Feeding and mouthpart morphology in the semaphore crabHeloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

The mouthparts of the Australian semaphore crabHeloecius cordiformis (H. Milne-Edwards, 1837) are described. Male and female semaphore crabs were observed and collected from mangrove swamps around the south side of Botany Bay, Australia between 1983 and 1987. Semaphore crabs inhabit mangrove mud/sand flats between the midlittoral intertidal zone and the supralittoral fringe of bordering saltflats. Scanning electron micrographs provide detailed pictures of mouthpart morphology and the setae present on the third, second, and first maxillipeds; the second and first maxillae; and the mandibles. Amongst other setal types, spoon-tipped, corn, and bottle-brush setae are described. While semaphore crabs are primarily deposit feeders (microphagous), they have well developed mandibles and are, therefore, also able to eat larger plant and animal material (macrophagous). A brief comparison is made between the mouthparts of semaphore crabs and fiddler crabs (Uca spp.), since the two genera are closely related, occupy similar niches, and resemble each other in appearance. This comparison reveals that while the second maxilliped setal morphology differs between the two genera (Heloecius possesses corn setae,Uca possesses spoontipped setae) these setae may have similar functions. The feeding behaviour ofH. cordiformis is related to substrate composition, burrow construction and various mouthpart specialisations. It is conlcuded that, within the context of the present study, certain structural e.g. mouthpart modifications allowing both scavenging and deposit feeding, and behavioural modifications e.g. mound building in wet muddy habitats, enable semaphore crabs to occupy a wide range of habitat types within the mangrove.Please address all correspondence and requests for reprints to Dr Maitland at his present address at the University of the Witwatersrand     

Evidence for acclimation to hydrostatic pressure in Uca pugilator (Crustacea: Decapoda: Ocypodidae)

Groups of male Uca pugilator (Bosc) (Crustacea, Decapoda, Ocypodidae), acclimated to sublethal pressure (34 atm) subaqueously for 5 and 10 days, were observed subsequently at pressures up to 272 atm. Behavioral indicators of pressure resistance (“first response” and tetany) were employed to measure degrees of pressure acclimation in comparison with simultaneously and non-simultaneously conducted control experiments. No firm conclusions can be made on the basis of “first response” results, but the pressures required to induce tetany were significantly higher (P≤0.02, one-tailed comparison) in acclimated groups than in non-acclimated groups. These data and earlier studies by other investigators support the assertion that some shallow marine species are capable of at least limited short-term pressure acclimation.     

Über Bau und Funktion der Kiemen und Lungen von Ocypode ceratophthalma (Decapoda: Crustacea)

Electron micrographs reveal great differences between the epithelial linings of gills and lungs in the air-breathing crab Ocypode ceratophthalma. According to the fine structure, the gills have a mainly osmoregulatory function; they exhibit a very active transporting epithelium characterized by a large number of mitochondria, branched microvilli, and basal labyrinth. Blood spaces in the shaft of the gills are lined by podocytes, suggesting ultrafiltration. The lungs are typical respiratory organs, lined by a thin epithelium covered by a thin cuticle.     

Population dynamics of the commensal spider crab Inachus phalangium (Decapoda: Maiidae)

The ecology of the spider crab Inachus phalangium (Fabricius, 1775) (Decapoda: Maiidae) was studied in the field. I. phalangium inhabits the sublittoral on the sea anemone Anemonia sulcata Pennant. From July 1981 to April 1984 in the Mediterranean (Banyuls sur Mer, southern France) more than 3000 anemones were examined and ca 1800 I. phalangium were found on them. The population dynamics' generation cycles, reproductive activities and the dynamics of the sex ratio were investigated. The density of juveniles (crabs before the pubertal moult) on anemones changed in a yearly cycle from low in the first six months to very high in the second six months. The first occasional young crabs of a generation appeared in March/April (3rd and 4th decapodite stages) on the anemones. Their density increased enormously in the following months. The generation grew gradually on the anemones and moulted into puberty in September-January. Density of adults (crabs after the pubertal moult) on anemones changed in a yearly cycle from low to high from the summer to winter months. A new adult generation was recruited every autumn through the pubertal moult and disappeared in the following summer. Female reproductive activity continued throughout the year. Females carried several broods in succession, but the frequency of breeding females fluctuated on a yearly cycle. The highest percentage of egg-carrying females, i.e. the peak of the reproductive season, lay in the first half of the year. The maximal life span of a generation, from the hatching of the first larvae to the disappearance of the last adults, lasted 1.5 to 2 years. Males moulted into puberty ca one month later than females. The moulting distribution of adult males had roughly the same course as in females. An adult male generation diet out about one to two months before the female generation. Life expectancy was therefore 14 to 17 months for females and 12 to 15 months for males. The sex ratio of juveniles shortly before the pubertal moult was balanced. The sex ratio of adults shifted from 1:1 at the beginning of the reproductive period to ca 1:9 in favour of females at its end.     

