Influence of sediment characteristics on density and distribution of Ocypodoid crab burrows (superfamily: Ocypodoidea) along the coastal areas of Pakistan

Crabs belong to the superfamily Ocypodoidea are a significant component of benthic fauna and considered as ecosystem engineers because of their dynamic role as an active burrower in mangrove and estuarine environment. The current investigation was to evaluate the crab burrow density, diameter and total area of burrow opening along the coast of Pakistan. The variations in burrow properties and their relation to sediment characteristics were also evaluated to recognize the most influencing variables of sediments that effects on crab burrows. All crab burrow and sediment characteristics differed significantly (p < 0.05) among the monitoring sites. Regression analysis showed that crab density was significantly correlated with burrow density (P < 0.001). Moreover, burrow density was noticed significantly greater (p < 0.05) than crab density. Pearson correlation analysis reveals that moisture, porosity, organics, sand and mean grain size observed as most influencing the features of sediment to determine the ecological functioning of crab burrows in mangrove and mudflats of Pakistan.     

Competition for mangrove leaf litter between two East African crabs, <Emphasis Type="Italic">Neosarmatium meinerti</Emphasis> (Sesarmidae) and <Emphasis Type="Italic">Cardisoma carnifex</Emphasis> (Gecarcinidae): a case of kleptoparasitism?

Many Indo-Pacific mangrove macroinvertebrates are herbivorous and heavily dependent on leaf litter. As a consequence, fallen leaves become a limiting factor and competition occurs among conspecifics and heterospecifics. Neosarmatium meinerti and Cardisoma carnifex are two of the most common herbivorous crabs of the landward mangrove belt in East Africa, often sharing an area and time of activity. This study used a series of field experiments to investigate their feeding habits when co-existing. The high density reached by both species led to overlapping of the individual feeding ranges: during the feeding excursions each crab inevitably encountered, and actively interacted with, other conspecifics and heterospecifics. Competition for food was high: N. meinerti lost approximately 50% of its leaves to theft by C. carnifex. Thus, approximately half of the leaves obtained by C. carnifex were stolen from a foraging N. meinerti. Considering the frequency of such thefts, C. carnifex may be regarded as a facultative kleptoparasitic species. This is the first time that a such strategy has been recorded for a crab species and for a vegetable resource.     

Mangrove sesarmid crab feeding experiments in Peninsular Malaysia

The feeding ecology of mangrove sesarmid crabs in Peninsular Malaysia was investigated by field and laboratory experiments using four mangrove leaf species (Avicennia officinalis, Bruguiera gymnorrhiza, B. parviflora and Rhizophora apiculata) and leaves of different condition (fresh and senescent). Leaves tethered on strings at high (Bruguiera zone) and low (Rhizophora zone) intertidal positions, both upstream (Sungai Pasir) and downstream (Lower Merbok) showed significant amounts of leaf litter removal in 24 h (mean 79±3% initial dry mass). Significantly more B. gymnorrhiza was consumed in Bruguiera zones and significantly less senescent A. officinalis in the upstream Rhizophora zone. In Bruguiera zones, significant numbers of leaves were taken down burrows but there were no preferences for leaf species or condition of leaf taken down burrows at all sites. In 24 h, under laboratory conditions, the sesarmid crabs Sesarma (Perisesarma) eumolpe and S. (Perisesarma) onychophorum were offered with a mangrove species choice of either fresh or senescent leaves. There was no difference in mangrove species taken when the leaves were senescent for both crab species, but when the leaves were fresh, significantly more A. officinalis leaves were consumed by both sesarmid crab species. S. onychophorum ate significantly more B. parviflora than did S. eumolpe. The crab distribution in the field was related to the preferred tree species dominance, indicating that tree species may be important for crab species distribution, or vice versa. The mean rate of leaf consumption was not significantly different between the crab species; S. eumolpe was 29.9±5.9 and S. onychophorum was 35.3±7.2 mg dry mass per wet mass gram of crab in 24 h. Rhizophora spp. were the least preferred species in all feeding experiments, a finding which may have implications for ecosystem functioning in monoculture rehabilitation projects.     

