Ghost Crab Research Articles

Characteristics of turtle laying habitat on vemara beach, Banyuwangi Regency, East Java

Turtles have a unique behavior, namely laying eggs on the same beach where they hatched. Turtles as protected animals continue to experience a decline in population caused by various factors including the degradation of nesting habitats. This study aims to determine the condition of the Cemara Beach habitat as a turtle nesting habitat. The research was conducted during September-November 2020 with a survey method by measuring the parameters of the Cemara Beach habitat which include sand temperature, air temperature, air humidity, beach width, beach slope, vegetation types and predators. The data collected was then analyzed descriptively qualitatively. The average air temperature is 28.07oC, the average sand temperature at a depth of 50 cm is 29.95oC, the average air humidity is 71.53%, the average beach width is 40 m and the average beach slope is 11.80 which shows the sloping beach category. The types of vegetation that grow along the coast are ketapang (Terminalia catappa), sea pine (Casuarina equisetifolia), horse tread (Ipomoea pes-caprae), cikumpai cikarao (Lepturus repens). As for the presence of predators identified during the observation, namely ghost crabs (Ocypode cursor).

Hayalet yengeç Ocypode cursor (Linnaeus, 1758) yuvalarının insan etkileri altında morfolojik değişimleri

Ghost crabs are common bioindicator species for human disturbance on sandy shores. Ghost crabs often alter their population dynamics under human disturbance. Ghost crabs, further, alter their burrowing behavior under human influence, however, these changes are not well known on the Turkish coast of the Mediterranean Sea. Therefore, burrowing morphology of Ocypode cursor at two sites that differ in the degree of human disturbance was compared. Ghost crabs created smaller, steeper and simpler burrows at the site under higher human disturbance compared to the crabs living at the sites with lower human influence. Further, there was no difference in the ghost crab burrow depth and the frequency of existence of chambers between sites. Moreover, the results of this study revealed that larger crabs preferred higher parts of the beach at both sites, suggesting that this is a common behavior for the populations of O. cursor. Consequently, the results of this study emphasized that O. cursor alter their burrowing morphology and characteristics under human disturbance besides their population demographics; suggesting that studies that focus on the use of ghost crabs for human disturbance should include burrow morphology in their assessments.

DNA-barcoding reveals cryptic diversity and re-evaluation of Ocypode (family: Ocypodidae) from the Sundarbans - UNESCO World Heritage Centre

Crabs are one of the most diversified crustaceans among metazoans, from both morphological and ecological point of view. Among them, ghost crabs (Genus Ocypode; Family Ocypodidae) play an important role in the tropical and sub-tropical intertidal ecosystems. Due to a lack of comprehensive data, their cryptic behaviour, mimicry or camouflage, and a lack of formal taxonomic documentation, identification of this group is often difficult. Molecular taxonomy can help to overcome these barriers by assisting in species identification. The present study is the first large scale attempt to identify ghost crabs using DNA barcodes, which are now available globally, for 16 morphospecies in the genus Ocypode. A total of 164 barcodes were analysed for species delimitation that are available globally including specimens collected from the Indian Sundarbans. Various species delimitation methods (K2P, NJ, Bayesian supported PTP and Bayesian tree) revealed a total of 19 MOTUs for 16 distinct species where multiple MOTUs were observed in 3 species with inconsistencies in genetic distances and tree topologies. We recognised cryptic diversity in Ocypode macrocera, O. platytarsis and O. quadrata with intraspecies distances greater than the species delimitation threshold of 0.053 ± 0.01. The current study also concluded that O. platytarsis and O. brevicornis are two distinct species, putting an end to the debate over their species synonymy. Furthermore, our Bayesian analysis confirmed the retraction of the genus Hoplocypode specified only for O. occidentalis. As a result, the current research added a new dimension to ghost crab taxonomy by contributing to the detection of cryptic species, thus speculating the possibility of new species and reaffirming the effectiveness of the DNA barcoding while demanding enrichment of the global database for comprehensive species identification and extensive approach of molecular taxonomy as well as morphological interventions in solving taxonomic puzzles.

Is the ghost crab’s feeding behavior a good early indicator of human pressure in sandy beaches?

