Dominant Crab Research Articles

Tidal zone effects on the diet composition of leaf-eating crabs in natural mangrove communities: a stable isotope analysis

BackgroundIn natural mangrove communities, mangrove species are often distributed zonally. Leaf-eating crabs are one of the most abundant and iconic arboreal brachyurans in mangrove forests, but variation in the composition of crab diets in different mangrove tidal zones is unknown.MethodsTo determine the contributions of mangrove leaves and other organic carbon (C) sources to leaf-eating crab diets, dual stable C and nitrogen (N) isotope signatures (δ13C and 1δ5N) were used in a Bayesian stable isotope mixing model. We conducted experiments at various tidal levels in the Dongzhaigang Bay National Natural Reserve in China. We analyzed δ13C and δ15N of leaf-eating crabs, mangrove leaves, sediment organic matter (SOM), and animal tissues (prey).ResultsThe food composition of the dominant crab species, Parasesarma continentale, exhibited significant differences among the four tidal zones. From the margin to the high tide zone, the main food source shifted from predominantly mangrove leaves and SOM to primarily SOM and animal tissues. We observed a significant negative relationship between the C/N ratios of mangrove leaves and the proportion of leaves consumed by leaf-eating crabs. Additionally, as the tidal level increased, the C/N ratio of mangrove leaves also increased, whereas the proportion of leaves consumed by crabs decreased.ConclusionLeaf-eating crab diets vary significantly across tidal zones, highlighting the importance of considering tidal zone differentiation when studying consumer diets in mangrove ecosystems.

Microplastic contamination in the dominant crabs at the intertidal zone of Chongming Island, Yangtze Estuary

Crabs are one of the most critical and dominant species of the intertidal zone. Their feeding, burrowing, and other bioturbation activities are common and intense. However, baseline data on microplastic contamination in wild intertidal crabs are still lacking. In this study, we investigated the contamination of microplastics in the dominant crabs, Chiromantes dehaani, of the intertidal zone in Chongming Island, Yangtze Estuary, and explored their probable relationship with the microplastic composition in sediments. A total of 592 microplastic particles were observed in the crab tissues, with an abundance of 1.90 ± 0.53 items·g−1 (1.48 ± 0.45 items·ind−1). The microplastic contamination in the tissues of C. dehaani varied significantly among different sampling sites, organs, and size groups, but not among different sexes. Microplastics in C. dehaani were mainly rayon fibers with small sizes (<1000 μm). Their colors were mostly dark, which is consistent with the sediments samples. A linear regression showed significant correlations between the composition of microplastics in the crabs and that in sediments, although they differed in various crab organs and sediment layers. The target group index identified the feeding preference of C. dehaani on the microplastics with specific shapes, colors, sizes, and polymer types. In general, the microplastic contamination in crabs is affected by both objective environmental conditions and subjective feeding habits of crabs. In the future, more potential sources should be considered to completely distinguish the relationship between the microplastic contamination in crabs and adjacent environment.

The clinical features and genomic epidemiology of carbapenem-resistant Acinetobacter baumannii infections at a tertiary hospital in Vietnam

To characterise the clinical features of A. baumannii infections and investigate the phylogenetic structure and transmission dynamics of A. baumannii in Vietnam. Between 2019 and 2020, a surveillance of A. baumannii (AB) infections was conducted at a tertiary hospital in Ho Chi Minh City, Vietnam. Risk factors for in-hospital mortality were analyzed using logistic regressions. Whole-genome sequence data were used to characterise genomic species, sequence types (STs), antimicrobial resistance genes, surface antigens and phylogenetic relatedness of AB isolates. Eighty-four patients with AB infections were enrolled in the study, 96% of whom were hospital-acquired. Half of the AB isolates were identified from ICU-admitted patients while the remaining isolates were from non-ICU patients. The overall in-hospital mortality was 56%, with associated risk factors including advanced age, ICU stay, exposure to mechanical ventilation/central venous catheterization, pneumonia as source of AB infection, prior use of linezolid/aminoglycosides, and AB treatment with colistin-based therapy. Nearly 91% of isolates were carbapenem-resistant; 92% were multidrug-resistant and 6% were colistin-resistant. ST2, ST571 and ST16 were the three dominant CRAB genotypes, exhibiting distinct AMR gene profiles. Phylogenetic analysis of CRAB ST2 isolates together with previously published ST2 collection provided evidence of intra- and inter-hospital transmission of this clone. Our study highlights a high prevalence of carbapenem resistance and multidrug resistance in A. baumannii and elucidates the spread of CRAB within and between hospitals. Strengthening infection control measures and routine genomic surveillance are crucial to reducing the spread of CRAB and timely detecting novel pan drug-resistant variants.