Comparative Burrow Architectures of Resident Fiddler Crabs (Ocypodidae) in Indian Sundarban Mangroves to Assess Their Suitability as Bioturbating Agents

Excavation of burrows by fiddler crabs (genus Uca) is an important component in mangrove ecosystem functioning. This bioturbation activity can be measured by analysing the burrow architecture of these crabs. The aim of the present study is to describe and evaluate inter specific differences in the burrow morphologies of four species of fiddler crabs (Uca rosea, Uca triangularis, Uca dussumieri and Uca vocans) using polyester resin casts of the burrows. For each of the species, sex and carapace width (CW; mm) were determined for all the individuals. Three burrow morphological characters viz. burrow diameter (BD; mm), total burrow depth (TBD; mm) and burrow volume (BV; cm³) were considered during the study. Density of each species throughout the year was also assessed. For all the species BD and BV were higher in case of males compared to the females and they showed significant positive correlation with the CW of the burrow inhabitants. The amount of sediment excavated by each crab was evaluated in terms of BV. Among all the studied species, U. rosea was established as the most potent bioturbative candidate in the studied mangrove due to their greater density and moderate ability to excavate burrow.     

Divergence of water balance mechanisms in two sibling species (Drosophila simulans and D. melanogaster): effects of growth temperatures

Drosophila simulans is more abundant under colder and drier montane habitats in the western Himalayas as compared to its sibling D. melanogaster but the mechanistic bases of such climatic adaptations are largely unknown. Previous studies have described D. simulans as a desiccation sensitive species which is inconsistent with its occurrence in temperate regions. We tested the hypothesis whether developmental plasticity of cuticular traits confers adaptive changes in water balance-related traits in the sibling species D. simulans and D. melanogaster. Our results are interesting in several respects. First, D. simulans grown at 15 °C possesses a high level of desiccation resistance in larvae (~39 h) and in adults (~86 h) whereas the corresponding values are quite low at 25 °C (larvae ~7 h; adults ~13 h). Interestingly, cuticular lipid mass was threefold higher in D. simulans grown at 15 °C as compared with 25 °C while there was no change in cuticular lipid mass in D. melanogaster. Second, developmental plasticity of body melanisation was evident in both species. Drosophila simulans showed higher melanisation at 15 °C as compared with D. melanogaster while the reverse trend was observed at 25 °C. Third, changes in water balance-related traits (bulk water, hemolymph and dehydration tolerance) showed superiority of D. simulans at 15 °C but of D. melanogaster at 25 °C growth temperature. Rate of carbohydrate utilization under desiccation stress did not differ at 15 °C in both the species. Fourth, effects of developmental plasticity on cuticular traits correspond with changes in the cuticular water loss i.e. water loss rates were higher at 25 °C as compared with 15 °C. Thus, D. simulans grown under cooler temperature was more desiccation tolerant than D. melanogaster. Finally, desiccation acclimation capacity of larvae and adults is higher for D. simulans reared at 15 °C but quite low at 25 °C. Thus, D. simulans and D. melanogaster have evolved different strategies of water conservation consistent with their adaptations to dry and wet habitats in the western Himalayas. Our results suggest that D. simulans from lowland localities seems vulnerable due to limited acclimation potential in the context of global climatic change in the western Himalayas. Finally, this is the first report on higher desiccation resistance of D. simulans due to developmental plasticity of both the cuticular traits (body melanisation and epicuticular lipid mass) when grown at 15 °C, which is consistent with its abundance in temperate regions.     

Cladophialophora abundans,a novel species of Chaetothyriales isolated from the natural environment

A novel species of Cladophialophora is described from the natural environment of the mangrove land crab (Ucides cordatus) along the coast, and from plant sources in Brazil. It is morphologically very similar to Cladophialophora bantiana, though with moderately melanized conidia produced in strongly coherent and poorly branched chains which arise directly from undifferentiated hyphae, but deviates unambiguously on the basis of molecular phylogeny. The species has a maximum growth temperature of 36 °C and seems to be a strict saprobe.     

