Invasive Crab Research Articles

Donor-side and user-side evaluation of the Atlantic blue crab invasion on a Mediterranean lagoon

The recent invasion of Callinectes sapidus in the Lesina Lagoon has raised great concern about its potential impacts on the ecosystem and on local fisheries. The effects of the blue crab presence on the receiving ecosystem were evaluated from both a donor-side perspective, through the application of emergy analysis, and a user-side perspective, by means of interviews to the local fishermen. While emergy analysis showed that C. sapidus brings to an increase of both natural capital and ecosystem functions values, results from interviews highlighted that the major problem caused by the presence of the blue crab in the lagoon concerned the local economy. As the first quantitative assessment of the ecological and economic impact of C. sapidus in invaded habitats, the present investigation provided original and useful information for a comprehensive risk assessment of the species in European waters and in Mediterranean Sea.

Is the population increase of an invasive portunid crab (Charbydis hellerii) a concern? The effect on native prey

Biological invasions have the potential to change the local marine biodiversity through increasing predation pressure and interactions among species. Charybdis hellerii is a swimming crab native to the Indo-West Pacific, it was first collected in the Atlantic Ocean in 1987 and is currently found in high abundance in coastal areas of southeastern Brazil. We evaluated the presence of the invasive crab C. hellerii from the coast of São Paulo state, Brazil, analyzing the stomach contents and performing laboratory-based feeding experiments. In crabs with stomachs full enough to be analyzed (N = 19), mussels (30%) and brachyuran crabs (14.21%) were the most frequent prey items found. Based on these data, we experimentally tested how different densities and life stages (adults and juveniles - differentiated by carapace width - CW) of the invasive crab affected feeding patterns. Results indicated that predator density effects on the predation pressure were dependent on the prey type. Mussels were consumed highest at medium predator densities (30 crabs/m3), whereas crabs were consumed highest at high predator densities (60 crabs/m3). There was no influence of the life stage on prey consumption, suggesting that adults (CW = 57.12–67.59 mm) and juveniles (CW = 39.77–43.18 mm) exhibit similar predation. Charybdis hellerii is an important consumer of benthic native prey, having the potential to change food webs through predation pressure on bioengineers and associated fauna. As the removal of C. hellerii from the environment is difficult, the next step toward is to understand the effect of the invasive crab on the native trophic web.

Impacts of an invasion by green crab Carcinus maenas on the intertidal food web of a Patagonian rocky shore, Argentina

The green crabCarcinus maenas(L., 1758) is a highly invasive species that has altered various coastal marine ecosystems worldwide. Green crabs were first found on the Argentinian Patagonian coast in 2001 and were detected in Golfo Nuevo (Chubut, Argentina) in 2015. In this study, we described a rocky intertidal food web in the Golfo Nuevo and evaluated the effect of green crab invasion on the network. We assembled the intertidal food web from a compilation of diet studies and compared 2 scenarios: pre-invasion (without green crab) and post-invasion (with green crab). We calculated several structural network metrics to compare the scenarios. The green crab was positioned as a top predator in the intertidal food web, consuming prey from different trophic levels and exhibiting the capacity to exert top-down control. Green crab presence altered the structure and stability of the food web. Additionally, we evaluated the effect of potential competitive interactions between native species and the green crab on the food web. Possible competitive interactions increased the effect the green crab had on the structure of the food web. Our results show that green crab invasion decreased food web stability by reducing the capacity of the food web to contain small- and long-range disturbances. These results contribute to the assessment and monitoring of the possible effects of other factors of global change. The system is less stable than before green crab invasion, and the drastic changes in community composition already recorded in rocky intertidal ecosystems in Patagonia are more likely to amplify through the food web.