Latitudinal variation in the reproductive biology of the burrowing ghost shrimp Callianassa filholi (Decapoda: Thalassinidea)

Population structure and reproductive ecology of the burrowing ghost shrimp Callianassa filholi Milne-Edwards, 1878 were studied in populations along a latitudinal gradient throughout New Zealand during the breeding season. Size-frequency distributions revealed unimodal populations, with predominantly sexually mature shrimp. All populations showed an unbiased sex-ratio, and there appeared to be no significant difference in size (carapace length, CL) between sexes. At the same time, CL and size at maturity differed significantly between populations; however, a general increase in sizes from north to south was not consistent throughout the latitudinal range studied. The timing of the breeding cycle differed significantly between populations, and breeding started earlier in southern populations. Number of embryos (fecundity) increased linearly with female CL at each location, but rates differed significantly between populations. Embryo size was not related to number of embryos, and the former increased significantly with latitude. With the exception of embryo size, observed differences in body size/size at maturity and reproductive timing between C. filholi populations are thought to be determined by food availability rather than temperature. Thus, further study is suggested on these aspects of thalassinid reproductive biology. Received: 17 June 1999 / Accepted: 8 January 2000     

Rhythms in larval release of the sublittoral crab Neopanope sayi and the supralittoral crab Sesarma cinereum (Decapoda: Brachyura)

Ovigerous females of the subtidal xanthid crab Neopanope sayi (Smith) and the high intertidal grapsid crab Sesarma cinereum (Bosc) were collected during the summers of 1986 and 1987 in the Beaufort, North Carolina (USA), area and brought into the laboratory, where rhythms in larval release were monitored. When crabs with late-stage embryos were put under a 14 h light:10 h dark cycle in an otherwise constant-environment room, an apparent tidal rhythm in release of larvae was observed for both species, with N. sayi releasing near the time of day and night high tides, and S. cinereum releasing around the time of night high tides. The time of sunset relative to high tide was a complicating factor, since larval release for both species was often concentrated around sunset when evening high tides fell several hours before sunset. When a group of N. sayi and S. cinereum were brought into the laboratory and placed under constant lowlevel light for 5 d, the release rhythm of the population persisted, thus implying that the rhythm is endogenous. Larval release near the time of high tide and often at night is common among brachyurans living in tidal areas, regardless of specific adult habitat, suggesting a common functional advantage. Possibilities include transport of larvae from areas where predation and the likelihood of stranding and exposure to low-salinity waters are high, as well as a reduced probability of predation on adult females. Results of the present study suggest that the importance of release after darkness may increase with increasing tidal height of the adult.     

Vertical migrations in the tree crab Sesarma leptosoma (Decapoda,Grapsidae)

Sesarma leptosoma, somewhat similar to the Atlantic related species, Aratus pisonii, is an East-African mangrove crab which spends its entire life on the roots and branches of mangrove trees (mostly Rhizophora mucronata, Bruguiera gymnorhiza and Ceriops tagal). S. leptosoma never enters the water, nor does it ever venture onto the free mud surface at low tide. Part of the day and night it remains on the lower parts of the mangrove aerial roots, which are often encrusted with a wet algal mat of Bostrichia spp., searching for food and water. Twice a day, from ca. 06:00 to 08:00 hrs in the morning and 16:00 to 18:00 hrs in the afternoon, many of the crabs migrate as far as the leaves at the top of the tree on which they feed. However, they only spend a brief period among the leaves, from ca. 07:00 to 10:00 and 17:00 to 19:00 hrs, after which time they make their way back towards the roots again in two downward migrations. In the morning, the downward migration brings all the crabs back to the roots, but in the evening not all the crabs take part in the downwards migration and some of them pass the whole night in the tree tops. A comparison of the migration time patterns for two different periods of the year (June–July and November) shows that the number of crabs migrating along the tree trunk is modulated by the spring-neap tidal cycle, while the onset of daily migration seems to be controlled mostly by the light level and/or other climatological cues. The adaptive significance of this migratory behaviour is discussed. Observations reported in our study were made in Mida Creek, Dabaso, Kenya in 1991 and 1992.     