Resistance to fresh and salt water in intertidal mites (Acari: Oribatida): implications for ecology and hydrochorous dispersal

The resistance to fresh water and seawater in three intertidal oribatid mite species from Bermuda, Alismobates inexpectatus, Fortuynia atlantica and Carinozetes bermudensis, was tested in laboratory experiments. Larvae are more sensitive to fresh and salt water, nymphs and adults showed equal tolerances. Fortuynia atlantica and A. inexpectatus were more resistant to salt water whereas C. bermudensis survived longer in fresh water. Differences in the resistance to fresh and salt water among the three species may be related to their different vertical occurrences in the eulittoral zone but also to the ability of single species to dwell in periodically brackish waters. In all three species half of the specimens survived at least 10 days in fresh water and more than 18 days in salt water. Maximal submersion time in fresh and salt water ranged from 40 to 143 days. Based on median lethal times it could be estimated that each species would be able to survive transport in seawater along the Gulf Stream over a distance of 3,000 km, from Central America to Bermuda. Thus hydrochorous dispersal should be assumed as the most likely mode of dispersal in intertidal fortuyniid and selenoribatid mites.     

Microbial carbon oxidation rates and pathways in sediments of two Tanzanian mangrove forests

Temporal and spatial variations in benthic metabolism and anaerobic carbon oxidation pathways were assessed in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. The objectives were (1) to evaluate how benthic metabolism is affected by organic carbon availability; (2) to determine the validity of diffusive release of CO₂ as a measure benthic carbon oxidation; and (3) to assess the partitioning of anaerobic carbon pathways and factors controlling the availability of electron acceptors (e.g. oxidized iron). Microbial carbon oxidation measured as diffusive exchange of O₂ and CO₂ (32?C67 and 28?C115 mmol m^?2 day^?1, respectively) showed no specific temporal patterns. Low intertidal sediments at Mtoni fed by labile algal carbon of anthropogenic origin had higher diffusive CO₂ release than high intertidal sediments that primarily received less reactive mangrove detritus. Diffusive release of CO₂ apparently underestimated total sediment carbon oxidation due to CO₂ loss from deep sediments via emission through biogenic structures (i.e. crab burrows and pneumatophores) and porewater seepage into creeks. We propose that diffusive fluxes in the present mangrove sediments are roughly equivalent to depth-integrated reactions occurring in the upper 12 cm. Anaerobic carbon oxidation was dominated by FeR irrespective of anthropogenic influence in sediments where the oxidizing effects of biogenic structures increased the Fe(III) level. More than 80% of the anaerobic carbon oxidation in Mtoni and Ras Dege sediments was due to FeR when reactive Fe(III) exceeded 30 ??mol cm^?3. The anthropogenic influence at Mtoni was primarily noted as up to one order of magnitude higher denitrification than at Ras Dege, but this process always accounted for less than 1% of total carbon oxidation. It is noteworthy that organic and nutrient enrichment of anthropogenic origin in Mtoni has no measurable effect on microbial processes, other than carbon oxidation in the low intertidal area and denitrification throughout the forest, and indicates a strong resilience of mangrove environments towards disturbances.     

The occupation of artificial burrows by Helice tridens (De Haan) and the length of its stay

The mud-crab Helice tridens (De Haan) influences the cycling of matter in salt-marsh ecosystems through its burrowing activity. If the crabs occupy and stay in their burrows for a short time, their burrowing activity will be great, since they will continuously construct new burrows. Therefore, investigation of the relation between the crabs and their burrows is considered to be important. In the present study, the relation between pipes as a form of artificial burrow and their occupation by the crab was analyzed. A close relationship was recognized between the diameter of the pipe opening and the carapace width of the crab which occupied the pipe, while pipes with a length shorter than the depth of the crab burrows were hardly occupied. These results indicate that the diameter and length of an artificial burrow affects the likelihood of its occupation by this species of crab. The length of the crab's stay in this type of artificial burrow was generally 1 day. This result may be related to the field observation that newly made burrows frequently collapse due to water current occurring through tidal action after the crabs have left.     