Role of crab holobionts in benthic N cycling in mangroves with different trophic status

Microbial dinitrogen (N2) fixation and intense bioturbation by macrofauna can contribute to reduce nitrogen (N) limitation in mangrove systems. In particular, crabs are important ecosystem engineers that rework sediments, redistribute organic matter, accelerate nutrient cycling and shape microbial communities in mangrove sediments. Hosting functionally diverse microbial communities, crabs form a discrete ecological unit (a holobiont). In this study, we report rates of respiration, inorganic N fluxes, net N2 fixation, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) measured in the fiddler crab Leptuca thayeri and sesarmid crab Armases rubripes holobionts, which are dominant in oligotrophic and eutrophic mangrove systems of southeast Brazil, respectively. We measured lower biomass-specific rates of respiration and ammonium (NH4+) production for the larger L. thayeri compared to A. rubripes, with very different molar ratios of O2 respiration to NH4+ production (152:1 vs. 20:1, respectively). This suggests a size-metabolism relationship, different food quality or different coupling of N excretion and assimilation by the crab holobionts in the 2 systems. Both crab holobionts contributed to net denitrification and DNRA, with faster N cycling in A. rubripes in the eutrophic system. Net N2 fixation was also detected, with nearly 4-fold higher rates in A. rubripes compared to L. thayeri. Overall, our results illustrate active and complex N cycling associated with the 2 dominant crab holobionts and highlight their potential and overlooked role as important conduits of fixed N, which may double N2 fixation rates in the mangrove’s rhizosphere.

Aggravation of nitrous oxide emissions driven by burrowing crab activities in intertidal marsh soils: Mechanisms and environmental implications

Coastal wetlands are hotspots for nitrogen (N) cycling and a significant natural source of the potent greenhouse gas nitrous oxide (N2O). Burrowing benthos are known to transform N in intertidal marsh soils, but their contribution to N2O emissions and the underlying molecular mechanisms remain unclear. Here, the effects of crab bioturbation on N2O emissions in coastal marshes, where Chiromantes dehaani and Helice tridens tientsinensis were the dominant crab species, were investigated in field and indoor experiments. The N2O emissions increased significantly in the presence of crabs, being positively correlated with the intensity of crab bioturbation but differing among crab species. Natural-abundance isotope analyses indicated that crab bioturbation greatly promoted the contribution of hydroxylamine oxidation to N2O production; nevertheless, bacterial denitrification (including heterotrophic denitrification and nitrifier denitrification) remained the dominant pathway. Molecular analyses suggested that the increased N2O emissions in crab-disturbed habitats might be driven by underlying changes to microbial communities, especially by the disproportionate stimulation of nitric oxide reductase-carrying microbes over nitrous oxide reductase-carrying microbes. This study highlights the importance of considering the burrowing activity, density, and species of benthos when evaluating the N cycle in coastal wetlands.