Carapace and branchial water circulation,and water-related behaviours in the semaphore crabHeloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

Water uptake, branchial water circulation and various water-related behaviours and anatomical specialisations, are described for the Australian semaphore crabHeloecius cordiformis (H. Milne-Edwards 1837). Male and female semaphore crabs were observed and collected from mangrove swamps around the south side of Botany Bay, Australia between 1983 and 1987. Semaphore crabs are active at low tide in air. Their branchial chambers are modified for both air breathing and water circulation. Water is held within the branchial chambers and is used for feeding and, to a certain extent, respiration. Crabs carry between 0.35 and 0.5 ml of water (7 g live body wt). Branchial water is continuously pumped out by the scaphognathites over specialised setae-bearing regions of the carapace and back through the branchial chambers over the gills, in a manner similar to that found in many grapsid crabs. Setae associated with water circulation are described. Water falling ventrally is collected by the abdominosternal cavity (formed between the abdomen and sternum) from where it returns to the branchial chambers via branchiosternal canals. Several novel water-related behaviours are described: Water shoogling — branchial water is drawn out between the walking legs where it is worked by scissor-like up and down movements of the legs. Abdomen flap — branchial water volume is adjusted by the extension and flexion of the abdomen against the cephalothorax. Water dumping — by tilting forwards and kissing the substrate, branchial water is voided to allow an entirely fresh load to be taken up. Statuesque posing — crabs remain erect and motionless for long periods. Branchial water is absent and external body surfaces dry out. Posing behaviour may function in thermoregulation, osmoregulation or as an anti-fouling mechanism against settling organisms. The significance of these various behaviours is discussed.     

Larval settlement and metamorphosis in the sand crab Emerita talpoida (Crustacea: Decapoda: Anomura)

The effects of various potential cues on the survival and time to metamorphosis of larvae of the sand crab Emerita talpoida (Say) were examined. Zoeal duration, which ranged from 25 to 43 d, was not correlated with subsequent megalopal survival but had a weak, negative correlation with the duration of the megalopal stage. Neither food, sand nor water from containers with adults directly affected megalopal survival or duration. In a second experiment, the presence of sand both increased the probability of survival and shortened the duration of late zoeal stages. This is the first experimental evidence for delayed zoeal metamorphosis in a decapod. Settlement of E. talpoida appears to occur primarily during the zoeal phase, not at the megalopal stage.     

Larval development of the red crab Pleuroncodes monodon (Decapoda Anomura: Galatheidae) under laboratory conditions

Larvae of Pleuroncodes monodon (Milne-Edwards, 1837), a red crab of commercial importance in South America, were reared in the laboratory at 2 different temperatures (15° and 20°C), from hatching up to the last larval stage. The 5 typical stages, with their corresponding functional appendages, are described and figured. The main characteristics useful in differentiating larvae of P. monodon from those of the other Chilean species of Galatheidae and its northern congener P. planipes are discussed. Data on duration of each larval stage, length of moulting intervals and mortality at the 2 test temperatures are also given.This study was financially supported by the Chilean Ministry of Agriculture and by the National Commission for Scientific and Technological Research (CONICYT).     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.     

Differences in context and function of two distinct waving displays in the fiddler crab, <Emphasis Type="Italic">Uca perplexa</Emphasis> (Decapoda: Ocypodidae)

To respond appropriately to communication signals, animals must have the ability to decipher signal meaning. At a basic level, interpreting the difference between territorial and courtship signals can be vital for the survival and reproduction of social animals. Male and female fiddler crabs communicate with claw-waving displays, but the function of these waves remains uncertain. Species differ in the context in which they wave: Some wave during courtship, some during territorial defence and some during both. In this paper, we provide evidence that males of an Australian species of fiddler crab, Uca perplexa, use two different types of claw waving display, lateral and vertical. Lateral waves are employed solely in a courtship context, whilst vertical waves are employed during courtship as well as territorial interactions. Using video recordings, we show that lateral waves were produced spontaneously (broadcast), and their frequency increased only in the presence of female wanderers. Vertical waves were not broadcast but were elicited by male wanderers during agonistic interactions and female wanderers during close range courtship. Male resident U. perplexa were able to discriminate the sex of wandering crabs on the mudflat at distances of 32 cm. During all resident–wanderer interactions, residents attempted to maintain a position directly between the wanderer and the home burrow and orient themselves to face females and to present the major claw towards males. To our knowledge, this is the first demonstration of the multiple use of waving displays in a fiddler crab species.     