Evidences of habitat displacement between two common soft-bottom SW Atlantic intertidal crabs

The intertidal burrowing crab Chasmagnathus granulatus Dana is the dominant species in soft sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil 28°S to the northern Argentinean Patagonia 41°S) where it produces dense and extensive burrowing beds. The mud crab Cyrtograpsus angulatus Dana coexists with Ch. granulatus in this area, but it also inhabits areas to the south (northern and central Argentinean Patagonia). A survey covering both areas showed that C. angulatus rarely live in burrows when coexisting with Ch. granulatus, but form large burrowing beds when not coexisting with Ch. granulatus. When both species coexisted, burrowing beds of C. angulatus are restricted to sandy-muddy areas. Only rarely are burrows of C. angulatus found within Ch. granulatus beds. However, when Ch. granulatus were experimentally excluded within their burrowing beds, new settlers of C. angulatus made burrows and maintained them until they reached large size. Paired (inside and outside Ch. granulatus burrowing bed) sampling during high tide using beach nets showed that C. angulatus rarely venture inside the Ch. granulatus crab beds. Other field experiments showed that adults Ch. granulatus always displace C. angulatus from burrows. Furthermore, in several sites located south of the limit of distribution of Ch. granulatus at the Patagonian coast, soft bare intertidals are dominated by burrowing beds of C. angulatus mixed with the congener C. altimanus Dana. Together, these evidences suggest that the mud crab C. angulatus is displaced from soft bottom areas by the burrowing crab Ch. granulatus. It is an example of competitive exclusion through aggressive interference in soft-bottom habitats when the shared resource is the access to sediment surface, a two-dimensional well-defined resource.     

The bulk hydraulic conductivity of mangrove soil perforated with animal burrows

Flow of groundwater from mangrove swamp sediment to mangrove creeks is likely to be an important pathway in mangrove swamps, particularly for the removal of salt excluded at the mangrove root. The swamps are generally saturated with water, and are perforated with animal burrows, allowing significant groundwater flow to mangrove creeks to occur. The hydraulic conductivity of the sediment is thus an important physical parameter but is very difficult to measure in-situ. In this work, we describe a simple method for determining the hydraulic conductivity of mangrove sediment, including the effect of macropores such as crab burrows, which uses the existing animal burrows as piezometers. Experiments to measure the hydraulic conductivity of the sediment were carried out in a variety of mangrove forests. It was found that hydraulic conductivity varied from around 1 to 10 m per day, which is at least 10 times greater than would be expected if there were no burrows. In order to check the validity of the method, conventional piezometers were used to determine the free water table level in an area of mangroves fringing a creek. From these measurements, hydraulic conductivity was determined independently and found to be consistent with the new methodology.     

Impact of fiddler crabs (Uca spp.) on rates and pathways of benthic mineralization in deposited mangrove shrimp pond waste

The impact of fiddler crabs (Uca spp.) on benthic mineralization rates and pathways in deposits of shrimp pond waste (SPW) with planted mangrove trees (Rhizophora apiculata) were determined in the Ranong mangrove forest, Thailand. Sediment metabolism, measured as CO₂ flux, increased by 2- to 3-fold when either fiddler crabs or mangrove trees were present compared to control plots. Sulfate reduction rates (SRR) were always high and partitioning of various electron acceptors to total carbon oxidation revealed that sulfate reduction contributed by >90%, with iron reduction being important only near the sediment-water interface. However, significant iron reduction appeared down to 7 cm when bioturbation and plant roots were combined in the easily oxidizable mangrove sediment (MS), indicating that infaunal activity and plant roots were able to alter the substratum. Microprofiles around individual Uca burrows showed 46% lower SRRs in a 15-mm-thick oxidized layer around the burrows compared to the surrounding sediment. The burrow wall environment appears to be a zone of intense reoxidation of reduced compounds as indicated by low pools of reduced sulfide compounds and a high Fe(III) content. Despite the decreased SRRs near the burrow, and the introduction of Fe(III) to deeper sediment layers, fiddler crabs and mangrove trees have only limited impact on rates and partitioning of anaerobic carbon mineralization in the SPW. This lack of response was attributed to the relative small volume of sediment affected by crab activities.     