Phenotypic plasticity is a trait found among organisms that dwell in dynamic ecosystems such as sandy beaches. One of the main model of ecological studies in this ecosystem are ghost crabs (Crustacea: Ocypodidae), which present trophic plasticity and are considered ecological-disturbance indicator species. Their reactions to these impacts can manifest as sublethal responses, including behavioral aspects. We aimed to evaluate possible effects of urbanization on the feeding behavior of the ghost crab Ocypode quadrata (Fabricius, 1787). The study was conducted in a beach arc categorized into three urbanization levels located in the northern Rio de Janeiro state, Brazil. Each sector was sampled twice during high and low tourist seasons. The crabs’ diet was described by inspecting their digestive tracts with a stereomicroscope. Food preference (the choice of food items by each individual) and behavioral aspects (i.e., time of emergence from burrows, look-out time, number of choices, and handling time of the resource provided) were observed through in situ experiments, where food items were placed around burrows. The behavioral aspects were not affected by urbanization level. The diet mainly consisted of insects and macroalgae, though during experiments the species selected the most caloric items (fish and the bivalve Donax hanleyanus), regardless of the urbanization level. Local human disturbances seemed neither to change the availability of local resources nor to select individuals by feeding behavior. Therefore, there was no evidence that the feeding behavior of ghost crabs can be considered as a potential early indicator of human disturbance.

Ghost crab predation of loggerhead turtle eggs across thermal habitats

The reproductive success of sea turtles is highly influenced by the environmental and biological conditions of the nesting beach. Maio Island, Cabo Verde, one of the main nesting sites for the Northeast Atlantic loggerhead subpopulation, displays marked heterogeneity of sand coloration, with dark, mixed and light sandy beaches, resulting in different thermal habitats. Considering that sand temperature can influence both sea turtle embryo development and predatory activity by ghost crabs – the main predators of clutches and hatchlings at Cabo Verde – we surveyed loggerhead nesting beaches at Maio Island, with three sand colorations (‘beach type’), to assess: 1) the density and size of ghost crab burrows, as a proxy for ghost crab density and size, and 2) ghost crab predation on 70 loggerhead nests. We further assessed nest site selection, by considering the number of nesting activities and clutches laid across beach type. There were no evident trends in the distributions of ghost crab density and size between years or beach type. We found that ghost crab predation is a major source of mortality in Maio Island, affecting 67.8% (n = 59) of the nests. Ghost crab predation was variable between beaches, but generally, at the warmer dark sand beaches, clutch mortality was mostly caused by ghost crab predation (53.2%, n = 17), while at the mixed sand beaches mortality by predation was low (7.5%, n = 18), compared to mortality due to other causes (49.9%), indicating that other factors can also significantly impact clutch survival. The mixed sand beaches had more nesting activities and higher nest density (2.29/m2; 1.25/m2, respectively), compared to the light sand (0.72/m2; 0.35/m2) and the dark sand beaches (0.73/m2; 0.27/m2), suggesting a possible predation-free nesting preference. Our findings show that some beaches are in need of nest protection, thus we recommend both in situ nest protection and egg translocation to safe hatcheries, depending on the threats identified, to enhance clutch survival at such heterogeneous nesting areas as Maio Island.

Light Sandy Beaches Favour Hatching Success and Best Hatchling Phenotype of Loggerhead Turtles

