Mud Crab Rhithropanopeus Harrisii Research Articles

Effects of an Invasive Mud Crab on a Macroalgae-Dominated Habitat of the Baltic Sea under Different Temperature Regimes

The risks imposed by biological invasions on marine ecosystems are increasing worldwide. The mud crab Rhithropanopeus harrisii has recently expanded its distribution to the northeastern Baltic Sea, where low predatory pressures and the absence of functionally similar competitors favored the establishment of the species. Few studies have addressed the effects of the mud crab on Baltic benthic communities and habitats. Even fewer have looked at the consequences of the invader on habitats dominated by Fucus vesiculosus, the main habitat-forming macrophyte in the Baltic Sea. The present study experimentally analyzed, under laboratory conditions, the effects of R. harrisii on Baltic F. vesiculosus habitats and associated communities under different temperatures simulating summer and winter regimes. Our results show that the effects of the mud crab are modulated by temperature, being more pronounced under summer conditions when the metabolic demands and food intake requirements are higher. The experiment provided new insights into the capacity of R. harrisii to disrupt recruitment in native snail populations, jeopardizing the persistence of healthy populations of key grazers in F. vesiculosus habitats. Moreover, our results conclusively demonstrated the capacity of the invader to decimate native blue mussel populations. The impacts on functionally relevant invertebrates can have far-reaching ecological consequences, altering the food web and disrupting entire coastal ecosystems in the Baltic Sea.

Functional responses of an invasive mud crab across a salinity gradient

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.

Risk screening of the potential invasiveness of non-native marine crustacean decapods and barnacles in the Mediterranean Sea

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.

Citizen science provides added value in the monitoring for coastal non-indigenous species

Continuous and comprehensive monitoring is one of the most important practices to trace changes in the state of the environment and target management efforts. Yet, governmental resources are often insufficient for monitoring all required environmental parameters, and therefore authorities have started to utilize citizen observations to supplement and increase the scale of monitoring. The aims of the present study were to show the potential of citizen science in environmental monitoring by utilising citizen observations of the non-indigenous Harris mud crab Rhithropanopeus harrisii in Finnish waters, where coastal monitoring is insufficient to estimate the distribution and spread of non-indigenous species. Harris mud crab has shown measurable impact locally and is considered invasive. For reporting the status of invasions to national and European authorities and planning for potential eradication efforts, up to date knowledge on NIS ranges are needed. Citizen observations on the species were collected from the first observation onwards between 2009 and 2018, at first via email and later through an active citizen observation web portal (Invasive Alien Species Portal). The outcomes of the study indicate that species-specific citizen observations can be a beneficial addition to supplement national monitoring programs to fulfil legislative reporting requirements and to target potential management. Recognizable species and geographical areas with low biodiversity provide a good opportunity to utilize citizen observations. Moreover, citizen observations may enable distribution assessments for certain species that would otherwise require excessive resources and sampling efforts.

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.

Knowledge to decision in dynamic seas: Methods to incorporate non-indigenous species into cumulative impact assessments for maritime spatial planning

Incorporating ecosystem changes from non-indigenous species (NIS) is an important task of maritime spatial planning. Maritime spatial planning requires a framework that emphasises ecological functioning in a state of dynamic change, including changes to ecosystem services from functions introduced by new NIS. Adaptable modelling toolsets should be developed that can readily incorporate knowledge of new NIS. In the Baltic Sea, recent NIS examples are the North American mud crab Rhithropanopeus harrisii and the Ponto-Caspian round goby Neogobius melanostomus. We performed environmental niche modelling that predicted N. melanostomus will spread across large areas of the Baltic Sea coast while R. harrisii will be limited to regions with high temperature and low salinity conditions. We then performed a meta-analysis on literature showing effects in the Baltic Sea from these NIS and calculated the standardised effect-sizes on relevant ecosystem services. Half the impacts identified for N. melanostomus were considered to increase ecosystem service outcomes, while all R. harrisii impacts caused apparent decreases. Effect coefficients were incorporated into an online impact assessment tool developed by the Estonian Marine Institute. Users with or without science training can use the portal to estimate areas impacted and changes to natural assets (km2) caused by these NIS and cumulative effects from other pressure-types. Impact estimates are based on best available knowledge from manipulative and correlative experiments and thus form a link between science and management. Dynamic modelling techniques informed from varied ecological and methodological perspectives will effectively advise spatial planners about rapid maritime changes and mitigation actions to reduce NIS impacts especially in the focus areas.

Post-invasion demography and persistence of a novel functional species in an estuarine system

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.

