Native Crab Research Articles

The status of Clibanarius erythropus after a recent range expansion to Great Britain, with the highest latitude recording of a gravid individual

BackgroundIn 2016, the range of the hermit crab Clibanarius erythropus expanded to South West Britain for the second time. C. erythropus primarily lives in the Mediterranean and the Atlantic coast of Europe from the Bay of Biscay to Morocco. The species has now been recorded on both the north and south coast of the South West peninsula of the UK from Newtrain Bay, on the north coast of Cornwall, to Wembury, on the south coast of Devon. It is unknown if the crab’s reappearance in the UK has been caused by a one-off colonisation event or by a continued influx of larvae.ResultsThe population in the UK is made up of individual within a narrow size bracket, indicating a single colonisation event took place, and that the population is an ageing one. However, we also report the highest latitude recording of a gravid individual for the species.ConclusionA lack of gravid individuals was suggested to be why the species was unable to sustain its presence in the UK following a previous colonisation in 1960. This discovery hints that rising water temperatures may allow C. erythropus and other warm-water species to expand and sustain themselves in the UK. We also found crossover in shell utilisation between C. erythropus and the native hermit crab Pagurus bernhardus, suggesting that competition might occur between the two species.

Prey size selection in invasive (Hemigrapsus sanguineus and H. takanoi) compared with native (Carcinus maenas) marine crabs

AbstractIntroductions of predators can have strong effects on native ecosystems and knowledge of the prey size selection of invasive predators is pivotal to understand their impact on native prey and intraguild competitors. Here, we investigated the prey size selection of two invasive crabs (Hemigrapsus sanguineus and Hemigrapsus takanoi) recently invading European coasts and compared them with native shore crabs (Carcinus maenas) which are known to feed on similar prey species. In laboratory experiments, we offered different size classes of native blue mussels (Mytilus edulis) to different size classes of the crab species in an effort to identify the respective prey size preferences and potential overlap in prey size range of native and invasive crabs. In all three species, the preferred prey size increased with crab size reflecting general predator–prey size relationships. Prey size preference did not differ among the crab species, i.e. crabs showed similar mussel size preference in relation to carapace width. Given that additional morphological measurements showed that both of the invasive crab species have much larger claws relative to their body size compared with the native species, this finding was surprising and may relate to differential claw morphologies or structural strength. These results suggest that the invasive crabs exert predation pressure on the same size classes of native mussels as the native crabs, with potential effects on mussel population dynamics due to the high densities of the invaders. In addition, the overlap in prey size range is likely to result in resource competition between invasive and native crabs.

Physiological Effects of Limb Loss on the Asian Shore Crab, Hemigrapsus sanguineus

Invasive species pose a considerable threat to biodiversity and the functioning of the ecosystem. Hemigrapsus sanguineus (Asian Shore Crab) has outnumbered native crabs on the northeast coast of North America since shortly after its introduction in the late 1980s. Asian Shore Crabs occur in high densities along much of the Atlantic coast from Maine to North Carolina. Our research focused on the relationship between limb loss and energy use and storage in both male and female Asian Shore Crabs as a means of understanding their ability to reach high population densities. We sampled 154 crabs of both sexes from Odiorne Point State Park in Rye, NH. We then dissected the individual specimens and measured limb loss and the mass of the hepatopancreas (an energy storage organ) and gonads. Our findings reveal that limb loss has similarly limited impacts on male and female crabs in terms of both energy storage and reproductive effort. We conclude that despite a high frequency of injury, the energetics of Asian Shore Crabs were largely unaffected, and that this may be one reason why this species has been able to achieve sustained high densities throughout much of its invaded range.

