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By shuffling biogeographical distributions, biological invasions can both disrupt long-standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host-parasite interactions. In estuaries of the Gulf of Mexico, the white-fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle, Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behaviour. In the 1960s, L. panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host's transcriptomic response to parasitic infection and investigate how this response varies with the parasite's invasion history, comparing populations representing (i) long-term sympatry between host and parasite, (ii) new associations where the parasite has invaded during the last 60 years and (iii) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and moulting. The transcriptional response differed between hosts from the parasite's native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite's introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host-parasite interactions.

Rhithropanopeus harrisii are small, estuarine crabs native to the Atlantic and Gulf coasts of North America. They have become an invasive species, establishing populations on the west coast of the United States, Europe, Panama, and Japan. Reproducing populations are also established in freshwater reservoirs in Texas and on the Texas/Oklahoma border. In order to compare levels of genetic diversity within introduced reservoir populations with those of native estuary populations and to determine possible source populations and routes of colonization among Texas reservoir populations, we obtained mitochondrial DNA sequences from reservoirs and several estuaries along the Texas and Louisiana coast. Overall, genetic diversity within reservoirs was lower than within estuaries; however, some reservoirs exhibited relatively high levels of genetic diversity indicating that they were founded by numerous individuals or individuals from divergent source populations. In contrast, two genetically divergent reservoir populations had greatly reduced genetic diversity suggestive of extreme founder effects. All estuary and reservoir haplotypes formed a monophyletic group separate from Atlantic coast haplotypes, thus colonization of Texas reservoirs occurred from the Gulf Coast as expected based on geographic proximity. There was minimal DNA sequence divergence among Gulf Coast and reservoir haplotypes and a lack of phylogeographic structure among estuary populations. However, there was significant population divergence among some estuaries based on haplotype frequencies. Genetic differences among estuaries were subtle in most cases, preventing identification of source populations using mitochondrial DNA sequences.

Non-native marine crustaceans can exert detrimental impacts on native marine communities by altering habitat and ecosystem function. The Mediterranean Sea is particularly vulnerable to introductions of non-native crustaceans, as evidenced by their remarkably high establishment success. In this study, 20 species of non-native marine crustacean decapods and barnacles of which eleven extant and nine ‘horizon’ were screened for their potential invasiveness in the Mediterranean Sea. Using the Aquatic Species Invasiveness Screening Kit and including an additional nine native species to increase accuracy, calibrated risk thresholds of 3.5 for the BRA (Basic Risk Assessment) and 8.5 for the BRA + CCA (BRA + Climate Change Assessment) were obtained that distinguished reliably between invasive and non-invasive species. All 20 non-native species were classified as carrying a high risk of invasiveness for the Mediterranean Sea, both for the BRA and the BRA + CCA. Chinese mitten crab Eriocheir sinensis was by far the highest risk species, followed by Harris mud crab Rhithropanopeus harrisii, Asian shore crab Hemigrapsus sanguineus, bay barnacle, Amphibalanus improvisus, and lesser swimming crab Charybdis (Goniohellenus) longicollis. The findings of this study will provide management and control directions for non-native marine crustaceans in the Mediterranean Sea, with special emphasis on regulations regarding ballast waters, which represent one of the main introduction pathways for these aquatic organisms.

Highlights: • Salinity can be highly variable spatiotemporally in enclosed sea systems. • Functional response of invasive mud crab Rhithropanopeus harrisii quantified. • Invasive crab feeding followed a hyperbolic Type II functional response. • Feeding rates were highest at 10 ppt and 7 ppt compared to 4 ppt. • Ecological impacts are reduced at the lowest salinity level. Abstract: Environmental gradients may alter the ecological impacts of invasive alien species. In marine systems such as the Baltic Sea, current salinity is variable and seawater freshening is projected in future, potentially facilitating novel keystone predators. Here, we examine the influence of salinity variation in the western Baltic Sea (i.e. ambient 10, then 7 and 4 ppt) on the functional response (FR) of the Harris mud crab Rhithropanopeus harrisii towards benthic macroinvertebrate prey at different densities. Rhithropanopeus harrisii displayed a Type II FR across salinities towards larval chironomids, due to a consistently high resource consumption rate at low prey densities. Feeding rates were significantly reduced at 4 ppt (mean 6 chironomid prey killed day−1) compared to 10 ppt and 7 ppt (9 killed day−1). Search efficiencies tended to be greatest at 10 ppt, whereas handling times were shortest — and maximum feeding rate highest — at the intermediate 7 ppt. These results suggest a slight reduction in predatory impact by R. harrisii at lower salinities. Nevertheless, across most prey densities, FRs were not significantly different, indicating sustained interaction strength across a range of salinity regimes.

