Asian Shore Crab Research Articles

Genetic Variation in the Asian Shore Crab Hemigrapsus sanguineus in Korean Coastal Waters as Inferred from Mitochondrial DNA Sequences

Genetic variation in the Asian shore crab Hemigrapsus sanguineus was determined from partial mitochondrial DNA (mtDNA) sequences of the cytochrome b (Cytb) gene. Samples included 143 crabs from six localities along three coastlines in South Korea. A nucleotide sequence analysis revealed 38 variable sites in a 470-bp sequence, which defined 37 haplotypes. The haplotypes were not associated geographically and had a shallow genealogy. Pairwise <TEX>$F_{ST}$</TEX> tests and a two-dimensional scaling analysis revealed no significant genetic differentiation among most of the populations. The low pairwise comparison values, but significant genetic differentiation of a northeastern population from all other populations, might have been influenced by a restriction in gene flow caused by hydrographic conditions such as ocean boundaries. The high haplotype diversity, low nucleotide diversity, and time since H. sanguineus expansion in Korean coastal waters indicate rapid population growth and a recent, sudden expansion in the Late Pleistocene.

Development and behavior of megalopae of the non-native crab Hemigrapsus sanguineus in response to chemical cues from coastal fishes

Understanding the invasibility of marine species with complex life cycles requires examination of the ecology of both larval and adult stages. The goal of our study was to determine whether several species of coastal fish native to the western North Atlantic Ocean can consume megalopae of the nonindigenous Asian shore crab Hemigrapsus sanguineus and, if so, whether megalopae can respond to chemicals from potential fish predators by either molting faster to a benthic crab stage or exhibiting avoidance behaviors. Laboratory predation experiments showed that all fish species tested (cunner, Tautogolabrus adspersus; tautog, Tautoga onitis; grubby, Myoxocephalus aeneus; scup, Stenotomus chrysops; and mummichog, Fundulus heteroclitus) consumed H. sanguineus megalopae. When megalopae were reared in seawater in which fish or adult crabs had been housed, fish chemical cues had no effect on molting rate whereas chemicals from adult conspecific crabs accelerated molting. Behavioral responses of H. sanguineus megalopae to chemicals from fish and crabs were tested in still and flowing water. In still water, megalopae moved away from chemicals from T. adspersus and M. aeneus. In flowing water, chemicals from T. onitis caused a behavioral reaction that led to enhanced movement away from the source of the cue. All 3 species are related to fishes present in the native range of H. sanguineus. In contrast, chemicals from adult crabs and F. heteroclitus had no effect on behavior of megalopae. Behavioral responses of H. sanguineus megalopae to chemical cues from coastal fish species might function as antipredator strategies that enhance survival of this nonindigenous species.

Prey selection in crustacean-eating fishes following the invasion of the Asian shore crab Hemigrapsus sanguineus in a marine temperate community

The Asian shore crab Hemigrapsus sanguineus invaded the coast of Long Island Sound approximately twenty years ago and has become hyper-abundant and the most common crab species throughout the intertidal region. The success of the species is hypothesized to be due to reduced predation pressure in the invaded region. Recent observations document the expansion of H. sanguineus into shallow subtidal habitats (i.e., up to 5m depth and up to 180 crabs m−2 in some habitats) where it is more accessible to a diversity of crustacean-eating predators. The role that higher trophic level predators might play in controlling populations of invasive species has seldom been investigated in marine communities. Here we conducted a series of prey-preference experiments under laboratory conditions to determine whether crustacean-eating fishes prefer H. sanguineus rather than native crab species, and to provide insight into how predator size and habitat type influence prey preference. Small size-class predators exhibited a clear preference for H. sanguineus in paired offerings of the invader versus native crab species while paired offerings for large size-class fishes resulted in mixed findings. Small size class predators demonstrated no preference when prey were set in a range of sediment type treatments (i.e., sand, pebble, cobble), while paired offerings for large size class predators resulted in mixed findings. In general, the results from this study support our hypothesis that H. sanguineus is preyed upon preferentially by native crustacean-eating fishes but sediment type and predator size play an important role in determining that preference. Preference for the invasive crab over the native prey items in some settings suggests prey switching could occur in areas where the invader is abundant. We suggest that future field studies focus on the role that crustacean-eating fishes can play in biological control of invasive crab populations and how management of predators can influence the impact of invaders.