A taste for aliens: contribution of a novel prey item to native fishes\u2019 diet

Non-indigenous species (NIS) can alter food web structure and function in many ways. While the predatory and competitive roles of NIS in aquatic environments are commonly studied, their role as a prey item for native predators is often overlooked. As the northern Baltic Sea lacks native crabs, the omnivorous estuarine Harris mud crab (Rhithropanopeus harrisii) is a novel invader to the system and provides an opportunity to observe how the species enters the prey field of predatory fish. In fall 2013, 1185 stomachs from 17 fish species were dissected and analyzed for the presence of R. harrisii. Fishermen had previously reported finding crabs mostly in the stomachs of perch (Perca fluviatilis), a frequent catch in recreational and commercial fisheries, but our study also found large numbers of crabs in four-horned sculpins (Myoxocephalus quadricornis) and small numbers in other species’ stomachs (Rutilus rutilus, Leuciscus ide, Gymnocephalus cernuus, and Blicca bjoerkna). In the study area occupied by R. harrisii, four-horned sculpins were the most frequent predator, with 83% having at least one crab in their stomach. In comparison, 7% of perch and roach had consumed R. harrisii. Most crabs eaten were 10–12 mm (carapace width), despite broader size range available (1–26 mm). Predation on R. harrisii in this system may be limited by the predators’ gape size (i.e., physical feeding restriction). These results highlight the need to understand the role of novel invasive species as prey items for native species, ultimately increase understanding of whether native predators can control NIS populations.

Competition between a native freshwater crab and an invasive crayfish in tropical Southeast Asia

The freshwater crayfish, Cherax quadricarinatus, has been introduced across many tropical regions globally. This popular aquarium and aquaculture species, similar to many other non-native crayfish, is widely establish and can negatively affect native populations and ecosystems. Studies quantifying the impacts of C. quadricarinatus, however, are notably lacking. This study aims to address this paucity through investigations of potential interspecific competition in the tropical Southeast Asia. Owing to the lack of native crayfish within Sundaic Southeast Asia, we focus on the interactions between C. quadricarinatus and Parathelphusa maculata, a tropical lowland freshwater crab. The native crab is a functional equivalent freshwater decapod crustacean that is found in forest streams with the non-native crayfish, and interaction between the two species can possibly result in population level changes. As such, we quantify the factors (i.e. aggressiveness, size, and species combinations) that are associated competitive outcomes (for shelter) via ex situ experiments; and utilize in situ surveys to determine if these factors can influence the distribution of both species in streams where they co-occur. Results indicate that an asymmetry resulting from large C. quadricarinatus being able to effectively outcompete smaller P. maculata can explain the negative correlation between the size of the two species in situ. This is congruent with the relative distribution patterns of the two species, and suggests that healthy populations of P. maculata (i.e., with a wider range of sizes, including larger individuals) can prevent/slow the spread of the alien crayfish in recipient habitats. Findings from this study represent an important first step towards understanding and managing the impacts of this increasingly popular and worrisome tropical non-native species.

Changes in Population Demography and Reproductive Output of the Invasive Hemigrapsus sanguineus (Asian Shore Crab) in the Long Island Sound from 2005 to 2017

Cross-intertidal transects at a western Long Island Sound estuary site provided estimates of the density of the non-native Hemigrapsus sanguineus (Asian Shore Crab) from 1998 to 2017, and measurements of crab size (carapace width; CW) from 2005 to 2017. Since 2001, average intertidal density declined by ∼5% per year. This decline was driven by decreases in the density of larger crabs, with consequent reductions in average and maximum sizes of both males and females. The proportion of the largest crabs (>24 mm CW) dropped from 10.1% of the population in 2005 to 1.4% in 2017. Individual reproductive output scales with size; thus, I estimate the loss of the largest females to have reduced population reproductive output by half between 2005 and 2017. Also, the frequency of ovigerous females in the smallest reproductively mature classes (12–14 mm CW) increased. Though the density and average size of Asian Shore Crab have declined significantly, resident and native crab populations have still not recovered.