Burrows of the Semi-Terrestrial Crab Ucides cordatus Enhance CO2 Release in a North Brazilian Mangrove Forest

Ucides cordatus is an abundant mangrove crab in Brazil constructing burrows of up to 2 m depth. Sediment around burrows may oxidize during low tides. This increase in sediment-air contact area may enhance carbon degradation processes. We hypothesized that 1) the sediment CO₂ efflux rate is greater with burrows than without and 2) the reduction potential in radial profiles in the sediment surrounding the burrows decreases gradually, until approximating non-bioturbated conditions. Sampling was conducted during the North Brazilian wet season at neap tides. CO₂ efflux rates of inhabited burrows and plain sediment were measured with a CO₂/H₂O gas analyzer connected to a respiration chamber. Sediment redox potential, pH and temperature were measured in the sediment surrounding the burrows at horizontal distances of 2, 5, 8 and 15 cm at four sediment depths (1, 10, 30 and 50 cm) and rH values were calculated. Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment. CO₂ efflux rates of plain sediment and individual crab burrows with entrance diameters of 7 cm were 0.7–1.3 µmol m⁻² s⁻¹ and 0.2–0.4 µmol burrows⁻¹ s⁻¹, respectively. CO₂ released from a Rhizophora mangle dominated forest with an average of 1.7 U. cordatus burrows⁻¹ m⁻² yielded 1.0–1.7 µmol m⁻² s⁻¹, depending on the month and burrow entrance diameter. Laboratory experiments revealed that 20–60% of the CO₂ released by burrows originated from crab respiration. Temporal changes in the reduction potential in the sediment surrounding the burrows did not influence the CO₂ release from burrows. More oxidized conditions of plain sediment over time may explain the increase in CO₂ release until the end of the wet season. CO₂ released by U. cordatus and their burrows may be a significant pathway of CO₂ export from mangrove sediments and should be considered in mangrove carbon budget estimates.     

The influence of habitat, season and tidal regime in the activity of the intertidal crab Neohelice (=Chasmagnathus) granulata

The activity pattern of intertidal crabs is influenced by factors that usually change rhythmically following tidal and/or diel cycles, and is often associated with the use of refuges. The movement activity of the burrowing crab Neohelice granulata was compared among three populations from SW Atlantic coastal areas where they face different tidal regimes, water salinities, substrata and biological factors. At each site, we examined the seasonal activity of the crabs (individuals collected in pitfall traps) in two types of habitat: mudflat and salt marsh. The working hypothesis is that the activity would vary according to the diverse environmental conditions encountered at geographical and local scales. Crab activity varied between sites and seasons showing to be more intense when habitats were covered by water. The most active groups were large males, followed by large non-ovigerous females. Ovigerous females were almost inactive. Most crabs were near or inside burrows at low tides in Mar Chiquita and Bahía Blanca, but they were active at both low and high tides in San Antonio during spring and summer. N. granulata were active in a wide range of temperatures: from 10 to 37 °C at low tides and at temperatures as low as 2 °C when covered by water. Differences of activity between mudflat and salt marsh varied among sites depending on flooding frequencies. Movement activity of N. granulata varied both in space and in time; crabs move under very different abiotic conditions (e.g., low or high tide, daylight or night, low and high temperature) and their movement may also be prevented or elicited by biotic conditions like burrow complexity, food quality and predation pressure. The wide set of conditions under which N. granulata can be active may explain why this is the only semiterrestrial crab inhabiting latitudes higher than 40°S in South America.     