Parasitism can represent a potent agent of selection, and introduced parasites have the potential to substantially alter their new hosts' ecology and evolution. While significant impacts have been reported for parasites that switch to new host species, the effects of macroparasite introduction into naïve populations of host species with which they have evolved remain poorly understood. Here, we investigate how the estuarine white‐fingered mud crab (Rhithropanopeus harrisii) has adapted to parasitism by an introduced rhizocephalan parasite (Loxothylacus panopaei) that castrates its host. While the host crab is native to much of the East and Gulf Coasts of North America, its parasite is native only to the southern end of this range. Fifty years ago, the parasite invaded the mid‐Atlantic, gradually expanding through previously naïve host populations. Thus, different populations of the same host species have experienced different degrees of historical interaction (and thus potential evolutionary response time) with the parasite: long term, short term, and naïve. In nine estuaries across this range, we examined whether and how parasite prevalence and host susceptibility to parasitism differs depending on the length of the host's history with the parasite. In field surveys, we found that the parasite was significantly more prevalent in its introduced range (i.e., short‐term interaction) than in its native range (long‐term interaction), a result that was also supported by a meta‐analysis of prevalence data covering the 50 years since its introduction. In controlled laboratory experiments, host susceptibility to parasitism was significantly higher in naïve hosts than in hosts from the parasite's native range, suggesting that host resistance to parasitism is under selection. These results suggest that differences in host–parasite historical interaction can alter the consequences of parasite introductions in host populations. As anthropogenically driven range shifts continue, disruptions of host–parasite evolutionary relationships may become an increasingly important driver of ecological and evolutionary change.

Anthropogenically influenced habitats are becoming increasingly impacted by multiple invasive species that can regionally control main ecological processes and functions. Management requires predictions of invasive species’ effects, but multiple invasions may cause unpredictable outcomes, for example, synergistic impacts or interactions among trophic levels causing trophic cascades. The Baltic Sea is prone to species invasions that increasingly occur at multiple trophic levels. We used a laboratory experiment to test whether multiple invasive predators may cause interactive effects in the Baltic Sea. In aquaria, we simulated a coastal community that has developed dominated by invasive species—the decapod predators Palaemon elegans and Rhithropanopeus harrisii, the amphipod grazer Gammarus tigrinus, and the filter‐feeder Dreissena polymorpha. The orthogonal experiment determined separate and interactive effects from predators on the lower trophic level invasive species and native algae including the foundation species Fucus radicans. The main result was that while both predators significantly impacted the community, in no cases were their effects interactive. Another important result was that P. elegans appeared to cause a trophic cascade, as in its presence F. radicans and its epiphytes had the greatest biomass while G. tigrinus grazers were heavily reduced. G. tigrinus were negatively correlated with F. radicans biomass, so variable amphipod grazing may be the link allowing an indirect effect of P. elegans on F. radicans. R. harrisii also reduced G. tigrinus abundance but did not affect F. radicans biomass. Both predators significantly affected the lengths of F. radicans plant stems that were comprised of new vegetative growth—P. elegans reduced the lengths of new vegetative tissue while R. harrisii increased it. Thus, the presence of P. elegans induced shorter and denser F. radicans bushes compared to taller and thinner bushes observed in other treatments. Lastly, R. harrisii caused significant declines in D. polymorpha numbers. Overall, ecological management needs to consider positive effects from predator invasion which may reduce grazing pressure on low trophic level foundation species. A trophic cascade involving two invasive species highlights the importance of multi‐species approaches to management of Baltic Sea invasive species and in other regions prone to biological invasions.

The present investigation aimed to estimate the individual growth and mortality of an invasive species found in the estuarine region of Patos Lagoon (Southern Brazil). For 20 months crabs were sampled, and in the laboratory specimens of Rhithropanopeus harrisii (Gould, 1841) were measured (carapace width, CW, and weight). Carapace width data was utilized for a modal progression analysis and to estimate the individual growth curve (von Bertalanffy growth model), and a size-converted catch curve. Von Bertalanffy parameters estimated were CW∞ = 16.92 mm and k = 1.28 year-1. Maximum longevity was estimated at 3.5 years. Instantaneous total mortality was estimated at 2.17 ± 0.30 year-1. It has been suggested that longevity may be explained by a low predation impact on R. harrisii, which, as a consequence, may lead to slow individual growth of this species in the estuarine region of Patos Lagoon.

