations were made from June 1984 to June 1985 at Fukuro River Estuary, central Japan.

Influence of light on endocrine system and ovarian activity in the ocypodid crabs Ocypoda platytarsis and O. macrocera

Influence of light on endocrine system and ovarian activity in the ocypodid crabs Ocypoda platytarsis and O. macrocera

Influence of light on endocrine system and ovarian activity in the ocypodid crabs Ocypoda platytarsis and O. macrocera: Nadarajalingam, K. and T. Subramoniam, 1987. Mar. Ecol.-Prog. Ser., 36(1):43–53. Subramoniam: c/o Wallis Clark, Bodega Mar. Lab., Univ. of Calif., Davis, Bodega Bay, CA 94923, USA

Influence of light on endocrine system and ovarian activity in the ocypodid crabs Ocypoda platytarsis and O. macrocera: Nadarajalingam, K. and T. Subramoniam, 1987. Mar. Ecol.-Prog. Ser., 36(1):43–53. Subramoniam: c/o Wallis Clark, Bodega Mar. Lab., Univ. of Calif., Davis, Bodega Bay, CA 94923, USA

Eastern Curlews Numenius Madagascariensis Feeding on Macrophthalmus and Other Ocypodid Crabs in the Nakdong Estuary, South Korea

Foraging Eastern Curlews were studied in the Nakdong Estuary, South Korea, in September 1984. During low tide Eastern Curlews spent on average 75-900io of their time foraging. They only ate crabs that had carapace widths 0.6 to 4 cm. Most crabs were captured with bill-deep probes in the crab-burrows. The majority of prey were the ocypodid crab species Macrophthalmus japonicus. Crabs with carapace widths longer than 2 cm were softly shaken to dismember their legs before consumption. The Eastern Curlew's average intake rate was estimated at 1.95 mg ash-free dry weight (AFDW) per sec foraging. Profitability (mg AFDW/ sec-handling) increased more than threefold over the range 0.6-3 cm carapace width. Comparisons with the foraging behaviour of two other curlew species, the Whimbrel Nurnenrus phaeopus and the Eurasian Curlew N. arquata, feeding on ocypodid fiddler crabs, are made. It is suggested that the easily available and abundant small crabs are not consumed because their profitability is too low.

Branchial Water Movement in the Grapsid Crab Sesarma Reticulatum Say

Dehydrated Sesarma reticulatum first test water with their setose pereopods before immersing themselves in it. Water is then conducted from the substrate to the branchial chamber by capillary action of closely spaced plumed setae at the bases of pereopods 1-5. In contrast to the case of the ocypodid crabs Ocypode and Uca, there is no negative pressure in the branchial chamber to assist in water uptake. Branchial water flows out of the mouth primarily across the pterygostomial region of the branchiostegite where geniculate setae and pairs of cuticular ridges are present. The face of each ridge is covered by a thin cuticle beneath which is a pore opening to the spongy vascular epithelium of the dorsal branchial chamber. Staining with reduced methylene blue suggests that some gas exchange may occur across the cuticular ridges and that the spongy vascular epithelium may act as a lung. Stout comb setae on the medial surface of the cheliped clean the geniculate setae of the pterygostomial region. The morphology of the cuticular terraces of the lateral, dorsal surface of the carapace and the setae and ridges of the branchiostegal region both aid in returning water to the branchial