We conducted a 5-year field (2017–2021) and laboratory study of the relationship between type of substrate and hatching success, embryonic development, and the quality of hatchlings in loggerhead turtle nests. Our study site, the island of Maio in the archipelago of Cabo Verde, one of the world’s largest loggerhead turtle nesting colonies, displays marked heterogeneity of sand colouration, with dark, mixed, and light sandy beaches. We experimentally incubated eggs, comparing different nesting substrates under standard temperature and humidity conditions. Females nest in all sand types without preference. However, both the field and experimental study revealed a significant difference in hatching success depending on the type of substrate. Substrate of volcanic origin, dark in colour, with a lower amount of calcium carbonate, had a lower hatching success (HS; 30.3 ± 20.2%) compared to substrates of mixed (HS = 46.1 ± 26.5%) or light (HS = 78.1 ± 18.2%) colour. Eggs experimentally incubated in substrate that was light-coloured, with a larger grain size and higher calcium carbonate concentration, produced significantly more and larger offspring. Incubation temperatures were significantly higher in dark substrate, which partially explains the lower hatching success in this type of sand. However, experimental incubation with controlled temperatures consistently showed lower hatching success in dark sand. Thus, we found that not only the temperature, but also the specific characteristics of each substrate determine hatching success. The main predator of eggs and hatchlings (the ghost crab Ocypode cursor) showed no significant differences in abundance or size between different substrate types. Our results indicate that nest site selection between beaches or even within the same beach with different substrate conditions affects hatching success, hatchling physical condition, and subsequently the reproductive success of each female. The results of this study can inform conservation programmes with nest management and controlled incubation in the field and optimise adaptive nest management under future scenarios of rising global temperatures.

Factors influencing the feeding habits of the ghost crab Ocypode quadrata (Fabricius, 1787) on subtropical sandy beaches

Studies on feeding habits are fundamental to characterising the trophic role that species play in an ecosystem. They also help to understand the dynamics of populations involved in ecological relationships. Among the existing populations on tropical and subtropical sandy beaches in the world, the ghost crab (Ocypode) is the most conspicuous invertebrate. Despite its wide distribution, there is arguable information on the trophic ecology of this crab. Our study thus aimed to characterize the diet of the Ocypode quadrata on three morphologically distinct beaches in southern Brazil. Considering such factors as environmental differences, seasons, sex, and ontogeny, we evaluated which of these would be responsible for differences in the crab's food composition and quantity of items consumed. In addition, we used the repletion index (RI) to check the presence of food resource throughout the year. The samples were collected monthly, from March 2017 to February 2018, on three subtropical beaches in southern Brazil. We performed the biometry of the crabs, which involved weighing and measuring the size of the individuals, followed by the weighing of the stomachs to calculate the repletion index. We examined the contents of 660 stomachs, which were grouped into major food categories. Feeding index (IAi) indicates that feeding patterns varied only between seasons, demonstrating that the availability of prey is reflected in the diet of the ghost crab. The most significant items in its diet were insects, unidentified organic matter, and crustaceans. The RI tended to increase as the sand temperature increased. An increase in daytime foraging activity during cold months in contrast to a greater night-time foraging during warmer months shows a plasticity in the time of foraging. Finally, we conclude that the variety of prey consumed suggests that the O. quadrata has mainly opportunistic detritivorous feeding habits, as well as other feeding modes.

The complete mitochondrial genome of the Atlantic ghost crabOcypode quadrata(Fabricius, 1787) (Brachyura: Ocypodidae: Ocypodinae)

AbstractThe semi-terrestrial Atlantic ghost crab Ocypode quadrata (Fabricius, 1787) is a medium-sized species that inhabits the supralittoral zone in sandy temperate and tropical beaches of the western Atlantic Ocean. Despite the relevant ecological role of O. quadrata and its use as a bio-indicator, there are currently few genetic and genomic resources for this species. This study assembled and characterized in detail the complete mitochondrial genome of O. quadrata from Illumina short paired-end reads. The software NOVOplasty assembled and circularized the complete mitochondrial genome of the Atlantic ghost crab with an average coverage of 162×, per nucleotide. The AT-rich mitochondrial genome of O. quadrata is 15,547 bp in length, consisting of 13 protein coding genes (PCGs), 22 transfer RNA (tRNA) genes, and two ribosomal RNA genes (rrnL and rrnS). A single 685 bp long non-coding nucleotide region is assumed to be the D-loop/control region. The observed gene order in O. quadrata is identical to that reported for all congeneric species with known mitochondrial genomes. A selective pressure analysis indicates that all the PCGs are under purifying selection. Differences in KA/KS ratios among genes indicate strong purifying selection in the cox1, cox2, cox3, and atp6 genes, and weaker purifying selection in the atp8 gene. The 22 tRNA genes range from 64 to 70 bp in length, and all the tRNAs show a conventional “cloverleaf” secondary structure except for trnS1 that is missing the D-arm, in agreement to that reported for other brachyuran crabs with tRNA secondary depictions published. A maximum likelihood phylogenetic analysis based on all PCGs that included a total of 18 species of crabs fully supported the monophyly of the family Ocypodidae. The monophyly of the subfamilies Ocypodinae and Ucinidae was also highly supported by the analysis. These results suggest that mitochondrial PCGs have “phylogenetic signal” to reveal natural relationships at high taxonomic levels in crabs belonging to the family Ocypodidae. This study represents a new genomic resource for this ecologically relevant bioindicator ghost crab.