The habitat preference of mangrove crabs in different mangrove forests of Penang, North Peninsular Malaysia

Different crab assemblage compositions may result in distinct pathways in mangrove ecosystem function, attributed to specific preferences and habitat selection criteria by each crab species. This study assessed the preference of crabs to different mangrove forests at Balik Pulau, Penang, Malaysia across temporal scales of four months and spatial scales across three forests. Sites were characterized by Avicennia, Rhizophora and Bruguiera species. Crabs were sampled using hand-catch method, which was then preserved in 70% ethanol and identified to the lowest taxonomic level possible. Environmental variables were determined by in-situ and ex-situ analysis and comprised the collection of canopy cover, root cover, surface temperature, sediment salinity and organic matter data. PERMANOVA analysis showed there was a difference in crab abundance and environmental variables across Month and Forest (p < 0.05). SIMPER analysis revealed that the Grapsidae family dominated mangroves of Balik Pulau, with Perisesarma eumolpe and Perisesarma foresti found to be most abundant in Avicennia and Bruguiera forests respectively. However, in the Rhizophora forest, dominant crab species varied, with Parasesarma sp2. and Perisesarma indiarum found in high abundance in June and August, respectively. In October and December, however Perisesarma foresti was the major contributor to patterns observed in crab assemblage composition in Rhizophora forest. BEST correlation varied among month and forest, with different combinations of salinity, pH, canopy cover and root density explaining patterns in crab assemblages.

Increasing habitat complexity enhances crab density: A case study from Thailand

AbstractThe problem of seagrass degradation in Southeast Asia region, which harbors some of the greatest marine biodiversity in the world, is increasing due to coastal development and the lack of efficient management. These factors have caused the decline of marine life and have impacted local fisheries. The present study investigated the species, sizes and abundance of swimming crabs in areas of differing seagrass cover at Koh Tha Rai in the Gulf of Thailand. Seagrass cover and crab populations were investigated on May 2006, September 2010 and August 2017. The results showed concomitant change in seagrass cover and the dominant crab species, Thalamita crenata. Seagrass increased from 27.69 ± 5.08% (mean ± SE) to 58.89 ± 5.61% at the low cover site between May 2006 and July 2017, while T. crenata abundance increased 10‐fold (p ≤ .0001). This study highlights the importance of conservation and the importance of seagrass in terms of providing ecosystem services and habitat/refuge for marine benthos in the region.

Burrowing crabs in arid mangrove forests on the southwestern Arabian Gulf: Ecological and biogeographical considerations

Many species of mangrove crabs are essential in the formation of mangrove ecosystems, and the bioturbation resulting from the excavation of their underground chambers is directly correlated with substrate oxygenation and carbon and nitrogen cycling within the ecosystem. This study examines the ecological and biogeographical characteristics of bioengineering crab assemblages that inhabit the environmentally challenging arid mangroves in the southwestern Persian-Arabian Gulf. Results demonstrated that a hyper-arid environment could directly impact crab diversity, reducing it to only one species per niche or coastal zone. A biogeographic comparison revealed an exclusive divergence of species composition in each Gulf region. Variations in seasonal temperatures were found to have a direct influence on the abundance of species and how the zonation is driven by sediment composition and trophic relations. Two crabs – Nasima dotilliformis in the salt march (supratidal zone) and Macrophthalmus (Mareotis) depressus in the intertidal – were considered to be the most influential functional species for this hyper-arid ecosystem due to their abundance, size, bioturbation potential and niche specificity for the intertidal zone. The limited number of species within the arid mangrove system emphasised the biogeographic pressure and inherent importance of the few active bioengineering species present and adapted to the harsh conditions, indicating that the dominant crabs within the biotope are directly related to the successful evolutionary establishment of these hyperarid mangroves. The study highlights important implications for future forest management strategies of the only forest ecosystem that tolerates the extremes of the southwestern Persian-Arabian Gulf area.

