Feeding habits of the pebble crab Eriphia smithi (Crustacea,Brachyura, Menippidae)

Eriphia smithi is a very common East African intertidal xanthoid crab. Its dietary input is based mainly in algal grazing (during the day) and predation (particularly at night). Predation appears quite opportunistic and mostly directed at crustaceans and molluscs, among which bivales largely predominate. Echinoderms are actively avoided and, contrary to common belief, predation on Prosobranchia is only accessory.     

The breeding cycles of two species of grapsid crabs (Crustacea: Decapoda) from the North Coast of Kyushu,Japan

The incidence of ovigerous females in populations of two grapsid crabs, Hemigrapsus penicillatus (de Haan, 1835) and Sesarma (Parasesarma) pictum (de Haan, 1835) were followed from August 1975 to November 1976. H. penicillatus, which inhabits the lower intertidal region near the mouth of Tatara-Umi Estuary, breeds from March to November. S. pictum, which inhibits crevices and abandoned holes of other species and is abundant at and above the upper intertidal region of the estuary, breeds from May to September. H. penicillatus matures when the female reaches 6 to 7 mm carapace width, whereas S. pictum becomes mature when the carapace width is 12 to 13 mm, although the maximum size attained by females of both species is almost the same. H. penicillatus produces 5 to 6 broods, S. pictum 2 to 3 broods, during a breeding season. The size of a newly laid egg of H. penicillatus is smaller than that of S. pictum. The number of eggs produced by a female H. penicillatus is greater than that of S. pictum during a breeding season. In both species the peak of the breeding season is during summer, at which time the ovarian activity is also apparently accelerated. The major environmental factor which controls the breeding in these crabs appears to be temperature. H. penicillatus is submerged at every high tide, and is relatively inactive from late November to February when the ambient water and air temperatures are rather low. S. pictum is dormant in crevices or understones of the splash zone from November to March. The length of the breeding season of these crabs appears to be inversely proportional to the period of their winter dormancy.     

Chela loss in the shore crab Carcinus maenas (Crustacea: Brachyura) and its effect on mating success

Field and experimental studies were conducted to determine the incidence of chela loss and its effect on mating success in a population of the shore crab Carcinus maenas (Linnaeus, 1758) inhabiting the Menai Straits, North Wales. The study was performed between 1989 and 1993. Male crabs showed a higher degree of chela loss (12.5%) than females (7.9%). In males, frequencies ranged from 10% at sizes 50 mm CW (carapace width) up to 30% in the largest crabs of 70 to 80 mm CW. The percentage of females with missing chelae appears to be unrelated to size. The most common type of chela loss in the population studied was of a missing crusher chela of right-handed crabs. Red crabs, which are assumed to be in prolonged intermoult, had a much higher degree of chela loss (20.5%) than the green, early intermoult crabs (9.7%). The proportion of red crabs with chela losses increased with size, possibly reflecting an increase in intermoult duration with size. In green crabs, there was no such increase. The proportion of male crabs with missing chelae found in mating pairs in the field was much lower than that found in the adult unpaired population, suggesting that the loss of a chela constitutes a handicap to a male crab when trying to mate. Also, by studying the relative frequencies of different categories of chela loss, it is suggested that the loss of a crusher chela exerts a more deleterious effect than the loss of a cutter. Experiments were performed in the laboratory where pairs in pre-copula were confronted with an additional single male in various combinations of sizes and patten of chela loss. These showed that the loss of a chela constitutes a handicap for a male crab when either competing for or defending a paired pre-moult female. This handicap was estimated to be equivalent to a reduction in size of 7 to 8 mm CW relative to the size of the competitor.     