Long-term population data of marine invaders are rarely collected although it provides fundamental knowledge of the invasion dynamics that is important for evaluating the impacts, interactions and range expansion of the invader and for management purposes. During a 6-year monitoring period, we studied the dynamics and population demographic characteristics of the newly introduced mud crab Rhithropanopeus harrisii. The overall abundance of R. harrisii appeared to follow the boom and bust pattern with a rapid initial abundance increase and subsequent decline. The recruitment and growth of juveniles were correlated with the temperature during the larval period indicating that the increase in water temperature caused by climate change could have a positive effect on the recruitment and have potentially facilitated the establishment of R. harrisii in the northern Baltic Sea. The changes in the survival of reproductive females influence most the growth rate of the studied population. Hence, native predators feeding on benthic fauna such as fish could regulate the population growth of R. harrisii in the study area by reducing female survival. Although the population size seems to be stabilized at the monitoring locations, R. harrisii continues to expand its distribution range, and the rapid initial population increase is likely occurring at newly invaded sites.

The Harris mud crab Rhithropanopeus harrisii recently expanded into much of the Baltic Sea. This invasion is expected to have significant effects on the structure and functioning of benthic ecosystems due to the lack of native crabs. Habitat type potentially modulates the effects as crabs are expected to behave differently in different habitats. In this study we experimentally evaluated the effect of R. harrisii on the species composition and dominance structure of shallow water meiobenthos within common habitat types of the north-eastern Baltic Sea. Among the studied environmental variables R. harrisii had by far the strongest effects on meiobenthos. The effects of R. harrisii varied among different habitats with the crab mostly modifying taxonomic composition and species abundances of meiobenthic communities on unvegetated soft bottom sediments. Our experiment also showed that boulders provided shelter for R. harrisii and thereby reduced their burrowing activity and effects on the adjacent soft bottom meiobenthos.

Specialized defense strategies are induced in zooplankton upon detection of predator chemical cues or kairomones. These defenses are well-described for freshwater zooplankters, with morphological defenses being particularly striking, but few studies have reported kairomone-induced morphological defenses in marine zooplankton. Here, we compare morphological responses to kairomones in the larvae of two marine crab species, estuarine mud crabs (Rhithropanopeus harrisii) and Asian shore crabs (Hemigrapsus sanguineus). When reared in the presence of fish kairomones, spine length increased by 2–3% in larval R. harrisii, while no morphological changes were identified in H. sanguineus. In subsequent feeding assays with a co-occurring fish predator (Atlantic silversides, Menidia menidia), consumption of R. harrisii was lower on larvae that had been reared with kairomones. In addition, we found that broods with smaller larvae are more likely to exhibit increases in spine length after kairomone exposure. Hence, the observed morphological response is likely influenced by larval size. This article is protected by copyright. All rights reserved.

The variability of the mtDNA locus COI in the Florida crab (Rhithropanopeus harrisii) of coastal populations of the northern Black Sea is studied. The introduction of this crab species is demonstrated to originate from European populations, most likely the Netherlands. The studied populations experienced a strong decline in the level of genetic variability based on the haplotype diversity, but to a lesser extent based on the nucleotide diversity. Analysis of the structure of decapod community of Crimea makes it possible to discuss the reasons underlying invasive success of the Florida crab in the region.

The structure of a fragment (523 nucleotide pairs) of the 1st subunit of mitochondrial cytochrome oxidase (COI) gene has been studied in the populations of alien crab Rhithropanopeus harrisii (family Panopeidae) that established in the basins of the Azov-Black and Caspian Seas in 1930–1950s. In the samples of 6 populations from this region, 4 haplotypes (A, B, T, Lerm1) have been found. One of them has been unique (Lerm1) to the northern part of the Black Sea. Haplotype T has only been found in the Black and Caspian seas region, while haplotype A is common in almost all European populations. Only 4 substitutions have been observed in the sampled sequence, one of which is non-synonymous and there have been 3 polymorphic sites. The diversity of haplotypes (h) of the Black Sea–Caspian region populations (from 0.181 ± 0.143 to 0.475 ± 0.098) is significantly lower than this in the other European populations, where the value of h ranged from 0.563 ± 0.063 to 0.795 ± 0.065, and in North American populations (from 0.725 ± 0.083 to 1 ± 0). Harris crab populations of the Black Sea–Caspian region have a common origin, and differ in their genetic structure from populations of the rest of introduction area in Europe. The population of the Caspian Sea originates directly from the Sea of Azov populations and, possibly, there have been numerously repeated exchange events due to shipping vector. The populations in the estuaries of rivers Shapsuho and Vulan in the northeastern Black Sea might be partly isolated since their haplotype composition is slightly different from other populations in the region.