Potential Effect of Bioturbation by Burrowing Crabs on Sediment Parameters in Coastal Salt Marshes

Burrowing crabs are main constituent of estuarine wetlands ecosystems, and provide a variety of ecosystem functions including providing food for waterbirds and fishes, promoting nutrients cycling, and processing sediments deposition. Helice tientsinensis is the dominant crab species which inhabits almost the entire intertidal marshes of the Yellow River Delta. However, for a long time we ignored the crab bioturbation in this area. We know little about whether crabs have potential effects on sediment environment. Here, we investigated the crab burrow characteristics in three marsh zones, and we also analysed the sediment parameters among crab burrow mounds (chimneys), flats (flat areas between burrows), controls (outside of crab bed) and crab fecal deposit. We found that sediment was softer in crab burrow mounds than in flat and control areas. Higher crab density indicates softer sediment. Crab burrow mounds had saltier soil than the flats. Our results showed that sediment total nitrogen, total carbon and organic matter varied among mounds, flats, controls and crab fecal deposit, which indicated that crab bioturbation have potential effects on sediments redistribution and nutrients cycling. Our study is essential to clear the roles of crabs in ecosystems and will benefit for coastal saltmarsh protection and restoration.

Comparison of the feeding ecology of Perisesarma eumolpe collected at the intact forest and gap areas of Can Gio mangrove forest after ten years of Durian typhoon

Perisesarma eumolpe is the dominant crab species in the Can Gio mangrove forest, which is affected by bidirectional interaction with the natural environment. After 10 years of Durian typhoon, Perisesarma eumolpe has had significant changes and adaptations on its growth in Can Gio mangrove forest. One of the main changes is their diets between the intact forest and the gap areas which are natural reforestation. The dry season results showed that the fullness of the stomach (S4) was the highest in the total analyzed stomaches. The fullness of the stomach of the P. eumolpe in the gap area (Hcut) is always higher than the rest area. The main diet composition of the P. eumolpe are seven food categories: decomposed leaves, bark, wood, animal debris, algae, sand, unidentified debris. Leaves are dominant food category in both forest and gap areas. To compare with the result obtained in 2007, the feeding ecology of P. eumolpe was initially recorded. These are the increase in stomach fullness, leaves are dominant in the gap area. There are the positive results from the natural reforestation of Can Gio mangroves in the gap area caused by Durian typhoon.&#x0D;

Diet of the Mud-Flat Crab Helice tientsinensis in a Korean Salt Marsh

Crabs live at high densities in intertidal zones with various halophytes in salt marshes. However, the ecological relationships between crabs and halophytes as well as the impacts of herbivorous crabs on the plant distribution are not fully understood. In this study, we identified halophytic plant species consumed by crabs and determined the relative contributions of halophytes and other food sources to the diet. A DNA analysis of stomach contents was used to determine plant food sources for crabs. We found that the dominant crab species Helice tientsinensis consumed Suaeda japonica, even though several halophytes inhabited the study site. These results indicated that H. tientsinensis is a selective feeder. Based on a stable isotope analysis, we observed a dietary shift during crab development. Immature individuals mainly ate soil organic matter, whereas mature individuals showed more diverse food sources. We observed greater plant (S. japonica) consumption by middle-sized crabs than by crabs of other sizes. Our results for the feeding relationship between crabs and plants extend our understanding of the benthic food web in salt marshes.

Cellulose digestion abilities determine the food utilization of mangrove estuarine crabs

Food utilization and cellulose digestion abilities of six crab species were examined to clarify the mechanisms driving trophic and spatial segregation among species within a mangrove estuary on the Urauchi River, Iriomote Island, southern Japan. Dual stable isotope signatures (δ13C and δ15N) of dominant crab species inhabiting three microhabitats (bare sandy flat, bare muddy flat and mangrove forest) showed that most crab species, such as the soldier crab Mictyris guinotae and fiddler crab Gelasimus jocelynae, primarily assimilated microphytobenthos (MPB), while the sesarmid crab Parasesarma bidens inside the mangrove forest substantially utilized cellulose-rich mangrove detritus and leaf litter. Analyses of the chemical properties of sediment organic matter indicated that it comprised mainly mangrove detritus, which was more abundant on the muddy flat and in the forest compared to the sandy flat. In contrast, the standing stocks of MPB were at consistently low levels in each microhabitat, particularly inside the mangrove forest than on the bare flats. The enzyme assay revealed that P. bidens exhibited much higher cellulase activity, enabling the species to utilize refractory mangrove materials, whereas the other crab species with lower cellulase activity were highly dependent upon nutritious and easily degradable MPB, although the amount of the latter was largely limited in the mangrove estuary. These findings suggested that the assimilation efficiency of cellulose-rich plant materials as a carbon source, dependent upon the level of cellulase activity, essentially controls trophic and spatial segregation among crab species in the mangrove estuary. Given the greater biomass of plant detritus, it is likely that P. bidens plays an integral part in establishing the detritus food chain in the mangrove ecosystem through the effective digestion/assimilation of cellulose materials.