Shelter Color Selection of Juvenile Swimming Crabs (Portunus trituberculatus)

Color preference testing for animals is a prerequisite for optimizing facilities and ensuring animal welfare in aquaculture. Swimming crabs (Portunus trituberculatus) are aggressive, and shelters are often installed in ponds to reduce the high mortality rate caused by their agonistic behavior. To test the preference of juvenile crabs for the color of shelters, this study observes the preferences of crabs for shelters of different colors (white, yellow, blue, and black). The counts and duration of crabs occupying different colored shelters were quantified. The probability of fighting and the probability of abandoning the shelter were also calculated. The results revealed that: (i) when all colors were presented simultaneously, the z-scores of the blue shelters were far higher than others during the day; (ii) when only one color was present, crabs occupied the blue shelter significantly more often and for longer periods of time than others during the day, with invasive crabs exacerbating this preference; and (iii) the probability of fighting between crabs was relatively low in the presence of the blue shelter, and the probability of abandoning the shelter was significantly lower than that of others. Based on these results, blue shelters are recommended for use in swimming crab ponds.

Lack of anti-predator recognition in a marine isopod under the threat of an invasive predatory crab

The prey naïveté hypothesis suggests that the failure of prey to recognize novel predators as a threat is caused by a lack of anti-predator adaptations. We tested this hypothesis in a unique natural setting, where the isopod Idotea balthica encountered the rapidly spreading invasive crab, Rhithropanopeus harrissii. Earlier research had indicated high mortality of the isopods during exposure to R. harrissii. The isopod exerted no co-evolutionary history with any littoral crabs and thus the strong impact could be caused by lack of pre-adaptations towards the new predator species. We tested this hypothesis by studying the anti-predator responses of the isopods with water-born cues of R. harrissii and of the native predatory fish Perca fluviatilis. Compared to control water, the isopods lowered their activity when exposed to the fish cue. Instead crab cue did not induce anti-predator behaviour. We also tested the hypothesis that mortality caused by novel predator, similar to predation by P. fluviatilis, would result in differential selection for the two sexes and contribute to the evolution of personalities. However, we found no differences in anti-predator behaviour nor in mortality between the sexes or personalities of the isopods. The outcomes reveal an interesting evolutionary scenario, where predation by a local predator induce soft selection on prey characteristics, but an invasive species cause hard selection without differentiating between prey individuals. Our study—conducted in the dawn of the population outbreak of R. harrissii—provides an excellent reference point for studies resolving the evolutionary impacts of invasive predators on naïve prey.

Relevance of feeding ecology in the management of invasive species: Prey variability in a novel invasive crab

The diet composition of non-indigenous species (NIS) provides essential information to recognise potential impacts on ecosystems. This study examined the feeding ecology of the novel invasive crab Cronius ruber from demographic and seasonal perspectives. It identified 52 prey items in crab gut contents (n = 278), and more than 18% of the studied specimens had empty guts. The high-frequency prey belonged to Brachyuran (51.54%) and Polychaete (34.36%), followed by Echinidea (22.47%), Gastropoda (21.15%) and Perciformes (20.70%). Additionally, the night sampling showed prey that were not observed in the examined stomach contents. The daily ingestion rates based on polychaeta indicated more prey consumption by juveniles (<55 mm carapace width (CW)) and adults crabs (55 mm–75 mm CW) than the old adults (>75 mm CW). This falls in line with the number of prey items retained in individuals’ guts, which changed seasonally and in ontogenic groups. Moreover, the visual night observations showed that native predators foraged on the invasive crab. These predators were groupers, octopus and elasmobranchs. The seasonal and ontogenic differences observed in diet through the stomach content analysis and daily ingestion rates suggest that C. ruber eats a generalist diet. The dissimilarity analysis suggested possible resource partitioning in ontogenic groups. Our results could represent the baseline for future studies into the possible impacts of this invasive NIS, as well as some arguments to include C. ruber on the list of invasive alien species of European Union concern.