Predicting regional spread of non-native species using oceanographic models: validation and identification of gaps

Predicting spread is a central goal of invasion ecology. Within marine systems, researchers have increasingly made use of oceanographic circulation models to estimate currents and track species dispersal. However, the accuracy of these models for predicting biological patterns, particularly for non-native species, has generally not been validated. Particularly, we wished to examine the ability of models to predict physical and biological processes, which jointly determine the spread of marine larval organisms. We conducted two empirical studies—a recruitment study and a drift card study—along the coast of New England, USA, focusing on two invaders of concern—the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), to explicitly evaluate the ability of oceanographic models to predict patterns of spread. We used data from the large-scale drift card study to validate our ability to capture dispersal patterns driven purely by physical processes. Next, we conducted a recruitment study to evaluate our ability to reproduce patterns of biological dispersal. We were generally capable of reproducing drift cards patterns—suggesting that the physical mechanics in the model were predictive. However, predicted biological patterns were inconsistent—we were able to predict dispersal patterns for H. sanguineus but not for C. maenas. Our results highlight the importance of validating models and suggest that more work is necessary before we can reliably use oceanographic models to predict biological spread of intertidal organisms.

Hemigrapsus sanguineus (De Haan, 1835) (Crustacea: Brachyura: Grapsoidea) a new invasive species in European waters: the case of the French English Channel coast (2008-2010)

The unintentional introduction of the Asian shore crab, Hemigrapsus sanguineus, along the French coast during the mid 1990s has revealed the problematic effects that invasive species can have on biodiversity, entering into competition with native crab species. This invasion along coastal ecosystems of northern France has become an ineluctable, irreversible phenomenon. The present study describes the distribution and abundance of H. sanguineus along the French side of the English Channel from the Cotentin to the Opal Coast on the Dover Strait in spring and summer 2010. The results were compared with those obtained previously in 2008 and 2009 for the same areas and now show that the crab has increased in numbers since its first sighting in 1999. In 2010, the maximal abundance reached 51 ind.m -2 in Dunkirk harbour, and 69 ind.m -2 at La Hougue in the eastern part of the Cotentin Peninsula. Hemigrapsus sanguineus has been sighted all along the southern coastline of the English Channel to the North Sea (approximately 1,500 km). Its high colonisation potential suggests that this brachyuran could continue its invasion in European waters. Therefore a European surveillance network might be necessary to monitor its progression in the north-eastern Atlantic Ocean.

Genetic diversity of the Asian shore crab, Hemigrapsus sanguineus, in Korea and Japan inferred from mitochondrial cytochrome c oxidase subunit I gene

The genetic diversity and population history of the Asian shore crab, Hemigrapsus sanguineus, were investigated with a nucleotide sequence analysis of 536 base pairs (bp) of the mitochondrial cytochrome c oxidase subunit I gene (COI) in 111 samples collected from four populations in Korea and one in Japan. In total, 28 haplotypes were defined by 27 variable nucleotide sites in the COI region examined. The observed haplotypes had a shallow haplotype genealogy and no geographical associations. Most of the populations had high haplotype diversity (0.656–0.788) and low nucleotide diversity (0.00165–0.00244), and significant negative values for Fu's F S , suggesting rapid and recent population growth from an ancestral population and sudden population expansion. The pairwise fixation indices (F ST) estimated with the exact test and the migration rates indicate that substantial gene flow occurs among these populations as a result of sea currents, except between the Yellow Sea coast of Korea (BUA) and the Pacific Ocean coast of Japan (JPA). These two populations (BUA and JPA) showed significant genetic differentiation and low migration rate.