Intraspecific diet shifts of the sesarmid crab, Sesarma dehaani, in three wetlands in the Han River estuary, South Korea

BackgroundHan River estuary is a national wetland reserve near the Demilitarized Zone (DMZ) between South Korea and North Korea. This trans-boundary estuary area has been well preserved and shows distinctive plant communities along the salinity gradient. To elucidate energy flows and nutrient cycling in this area, we studied trophic relations between the dominant sesarmid crab, Sesarma dehaani, and food sources in three wetlands with different environments along the estuarine gradients.ResultsStable isotope signatures (δ13C and δ15N) of the crabs were significantly different among the sites and body size classes. Seasonal changes in δ13C of small crabs were distinct from those of large individuals at all the sites. The isotopic values and fatty acid profiles of the crabs were more different among the sites in September than in May. In May, large-sized crabs utilized more plant materials compared to other dietary sources in contrast to small-sized crabs as revealed by a stable isotope mixing modeling, whereas contributions to diets of crabs were not dominated by a specific diet for different body size in September except at site 1. Based on PCA loadings, fatty acid content of 18:3ω3, known as a biomarker of plant materials, was the main factor to separate size groups of crabs in May and September. The δ13C value of sediment had high correlation with those of small-sized crabs at site 1 and 2 when 1-month time lag was applied to the value for crabs during the surveyed period.ConclusionsBased on the stable isotope and fatty acid results, the consumption habits of S. dehaani appear to be distinguished by sites and their size. In particular, smaller size of S. dehaani appears to be more dependent on fewer food sources and is influenced more by the diet sources from the sediments in Han River estuary.

Spatial and Temporal Associations Between Native Crabs and the Invading Green Porcelain Crab, Petrolisthes armatus, Throughout Its Northernmost Invaded Range

Increasing ocean temperatures have led to poleward range expansions of many marine organisms. The green porcelain crab, Petrolisthes armatus, was first reported on intertidal oyster reefs near Charleston, South Carolina in the mid-1990s, an expansion from its tropical to sub-tropical native range. In order to investigate the relative abundances of this introduced crab and a portion of the native crab community, resident crab assemblages were sampled on intertidal oyster reefs across four seasons from 2015 to 2016. Sampling occurred at five locations extending from Savannah, Georgia where P. armatus is now well-established, to Wilmington, North Carolina, where its inter-annual presence is intermittent. Petrolisthes armatus was the numerically dominant crab species at all locations except Wilmington, where the species was not collected in the winter. Differences between northern and southern sample locations in the taxonomic composition of crab assemblages were most pronounced in the summer (June–September) and fall (October–January), with dissimilarities largely attributed to high abundances of P. armatus at southern locations. Crab abundances of all species peaked in the summer and were lowest in the winter (February–March). Petrolisthes armatus was less abundant toward the northern range edge, whereas native crabs did not differ in abundance throughout the sampling range. Throughout the study area, adult P. armatus sex ratios shifted from unbiased or female-biased in the summer to male-biased in the fall. Adults were collected in the spring (April–June), indicating they had overwintered. While native crab densities (Panopeus herbstii, Eurypanopeus depressus) stayed relatively constant across locations, P. armatus densities varied greatly, suggesting that resources, such as shelter and food, are not limiting factors for the coexistence of these native and invading crabs.