Native herbivores enhance the resistance of an anthropogenically disturbed salt marsh to Spartina alterniflora invasion

AbstractThe extent by which human activities create an inroad for the invasion of exotic plant species and the mechanisms that drive a disturbed ecosystem's resistance to exotic invasion is largely unknown. We investigated the mechanisms by which salt marsh resists cordgrass (Spartina alterniflora) invasion by two key factors: anthropogenic disturbance by ditching and herbivory by the native crab Helice tientsinensis. In northern China, although abiotic resistance (i.e., hyper‐stresses) inhibited the landward invasion of cordgrass to high marshes, our transplant experiments showed that anthropogenic ditching created windows of opportunity for cordgrass invasion to high marshes by enhancing propagule pressure and providing favorable (i.e., low‐salinity and high‐inundation) microhabitats for colonization. Furthermore, a native herbivore exclusion experiment showed that crab grazing strongly suppressed seedling establishment and growth of cordgrass in ditched high marshes, which gradually created native biotic resistance to cordgrass invasion. We conclude that grazing by native herbivores can enhance the resistance of high marshes to cordgrass invasion triggered by anthropogenic ditching disturbance in northern China. These findings highlight that it is critical to investigate ecosystem resistance associated with anthropogenic disturbance to better understand the multiple mechanisms of exotic plant invasion, and we call for integration of these findings into invasion control strategies.

Apple seed stocks affected scion tree vigor and performance based on maternal self(in)compatibility

In a breeding program to increase uniformity of apple saplings size, shape and vigor the genetic improvement of seed rootstocks was considered as a key point. The Half-Sib seeds of two selected native crab parents, self-compatible “Morabbaei” and self-incompatible “Azayesh”, both dwarf, were considered as the main sources of variances into the six grafted scions. The inductive effects of the two seed masses were assessed on vegetative traits of 6 and 7-year-old scion trees. According to the results, shoot length, shoot thickness and internode length as main components of tree vigor showed significant differences at 1% level in all the six scions. The shoot length mean of the grafted scions on “Azayesh” seed progeny was higher than “Morabbaei” seed stock. The grafted scions on self-compatible “Morabbaei” seed stock gave place to the shoots with higher thickness than the same grafted on “Azayesh” seed source. Combinations of “Red Delicious”-“Morabbaei” and “Braeburn”-“Azayesh” demonstrated max and min values of internodes length during two consecutive years. Both rootstock and scion trunk diameters on self-incompatible “Azayesh” seeds resulted higher than seed progeny of self-compatible “Morabbaei”. Shoot number was not affected by rootstock type, whereas the effect of rootstock × scion, scion and year resulted significant.

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.

Native versus invasive crab effluent effects on byssal thread production in the mussel, Mytilus trossulus (Gould, 1950)

Mussels have evolved many adaptations to protect themselves, including the production of byssal threads. These are strong, proteinaceous fibres that mussels secrete to adhere themselves to rocks, preventing detachment by waves and predators. These byssal threads may be strengthened if mussels can recognize potential threats, such as native crabs, as their populations have a long history of coevolution. Unfortunately, the introduction of invasive predators poses a challenge for prey, which may not be capable of recognizing them. In this study, byssal thread production in the Pacific blue mussel (Mytilus trossulus ) was observed when exposed to effluent from the native red rock crab (Cancer productus) or the invasive European Green crab (Carcinus maenas). M. trossulus were placed in closed systems with effluent from either C. productus , C. maenas or control (no predator), over a 24-hour time period. Final measurements of number, length and diameter of byssal threads were recorded. M. trossulus exposed to effluent from C. productus produced byssal threads at a statistically significantly faster rate than in the control group over the first 7.5 hours. M. trossulus exposed to effluent from C. maenas produced byssal threads at a statistically significantly faster rate than both the C. productus and control groups. However, after 24 hours, there was no statistically significant difference between the mean number of byssal threads for any treatment. Additionally, we found no statistically significant difference between the mean diameter of byssal threads produced or length of byssal threads produced for any treatment.