Range expansion of the invasive portunid crab Charybdis japonica in New Zealand

ABSTRACT Charybdis japonica, a large invasive portunid, has been recorded in New Zealand since its detection in the Waitematā Harbour in 2000. In this study, the distribution, invasion history, abundance and population structure were investigated for C. japonica across the North Island of New Zealand. This was done using various distribution data available, trapping across several sites and interviews with commercial fishermen. Charybdis japonica was detected in the previously uninvaded Tauranga, Ohiwa, Hokianga, Manukau Harbours and Great Barrier Island. The rate of spread for C. japonica is continuous, with harbours or estuaries hundreds of kilometres apart having detections every two to three years. Population abundances reported by commercial fishermen constantly increased, with no signs of stabilisation or decrease. Catches were male-biased, with female abundance varying seasonally. Several possible pathways and vectors may be responsible for this spread, including shipping and aquaculture, on top of dispersal of larvae by currents across the North Island. Further research is required to determine population sources, with findings providing important information for invasive species monitoring and management.

On the occurrence of the invasive Atlantic blue crab Callinectes sapidus Rathbun 1896 (Decapoda: Brachyura: Portunidae) in Sicilian inland waters

The Atlantic blue crab Callinectes sapidus Rathbun, 1896 is included among the worst invasive alien species in the Mediterranean Sea. Here, we report the finding of the species in two Sicilian rivers, the Irminio and the Imera Meridionale, where it was collected up to 6 km from the river mouths. Although several records of the species are already available from Italy, this is the first evidence of the occurrence of this invasive crab so far from the coastline in the whole country. In the light of the well-known impact of the Atlantic blue crab on the invaded water bodies, the monitoring of the species and appropriate mitigation strategies should be implemented in order to protect the threatened native biota of Sicilian inland waters.

Challenges in eDNA detection of the invasive European green crab, Carcinus maenas

The early detection of invasive species is essential to cease the spread of the species before it can cause irreversible damage to the environment. The analysis of environmental DNA (eDNA) has emerged as a non-harmful method to detect the presence of a species before visual detection and is a promising approach to monitor invasive species. Few studies have investigated the use of eDNA for arthropods, as their exoskeleton is expected to limit the release of eDNA into the environment. We tested published primers for the invasive European green crab, Carcinus maenas, in the Gulf of Maine and found them not species-specific enough for reliable use outside of the area for which they were designed for. We then designed new primers, tested them against a broad range of local faunal species, and validated these primers in a field study. We demonstrate that eDNA analyses can be used for crustaceans with an exoskeleton and suggest that primers and probe sequences must be tested on local fauna at each location of use to ensure no positive amplification of these other species.

Fish Assemblages of a Sub-Arctic Fjord Show Early Signals of Climate Change Response Contrary to the Benthic Assemblages

Arctic benthic ecosystems are facing high-speed environmental changes, such as decreased sea ice coverage, increased temperature and precipitations, as well as the invasion by non-indigenous species. Few sub-arctic fjords have the particularity to have an inner-most part forming a basin in which water remains very cold. Those fjords may offer a refugee for cold-water arctic species as well as a small-scale “laboratory” of the changes that arctic assemblages located at higher latitudes might face soon. The Porsangerfjord in Northern Norway is a sub-arctic fjord with an inner arctic part and face red king crabs Paralithodes camtchasticus invasion since the end of the 1990s. It offers a case study of the dynamics of arctic ecosystems facing multiple stressors, i.e., climate change and invasive species. Based on a time series of megabenthic invertebrates and bentho-demersal fishes over 2007–2019, a complex multivariate analysis (STATICO) was used to identify the trends in the relationship between taxa and the environment. We showed the main environmental changes in the fjord were the freshening of the water, the increase of the seabed current, and the decrease of the maximum sea ice extent. A strong along-fjord gradient was visible for both benthic and fish assemblages. Species richness and Shannon diversity of fishes significantly increased into the fjord, due to the arrival of warm-water species over time that overlapped with cold-water species that have seen their biomass significantly reduced. No significant decrease in the biomass of the cold-water benthic species was visible, which could indicate an efficient refugee effect of the inner fjord. Yet, this refugee effect could be unbalanced by the red king crab invasion as it is a predator of several arctic species. In the Porsangerfjord, fish species thus respond to climate change while megabenthic assemblages are more threatened by invasive species.