Seasonal and habitat structures of crustacean decapod assemblages associated withZostera marinabeds in northern Jinhae Bay, Korea

Crustacean decapod assemblages were surveyed inZostera marinabeds adjacent to tidal flats (ET) and rocky shore (ER), and in unvegetated habitats (UV). Decapod samples were collected monthly throughout 2002 using a small beam trawl from northern Jinhae Bay, Korea. Water temperature, salinity, eelgrass biomass, sediment composition and organic matter were also monitored to assess any correlation between environmental variables and decapod fauna. A total of 31 decapod species belonging to five taxa (three prawns, 13 caridean shrimps, one hermit crab, one mud shrimp and 13 crabs) were collected at three different habitats. To assess variations in decapod assemblages in relation to habitat type and season, various multivariate analyses were used. The dominant caridean shrimps werePalaemon macrodactylus, Alpheus digitalisandCrangon uritai,and the dominant crabs wereCharybdis japonica, Hemigrapsus penicillatusandCharybdis bimaculata. The number, abundance and diversity of decapod species varied greatly with habitat type and season, peaking in eelgrass beds and during spring, and showing the lowest catch rate in unvegetated habitat and during winter months. The nMDS ordination and multivariate analyses revealed that habitat type and season were determinant factors affecting the structure of decapod assemblages. Seasonal shifts in the abundance of decapods corresponded with changes in eelgrass biomass and loss on ignition (LOI), but not with water temperature or salinity.

What drives the distribution of crab burrows in different habitats of intertidal salt marshes, Yellow River Delta, China

Crabs play important roles in coastal ecosystems and are useful indicators for evaluating ecosystem health. Many previous studies have examined the distribution patterns of crabs among different habitats. However, we know little about what the key factors determining crab burrow distribution among types of habitats. Different kind of crab species may have different preferences of environmental conditions, here, we focus on the dominant crab species Helice tientsinensis in the Yellow River Delta. To identify the drivers of crab burrow distribution in intertidal marshes of the Yellow River Delta, we examined crab burrow density among seven habitats across different marsh zones, with reference to abiotic (water depth, soil hardness, water content, bulk density, porewater salinity, organic matter, total nitrogen and total carbon) and biotic (plant coverage, above- and belowground biomass, macrofauna species richness, abundance and biomass) factors that might explain crab burrow distribution patterns. Differences of all above factors were examined by one-way Analysis of Variance (ANOVA) among different habitats. The best single predictors of crab burrow density were tested by liner regression across the entire study area. Our results showed that patterns of crab burrow distribution were more strongly affected by abiotic drivers (water depth, water content, salinity, soil hardness, organic matter and total carbon) than biotic drivers. Crabs prefer habitats with softer and wetter edaphic conditions. In the future of coastal management, building habitats first, thereafter attracting crabs settling down and regulating feeding area of water birds and other benthic communities are good strategies to follow.

Crab communities (Decapoda: Brachyura) in mangrove and estuaries in the Eastern Part of Lombok Island

Mangroves and estuary ecosystem in East Lombok which are appointed as Local Marine Conservation Areas (Kawasan Konservasi Laut Daerah/KKLD) are Gili Lawang, Gili Sulat, Sambelia and Jerowaru districts. Inventory of aquatic fauna in mangroves and estuaries is one of the important components of the marine conservation program. The objective of this study is to determine crab species composition in mangroves and estuaries of eastern Lombok during the East Lombok KKLD program. Targeted area for this study includes Gili Lawang, Gili Sulat in southern Lombok Island, Sugian in Sambelia, Ekas Beach, Tanjung Luar and Seriwe in Jerowaru, and Kidang in western Jerowaru. The crab was collected at 0 m to 100 m of seashore by digging the burrow. The crab community recorded was analyzed for resulting the Diversity, Evenness and Similarity Index. Ten families with 35 species of crab were found from two ecosystem types, mangrove and estuary. Each location has different diversity of ecosystem and habitat. The highest diversity is recorded in Kidang and Seriwe, while the lowest diversity in Gili Sulat. Species diversity is associated with ecosystem and habitat type diversity. Kidang and Seriwe has the highest ecosystem and habitat diversity, while Gili Sulat has the lowest diversity. In addition, the population of Ocypodidae is accounted as the dominant crab family for which Austruca perplexa is the dominant species.