Comparing residence time and natural enemies between low- and high- density invasions

Ecological and historical factors influence the probability that a known invader will experience success in new locations. Using field and laboratory studies, we investigated how residence time and natural enemies (co-evolved castrating parasite, and native crabs) differ between two introduced populations of the intertidal snail, Batillaria attramentaria. The populations have substantially different invasion histories (~ 10 vs. > 80 years) and exhibit markedly different densities and tidal distributions. The less-dense, vertically-restricted population was recently introduced, and thus has potentially had less opportunity to fill the fundamental niche at that site. However, no increase in density or intertidal range occurred in this population over 10 years, suggesting that it had reached its realized niche. The newer population experienced much greater effects of native cancrid crabs than the older, high-density population, particularly below the minimum tidal elevation of observed snail distribution, where crabs were found in the greatest densities. Prevalence of parasite infection did not differ between populations. This is the first study documenting effects of predators on this invasive snail, which is widespread along coastlines of the northeast Pacific, whereas previous studies have suggested that the primary restriction on population growth rate was likely to be parasitic castration. Further, this study supports the general understanding that, while novel predators can reduce the impacts or population growth rates of invasive species, such top-down effects are not likely to preclude persistence at a given site.

Assessing the aggregated risk of invasive crayfish and climate change to freshwater crabs: A Southeast Asian case study

Primary freshwater crabs represent a culturally and ecologically significant component of freshwater habitats globally that has a high percentage of threatened species. Invasive species (especially non-indigenous crayfish) and climate change are not only important standalone threats, but are also expected to compound existing threats (e.g., habitat loss/modification, pollution) and challenge the long-term survival of these decapod crustaceans. This study illustrates the importance of considering these two emerging and growing threats in conservation or management strategies by quantifying (via species distribution models) the individual and aggregated risks of these threats in Southeast Asia, a region with the highest diversity of primary freshwater crabs and a high proportion of imperiled species. Results predicted that most species of crabs (82.1%) will co-occur (and hence interact) with invasive crayfish to a moderate to high degree, and most species (69.2%) will also experience a reduction in suitable climate conditions in the future. In terms of aggregated risk, the results also predict an increased overlap between invasive crayfish and native crabs for three out of the seven species analyzed (namely Procambarus virginalis, Cherax destructor and Orconectes rusticus). Findings from this study provide a quantitatively derived rationale for the development of adaptive regulations and conservation plans in the region to minimize the risk of invasive species in a cost-effective way, thereby enabling the protection of Southeast Asia's natural heritage and its vital ecosystem services.

Effects ofSpartina alternifloraInvasion on the Diet of Mangrove Crabs (Parasesarma plicata) in the Zhangjiang Estuary, China

Gao, X.; Wang, M.; Wu, H.; Wang, W., and Tu, Z., 2018. Effects of Spartina alterniflora invasion on the diet of mangrove crabs (Parasesarma plicata) in the Zhangjiang Estuary, China.Spartina alterniflora, an exotic invasive plant, has become the most serious threat colonizing mangrove areas in China in the past two decades. The diets of a dominant mangrove crab, Parasesarma plicata, in two mangrove habitats (Kandelia obovata forest and Avicennia marina forest) and adjacent S. alterniflora marsh in a subtropical mangrove estuary in Fujian, China, were investigated using stable isotopes, while a feeding experiment was carried out. The results showed that in the Avicennia forest, Parasesarma was herbivorous, feeding mainly on macroalgae. In the Kandelia forest, the contribution of mangrove leaves, macroalgae, and sediment to the diet of Parasesarma were about 75.5%, 24.2%, and 0.2%, respectively. While Parasesarma had a higher δ13C value and also a higher δ15N value in the Spartina marshes relative to the two mangrove habitats, suggesting that they were feeding on Spartina detritus as well as some small invertebrates. The feeding experiment showed that the δ13C value of Parasesarma after 90-day feeding only on Spartina leaves was very close to the δ13C value of the crab caught from the Spartina marshes, indicating that Spartina was the main carbon source. These results demonstrated that the invasion of Spartina has changed the main food resources of native crabs by providing food resources, which could affect the impact of crabs as ecological engineers and eventually affect the integrity and function of native ecosystems.