Severe, rapid and widespread impacts of an Atlantic blue crab invasion

The Atlantic blue crab (Callinectes sapidus) has rapidly invaded coastal environments in the western Mediterranean, but there is no consistent assessment of its impacts yet. We use interviews and long-term data series in the Ebro Delta (NE Spain) to: i) characterise the evolution of the blue crab invasion; and ii) identify its impacts. The blue crab was first recorded in 2012, but its expansion started around 2016, with an exponential increase in abundance between 2017 and 2018. Aquatic communities have tended to be dominated by the blue crab, coinciding with the steep and consistent declines of several species, including threatened and commercially exploited ones. Blue crab impacts seem to be exerted even at low abundances, arguably hindering the recovery of declining species. The blue crab is becoming a keystone species in invaded systems and efforts should be made to understand its many-folds impacts in order to prevent or mitigate them.

Trematode parasites have minimal effect on the behavior of invasive green crabs

Trematode parasites have minimal effect on the behavior of invasive green crabs

Leonora Sansay's Secret History of Land Crabs

Using an unusual scene of a land crab invasion as a focal point, this essay traces the symbolic significance of this crustacean in eighteenth-century natural history writing to illustrate how Leonora Sansay's Secret History; or, The Horrors of St. Domingo (1808) incorporated scientific modes of description to both express and diffuse American concerns over the Haitian Revolution. Through an emblematic reading of these creatures, it becomes apparent how Sansay drew on the land crab's symbolic significance, which developed as natural historians turned to these animals as a means to express concerns surrounding slavery, specifically the dangers posed by the enslaved to European colonization. From this perspective, the land crab invasion in Secret History becomes an instance in which Sansay both represents the dangers posed by the Haitian Revolution and draws on scientific modes of description to diffuse said concerns. This analysis of Secret History advances the case for the importance of considering the role of natural history in early American literature to understand the political commentaries found in the era's works of fiction.

Identifying economic costs and knowledge gaps of invasive aquatic crustaceans

Despite voluminous literature identifying the impacts of invasive species, summaries of monetary costs for some taxonomic groups remain limited. Invasive alien crustaceans often have profound impacts on recipient ecosystems, but there may be great unknowns related to their economic costs. Using the InvaCost database, we quantify and analyse reported costs associated with invasive crustaceans globally across taxonomic, spatial, and temporal descriptors. Specifically, we quantify the costs of prominent aquatic crustaceans — crayfish, crabs, amphipods, and lobsters. Between 2000 and 2020, crayfish caused US$ 120.5 million in reported costs; the vast majority (99%) being attributed to representatives of Astacidae and Cambaridae. Crayfish-related costs were unevenly distributed across countries, with a strong bias towards European economies (US$ 116.4 million; mainly due to the signal crayfish in Sweden), followed by costs reported from North America and Asia. The costs were also largely predicted or extrapolated, and thus not based on empirical observations. Despite these limitations, the costs of invasive crayfish have increased considerably over the past two decades, averaging US$ 5.7 million per year. Invasive crabs have caused costs of US$ 150.2 million since 1960 and the ratios were again uneven (57% in North America and 42% in Europe). Damage-related costs dominated for both crayfish (80%) and crabs (99%), with management costs lacking or even more under-reported. Reported costs for invasive amphipods (US$ 178.8 thousand) and lobsters (US$ 44.6 thousand) were considerably lower, suggesting a lack of effort in reporting costs for these groups or effects that are largely non-monetised. Despite the well-known damage caused by invasive crustaceans, we identify data limitations that prevent a full accounting of the economic costs of these invasive groups, while highlighting the increasing costs at several scales based on the available literature. Further cost reports are needed to better assess the true magnitude of monetary costs caused by invasive aquatic crustaceans.