Anthropogenic beach-activities influences the endemic Red Sea Ghost Crab (Ocypode saratan)

International tourism and nature-recreation accounts for ca. > 10% of the international trade and has influenced urban planning, political thought, and land-use. Eilat, Israel, is just such a city of tourism-dependent development. We investigated whether beach tourism affected the ecology of the endemic Red Sea Ghost Crab (Ocypode saratan; RSGC). We hypothesized that we would find lower numbers of RSGC on the tourist beach because it results in the destruction of the burrows and the display pyramids of the male RSGC. All observations were conducted during August and September 2015, 2016, and 2018. We conducted a total of 221 h of observation of which 116 were on a beach without tourist activity i.e., of a fenced naval base beach and 105 on the tourist beach. We found that the number of crabs and those excavating sand from the burrows was highest at the tourist beach, while the number of pyramids was greater, and were higher, on the naval beach. Considering that the height of the pyramid and it’s complex are a reproductive signal for the females we speculate that there is segregation of beaches where on the tourist beach there are more food resources from anthropogenic activity and are occupied by large individuals, while on the navy beach the low human activity allows males to maintain higher pyramids, but which are built by the smaller individuals. Although we found that tourism appears to have benefited the RSGC population, the underlying effects of the food- web must be studied to understand the diet of the endemic species. Authorities need to regulate tourist activities and to educate them of the importance of the maintenance of a healthy environment and the conservation of biodiversity by placing appropriate billboards and signs at the tourist beach.

Social media in service of marine ecology: new observations of the ghost crab Ocypode quadrata (Fabricius, 1787) scavenging on Portuguese man-of-war Physalia physalis (Linnaeus, 1758)

Social media in service of marine ecology: new observations of the ghost crab Ocypode quadrata (Fabricius, 1787) scavenging on Portuguese man-of-war Physalia physalis (Linnaeus, 1758)

Use of attenuated total reflectance fourier transform infrared spectroscopy as a tool to determine effect of hot air-drying on yield (%) of chitin from crab integument

Washing, hot air drying, mechanical grinding, and chemical treatments are used to extract chitin from the integument of crustaceans (crabs). Variable drying times are documented in the literature, but none of the publications correlate drying time to the percent yield of chitin from crab integument, therefore this investigation. The effects of hot air-drying duration on the percent yield of chitin from Ocypode Ryderi (Pink Ghost Crab) (found along the east coast of South Africa) are investigated in this study. The impact of hot air drying on intermolecular changes inside the crab integument was investigated. Using an Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR Spectroscopy), the intermolecular interactions occurring within the crab integument with respect to hot air-drying period were observed. To cover a study gap, crab integument was dried at 0h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h,10h,11h, and 12h and extracted chitin at 0h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, and 12h. The highest chitin output was found after 12 hours of hot air drying.

Short-term effects of hurricane events on the bioindicator species Ocypode quadrata inhabiting an island in essence free of anthropogenic disturbances

The effects of high-energy weather events may be most dramatic on coast dominated by sandy beaches, characteristic habitat of the Atlantic ghost crab. This study evaluates the impact of two hurricanes over Ocypode quadrata populations based on the hypothesis that natural disturbances may bring on a decrease in crab burrow size (population structure) and/or a significant decline in the burrow density (relative abundance). Densities of crabs, estimated via burrow counts and their size, evaluated according to burrow opening diameter, were quantified at six sites around Isla de Aves, before (July) and after (November) two major hurricanes (Irma and Maria) that hit the coastal areas on islands of the Caribbean Sea in 2017. Six 2 × 2 m areas were sampled at each site. The results reveal an effect on the size structure, while the population density did not present any evident change between the pre and post-hurricane moments. The decrease in the diameter of the burrows after the passage of the hurricanes, suggests that the larger crabs could have been removed during this event followed by an arrival of new recruits into the ghost crab population. The results suggest a short-term resilience to the impact of extreme climatic events in terms of population density, a scenario that could had been favored by several conditions. Isla de Aves has sandy beaches exposed to ocean currents, which favor the transport of larvae and the recruitment of juveniles. The availability and quality of food, due to its characteristics of being a main nesting site for sea turtles (mainly green turtle); therefore, it offers various resources in abundance (e.g., turtle eggs). As well as the characteristic of being an island practically free of anthropogenic disturbances.