Settlement cues in successive developmental stages of the ghost shrimps Callichirus major and C. islagrande (Crustacea: Decapoda: Thalassinidea)

Larvae of Callichirus major (Say) and C. islagrande (Schmitt) were given unconditioned water with sand, water conditioned by previous exposure to adults (AW) without sand, or the combination of both AW and sand to determine if these factors served as settlement cues. Shrimp were first given stimuli upon reaching the last zoeal stage (ZIV), the decapodid stage (D), or the first juvenile stage (J1). Once initiated, exposure of shrimp to stimuli was maintained until termination of␣the experiment. Stage duration, burrowing activity of decapodids and early juveniles and location of exuviae were observed daily. Exposure to sand and AW did not decrease duration of the decapodid stage in either species. However duration of ZIV in C. major appeared to decrease when these stimuli were offered at this stage; this suggests that molting to Stage D may be delayed without such cues. When stimuli were examined separately, AW was found to have a significant effect on the duration of ZIV, while the effect of sand with unconditioned water and effects of simultaneously offered stimuli were not significant. Shrimp that received stimuli at ZIV subsequently burrowed more at D and J1 than individuals that did not receive stimuli at ZIV. Location of exuviae was recorded as on top of sand (not burrowed during molt) or within sand (burrowed during molt) for each shrimp's molt from Stages D to J1 (D molt), and from J1 to J2 (J1 molt). In C. major, the percentage of D exuviae and J1 exuviae found within sand as opposed to on top of sand was significantly higher in individuals which received stimuli at ZIV than for those that first received them at D or J1. When stimuli were examined separately in C. major, the effect of sand on burrowing activity was highly significant, while AW and the stimuli in combination had weaker effects. For C. major, AW appeared to accelerate development to D, while sand triggered settlement. Neither stimulus altered stage duration or burrowing activity of C. islagrande. Received: 7 December 1997 / Accepted: 24 July 1998     

On the introduction of the Kamchatka King crab Paralithodes camtschatica (Decapoda: Anomura: Lithodidae) into the Barents Sea

About 2,500 specimens of the Kamchatka king crab Paralithodes camtschatica (Tilesius), ca. 5 to 15 years old, and about 10,000 juveniles, ca. 1 to 3 years old, were released into the Barents Sea from 1961 to 1969. One large berried female was caught in 1974, and the number of records increased in 1976 (at least 100 records, including 6 reliable ones). The crab therefore seems to have become a permanent inhabitant of the Barents Sea. It will be important in future to continually record new occurrences of the crabs, especially of juveniles, in order to document the extent of their distributional range and to obtain evidence of successful reproduction of the species.     

Latitudinal variation in the reproductive biology of the commensal crab Pinnaxodes chilensis (Decapoda: Pinnotheridae) along the Chilean coast

The pinnotherid crab Pinnaxodes chilensis is a common commensal of the edible sea urchin Loxechinus albus along the Chilean coast. Several aspects of the reproductive biology of P. chilensis were examined between April and June 1999, along temperature and salinity gradients, at three sampling sites along the Chilean coast (23°45'S-39°24'S). Results demonstrated significant differences in egg number, egg volume, dry egg weight, and reproductive output of ovigerous females, between the studied populations of northern and central-southern Chile. Egg volume, egg dry weight, and reproductive output of females decreased from high to low latitudes, while egg number increased from high to low latitudes, exhibiting a clear trade-off with egg volume. It has been shown that changes in environmental conditions (e.g. temperature, salinity) along a latitudinal gradient, can generate clines in reproductive characteristics in both free-living and parasitic species.     