Entrainment of the larval release rhythm of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) by cycles in salinity change

Influences of salinity, Na, K, Ca and Mg on Na–K-ATPase activity in the posterior gills of Carcinus maenas (L.) have been investigated with respect to the role of the enzyme in hyperosmotic regulation. K and Mg ions were obligatory for enzyme activity. The dependence on the K concentration can be seen in a saturation curve of the Michaelis-Menten type. Low concentrations of Ca (0.2–3 mM) in the incubation medium strongly inhibited Na–K-ATPase activity. Activities inhibited by Ca could be reactivated to non-inhibited values by the addition of higher amounts of Mg (25 mM). Activity increased along with the salinity of the sea water used as incubation medium up to about 10 S. Here, maximum activity was observed. Further salinity increases of the incubating sea water were inhibitory. Salinity dependence is assumed to be based on Na dependence of the Na-pump. Comparative investigations of the Na–K-ATPase activity and its affinity to sodium in five species of decapod crustaceans indicated that levels of Na–K-ATPase differed in the posterior gills of stenohaline and euryhaline species. The results obtained confirm previous assumptions of a central role of the branchial Na–K-ATPase in hyperosmotic regulation. Properties of the Na–K-ATPase, such as affinity for substrates or dependence on ionic sea water constituents, are kept constant with respect to salinity changes. Modifications due to salinity only concern enzyme amounts especially in the posterior gills. The finding that the Na-pump is localized in basolateral parts of ion-transporting epithelial cells confirms the aforementioned results.     

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.     

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.     

Life-history patterns in two forms of Macrophthalmus japonicus (Crustacea: Brachyura)

Two behaviorally distinct forms — courtship signal — (Form L and V) of Macrophthalmus japonicus (De Haan) are known. Monthly samples of each form were collected from two areas in Japan: Form L from Amakusa, western Kyushu, between April 1985 and February 1986; Form V from Fukuoka, northern Kyushu, between November 1982 and December 1983. Life-history traits were compared between two populations and discussed. Individuals from the Amakusa population grew more slowly and matured at a smaller size than those from the Fukuoka population. Maturation period and longevity did not differ significantly. In the first year of reproduction, females in the Fukuoka population produced more, and larger broods than those in the Amakusa population and crab mortality was higher in every age group. Egg size did not differ significantly. The major environmental factors — air-temperature, nitrogen content of the surface mud and period of aerial exposure were similar in both areas, and it is suggested that the differences in life-history exhibited by these crabs are genotypic, and perhaps related to their different form.     

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.     

Larval development of Ocypode quadrata (Brachyura: Crustacea) under laboratory conditions

The larvae of Ocypode quadrata (Fabricius) have been reared in the laboratory, from hatching to megalopa stage, at 35 S, 25°C. The five zoeal stages and the megalopa are described, including functional appendages of each stage. On the basis of morphological characteristics, the first zoeal and megalopa stages of O. quadrata can be distinguished from similar stages of closely related Ocypodinae. At 25°C, the megalopa appeared in a minimum of 34 days following hatching.     

Ultrastructure of the spermatozoa of Hymenosomatidae (Crustacea: Brachyura) and the relationships of the family

The spermatozoa of the genus Odiomaris Ng and Richer de Forges, 1996 (=Amarinus Lucas, 1980) have the components typical of eubrachyuran (Heterotremata + Thoracotremata) sperm, but differ significantly from all other investigated eubrachyurans in at least ten characteristics: (1) presence of an epiopercular dome; (2) separation of all but the central region of the operculum from the remainder of the acrosome by an infra-opercular rim; (3) the fact that the acrosome is smaller in volume than the nucleus; (4) the acrosome is strongly emergent from the nucleus, being surrounded only basally by nuclear material; (5) the cytoplasmic sheath, ending anteriorly with the nucleus, is also basal; (6) division of the acrosome contents into an inner and outer acrosome zone is scarcely apparent in longitudinal section as the inner zone is narrow and of doubtful homology; (7) the thin, putative inner acrosome zone is anteriorly almost septate owing to several longitudinal corrugations; (8) basally there is a unique “fringe zone”; (9) the acrosome, including the epinuclear dome, is longer than wide; (10) the unique helical and posterolateral disposition of the nuclear arms. From a purely spermatological viewpoint, Odiomaris (as exemplified by O. pilosus and O. estuarius), and provisionally the Hymenosomatidae, are thus excluded from the Thora- cotremata, in which they were formerly placed, nor are they readily placeable in the Heterotremata. Received: 30 December 1996 / Accepted: 4 February 1997     