The ecosystem engineering role of the Neotropical crab <Emphasis Type="Italic">Cardisoma guanhumi</Emphasis> on mangrove soil properties

The land crab Cardisoma guanhumi is one of the most common species in mangroves of the American Atlantic coast and Caribbean islands however, studies of its effects on the physical and chemical soil properties are scarce. This study compares specific physicochemical properties of soil between C. guanhumi burrows (B) and adjacent zones (AZ), and provides the first insights on their role as an ecosystem engineer in mangroves. The study was conducted in an estuarine system dominated by Rhizophora mangle, located at the Río Chico estuary, Miranda state of Venezuela. Random soil samples were taken digging each burrow until reaching the bottom and at the same depth for AZ. Data analysis was carried out using Bayesian inference. Credible mean differences between B and AZ, were found for sand (B?=?26.53?±?10.76, AZ?=?17.25?±?5.7%), silt (B?=?73.16?±?10.77, AZ?=?82.42?±?5.69%), pH (B?=?8.71?±?0.36, AZ?=?9.12?±?0.30), soil organic matter (SOM, B?=?0.43?±?0.21, AZ?=?0.17?±?0.06%), total N (TN, B?=?786?±?232, AZ?=?529?±?107 µg g^?1), Mg (B?=?4.42?±?0.60, AZ?=?3.48?±?0.71 cmol_c kg^?1) and K (B?=?0.12?±?0.05 AZ?=?0.06?±?0.02 cmol_c kg^?1). Chemical variables as SOM, K, Mg and TN showed the highest values of effect size (>?1.4). With the exception of the pH, all chemicals variables—which were different between B and AZ—showed strong and decisive evidences of correlations with SOM. When SOM variable was controlled, the relationships between pH–TN, TN–K and Mg–K decreased, even though the correlation evidence between each pair remained. Differences in chemical contents found in B respect to AZ suggest that the activities of C. guanhumi (feeding, moulting, excretion and defecation) within their burrows promote the spatial heterogeneity of mangrove soils.     

Morphology of the first zoeal stage of the commensal southwestern Atlantic crab Austinixa aidae (Righi 1967) (Brachyura: Pinnotheridae), hatched in the laboratory

The first zoeal stage of the endemic southern Atlantic pinnotherid crab Austinixa aidae is described and illustrated based on laboratory-hatched material from ovigerous females collected from the upper burrows of the thalassinidean shrimp Callichirus major at Ubatuba, São Paulo, Brazil. The zoeae of Austinixa species can be distinguished from other pinnotherids and especially from zoeae of the closely related species of Pinnixa by the telson structure.     

Small- and large-scale effect of the SW Atlantic burrowing crab Chasmagnathus granulatus on habitat use by migratory shorebirds

Here we address the question of whether the presence of the burrowing crabs Chasmagnathus granulatus affects small- and large-scale habitat use by migrant shorebirds. This crab is the dominant species in soft bare sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil 28°S to the northern Argentinean Patagonia 42°S). They generate very extensive burrow beds in soft bottom intertidal areas. Our information shows that this burrowing crab affects the small-scale habitat use by shorebirds, given that shorebirds never walk through the funnel-shaped entrances of burrows. Given that crab burrow entrances occupy up to 40% of the intertidal area, there is a large decrease of available shorebird habitat in crab beds, restricting their activity to the spaces between the burrows. The southern migratory shorebird Charadrius falklandicus maximize the use of these areas by foraging closer to the burrows than the other bird species. Neotropical migrants, such as Calidris fuscicollis, Pluvialis squatarola and Tringa melanoleuca, used foraging paths that tended to maximize the distance from burrows, especially the distance to larger burrows. A field experiment showed that this was not necessarily due to a decrease in the availability of polychaetes near the crab burrows. A combination of landscape measurements and satellite images showed that crab beds covered up to 40% of the intertidal area of the Mar Chiquita coastal lagoon (37°40′S, Argentina), and nearly 100% of the intertidal area of the Bahia Blanca estuary (38°48′-39°25′S, Argentina). These two estuaries are located along the migratory flyway of Neotropical migratory shorebirds, but the Bahia Blanca estuary (area∼110,000 ha) shows a much lower shorebird diversity than Mar Chiquita (area∼4500 ha). The most common species in Bahia Blanca is the two-banded plover C. falklandicus, the species least affected by crabs at Mar Chiquita and which prefers to use high-density crab areas as foraging sites. The oystercatcher Haematopus palliatus was also most abundant in high-density crab areas, but they used these areas for resting. The abundances of preys varied during the study period and between the crab density areas, indicating that the use of these areas by birds is independent of crab density. However, burrowing crabs affect the depth distribution of polychaete and thus their availability to shorebirds. We suggest that this shorebirds-burrowing organism interaction could be generalized for other intertidal estuarine habitats.     