Unique Behavioral Strategies Adopted by Gravid Ghost Crab Ocypode gaudichaudii to Overcome Dehydration Stress while Minimizing Predation Risks.

Semi-terrestrial crabs require continual access to water to maintain life-sustaining processes such as circulation and feeding. When they emerge from their burrows during low tide to forage, they face the problem of dehydration as they leave the dampness of their burrows. While foraging above ground, water uptake is elicited through capillary action via the hydrophilic setae near the base of the crab's body. Extruded eggs that are borne on the abdominal flap of females tend to obstruct the contact of the setae with the wet sediment. The behavioral adaptations that enable the gravid female painted ghost crab, Ocypode gaudichaudii, to overcome dehydration stress and minimize predation risks at a sandy shore in Playa Venao, Panama were studied using field observations. Comparison of the morphometric measurements of setal tufts between 30 male and 30 female crabs was made to determine if there were morphological adaptations. Analysis of the water uptake behavior from video footage showed that gravid crabs spent a longer duration on water uptake than crabs that did not carry eggs. For the first time, masquerading behavior of a gravid O. gaudichaudii was observed, in which the crab minimized predatory detection by freezing its movement next to a stone enroute to the lower shore during the day. There was no sexual dimorphism in the length and width of the setal tufts between the male and female adult crabs. The results of this study provide the first evidence that the water-uptake behavior in gravid O. gaudichaudii is dependent on behavioral adaptations, as setal tuft morphology does not differ between the sexes.

Does Size Matter? The Case of the Courtship Pyramids in Red Sea Ghost Crabs (Ocypode saratan).

Simple SummaryMale ghost crabs (Ocypode spp.) are known to build sand structures near the entrance to their burrows. It has always been assumed that the structure played a role in sexual selection and mate attraction. We hypothesized that the larger males would make relatively larger pyramids in order to enhance fitness. We studied Red Sea ghost crabs at Eilat, Israel, and found that the larger crabs actually did not put much effort into building pyramids, and it was the medium-sized crabs that invested the most in building the pyramids.Display, wherein males attempt to maximize fitness by attracting sexually mature females to mate, is known to drive speciation by Sexual Selection. We researched the Red Sea Ghost Crab (Ocypode saratan; RSGC), in which males build display pyramids to attract females. The study was conducted at the beach in Eilat, Israel. At each session, we measured the height (in cm) of all pyramids and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the carapace width of the occupant. The mean (± SE) entrance volume was 230.8 ± 11.7 cm, and the height of the pyramid was 11.8 ± 0.49 cm (n = 54). The results of our study did not support our hypothesis because we had expected to find a linear correlation between body size and pyramid height, i.e., the larger the male, the larger the pyramid. However, our results show that the largest males in the population either built small pyramids or not at all, and the cut-off of the larger crab’s body size appears to be around 350 cm3. We discovered a step-wise function in the data in that crabs with the smallest body size of ca. 250 cm3 constructed the highest pyramids, with a declining tendency between 250–350 cm3 and extremely low pyramids beyond 350 cm3. However, our findings need to be further studied with a stress on the ambiance and elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are fast disappearing owing to anthropogenic development.