Managing the offspring environment: brood care in the bromeliad crab,Metopaulias depressus

Summary Maternal modification of the larval environment was studied in the bromeliad crab, Metopaulias depressus (Decapoda, Grapsidae). The bromeliad crab breeds in rain water stored in the leaf axils of large Jamaican bromeliads. The physico-chemical water conditions are highly unfavorable for the development of the larvae. Water in nursery axils contained no leaf litter and up to 14 empty snail shells, whereas other axils were partly or completely covered with leaf litter and rarely held snail shells. Mother crabs removed leaf litter from nursery axils, and occasionally from neighboring axils. Nursery axils contained twice as much dissolved oxygen (DO₂) at night when DO₂ is at a minimum, and less dissolved carbon dioxide (DCO₂) than axils unattended by a crab. The higher DO₂ content in nurseries meets the respiratory needs of an average sized brood, but the lower concentration in axils with litter may not. It is suggested that the higher DO₂ and lower DCO₂ concentrations in the nursery axils result from a water circulation produced by the mother and her leaf litter cleaning behavior. The low pH and the Ca²⁺ content in the water of unattended bromeliad axils are unfavorable for development of larvae and young. Mother crabs significantly increased pH and Ca²⁺ by adding empty snail shells to the nursery-axil water. In experiments where the brood was transferred to other axils, mothers switched from the nursery axil to the new axil containing the brood, and there continued caring for their offspring.     

The annual reproductive cycles of Uca annulipes,Portunus pelagicus and Metapenaeus affinis (Decapoda: Crustacea) from the South-west coast of India

Employing the gonad index method, the reproductive cycles of three decapod crustaceans, Uca annulipes (Latreille), Portunus pelagicus (Linnaeus) and Metapenaeus affinis (Milne-Edwards) have been studied. In these crustaceans breeding is not continuous all the year round, but extends over several months of the year with distinct peak periods of gonadal activity. The male and female reproductive cycles are not concurrent. The peak of the reproductive cycle of males occurs slightly earlier in the breeding season than that of females. These studies indicate the possibility of production of successive broods of eggs during the same breeding season. In these species, the low saline conditions of the monsoon period are unfavourable for breeding. The medium and high saline conditions during the post-monsoon and pre-monsoon months, respectively, with plenty of planktonic food for the larvae, seem to be the favourable periods for breeding activity.     

Maternal care in the bromeliad crab Metopaulias depressus (Decapoda) : maintaining oxygen,pH and calcium levels optimal for the larvae

Summary Harsh physico-chemical conditions during early development may select for parental care. However, no study on the evolution of parental care has focused on the physico-chemical conditions in the environment, the physiological needs of early life stages and the significance of parental care. Early development of the bromeliad crab is completed in small rainwater reservoirs in bromeliad leaf axils. Axils not cared for by mother crabs are acidic, hypoxic and contain very little Ca²⁺. Maternal care buffers axil water and increases oxygen and Ca²⁺ availability. Our results show that (a) bromeliad crab larvae die at pH levels usually found in unattended axils, but develop successfully into the first crab stage at the pH typical of cared-for axils; (b) oxygen concentration in unattended axils is below the critical concentration for larvae, but is high enough for normal respiration in cared-for axils; (c) the calcium demand of larvae for moulting and development cannot be satisfied in unattended axils, but is met by the higher calcium content of cared-for axils. Therefore, physicochemical conditions in the bromeliad axil habitat exert strong selection for the maintenance of parental care in the bromeliad crab. Correspondence to: R. Diesel     

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.     

Carotenoids in the hermit crab Clibanarius misanthropus (Crustacea,Paguridae) from the Black Sea

The authors investigated the carotenoids in the hermit crab, Clibanarius misanthropus (Risso), from the Black Sea. By means of columnar and thin-layer chromatography the following carotenoids were found to be present in that species; -carotene, canthaxanthin, lutein, astaxanthin and some kind of polioxyxanthophill.     

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.     