Reduced fecundity by one invader in the presence of another: A potential mechanism leading to species replacement

As invasive species proliferate and expand their ranges, they often interact either with natives or with other invasives across a broad geographic range. Moreover, because geographic ranges span a diversity of environments, the outcome of interactions between species pairs may vary spatially. The European green crab Carcinus maenas and the Asian shore crab Hemigrapsus sanguineus are both introduced species in North America where they co-occur over a large portion of the Atlantic coast. While interactions between the two crabs in the southern portion of this range within Long Island Sound resulted in the elimination of C. maenas within 2–3 years of H. sanguineus' arrival, species replacement appears to be taking much longer in northern areas within the Gulf of Maine. Previous work implicates predation by H. sanguineus on C. maenas recruits as the mechanism underlying species replacement. Here we explore an alternative or additional mechanism underlying this species replacement that can also account for the observed spatial variation in the timescale of species replacement between northern and southern areas. Specifically, we demonstrate that a previously documented shift in C. maenas diet which occurs in the presence of H. sanguineus can cause a reduction in C. maenas fecundity. This, combined with near-shore current patterns may explain the regional differences in the outcome of this species interaction.

Does consumer injury modify invasion impact?

Predicting the impacts of an invasive species solely by its abundance is common, yet it ignores other potentially important moderating factors. One such factor is injury. Severe injury can lead to mortality, which can directly reduce the abundance of the invader. However, more moderate, sublethal injury can also temper the impact of invasive species. Therefore, to predict impacts, it may be useful to examine not only abundance, but also moderating factors (e.g., injury) and predictors of these factors (e.g., density, size). We documented the density, injury (i.e., limb loss), and size of two conspicuous invaders, the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), at thirty sites from Shinnecock County Park, New York to Lubec, Maine. In addition, we used a field experiment to determine how injury influenced the consumption rate of mussels (Mytilus edulis) by each crab species. 31.6% of all C. maenas (1,493/4,721) and 30.7% of H. sanguineus (2,003/6,523) were missing append- age(s). Of the crabs injured, 38.4% (573/1,493) and 30.5% (611/2,003) were missing cheliped(s) for C. maenas and H. sanguineus, respectively. In our experiments, cheliped loss reduced consumption of both species on M. edulis .I njuredC. maenas consumed 21% fewer mussels than uninjured crabs. Injury completely eliminated mussel consumption by H. sanguineus. Previous studies have highlighted the detrimental impacts of these two invaders on native bivalve prey. While the loss of a single cheliped can greatly reduce or even eliminate the ability of C. maenas and H. sanguineus to consume M. edulis, our results suggest that injury has a relatively minor role in reducing overall population-level impacts on prey such as mussels. However, injury on an individual-level can play a role in moderating the consumptive impacts of these invaders.

Mating and Sperm Storage of the Asian Shore CrabHemigrapsus sanguineus

The Asian shore crab Hemigrapsus sanguineus is the principal invasive crab in many intcrtidal habitats on the east coast of the United States between Cape Hatteras and Maine. Previous work has described general aspects of mating for the genus Hemigrapsus; however, there has been no explicit study of mating behavior in H. sanguineus, and there has been little consideration of how this behavior might influence the success of H. sanguineus as a bio-invader. The objective of our investigation was to document the mating behavior of H. sanguineus under laboratory conditions and compare this pattern of behavior with that of other species of Hemigrapsus. Our observations show that mating in H. sanguineus was always initiated by the male and that both the male and female had calcified exoskeletons at the time of copulation. Small males were sometimes successful in securing mates, even in the presence of larger males. However, the male was larger than the female in 67% of the observed copulations. Duration of copulation in H. sanguineus was relatively long compared with other species of Hemigrapsus, and averaged ∼30 min. H. sanguineus differs from other species of Hemigrapsus in terms of positioning during mating. H. sanguineus typically used a vertical position relative to the substratum, with both crabs standing and facing each other, ventral surface to ventral surface. This position facilitated some degree of mobility in the copulating pair. Females were receptive to copulation within a few days of larval release, and were also capable of storing sperm and producing at least 2 broods from a single copulation. Mean incubation time of newly extruded eggs was around 16 days, and females often produced a second brood within a few days of larval release. Thus, an individual H. sanguineus could produce 2 broods within 40 days and presumably additional broods with subsequent copulation. This pattern of reproduction provides enhanced fecundity relative to co-occurring native species of crabs.