Beach profiling and ghost crab densities on a hawksbill turtle nesting beach in the Seychelles

Increasing beach sediment loss from erosion and high levels of crab Ocypode spp. predation are threatening turtle nests and nesting habitat. The 900 m long beach on Cousine Island, Seychelles, supports a nesting population of approximately 70–130 hawksbill turtle Eretmochelys imbricata nests each season. Seasonal and storm-related erosion and accretion cycles on Cousine Island have the potential of destroying 50% or more of all turtle egg clutches on the island in a single nesting season. Observed crab predation rates had reached 90–100% in preferred nesting beach zones in previous years. This has resulted in intensive management measures to minimise turtle egg and nest losses. We investigated the distribution and population density of ghost crabs and the morphology of the beach across the different beach area zones and across the turtle-nesting season during 2014–2015. Crab burrow numbers varied between beach zone areas and across the season and were highest on the backshore. Crab density correlated negatively with available beach area, and we found that crab density increased in the presence of turtle nests. When examining beach dynamics, we found them to be cyclical and found the nesting beach prone to higher levels of erosion than accretion with significant changes in beach width throughout the season. The mean vertical beach elevation drop on Cousine Island was higher than what hawksbill turtles have been reported to prefer. We suggest the continuation of beach elevation monitoring and management to use the beach morphology data to assist with hawksbill turtle nest translocations to minimise nest losses and maximise hatchling recruitment success.

Individual Laterality in Ghost Crabs (Ocypode saratan) Influences Burrowing Behavior

Behavioral handedness is known to enhance an individual’s handling capabilities. However, the ecological advantages in brachyuran crustaceans remain unclear, despite the Ocypode species having been studied extensively. Thus, in this study, we analyzed the laterality of the endemic Red Sea ghost crab on one beach in Eilat, Israel. We successfully documented the laterality of the large cheliped in 125 crabs; in 60 (48.0%), the right cheliped was larger, and in 64 (51.2%), the left. We also observed temporal segregation between the right- and left-clawed crabs. The right-handed crabs start activity just after sunrise, while left-handed crabs appear ca. 40 min after it. Similarly, temporal segregations were also observed in the evening. The right-clawed crab activity peaked ca. 20 min before sunset, while the left-clawed crabs were active uniformly. Additionally, burrow entrances corresponded to the larger cheliped of the resident individual and is probably a self-defense-related behavior. We conclude that cheliped laterality in O. saratan populations should be considered as a bimodal trait, where left- and right-handedness is not under natural selection pressure.

Hemolymph supply to locomotor muscles of the ghost crab Ocypode quadrata.

Ghost crabs are the fastest and most aerobically fit of the land crabs. The exceptional locomotory capacity of these invertebrate athletes seemingly depends upon effective coupling between the cardiovascular system and skeletal muscles, but how these systems are integrated has not been well defined. In the present study, we investigated the relationship between aerobic muscle fibers within the skeletal muscles used to power running and the blood vessels supplying these muscles. We used histochemical staining techniques to identify aerobic versus glycolytic fibers and to characterize membrane invaginations within the aerobic fibers. We also determined how the diameters of these two fiber types scale as a function of body size, across two orders of magnitude. Vascular casts were made of the blood vessels perfusing these muscles, and special attention was given to small, capillary-like vessels supplying the fibers. Finally, we injected fluorescent microspheres into the hearts of living crabs and tracked their deposition into different muscle regions to quantify relative hemolymph flow to metabolic fiber types. Collectively, these analyses demonstrate that ghost crab muscles are endowed with an extensive arterial hemolymph supply. Moreover, the hemolymph flow to aerobic fibers is significantly greater than to glycolytic fibers within the same muscles. Aerobic fibers are increasingly subdivided by membrane invaginations as crabs increase in size, keeping the diffusive distances relatively constant. These findings support a functional coupling between a well-developed circulatory system and metabolically active muscle fibers in these invertebrates.

Autotomy-induced effects on the locomotor performance of the ghost crab Ocypode quadrata.