Invasion genomics: genotyping-by-sequencing approach reveals regional genetic structure and signatures of temporal selection in an introduced mud crab

Introduced species can cause large impacts on communities and ecosystems. To prevent invasions and the impacts of invasions, a better understanding of species-specific invasion routes, establishment processes, demographic histories and range expansions is needed. Such valuable biological information can be obtained using population genomics approaches that allow fast and simultaneous screening of thousands of loci and SNP markers without prior knowledge of the genome of studied species. As a result, invasion genomics has the potential to reveal previously undetected population relationships, invasion routes and evolutionary patterns. Here, we characterized the genetic diversity, structure, temporal stability and putative footprints of selection in introduced Baltic Sea populations of the mud crab Rhithropanopeus harrisii using restriction-site associated DNA (RAD) sequencing. Similar to earlier mtDNA reports, analysis of 1013 SNPs revealed strong differentiation between the native and introduced populations. At a regional scale, clear evidence of population structuring was detected between Finnish and Estonian samples indicating that R. harrisii does not form a single panmictic population in the Baltic Sea. Clustering of samples according to the age groups (juvenile and adult) instead of geographical location within the Archipelago Sea revealed the presence of significant temporal variation at small spatial scale. Finally, we identified a number of outlier loci under temporal divergent selection between cohorts suggesting that contemporary selection in newly established areas may be stronger than selection associated with spatial heterogeneity within the Baltic Sea. These results demonstrate the utility of next-generation sequencing to increase understanding of the population diversity and structuring, and highlight the importance of temporal genetic analysis when dissecting fine-scale genetic structure for introduced marine species with high reproductive potential.

Genetic analysis of population structure of alien North American mud crab Rhithropanopeus harrisii (Gould, 1841) in the Black Sea–Caspian 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.

Habitat selection of the mud crab Rhithropanopeus harrisii in its newly invaded range

Habitat selection of the mud crab Rhithropanopeus harrisii in its newly invaded range

Can environmental DNA (eDNA) be used for detection and monitoring of introduced crab species in the Baltic Sea?

The need to detect and monitor introduced marine species has increased with the increasing number of marine invasions. To complement standard detection and monitoring techniques, new approaches using environmental DNA (eDNA) have recently been developed. However, most of the eDNA work has focused on vertebrate species in spatially limited freshwater habitats while benthic invertebrates in coastal environments have received much less attention. Here, we evaluated the suitability of the eDNA approach for detecting benthic, hard-shelled, crustacean mud crab species in a brackish water environment. We demonstrated for the first time that eDNA from an introduced mud crab Rhithropanopeus harrisii can be successfully amplified in aquarium water samples and detected in the brackish water environment. However, the detection rate was rather low. This suggests that in contrast to freshwater vertebrates, it may be more challenging to develop a highly sensitive eDNA method for detecting crustacean species in a marine environment.

The invasive mud crab enforces a major shift in a rocky littoral invertebrate community of the Baltic Sea

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.

Habitat expansion of the Harris mud crab Rhithropanopeus harrisii (Gould, 1841) in the northern Baltic Sea: potential consequences for the eelgrass food web

Habitat expansion of the Harris mud crab Rhithropanopeus harrisii (Gould, 1841) in the northern Baltic Sea: potential consequences for the eelgrass food web

Introduction of a functionally novel consumer to a low diversity system: Effects of the mud crab Rhithropanopeus harrisii on meiobenthos

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.

The low basin of the Arno River (Tuscany, Italy) as alien species hotspot: first data about Rhithropanopeus harrisii (Crustacea, Panopeidae)

1 - Harbours and ports, especially if located in the nearby of brackish-water environments, can provide a significant chance to biological invasions. To date, in the Livorno port, twenty alien species have been recorded, fifteen of which are established. 2 - Presence, abundance, size and sex ratio of the mud crab Rhithropanopeus harrisii, a newly introduced invasive species, have been assessed in six sampling stations along the brackish-water canals between Pisa and Livorno towns. Samplings were carried out in summer and fall 2013. 3 - R. harrisii appeared fully established in the majority of the sampling stations. Reproduction occurs between May and July and sex ratio varied between reproductive and post-reproductive period, with females more abundant before the reproduction. 4 - Individuals of R. harrisii were more abundant in stations close to Livorno port, whereas they were scarce or sporadic in the northernmost stations, close to the main flow of the Arno River. 5 - Due to the high invasive potential of R. harrisii, a closer monitoring of brackish-water environments along the north-western Italian coast is needed, in order to assess and prevent further invasions.

Food web positioning of a recent coloniser: the North American Harris mud crab Rhithropanopeus harrisii (Gould, 1841) in the northern Baltic Sea

Identifying resource use and functional traits of non-indigenous species are promising means to increase the ability to predict ecological consequences of invasions. One of the most widely spread brachyuran crab species, and a recent invader in the northern Baltic Sea, is the North American Harris mud crab, Rhithropanopeus harrisii (Gould, 1841). Although spread, establishment, and population structure have been studied for this species, little is known about its role and impact in a new environment. We investigated the position and role of R. harrisii i n the coastal food web by combining spatial and temporal estimates of trophic position using stable isotopes (δ 13 C and δ 15 N), with short-term food- and habitat-choice experiments. We observed a stable pattern in the trophic position between two environmentally different locations in the Archipelago Sea over the production season. The identification of a natural breakpoint in carbon stable isotopes at the size of 12 mm carapace width suggested a presence of an ontogenetic diet shift, which was confirmed by isotope signatures positioning large R. harrisii among secondary consumers and small individuals with primary consumers. The generalist consumer nature of R. harrisii and preference for structured habitat was supported by an active habitat and food choice, revealing no preference for prey species (polychaetes versus amphipod), but selection of brown algae over bare mud. To broaden the understanding of the functional role of R. harrisii, we combined our findings with other known biological and ecological traits of the species and qualitatively compared these to characteristics of other benthic organisms in the northern Baltic Sea, suggesting a general similarity in traits.