Short Communication: Population structure of mangrove crab Scylla oceanica in mangrove ecosystem of Tanjung Lesung, Banten, Indonesia

Pudiawati T, Patria MP. 2017. Short Communication: Population structure of mangrove crab Scylla oceanica in mangrove ecosystem of Tanjung Lesung, Banten, Indonesia. Biodiversitas 18: 813-817. The mangrove crab Scylla oceanica is one of the dominant crabs in the mangrove ecosystem at Tanjung Lesung Beach, Banten, Indonesia. The aim of the study was to determine the temporal distribution, carapace width-weight relationship and condition factors of S. oceanica. The crabs were collected by using traps for four months from August to November 2015. It was observed that the carapace was larger in male crabs (9.97 cm) than in female crabs (9.34 cm) and the average weight of the males (206.08 g) was higher than that of the females (183.83 g). b value of male (1.955) and female (2.123) crabs were significantly different (P &lt; 0.05). Both of them have a negative allometric growth pattern. The result of the distribution analysis was a Morisita spread index Id of 1.5176; this indicates the crabs have clustered distribution patterns and their distribution was allegedly associated with the reproductive cycle.

Population structure and morphometric variation in the sand-bubbler crab Scopimera crabricauda (Brachyura: Dotillidae)

In the present study, population ecology and relationships between various morphometric characters of the sand-bubbler crab Scopimera crabricauda from the Persian Gulf (Iran) were studied. Crabs were collected monthly by excavating nine quadrats in high-density areas of open burrows at low, mid and high intertidal levels during spring low tides for one year. A total of 534 crabs was collected, of which 70% were males (and 30% females). Mean carapace width and total weight in both sexes showed significant differences. Crabs with a carapace width ranging from 5 to 7 mm were the dominant crabs in the population. The highest numbers of crabs were found in the higher intertidal area. The mean size of crabs decreased towards the sea. The aggregation of small crabs was found towards sea in female crabs. Juveniles were abundantly found from January to March whereas the sub-adults and adults were mostly found from April to January. The carapace length to carapace width relationship differed between males and females, as did the carapace width and carapace length to total weight relationships. Finally, the relationship between carapace width and weight for both sexes showed that the growth of this species is allometric.

Patterns and intensity of ghost crab predation on the nests of an important endangered loggerhead turtle population

Predation is one of the most important threats to the early life stages of most endangered vertebrates. On small oceanic islands that host very important endangered sea turtle rookeries, ghost crabs are the main nest predators. Mortality in nests was evaluated on the island of Boa Vista which hosts around 75% of the nests in the Cape Verde archipelago, which is one of the world's largest loggerhead turtle (Caretta caretta) rookeries. In an extensive survey of the island, egg mortality significantly varied between beaches and averaged 70%. One of the main causes of egg mortality was predation by ghost crabs (Ocypode cursor) that stole an average of 33 eggs per nest. No other egg predator was observed during the study. In an intensive field experiment, the egg mortality for non-protected nests was 82% and ghost crabs predated an average of 50% of the total number of eggs. Even though female tracks on the beach are very conspicuous immediately after egg laying, very few nests were predated during this period. In contrast, most of the nests were predated at the end of the incubation period (after day 40 of incubation), when female tracks are not visible on the beach. Nests predated by larger crabs suffered a lower predation rate, suggesting that these larger dominant crabs defend the nest they prey upon. On-beach nest relocation had no significant influence on reducing egg predation. Females preferred nesting on beaches with higher hatching success although predation was not a risk that they seemed able to assess.