An empirical probability model of detecting species at low densities

False negatives, not detecting things that are actually present, are an important but understudied problem. False negatives are the result of our inability to perfectly detect species, especially those at low density such as endangered species or newly arriving introduced species. They reduce our ability to interpret presence-absence survey data and make sound management decisions (e.g., rapid response). To reduce the probability of false negatives, we need to compare the efficacy and sensitivity of different sampling approaches and quantify an unbiased estimate of the probability of detection. We conducted field experiments in the intertidal zone of New England and New York to test the sensitivity of two sampling approaches (quadrat vs. total area search, TAS), given different target characteristics (mobile vs. sessile). Using logistic regression we built detection curves for each sampling approach that related the sampling intensity and the density of targets to the probability of detection. The TAS approach reduced the probability of false negatives and detected targets faster than the quadrat approach. Mobility of targets increased the time to detection but did not affect detection success. Finally, we interpreted two years of presence-absence data on the distribution of the Asian shore crab (Hemigrapsus sanguineus) in New England and New York, using our probability model for false negatives. The type of experimental approach in this paper can help to reduce false negatives and increase our ability to detect species at low densities by refining sampling approaches, which can guide conservation strategies and management decisions in various areas of ecology such as conservation biology and invasion ecology.

Molting of megalopae of the Asian shore crab Hemigrapsus sanguineus in intertidal habitats of Northeastern North America

Planktonic larvae of many benthic taxa settle and metamorphose in response to certain habitat cues. Although laboratory investigations of the importance of potential cues are numerous, field experiments are less common. We modified a field caging technique first developed for analysis of molting specificity of fiddler crab megalopae to test potential habitat cues affecting molting of megalopae of the non-native Asian shore crab Hemigrapsus sanguineus (de Haan). Potential cues consisted of waterborne substances from 2 potential habitats (cobble beach and salt marsh), and the material used to construct experimental cages. Experiments were conducted in 2002, 2003, and 2004 in Massachusetts and New York (USA). Megalopae (4 or 5 d post molt) were placed in either nylon mesh (500 μm) cages open to flooding seawater or transparent glass jars containing filtered seawater. Cages and jars were placed at identical intertidal heights at the field sites and retrieved 3 or 4 d later. The proportion of megalopae molting to the first crab stage was determined after the period of field exposure and for 2 d thereafter. More megalopae molted in cages than jars placed in the adult habitat (cobble beach) and in a marsh without adults. The cage mesh had little effect on molting response. We conclude that waterborne cues stimulate molting of H. sanguineus megalopae, and that cues are present in both the adult habitat and marsh. Molting of H. sanguineus megalopae is substantially less habitat-specific than molting of native fiddler crab megalopae.

Response of the Asian shore crab Hemigrapsus sanguineus to metamorphic cues under natural field conditions

For brachyuran crabs like Hemigrapsus sanguineus, survival past the planktonic life stage requires settlement out of the water column onto appropriate benthic habitat, followed by metamorphosis to the 1st juvenile stage. In the laboratory, H. sanguineus has been shown to respond to cues produced by conspecific adults and to various cues associated with the substratum. The objective of the present investigation was to determine the response of megalopae to cues produced by natural populations of adult H. sanguineus. In this study, laboratory-reared megalopae were deployed in cages at four locations along each of two transects that extended 20 m from rocky intertidal habitat that contained a dense population of adult H. sanguineus. One transect extended perpendicular to shore and into open water, while the second extended parallel to shore and adjacent to salt-marsh habitat. The percentage of megalopae undergoing metamorphosis was greatest in the cages that were closest to the adult population and diminished with distance from that population, regardless of transect. Moreover, a comparison of cages at comparable positions on the respective transects showed lower percentage metamorphosis in cages on the marsh transect than on the open-water transect. Our findings are coherent with results of previous laboratory studies and indicate that H. sanguineus megalopae can sense water-soluble metamorphic cues produced by conspecific adults at distances up to a few meters from the source.

Discovery ofMaritrema jebuensisn. sp. (Digenea: Microphallidae) from the Asian Shore Crab,Hemigrapsus sanguineus, in Korea

Maritrema spp. (Digenea: Microphallidae) are parasites of birds, but have not been found in the Republic of Korea. In this study, metacercariae of Maritrema sp. were discovered in the Asian shore crab, Hemigrapsus sanguineus, caught in the mud-flats of Jebu-do, Hwasung-gun, Gyeonggi-do, and the adult flukes were confirmed by experimental infection into mice. Based on the symmetric ribbon-like vitellarium, adult flukes of Maritrema sp. were identified, but did not belong to previously described species in terms of the following morphologic characteristics: ceca reaching to the lateral wall at the anterior border of the ovary; ventral sucker larger than oral sucker; a prominent metraterm; and vitellarium forming a complete ring. Hence, we named this microphallid M. jebuensis n. sp. after the island where the second intermediate hosts were collected. From this study, it has been shown that Maritrema sp. is distributed in Korea and transmitted by the Asian shore crab, H. sanguineus.