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. peerReviewed

In this study, we determined the levels of essential and non-essential elements in the Harris mud crab (Rhithropanopeus harrisii, Maitland, 1874) from the southern Baltic Sea. Results revealed high levels of Ca (246,000 ppm), Mg (11,000 ppm), Na (8160 ppm), K (3,780 ppm), and Fe (1830 ppm). The concentrations of essential metals such as Zn (62.5 ppm) and Cu (25 ppm) were similar to those recorded in other crab species. The concentrations of non-essential metals such as Pb (0.140 ppm), Cd (0.0017 ppm), and As (0.288 ppm) were well below the International Standards for Maximum Levels for Food. In view of the above, the Harris mud crab from the southern Baltic is safe to be used as a component of well-balanced feeds for terrestrial and aquatic animals.

In dynamic systems, organisms are faced with variable selective forces that may impose trade-offs. In estuaries, salinity is a strong driver of organismal diversity, while parasites shape species distributions and demography. We tested for trade-offs between low-salinity stress and parasitism in an invasive castrating parasite and its mud crab host along salinity gradients of two North Carolina rivers. We performed field surveys every six to eight weeks over 3 years to determine factors influencing parasite prevalence, host abundance, and associated taxa diversity. We also looked for signatures of low-salinity stress in the host by examining its response (time-to-right and gene expression) to salinity. We found salinity and temperature significantly affected parasite prevalence, with low-salinity sites (less than 10 practical salinity units (PSU)) lacking infection, and populations in moderate salinities at warmer temperatures reaching prevalence as high as 60%. Host abundance was negatively associated with parasite prevalence. Host gene expression was plastic to acclimation salinity, but several osmoregulatory and immune-related genes demonstrated source-dependent salinity response. We identified a genetic marker that was strongly associated with salinity against a backdrop of no neutral genetic structure, suggesting possible selection on standing variation. Our study illuminates how selective trade-offs in naturally dynamic systems may shape host evolutionary ecology.

Predation of newly settled juvenile Crassostrea virginica often dominates post-settlement mortality. Resident mesopredators such as the xanthid mud crabs are abundant (>200/m2) on constructed subtidal oyster reefs in the New York metropolitan region and may contribute to post-settlement oyster mortality. Two study sites with differing mesopredator species, Hastings and Soundview Park, were selected to examine the role of small crustacean predators in post-settlement mortality. The white-fingered mud crab (Rhithropanopeus harrisii) inhabits Hastings, whereas the flat mud crab (Eurypanopeus depressus) and Sayi mud crab (Dyspanopeus sayi) inhabit Soundview Park. Using size-selective mesh cages to exclude predators, the effects of predator size on oyster predation and recruitment at Hastings and Soundview Park were examined. Overall, Soundview Park had higher consumption rates than Hastings. The highest consumption at Soundview Park occurred when predators of all sizes had access to the oyster prey. ...

In rocky littoral communities, intense herbivory allows for the occurrence of trophic cascades where higher trophic levels influence producer communities. Invasive predators can be especially effective in imposing trophic cascades. The North American mud crab Rhithropanopeus harrisii is a recent invader in the Baltic Sea, with an expanding distribution range. Here, we document the effects of mud crab on the native invertebrate community associated with the key foundation species Fucus vesiculosus. During the initial 3 years of invasion, mud crab abundance in F. vesiculosus increased from 2 % to about 25 % of the algae being inhabited by crabs. Simultaneously, the invertebrate community underwent a major transition: Species richness and diversity dropped as a consequence of decreasing abundance and the loss of certain taxa. The abundance of gastropods decreased by 99 % and that of crustaceans by 75 %, while chironomids completely disappeared. Consequently, the community dominated earlier by herbivorous and periphyton-grazing gastropods and crustaceans shifted to a mussel dominated community with overall low abundances of herbivores. At the same time filamentous epiphytic algae prospered and the growth rate of F. vesiculosus decreased. We suggest that this shift in the invertebrate community may have far reaching consequences on ecosystem functioning. These arise through changes in the strength of producer–herbivore interaction, caused by mud crab predation on the dominating grazer taxa. This interaction is a major determinant of ecological function of ecosystems, i.e. productivity and energy flow to higher trophic levels. Therefore, the decrease in herbivory can be expected to have a major structuring role in producer communities of the rocky littoral macroalgal assemblages.