Effect of temperature on physiology and bioenergetics of adult Harris mud crab Rhithropanopeus harrisii (Gould, 1841) from the southern Baltic Sea

Abstract Rates of physiological processes and bioenergetics of the Harris mud crab Rhithropanopeus harrisii were determined during a 7-day experiment on adult males (mean wet weight 0.83 ± 0.16 g) exposed to temperatures of 15°C and 20°C (S = 7). The results show that the change in temperature by 5°C caused detectable changes in locomotor activity, food consumption and faeces production and significant (p < 0.05) changes in metabolic rates. Food assimilation efficiency and the ammonia excretion rate did not change significantly (p > 0.05). The energy expended on metabolic processes was similar at both temperatures (15°C and 20°C) and amounted to 17.7 ± 6.4% and 16.7 ± 4.3% of the assimilated energy, respectively. Similar values were obtained for net production efficiency K2 (P/A) at 15°C and 20°C, i.e. 80.4 ± 22.4% and 82.9 ± 9.7%, respectively. The amount of energy available for production was 2-fold higher at a temperature of 20°C than at 15°C and amounted to 103.69 ± 25.61 and 206.40 ± 20.76 J d−1g−1 wet wt, respectively. The results show that from the bioenergetic point of view, higher experimental temperature is more “profitable” for adult R. harrisii specimens because it provides better conditions for the growth and reproduction.

Non-native crab Rhithropanopeus harrisii (Gould, 1984) – a new component of the benthic communities in the Gulf of Gdańsk (southern Baltic Sea)

The aim of this study was to determine the occurrence, spatial distribution and abundance pattern of the Harris mud crab Rhithropanopeus harrisii in the Gulf of Gdańsk (southern Baltic Sea). Between 2006 and 2010, this species was found at 69 out of 129 sampling stations, at depths from 0 to 20m. Two main aggregations of the Harris mud crab were established: (1) in Puck Bay (max. density 19 indiv. 100m−2) and (2) in the Gdynia and Sopot area (max. density 5 indiv. 100m−2). 920 specimens were collected during the whole sampling period: 150 juveniles, 370 females and 400 males. The minimum measured carapace width was 1.96mm, the maximum 21.40mm (mean 9.03±4.11mm).

Population structure, morphometry and individual condition of the non-native crab Rhithropanopeus harrisii (Gould, 1841), a recent coloniser of the Gulf of Gdańsk (southern Baltic Sea)

The aim of this study was to characterise the introduced North American Harris mud crab Rhithropanopeus harrisii, which occurs in the Gulf of Gdańsk, Poland (southern Baltic Sea). Of the 920 specimens caught between 2006 and 2010, males and females made up 44 and 40% respectively, whereas juveniles (< 4.4mm carapace width) comprised 16%. Overall carapace widths ranged from 1.96mm to 21.40mm (mean 9.03±4.11mm). Ovigerous females (mean 11.12±2.76mm) were present in the population from June to October. Most of the adult specimens collected (n=158) had carapace widths between 10.1 and 12.0mm. The wet weight of R. harrisii varied from 0.005 to 4.446g (mean 0.410 ± 0.569g). Females exhibited a negative allometric increase in weight (b=2.77), males an isometric increase in weight (b=3.02). The condition factor (K) in R. harrisii varied from 0.02 to 0.08 (mean 0.05±0.01).

The North American mud crab Rhithropanopeus harrisii (Gould, 1841) in newly colonized Northern Baltic Sea: distribution and ecology

Here we present the known distribution and population demography of the most northern known population of the North American whitefingered mud crab, Rhithropanopeus harrisii, from southwest Finland in the Baltic Sea. This species was first reported in Finland in 2009 from the archipelago close to Turku and has been found from 82 locations within a 30 km radius since then. Due to the presence of young of year, juveniles, and gravid females observed at three sites in Finland, R. harrisii has established successful populations that are able to overwinter under ice and can opportunistically occupy diverse habitats, such as shafts of dead marsh plants, self-made burrows in muddy bottoms, and the brown algae Fucus vesiculosus in hard bottoms. In its native range, a rhizocephalan barnacle parasitizes R. harrisii, but this parasite was not found in the introduced Finnish population. While R. harrisii is expected to expand its range along the coast of the northern Baltic Sea, the ultimate impact of this species on food web dynamics, both as a predator and prey item, remains to be seen.