Asian Shore Crabs Hemigrapsus spp. (Crustacea: Brachyura: Grapsoidea) continue their invasion around the Cotentin Peninsula, Normandy, France: Status of the Hemigrapsus population in 2009

This paper reports on the state of the Asian shore crab Hemigrapsus sanguineus (de Haan, 1835) population around the Cotentin Peninsula (Normandy, France) for 2009. As in 2008, the year of the first survey, the northern and eastern Cotentin coasts remain the most densely colonised. On the western shore, H. sanguineus remains rare, except in two sites not surveyed in 2008. In the east most colonised sites, Gatteville-Phare and La Hougue, the populations for both years indicate a rapid increase of abundance: maximum density > 50 .ind.m -2 in 2009 compared to 10 ind.m -2 in 2008. This observation probably demonstrates that the species' current significant increase is comparable to that of an invasive species. A second species of Asian shore crab Hemigrapsus takanoi Asakura & Watanabe, 2005 was only present on one eastern site off Saint-Vaast-La-Houge, but remains isolated.

Characterization of the conspecific metamorphic cue for Hemigrapsus sanguineus (De Haan)

The Asian shore crab, Hemigrapsus sanguineus, is one of the most abundant invasive crabs along the east coast of the United States. Larval stages are generally planktonic, but the megalopa stage settles to the substratum near the time of metamorphosis. Reducing the time to metamorphosis may result in higher recruitment and survival. Previous work has shown that a water-soluble cue produced by adult H. sanguineus can induce metamorphosis of conspecific megalopae. Here we report the results of experiments in which megalopae were exposed to cues produced by different life stages of H. sanguineus. We also provide data from experiments that investigated the temporal stability, detection threshold, and chemical classification of the cue. Our results indicate that an active cue is produced by juveniles as well as adults. The cue is proteinaceous and begins to degrade within 2 days of production. The threshold for detection of the cue by megalopae lies between 0.1 and 0.01 µg of protein per ml.

Induction of metamorphosis in the Asian shore crab Hemigrapsus sanguineus: Characterization of the cue associated with biofilm from adult habitat

Recruitment of crabs to nursery habitat requires settlement of the megalopal stage on suitable substratum followed by metamorphosis into the first juvenile stage. Reducing the time to metamorphosis may result in higher recruitment and survival. Previous work has shown that metamorphosis of the Asian shore crab is accelerated by cues from three different sources: (a) water-soluble exudate produced by conspecific adult crabs; (b) biofilm covering rocks in natural habitat for this species; and (c) abiotic rock from natural habitat. The objective of the present investigation was to characterize the metamorphic cue associated with biofilm from rocky intertidal habitat and to compare the three metamorphic cues (exudate from conspecific adults, biofilm from rocky intertidal, and texture of substratum) that have been identified for H. sanguineus. Results of our study show that megalopae of the Asian shore crab respond strongly to biofilm associated with rocky intertidal habitat that has developed for at least 8 days. We also found that megalopae respond to textured rock surfaces from natural habitat, even when those surfaces had been rendered abiotic. The cue remains active after the biofilm has been exposed to − 20 ºC for 12 h, but is de-activated by a few minutes exposure to 100 °C. Moreover, the biofilm cue appears to work in synergy with cues from other sources, but requires actual contact with the biofilm. Our findings show that addition of biofilm to an abiotic textured rock surface significantly decreases mean time to metamorphosis, and simultaneous exposure of megalopae to biofilm-covered rock and to exudate from adult H. sanguineus decreases mean time to metamorphosis even further. The response of this species to multiple cues—and particularly to biofilm in the absence of adult conspecifics—provides a clear advantage in the colonization of virgin habitat and helps explain the very rapid spread of this invasive species along the majority of the east coast of the United States in only two decades.