The ingestion of microplastics has been recorded in hundreds of species. The ingestion rate and degree of impact is species-specific and depends on food preferences, foraging behaviour, and plastic pollution of the area. Currently there is a large knowledge gap regarding ingestion of marine litter by invertebrates in brackish water bodies. Therefore, experiments were conducted to investigate microplastics uptake and potential accumulation in the digestive system of the Harris mud crab Rhithropanopeus harrisii. Effects of microplastics on the growth of crabs were also tested. The results show that R. harrisii consume microplastics together with food, only plastic fragments too large for the digestion system were removed by crabs. The effect and duration of passage of plastic are not consistent and depend on the size and type of plastic. Microplastic fragments (

Mercury is a potent neurotoxin. Its main source of entry into the human body is the consumption of fish and seafood. Within the past few decades a new species of crab has appeared in the food web of the southern Baltic: Rhithropanopeus harrisii. The aim of the present study was to estimate the level of total and labile mercury concentrations in this species collected from the southern Baltic Sea. Analyses were performed using the thermodesorption method. The share of organic mercury fraction, as well as the Hgtot, increased with the size class of the crabs. Due to the increasingly common occurrence of R. harrisii and the low HgTOT concentration in its body, and assuming that it is bound to become a more and more common component of the diet of fish, it can be supposed that the load of toxic mercury entering the food web is likely to decrease.

Crab larvae (Rhithropanopeus harrisiiere exposed to a range of free cupric ion concentrations, [Cu2+], regulated in sea water by a metal chelate buffer system. We found a biphasic relationship between intracellular copper distribution and [Cu2+] in sea water. At [Cu2+] within the ambient range (10-12.4 to 10-10.6 M), cytosolic copper was associated with both metallothionein (MT) and high molecular weight (HMW) ligands, and was independent of external [Cu2+]. At higher [Cu2+], copper was also associated with very low molecular weight (VLMW) ligands, and accumulated in this ligand pool and the MT pool as external [Cu2+] increased. In marked contrast, copper in the HMW ligand pool did not correlate with [Cu2+] in sea water over the entire range of exposures. Reductions in larval growth occurred at greater than estimated ambient [Cu2+] and correlated with copper accumulation in the MT and VLMW pools.

The ontogeny of behavioral responses of larvae of the crabs Rhithropanopeus harrisii and Neopanope sayi to rates of change in temperature were analyzed using a video system. A temperature decrease evoked an ascent in both species. The threshold rates of decrease for Stages I and IV zoeae of R. harrisii, and Stage I zoeae of N. sayi, were 0.06, 0.1, and 0.09°C min-1, respectively. Stage IV zoeae of N. sayi were unresponsive to any rate of decrease. Larvae descended upon a temperature increase. For Stages I and IV zoeae of R. harrisii and Stage I of N. sayi the threshold rates of temperature increase were 0.07, 0.24, and 0.18°C min-1, respectively. Stage IV zoeae of N. sayi were again unresponsive. In general, there was an ontogenetic change in responsiveness as Stage IV zoeae of both species were less sensitive than Stage I zoeae. The average absolute amounts of temperature change needed to evoke a response was independent of the rate of change at rates above threshold and ranged from 0.29 to 0.49°C for both species. A consideration of larval sinking rates and ascent speeds, as well as normal environmental temperature gradients, shows that larvae of both species can respond to the rates and amounts of temperature change found in their environments. These responses constitute a negative feedback system that could be used to regulate depth relative to temperature.

The ontogeny of behavioral responses of larvae of the crabs Rhithropanopeus harrisii and Neopanope sayi to rates of change in salinity were analyzed with a video system. A salinity increase evoked an ascent in both species. For R. harrisii the threshold rate of increase was 1.1 x 10-3 ppt s-1 for the first and last zoeal stages and changed little with acclimation salinity. N. sayi larvae were more sensitive, as thresholds were 2.8 x 10-4 ppt s-1 for Stage I zoeae and 7.0 x 10-4 ppt s-1 for Stage IV. This difference in sensitivity may relate to the magnitude of salinity gradients in the estuarine/coastal areas inhabited by the larvae. At threshold rates of salinity increase the absolute amount of change before a response was lower for Stage I zoeae (0.09-0.11 ppt) than Stage IV zoeae (0.21-0.29 ppt) for both species. Decreases in salinity did not induce the expected descent response in either species at rates up to 4.7 x 10-2 ppt s-1. The different responses in a salinity gradient may have resulted because the rate threshold and absolute amount of change before a response to a salinity increase were below those for a salinity decrease. Considering larval sinking rates and normal environmental salinity gradients, larvae of both species can respond to rates and amounts of salinity increase in their environment. The ascent response may be important for keeping larvae up in the water column and reducing the likelihood that they will encounter the bottom.