Seasonal trophic ecology of the invasive crab Percnon gibbesi (Brachyura, Plagusiidae) in the southwestern mediterranean: Insights from stomach contents and stable isotope analyses

The invasive sally lightfoot crab Percnon gibbesi (H. Milne Edwards, 1853) has spread among the coasts of the Mediterranean Sea, including the coasts of Annaba Gulf (Algeria). Investigating the trophic position of the species and looking for the seasonal variations in the diet of this alien decapod was the aim of this study. To do this, samples of P. gibbesi were collected along Annaba coasts within a year. The traditional stomach content analysis (SCA) was integrated to the stable isotope analysis (SIA) of nitrogen and carbon to provide a comprehensive evaluation of the feeding ecology of P. gibbesi, and its within-year variability. Results highlighted, for the first time, significant seasonal variation in P. gibbesi diet, improving our understanding of its trophic plasticity and potential dietary overlaps with other herbivore species. Its feeding plasticity is an asset in the successful expansion of its distribution. Relating its diet composition through the different seasons with the interactions with native herbivores will be essential to fully appreciate the impact of the spread of P. gibbesi in the Mediterranean Sea.

Selection of shelter shape by swimming crab (Portunus trituberculatus)

Placing shelter is an effective way to mitigate cannibalism in the pond culture of swimming crab (Portunus trituberculatus). However, it is still unclear what shape of shelter the crabs prefer. To determine their preference for shelter shapes (circular, square, semicircular, and triangular), we quantified the counts and duration of the crabs occupying the different shelters. We also calculated the probability of fighting and abandoning these shelters. The results reveal that: (1) The z-scores for circular shelters were significantly higher than others, but the differences among the z-scores for square, semicircular, and triangular shelters were not significant. These indicate that the crabs had a significant preference for circular shelter when all four shapes were present in the same area. (2) When only one shape was present, the crabs spent more time occupying circular shelters and had a higher count of occupations. The differences in the counts and durations of occupation among the non-circular shelters were also not significant. (3) When the invasive crab was present, the occupancy counts and duration of the focal crab significantly increased, but its preference for the circular did not substantially change. (4) When only circular shelter was available, the aggression of the crabs was reduced, and the probability of abandoning shelter was also the lowest. These results suggest that swimming crabs have a preference for circular shelter and exhibit a relatively low willingness to fight in the arena with the circular shelter. The structural properties of circular shelters account for the observed preference of the crabs. The circular shelters are recommended to be used to reduce cannibalism and improve survival rates in swimming crab pond cultures.

Balanced polymorphism fuels rapid selection in an invasive crab despite high gene flow and low genetic diversity.

Adaptation across environmental gradients has been demonstrated in numerous systems with extensive dispersal, despite high gene flow and consequently low genetic structure. The speed and mechanisms by which such adaptation occurs remain poorly resolved, but are critical to understanding species spread and persistence in a changing world. Here, we investigate these mechanisms in the European green crab Carcinus maenas, a globally distributed invader. We focus on a northwestern Pacific population that spread across >12degrees of latitude in 10years from a single source, following its introduction <35years ago. Using six locations spanning >1500km, we examine genetic structure using 9376single nucleotide polymorphisms (SNPs). We find high connectivity among five locations, with significant structure between these locations and an enclosed lagoon with limited connectivity to the coast. Among the five highly connected locations, the only structure observed was a cline driven by a handful of SNPs strongly associated with latitude and winter temperature. These SNPs are almost exclusively found in a large cluster of genes in strong linkage disequilibrium that was previously identified as a candidate for cold tolerance adaptation in this species. This region may represent a balanced polymorphism that evolved to promote rapid adaptation in variable environments despite high gene flow, and which now contributes to successful invasion and spread in a novel environment. This research suggests an answer to the paradox of genetically depauperate yet successful invaders: populations may be able to adapt via a few variants of large effect despite low overall diversity.