Widespread occurrence of extensive epimural rod bacteria in the hindguts of marine Thalassinidae and Brachyura (Crustacea: Decapoda)

Direct observation by scanning electron microscopy indicates that the presence of bacteria (epimural and unattached) in the hindguts of Crustacea is widespread, occurring across taxa (two infraorders, i.e., Brachyura and Thalassinidae, nine genera, 16 species), feeding types (detritivores, scavengers and carnivores), habitats (mangroves, saltmarshes, sand/mudflats) and continents (North America, South Africa, Australia). Crustacean hindguts clearly represent suitable environments for colonization by micro-organisms, despite the lack of specialized structures or modifications of the gut to facilitate this. Mats of closely-packed epimural rods and scattered epimural rods were the most common types of bacteria observed in the guts of the Crustacea examined, although unattached rods and scattered epimural cocci occurred in some species. There were, however, taxon-dependent differences in colonization characteristics of hindgut bacteria, possibly related to differences in gut lining. Abundance of hindgut microflora was unrelated to the host's taxon, habitat or geographical locality, but appeared to be affected by the feeding habits of the animal. Mats of epimural rods were associated exclusively with detritivores, while cocci were only observed in the hindguts of scavengers and carnivores. Moreover, extensive colonization by epimural rod bacteria (covering >50% of the hindgut lining) was observed in detritivores only, while carnivores harboured few or no rod bacteria. The detritivore hindgut appears to provide a better environment for microbial habitation than does that of carnivorous crustaceans. In all cases the rod bacteria were monocultures of morphologically identical bacteria and were remarkably similar among crustacean species. The potential significance of prolific microbial colonization in the hindguts of crustaceans deserves consideration.Communicated by O. Kinne, Oldendorf/Luhe     

Indirect evidence indicates female semiochemicals release male precopulatory behaviour in the snow crab,Chionoecetes opilio (Brachyura: Majidae)

Summary Experiments were conducted in aquaria to test the hypothesis that females of the snow crab,Chionoecetes opilio, release a sex pheromone to attract mates. Males exhibited significantly increased activity to water from a source aquarium containing recently-moulted pubescent females, egg-stripped multiparous females and recently-moulted immature females than to water from an aquarium containing berried multiparous females, eggs alone, adolescent males or an empty aquarium. Males without their cephalic chemoreceptors maintained low activity levels in the presence of recently-moulted pubescent females, whereas maxilla-ablated males reacted as strongly as intact males. These findings are discussed within the context of the ecdysteroid-sex pheromone hypothesis, proposed by Kittredgeet al. (1971) and Kittredge & Takahashi (1972), but subsequently rejected. We propose that ecdysteroids from both pubescent and multiparous females may elicit male search-and-clasp behaviour inC. opilio and that the reproductive biology of species used to refute the hypothesis was inappropriate to test the role of ecdysteroids as a cue in the mating process.     

Behavioral responses of larvae of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) during diel vertical migration

Larval Rhithropanopeus harrisii (Gould) show nocturnal vertical migration. Larval behavioral responses to different rates of increase and decrease in light intensity were measured in an apparatus with a natural angular light distribution. A central objective was to establish whether phototaxis actually participates in vertical migration. At sunset the level of light adaptation controlled the readiness of the larvae to migrate, while an ascent was initiated by a preductable relative decrease in intensity (e.g. 4.0x10^-3s^-1). Rates of relative decrease around sunset would evoke continuous upward swimming. Gravity was the orienting cue and there was no change in swimming speed during the ascent. At sunrise, the larval descent was initiated by exposure to an absolute light intensity of about 0.23 log unit above the lower visual threshold. Light served as an orienting cue, as larvae descended by a negative phototaxis. Thus, phototaxis is not a laboratory artifact and does participate in vertical migration. A consideration of behavioral responses of other crustacean zooplankton indicates there is considerable variation in the initiating and directing cues for vertical movements. The variety of behavioral responses of R. harrisii suggests that a synthesis of hypotheses about migration may provide the proper basis for explaining the mechanisms underlying diel vertical migration.