Differential escape from parasites by two competing introduced crabs

Although introduced species often interact with one another in their novel communities, the role of parasites in these interactions remains less clear. We examined parasite richness and prevalence in 2 shorecrab species with different invasion histories and residency times in an introduced region where their distributions overlap broadly. On the northeastern coast of the USA, the Asian shorecrab Hemigrapsus sanguineus was discovered 20 yr ago, while the European green crab Carcinus maenas has been established for over 200 yr. We used literature and field surveys to evaluate parasitism in both crabs in their native and introduced ranges. We found only 1 parasite species infecting H. sanguineus on the US East Coast compared to 6 species in its native range, while C. maenas was host to 3 parasite species on the East Coast compared to 10 in its native range. The prevalence of parasite infection was also lower for both crabs in the introduced range compared to their native ranges; however, the difference was almost twice as much for H. sanguineus as for C. maenas. There are several explanations that could contribute to C. maenas’ greater parasite diversity than that of H. sanguineus on the US East Coast, including differences in susceptibility, time since introduction, manner of introduction (vector), distance from native range, taxonomic isolation, and the potential for parasite identification bias. Our study underscores not just that non-native species lose parasites upon introduction, but that they may do so differentially, with ramifications for their direct interactions and with potential community-level influences.

Recent expansion of two invasive crabs species Hemigrapsus sanguineus (de Haan, 1835) and H. takanoi Asakura and Watanabe 2005 along the Opal Coast, France

Nowadays, invasions of invertebrate species in coastal ecosystems have become an ineluctable and irreversible phenomenon. The recent introduction of two western pacific crustacean decapods—the Asian shore crab, Hemigrapsus sanguineus, and the brushclawed shore crab, Hemigrapsus takanoi—along the French coast has revealed the problematic effects that invasive species can have on biodiversity and also the competition that invasive species represent for native crab species. This study describes the distribution and abundance of both Hemigrapsus species along the Opal coast on the French side of the Dover Strait in spring 2008. Both species occupy habitats similar to that of the green crab, Carcinus maenas. However, the habitats colonised by the two species are clearly segregated: low hydrodynamic muddy habitats for H. takanoi and high hydrodynamic habitats with fine and medium sands for H. sanguineus. Both species can live in sympatry in harbours. In spring 2008, the maximum density outside Dunkirk harbour was 12 ind.m for H. sanguineus, and inside Dunkirk harbour, the maximum density was 60 ind.m for H. takanoi. In this location, H. takanoi dominated C. maenas significantly. No ovigerous females of either invasive species were found during the spring. Both species have high colonisation potential, ranging from south of the Bay of Biscay to Germany for H. takanoi and from the western part of the English Channel to Germany for H. sanguineus.

Use of Subtidal Habitat by the Asian Shore CrabHemigrapsus sanguineusin Long Island Sound

Abstract Hemigrapsus sanguineus Asian Shore Crab is an introduced but now common crab found intertidally along the Connecticut coastline. Little is known of its subtidal occurrence. This species was found to be seasonally abundant subtidally, at depths varying from 1.3–3.9 m, during a 2-year study conducted within a commercial marina in Clinton Harbor, CT. Hemigrapsus sanguineus was trapped at three subtidal locations, with highest concentrations observed during the winter. A total of 2020 crabs were caught: 1255 males, 741 females, and 24 crabs that were 9 mm or smaller and sexually indistinguishable. Large males with carapace widths between 45–48 mm were captured at all three locations. These sizes are among the largest reported for this species. This work documents year-round use of subtidal habitat by Asian Shore Crab in Long Island Sound.

Establishment of the invasive Asian shore crab Hemigrapsus sanguineus (De Haan, 1835) (Crustacea: Brachyura: Grapsoidea) from the Cotentin Peninsular, Normandy, France

The occurrence of the invasive Asian shore crab Hemigrapsus sanguineus (de Haan, 1835), around the Cotentin Peninsular, Normandy, France, is reported. The northern and eastern Cotentin coasts are more densely colonised (maximum density ≅ 10 ind.m -2 ) than western shore, where the crab remains rare. These colonisation and establishment demonstrate probably the western progression of the species from its initial introduction into the Le Havre harbour during 1999.