Mangrove habitat partitioning by Ucides cordatus (Ucididae): effects of the degree of tidal flooding and tree-species composition during its life cycle

Environmental factors strongly affect mangrove crabs, and some factors modulate population structure and habitat partitioning during the crabs’ life cycle. However, the effect of these environmental factors on habitat selection by mangrove crabs is still unknown. We evaluated habitat selection by the mangrove crab Ucides cordatus in mangrove forests with different degrees of predominance of Rhizophora mangle, Laguncularia racemosa or Avicennia schaueriana, two tidal flooding levels (less- and more-flooded), and two biological periods (breeding and non-breeding seasons). Sampling was conducted in four mangrove forests with different influences of these biotic and abiotic parameters. We used the data for sex ratio to explain environmental partitioning by this species. Females predominated in R. mangle mangroves, independently of the biological period (breeding or non-breeding seasons), and males predominated only in the less-flooded L. racemosa mangroves. The flooding level affected the sex ratio of U. cordatus, with a predominance of males in less-flooded mangroves, independently of the biological period; and a gender balance in the more-flooded mangroves only during the breeding season. Outside the breeding season, the largest specimens were recorded in the R. mangle mangroves, but in the breeding season, the largest crabs were recorded in the L. racemosa mangroves with a higher level of flooding. These results suggest that tree-species composition and tidal flooding level can have a significant effect on the habitat partitioning of sexes and sizes of the mangrove crab U. cordatus both during and outside the breeding season.     

Factors determining active dispersal capacity of adult Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis> (Decapoda,Varunidae)

The Chinese mitten crab (Eriocheir sinensis) is an invasive crustacean with a widespread distribution, sometimes overlapping with the red swamp crayfish (Procambarus clarkii). E. sinensis performs long river migrations, often moving overland to cross obstacles, but the factors affecting its movement are not well known. We studied its movement speed in and out of water, the survival time out of water and also its interaction with the red swamp crayfish during dispersal. At 16°C the LT₅₀ (time to death of 50% of the individuals) was 70 h, with a mean weight loss of 20%, and at 24°C the LT₅₀ was 31 h, with a mean 22% weight loss. In and out of the water, these crabs moved with mean velocities of 0.074 and 0.016 m s^?1, respectively. P. clarkii did not affect the dispersion of E. sinensis. This crab was able to disperse under various environmental conditions and its speed was affected by density, temperature, relative humidity, carapace length, and condition of the individuals (Fulton index). Moreover, we found that this species has a great capacity to resist desiccation. These characteristics give them all the requirements to successfully invade and adapt to new areas.     

Brood ball construction by the non-brooding Coprini Sulcophanaeus carnifex and Dichotomius torulosus (Coleoptera, Scarabaeidae)

ABSTRACT.

• 1 Feeding burrows made by S.carnifex and D.torulosus adults consisted of tunnels filled with sausage-shaped masses of dung. Brood balls were made by taking fragments of dung from an adjacent feeding burrow and aggregating them into a small sphere which was gradually enlarged and then coated with soil.
• 2 S.carnifex adult females showed no response to their own eggs (unlike Copris lunaris: Klemperer, H.G. (1982) Ecological Erltonzology, 7, 155–167). S.carnifex larvae made and maintained an air channel to the upper pole of the ball and they are in this respect preadapted to receive parental care.
• 3 Compared with a brood mass, a brood ball was less likely to be attacked by Meptoparasitic larvae. The soil coat retarded drying of the brood ball by increasing the total mass of moisturecontaining material.