Genetic diversity and genetic structure of farmed and wild Chinese mitten crab (Eriocheir sinensis) populations from three major basins by mitochondrial DNA COI and Cyt b gene sequences

The Chinese mitten crab, Eriocheir sinensis, is one of the important native crab species in East Asian region, which has been widely cultured throughout China, particularly in river basins of Yangtze, Huanghe and Liaohe. This study was designed to evaluate the genetic diversity and genetic structure of cultured and wild E. sinensis populations from the three river basins based on mitochondrial DNA (mtDNA) cytochrome oxidase subunit I (COI) and cytochrome b (Cyt b). The results showed that there were 62 variable sites and 30 parsimony informative sites in the 647 bp of sequenced mtDNA COI from 335 samples. Similarly, a 637 bp segment of Cyt b provided 59 variable sites and 26 parsimony informative sites. AMOVA showed that the levels of genetic differentiation were low among six populations. Although the haplotype diversity and nucleotide diversity of Huanghe wild population had slightly higher than the other populations, there were no significant differences. There was no significant differentiation between the genetic and geographic distance of the six populations, and haplotype network diagram indicated that there may exist genetic hybrids of E. sinensis from different river basins. The results of clustering and neutrality tests revealed that the distance of geographical locations were not completely related to their genetic distance values for the six populations. In conclusion, these results have great significance for the evaluation and exploitation of germplasm resources of E. sinensis.

Distribution and ecological relations among the alien crab, Percnon gibbesi (H. Milne-Edwards 1853) and autochthonous species, in and out of an SW Mediterranean MPA

The distribution of the allochthonous crab Percnon gibbesi and its relationships with other benthic invertebrate species was assessed inside the marine reserve of Cabo de Palos—Islas Hormigas (Mediterranean sea, Spain) and neighbouring non-protected sites. Although a significant spatial variability was detected at finer spatial scale, there was no influence of protection measures or insularity on the abundance of P. gibbesi. The presence of small holes, encrusting algae and low slope favour the colonization success of this crustacean, and the spatial distribution of these habitat features could explain the observed pattern. The abundance of P. gibbesi was similar to that of native crab species; however, a non-significant negative relationship between the abundance of P. gibbesi and native crabs (Pachygrapsus marmoratus and Eriphia verrucosa), urchins (Arbacia lixula and Paracentrotus lividus) and a snail (Phorcus turbinatus) was observed. This work highlights the importance of monitoring alien crab population densities taking structural habitat and other potentially influential factors into account and the likely effect of this alien species on the native ones.

Clash of the crabs: Interspecific, inter-cohort competition between the native European green crab, Carcinus maenas and the exotic brush clawed crab Hemigrapsus takanoi on artificial oyster reefs

Interaction between cohorts was investigated with juveniles of the native crab Carcinus maenas and adults of the exotic crab Hemigrapsus takanoi on artificial, intertidal oyster reefs. The reefs are occupied by C. maenas seasonally as a nursery habitat and consistently by adult H. takanoi. There was a distinct decrease in abundance of C. maenas of the same carapace width as most adult H. takanoi, suggesting competition at this size was occurring. Laboratory experiments indicated that H. takanoi was a more aggressive competitor for food and, with consistently high abundance on the reefs, may result in some exclusion of C. maenas from their nursery habitat. While total exclusion of C. maenas on the oyster reefs is unlikely, cohabitation may result in reduced population size or increased use of alternative nursery habitats.