Ultrastructural changes in the gill epithelium of the crab Chasmagnathus granulatus (Decapoda: Grapsidae) in diluted and concentrated seawater

Chasmagnathus granulatus Dana, 1851 is an intertidal estuarine crab that experiences acute salinity changes ranging from <1‰ to full-strength seawater and even hypersaline waters in tide pools concentrated by evaporation. Ultrastructural changes induced by salinity in the posterior gills were examined in crabs collected from the Rio de la Plata estuary Argentina during March 1999. The posterior gills of C. granulatus are involved both in ion uptake and ion secretion depending on the acclimation medium. These organs are mostly lined with a thick tissue, which presents the characteristics of a typical salt-transporting epithelium. Electron microscopy analysis of gill tissue from crabs acclimated to dilute, full, and concentrated seawater (12‰, 34‰, and 45‰ salinity) showed significant development of basolateral membrane interdigitations, with numerous mitochondria and conspicuous apical membrane infoldings. Morphometrical analysis indicated that the subcuticular space delimited by the infolding of the apical membrane was significantly increased in the gills of high-salinity acclimated crabs. Septate junctions, which are thought to define the paracellular permeability, were significantly shorter in high-salinity acclimated crabs, suggesting a possible role of the paracellular pathway in salt secretion.     

Differential utilization of biochemical components during larval development of the spider crab Maja brachydactyla (Decapoda: Majidae)

Changes in lipid class, fatty acid, fat-soluble vitamins, amino acid and minerals were studied during larval development of Maja brachydactyla Balss, 1922 in order to provide information of its ontogeny and evaluate possible dietary deficiencies and constraints. Four different batches were analyzed from hatching to metamorphosis using enriched Artemia as food. Cultured larvae were in a good nutritional condition as confirmed by the continuous lipid accumulation throughout ontogeny. A regulation of polyunsaturated fatty acids (PUFA) occurred during development in order to maintain adequate basal levels of ω-3 fatty acids (likely through a retro conversion of C₂₀ and C₂₂ into C₁₈ PUFA). Variations in the tocopherol levels indicated its possible role in PUFA protection against oxidation. Essential amino acid balance during development was not correlated with the Artemia feeding regime, but rather reflected inherent variations of the own species ontogeny. Larval requirements in essential minerals were fully supplied by the enriched Artemia.     

Larval development of the spider crab Pisoides edwardsi (Decapoda,Brachyura) under laboratory conditions

Larvae of Pisoides edwardsi (Bell, 1835) have been reared in the laboratory at 2 different temperatures (13.8° and 18.5°C), from hatching to megalops stage. The two zoeal stages and the megalops, as well as the setation of the functional appendages are described and illustrated. The main characteristics useful to differentiate the larvae of P. edwardsi from those of Libidoclaea granaria, the other Chilean species belonging to the same sub-family, are discussed. Data on duration of zoeal development, length of moulting intervals, and mortality at the 2 test temperatures, are also given.This study was financially supported, in part, by the Chilean Ministry of Agriculture.     

Mating behaviour of Macrophthalmus hirtipes (Brachyura: Ocypodidae)

 We examined the mating behaviour of the New Zealand ocypodid crab Macrophthalmus hirtipes in the laboratory between February and June 1998. This species has a discrete breeding season. Mating and moulting were not linked and only intermoult females with mobile gonopore opercula were attractive to males. Allometry and compatibility of gonopods and gonopores of different-sized crabs was investigated. Under laboratory conditions, the opercula of intermoult females remained mobile on average for 11.4 d, but the duration of receptivity did not appear to be under female control. The operational sex ratio in the laboratory fluctuated greatly, but was always male-dominated. During the period of opercular mobility, females mated many times with several different males. Matings in the absence of burrows were relatively short (mean duration = 23 min, max. = 122 min) and the mating behaviour of M. hirtipes lacked courtship and mate-guarding. Males used a search-intercept method to acquire mates, with very low levels of intrasexual competition. There was no evidence of mate preference in M. hirtipes, and males spent just as long mating with ovigerous females as with non-ovigerous ones. Although M. hirtipes has ventral-type spermathecae, as do several other ocypodid crabs, it is unclear whether this promotes last-male sperm precedence. The role of burrows in modifying the mating behaviour of M. hirtipes in the field remains to be established. Received: 7 January 2000 / Accepted: 5 June 2000     

Mound building in Ilyoplax pingi (Crustacea: Brachyura: Ocypodidae)

The ocypodid crab Ilyoplax pingi, observed in Kanghwa I., Korea in 1992, builds a mound at the burrow entrance, by piling mud dug out from the burrow. The mounds were made by both waving and non-waving males, and by both ovigerous and non-ovigerous females. The burrow diameter at the widest part tended to be larger in crabs with mounds than in crabs without mounds, whereas the burrow depth was not different between them. The mound density increased in the late exposure period, when the crabs' surface activities declined. Mound removal and rebuilding experiments revealed that the presence of the mounds has the effect of keeping neighboring crabs away.