Harris Mud Crab Rhithropanopeus Harrisii Research Articles

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.

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.

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).

SHORT COMMUNICATION. Rapid establishment of the alien crabRhithropanopeus harrisii(Gould) in the Gulf of Riga

INTRODUCTION Owing to its low salinity and short evolutionary history, the Baltic Sea virtually lacks native top predatory crabs. This contrasts to true oceanic waters where crabs constitute an essential element of the nearshore benthic ecosystems (e.g. Lee, 1998). To date, the only 'iconic' species in the Baltic Sea range is the Chinese mitten crab Eriocheir sinensis (H. Milne-Edwards). Despite occasional findings of this invasive species all over the coastal Baltic Sea, the reproduction of the mitten crab in the central, northern, and eastern Baltic regions is considered unlikely due to the low salinity, and the individuals caught are assumed to have actively migrated into the region over 1500 km distance (Ojaveer et al., 2007). However, the Baltic Sea also hosts the Harris mud crab Rhithropanopeus harrisii (Gould) (Fig. 1). This species has a native distribution from New Brunswick (Canada) to Veracruz (Mexico). In Europe the invasive species was first found in 1874 in the Netherlands, in the Baltic Sea area it was first observed in 1936 (Nikolaev, 1951). In contrast to E. sinensis, the mud crab is capable of reproducing in the diluted Baltic Sea and can form high-density populations (Maiju Lehtiniemi, pers. comm.); thus, it may exert strong pressure on the local benthic macrophyte and invertebrate communities. Despite its long invasion history, until very recently the distribution of R. harrisii was confined to Mecklenburg Bay, the Oder Estuary, the Gulf of Gdansk, and the Curonian Lagoon only (Jazdzewski & Konopacka, 1993; Bacevicius & Gasiunaite, 2008; Czerniejewski, 2009; Jazdzewski & Grabowski, 2011). Seemingly, R. harrisii has a large between population variability in Europe with more recent populations showing a tendency for increased genetic diversity (Projecto-Garcia et al., 2010). This suggests that R. harrisii is still in the process of expansion in Europe and its sudden northwards expansion seems to be a result of new introductions. In this study we report the sudden expansion of this alien invasive species over 500 km northwards and provide information on its distribution. [FIGURE 1 OMITTED] MATERIAL AND METHODS Crabs are not systematically monitored in the Estonian coastal sea. Nevertheless, since 1995 the Estonian National Monitoring Programme surveys benthic macrophytes and the associated invertebrates around the whole Estonian coastal range. In addition, the programme also surveys pelagic communities. The phytobenthos and zooplankton sampling and sample analysis follow the guidelines developed for the HELCOM COMBINE programme (HELCOM, 2012). Although not specifically targeted towards large and mobile invertebrates, the national monitoring programme is potentially capable of sighting the mud crab both in benthic and pelagic ecosystems. In addition, there is another local long-term activity that provides semiquantitative data on crabs. Specifically, this is done through the provision of artificial spawning substrata for the commercially valuable fish pike-perch in Parnu Bay. This activity was started already in the late 1980s and has been done every year since then. Most of these artificial spawning substrata consist of linen gillnets of small mesh size. Such substratum may also provide a suitable habitat for the Harris mud crab and, therefore, may provide occurrence information on the species. These artificial spawning substrata were checked for the mud crab occurrence in 2011-2012, also with SCUBA diving, which was also performed in several additional localities in Parnu Bay to map the distribution of the species. Finally, owing to good long-term relations with local professional fishermen, several occurrence data on the crab were obtained from them. RESULTS AND DISCUSSION The Harris mud crab R. harrisii was first found in the Estonian waters in August 2011. Seven individuals were found in three deployed lines of pike-perch artificial spawning substrata at the northern coast of Parnu Bay (NE Gulf of Riga) (Fig. …

Nekton use ofVallisneria americana Michx. (Wild celery) beds and adjacent habitats in Coastal Louisiana

We compared nekton use ofVallisneria americana Michx. (submerged aquatic vegetation, SAV) with marsh shoreline vegetation and subtidal nonvegetated bottom (SNB) using a 1-m2 drop sampler in the oligohaline area of Barataria Bay, Louisiana. Mean densities of most abundant species were significantly different among six habitat types. Harris mud crabRhithropanopeus harrisii, Ohio shrimpMacrobrachium ohione, blue crabCallinectes sapidus, daggerblade, grass shrimpPalaemonetes pugio, white shrimpLitopenaeus setiferus (fall), rainwater, killifishLucania parva, naked gobyGobiosoma bosc, code gobyGobiosoma robustum (fall), speckled worm eelMyrophis punctatus (fall), and gulf pipefishSyngnathus scovelli (spring), were much more abundant, and species richness also was greater, inVallisneria than over SNB.Vallisneria supported densities of most species that were similar to those in marsh vegetation, although naked goby and gulf pipefish were more abundant inVallisneria, and speckled worm eel and saltmarsh topminnowFundulus jenkinsi were more abundant in marsh. Within theVallisneria bed, densities of Harris mud crab, rainwater killifish, and speckled worm eel were higher at sites near the marsh (SAV Inside Edge) than at sites more distant from the marsh (SAV Outside Edge), and Ohio shrimp (fall) densities were higher in the interior of the bed than along the edges. The mean size of blue crab was larger in marsh thanVallisneria and large inVallisneria than SNB. White shrimp did not differ in size among habitat types.Vallisneria beds may provide an important nursery habitat for young blue crab and white shrimp that use oligohaline estuarine areas. These SAV beds can provide an alternative structural habitat to emergent vegetation during periods of low water, becauseVallisneria occurs in the subtidal and generally persists throughout the year on the Gulf coast. Species whose young thrive in low-salinity waters and also depend on structure would benefit most fromVallisneria habitat in estuaries.