Native crab and crayfish co-occurrence: First evidence in Europe

AbstractCases of co-occurrence among freshwater decapods are few. In their European range, the crab

Foraging at a safe distance: crab spider effects on pollinators

1. The ability of pollinating insects to discover and evade their predators can affect plant–pollinator mutualisms and have cascading ecosystem effects. Pollinators will avoid flowers with predators, but it is not clear how far away they will move to continue foraging. If these distances are relatively small, the impact of predators on the plant–pollinator mutualism may be lessened. The plant could continue to receive some pollination, and pollinators would reduce the time and energy needed to search for another patch.2. A native crab spider, Xysticus elegans, was placed on one cluster in a small array of Baccharis pilularis inflorescence clusters, and the preferred short‐range foraging distances of naturally visiting pollinators was determined.3. Nearly all pollinator taxa (honey bees, wasps, other Hymenoptera, and non‐bombyliid flies) spent less time foraging on the predator cluster.4. The key result of this study is that inflorescences within 90 mm of the crab spider were avoided by visiting honey bees and wasps, which spent three‐ and 18‐fold more time, respectively, foraging on more distant flower clusters.5. Whether honey bees can use olfaction to detect spiders was then tested, and this study provides the first demonstration that honey bees will avoid crab spider odour alone at a food source.

Understanding and forecasting dispersal of non-indigenous marine decapods (Crustacea: Decapoda) in East European and North Asian waters

A survey of publications and collections databases reveals a pattern of non-indigenous decapods distribution in the 13 seas around Russia and adjacent countries. No alien species were reported from Russian territorial waters and exclusive economic zone in the Japan, Okhotsk, west Bering and most of the Siberian shelf Seas. From the seas and their basins in East Europe, 13 alien species have been recorded, with seven of these yet to become established. Established or commonly occurring species can be categorized as: ‘global invaders’ (Chinese mitten crab,Eriocheir sinensisin the White, Baltic, Black, Azov and Caspian Seas; and Harris mud crab,Rhithropanopeus harrisiiin all mentioned seas, except the White Sea); ‘regional aliens’ (Palaemon adspersusandP. elegansin the Caspian Sea and the latter species in the Baltic); and ‘Arctic invaders’ (Kamchatka king crabParalithodes camtschaticusand snow crabChionoecetes opilio).Eriocheir sinensisis the most widely occurring alien decapod species, but there are no indications of an established population in East Europe. For this and other mentioned crab species, invasion history, distribution and important biological data are reviewed. In the seas where few or no native crab species have been present, Harris mud crab (in the Azov and Caspian Seas), Kamchatka crab (in the Barents Sea) and snow crab (in the Barents and Kara Seas) have shown rapid establishment (within two decades) of an invasive population throughout an entire basis or its significant part.

The trophic position of the alien crab Rhithropanopeus harrisii (crustacea decapoda panopeidae) in the Taman Bay, Sea of Azov community

This work concerns the trophic web positioning of the alien crab Rhithropanopeus harrisii and other common marine invertebrate species and fishes in the benthic ecosystem of the shallows of Taman Bay, Sea of Azov. The base of the trophic web in this system is composed of phytoplankton, macrophytes (algae and marine grasses), and reeds that use atmospheric carbon for photosynthesis. Analysis of the isotopic composition of nitrogen and carbon has shown that although marine grasses are dominating primary producers in the shallows of the bay, primary consumers (such as Cerastoderma glaucum, Porifera gen. sp., Gammarus aequicauda, Deshayesorchestia deshayesii and Idotea balthica) only partially use this organic source; instead, they use a combination of different sources of primary production. It has been shown that the food source of the alien crab is primarily of animal origin. In Taman Bay, R. harrisii is on the same trophic level as other carnivores/scavengers: benthic fishes Syngnathus nigrolineatus, Gobius spp. and native crab Pilumnus hirtellus and shrimp Palaemon adspersus.