Prey preferences of invasive (Hemigrapsus sanguineus, H. takanoi) and native (Carcinus maenas) intertidal crabs in the European Wadden Sea

AbstractInvasive predators can have wide-ranging effects on invaded ecosystems and identifying the prey spectra and preferences of invaders are important steps in assessing their potential impacts on native biota. In this study, we investigated prey preferences of two invasive crab species (Hemigrapsus sanguineus and Hemigrapsus takanoi) that recently invaded Europe's shores and compared them with preferences of native shore crabs (Carcinus maenas) of similar size. In laboratory experiments, all three crab species preferred animal over algal prey. In general, sessile mussels (Mytilus edulis) were preferred over motile amphipods (Gammarus locusta) by all three crab species but amphipod predation was lower in the invasive compared with the native crabs. For the two invasive crab species, this pattern was the same in treatments where prey was offered separately (no-choice treatments) or simultaneously (choice treatments), while for the native crabs, mussel preference disappeared in choice treatments. The general preference of mussels by all three crab species suggests that local invasions of crabs most likely lead to increased competition among crabs. In addition, given that local densities of invasive crabs are often much higher than those of native crabs, predation pressure on native mussels can be expected to strongly increase at invaded sites. In contrast, local predation pressure on amphipods may be less affected by the crab invasions. Further field studies are needed to establish the magnitude of competition and predation pressure exerted by the invaders under natural conditions.

Invasive Species Control: Predation on the Alien Crab Percnon gibbesi (H. Milne Edwards, 1853) (Malacostraca: Percnidae) by the Rock Goby, Gobius paganellus Linnaeus, 1758 (Actinopterygii: Gobiidae)

Invasive alien species (IAS) are one of the greatest causes of native species extinction. Indeed, they represent a global threat for biodiversity and can also affect the economy and human health. The colonization success of IAS is presumably not only due to their biological and ecological characteristics, but also to the lack of predators and/or parasites in the invaded new areas. In the present work, we demonstrate evidence of predation of the invasive alien crab Percnon gibbesi (H. Milne Edwards, 1853) by the Rock Goby Gobius paganellus Linnaeus, 1758. The diet of G. paganellus was studied analyzing the stomach content of 162 specimens collected in the central Mediterranean Sea. The results obtained from the calculation of the diet indices, namely, frequency of occurrence (%F), percentage weight (%W), percentage abundance (%N), and the Index of Relative Importance (%IRI), showed that small benthic crustaceans were the main prey types. Additionally, these indices and the Levins’ index (Bi) clearly indicated that the invasive crab P. gibbesi was by far the most abundant prey type in the diet of G. paganellus. The relevance of this predator–prey interaction and the role of native species for the biological control of invasive ones are discussed. We also provide a general view on the diet of G. paganellus and other biological and ecological aspects of specimens studied from the central Mediterranean Sea.

Size affects intraspecific aggression and response to predation threat in juvenile American lobsters

Intraspecific aggression and competition can govern access to food and shelter in many marine organisms, but these interactions can be impacted by life stage and presence of predators. Juvenile lobsters (Homarus americanus) have social hierarchies that govern access to valuable resources like food and shelter, but these hierarchies could be impacted by the presence of invasive green crabs (Carcinus maenas). The goal of this study was to determine whether the presence of green crab effluent affected aggressive behavior in different sizes of juvenile lobsters, with the hypothesis that all juvenile lobsters would be more likely to share shelter under threat of predation. Small juveniles (15 mm carapace length) and larger juveniles (45 mm) had substantially different interactions and responses to predator threat cues, with small individuals more likely to both fight over shelter and share shelter when exposed to green crab effluent. There were also several size-based behavioral differences in control treatments, as small juvenile lobsters challenged each other more frequently for shelter and spent vastly more time in the shelter, less time stationary outside the shelter, and less time fighting. Despite being vulnerable to green crab predation, larger juvenile lobsters were generally unaffected by crab chemical cues. This suggests that life history plays a strong role in predator avoidance behavior and that both lethal and nonlethal effects of invasive species on native prey can vary markedly with life stage. Future research should examine these crab-lobster interactions in lobster nursery habitats in the field, as invasive green crabs in these habitats could change behavior, activity patterns and survival of juvenile lobsters.