The voluntary amputation of an appendage, or autotomy, is an effective defensive mechanism that allows an animal to escape aggressive interactions. However, animals may suffer long-term costs that can reduce their overall fitness. Atlantic ghost crabs (Ocypode quadrata) are one of the fastest terrestrial invertebrates, and regularly lose one or more limbs in response to an antagonist encounter. When running laterally at fast speeds, they adopt a quadrupedal gait using their first and second pairs of legs while raising their fourth, and sometimes the third, pair of legs off the ground. This suggests that some limbs may be more important for achieving maximal locomotor performance than others. The goal of this study was to determine whether the loss of certain limbs would affect running performance more than others, and what compensatory strategies were used. Crabs were assigned to four different paired limb removal treatments or the control group and run on an enclosed trackway in their natural habitat. Ghost crabs were found to adjust stride kinematics in response to limb loss. Loss of the second or third limb pairs caused a reduction in running speed by about 25%, suggesting that the remaining intact limbs were unable to compensate for the loss of either limb, either due to a lack of propulsive forces produced by these limbs or issues stemming from re-coupling limb arrangements. Loss of any of the other limbs had no detectable effect on running speed. We conclude that compensatory ability varies depending on the limb that is lost.

Low Densities of the Ghost Crab Ocypode quadrata Related to Large Scale Human Modification of Sandy Shores

Sandy beaches are the most common ecosystems of coastal regions and provide direct and indirect essential services for millions of people, such as coastal protection, fishing, tourism, and recreational activities. However, the natural habitats of sandy shores are being modified at rates never experienced before, making beaches key monitoring sites of marine ecosystems worldwide. The ghost crab species Ocypode quadrata is the most conspicuous crustacean of sandy beaches along the Western Atlantic coast and has been successfully used as an indicator of anthropogenic disturbance and environmental variability. To investigate the potential role of a “triple whammy” [(1) urbanization; (2) use of resources; (3) decreasing resilience] on the most common bioindicator of sandy shores, we compiled a dataset including 214 records of burrows density from 94 microtidal sandy beach sectors covering a range of over 65° of latitude. The response of burrows density to synergetic effects of human modification of natural systems and environmental changes was investigated using linear models. We used the cumulative Human Modification (HMc) index, a standardized geographic projection of changes of natural systems, as a predictor of urbanization, industrialization and use of resources. The predictor wave energy, tidal range and temperature (sea surface and air) were included as potential effects of climate changes. Literature review showed records mainly concentrated at sub-tropical and temperate regions. HMc values were clearly negatively related to burrows density, thereby supporting an effect of modification of natural habitat at large spatial scale. Sea surface temperature and air temperature were positive related with density and the lack of a general pattern of the relationship between burrows density, interactions between wave energy and tide range, supported unclear patterns reported at regional scales. Finally, we argue that ghost crabs are valuable targets for protection actions on sandy beaches that can benefit coexisting species and provide natural habitat conservation.

Burrow occupation rates and spatial distribution within habitat of the ghost crab Ocypode quadrata (Fabricius, 1787): Implications for impact assessments

The most conspicuous characteristic of ghost crabs (Crustacea: Ocypodidae) is the construction of semi-permanent burrows on the sand, widely used as tools for impact assessments. Thus, it is now critical to understand the factors driving burrowing activity and burrow occupation rates, including the effects of natural and anthropogenic disturbances. We tested three hypotheses in the present study with the ghost crab Ocypode quadrata: (i) overestimation of population size by traditional burrow counts depends on disturbance level at local scale; (ii) burrow occupation rate is density-dependent; and (iii) the predominant spatial distribution of burrows within the habitat is uniform. The last two predictions were assessed using a meta-analysis for a macro scale assessment. The comparison of distinct methods for burrow counting confirmed that ghost crab density is overestimated on non-urbanized beaches at local scale. A non-linear relationship between burrow occupation rates and burrow density was found at local and regional scales. When burrow density increases, the burrow occupation rate is also higher. However, from approximately 20 to 30 burrows/100 m2, the occupation rate reduces with increased density. Thus, the overestimation of the ghost crab density on non-urbanized beaches can be partially explained by a density-dependence in burrowing activity probably driven by a stronger intraspecific competition on non-urbanized areas. Finally, the distribution pattern of the ghost crab is predominantly uniform in most of its distribution range, despite of urbanization level and sampling design, hence suggesting intra-specific interactions as a driver of burrowing behaviour. In conclusion, burrow density, occupation rate and spatial distribution within the habitat evidenced at various spatial scales that burrowing activity of the ghost crab is density-dependent and this constitutes an issue never considered before in impact assessments inherent to coastal monitoring and management.