Atlantic Blue Crab Callinectes Sapidus Research Articles

Using species population structure to assist in management and decision-making in the fight against invasive species: The case of the Atlantic blue crab Callinectes sapidus

The blue crab Callinectes sapidus Rathbun, 1896 is an invasive species in the Mediterranean, with a remarkable ability to adapt to various habitats, and thereby having significant impacts on biodiversity and artisanal fishing activities. Currently, fishing is a measure being considered to control blue crab populations in invaded sites. However, it is necessary to understand the temporal structure of blue crab populations (e.g., growth, reproduction, sexual maturity) to determine specific periods when control measures need to be implemented. Considering the species' ability to adapt to various habitats, it is crucial to evaluate how temperature and salinity influence population structure. In this study, we present fishers-dependent monitoring on the temporal population structure of blue crabs in two lagoons in Corsica (France) over 12 months. Through this approach, we provide new information that can assist in decision-making for the implementation of control measures. Even though these two lagoons are geographically close, blue crab populations showed differences, particularly in terms of sexual maturity. Specimens from Biguglia mature later (males: 16.16 cm; females: 16.79 cm) than those in the Palo Lagoon (males: 14.38 cm; females: 13.86 cm). Seasonal size distribution also showed differences between the lagoons and within the same lagoon between males and females. Temperature and salinity had a significant effect on the monthly relationship between carapace width and wet weight (referred to here as growth rate) for males and females and between the lagoons. In the Biguglia Lagoon, the higher the temperature, the greater the growth rate over a wide salinity window (16–30 psu); for females, the environmental window was restricted (temperature: 20–30°C; salinities > 16 psu). The dynamics differed in the Palo Lagoon, with a more restricted high growth rate window for males, and females showed a much wider window, with high growth rates over the entire temperature and salinity range. By employing blue crab’s populations monitoring along with environmental parameters, we were able to determine how the environment influenced the blue crab’s population structure, thus identifying periods conducive to species control. The most effective strategy would undoubtedly be to eliminate females before their period of sexual maturity and copulation ensue. In our case, this would involve intensive control in summer for Biguglia and in spring for Palo. These recommendations have been translated into operations to be implemented as part of the "Territorial Plan for Combating the Blue Crab (Callinectes sapidus) in Corsica (2024–2027)".

When Nature Requires a Resource to Be Used-The Case of Callinectes sapidus: Distribution, Aggregation Patterns, and Spatial Structure in Northwest Europe, the Mediterranean Sea, and Adjacent Waters.

The Atlantic blue crab Callinectes sapidus, which is native to the western Atlantic coast and listed among the 100 most invasive alien species in the Mediterranean Sea, is attracting a great deal of interest because of its rapid colonisation of new areas, the significant increase in its population, and the impacts it may have on ecosystems and ecosystem services. Outside its natural distribution range, the species was first found on European Atlantic coasts in the early 1900s and was introduced into the Mediterranean Sea a few decades later, probably through ballast water. Currently, it is found in almost the entire Mediterranean Basin and is also expanding into the Black Sea and along the north African and Iberian Atlantic coasts. Based on a systematic review of C. sapidus occurrences, this study describes its distribution, aggregation patterns, and spatial structure in Northwest Europe, the Mediterranean Sea, and adjacent waters through a series of ecological indicators elaborated using GIS spatial-temporal statistics. The main results highlight that the species is expanding in the Mediterranean and adjacent waters, while in northern Europe, the population remains confined in some areas. Furthermore, the main species detection methods are analysed, finding that traps and nets are the most frequently used methods, and management suggestions are provided.

Diet of the Invasive Atlantic Blue Crab Callinectes sapidus Rathbun, 1896 (Decapoda, Portunidae) in the Guadalquivir Estuary (Spain)

The Atlantic blue crab Callinectes sapidus (Decapoda, Portunidae) Rathbun, 1896 is native to the east coasts of North and South America and has recently expanded its distribution in the non-native range into the Gulf of Cadiz (SW Iberian Peninsula, Europe). Considering the impacts caused by this invasive species in numerous estuarine ecosystems and its generalist feeding behavior, this study aims to provide the first account of the Atlantic blue crab diet on the East Atlantic coast. We studied the species’ feeding habits using stomach content analyses to predict food web interactions and putative impacts. Samples were obtained in the Guadalquivir estuary (SW Spain, Europe), which was colonized in 2017. The main food items identified on their stomach were, fish (49.9%), mollusks (44.4%) and crabs (32.3%). They also consumed plant material (27.2%), and the sediment (32.3%) in their digestive tract was likely the result of secondary ingestion. The Atlantic blue crab exhibited the same omnivorous behavior as in the native area. There was no sexual variation in diet composition or feeding activity in general, but there was a seasonal variation in the diet composition of females. The decrease of the caramote prawn Penaeus kerathurus (Forskål 1775) observed in the Guadalquivir estuary since 2021 is likely not due to the Atlantic blue crab because they seldomly eat this prey. Overall, our study provides clear baseline information to expand the knowledge about the ecological roles of the Atlantic blue crab in non-native ecosystems.

Far‐reaching blues: Long‐distance migration of the invasive Atlantic blue crab

Abstract Upstream migration of the Atlantic blue crab Callinectes sapidus is well described in its native range, but it is little known in invaded areas. Here, we report several long‐distance migration events of the blue crab in the Iberian Peninsula and use a global database to calculate the probability of occurrence of the species in relation to distance to sea. We then exemplify the potential of blue crab impacts on freshwaters by overlapping its probability of occurrence with that of the critically endangered European eel Anguilla anguilla. Finally, we evaluate the extent to which dam barriers can halt the upstream migration of the blue crab. Invasive blue crab has been detected at 108 km from the sea in the Guadalquivir River (the farthest distance reported in the non‐native range), at 71 km in the Guadiana River and at 53 km in the Ebro River. The probability of occurrence decreased steeply in the first upstream kilometres, but it is still concerning at a dozen kilometres from the river mouth (50% at 19 km, 25% at 38 km, and 3% at 100 km). The blue crab invasive potential widely overlaps (63%) with the Iberian range of the European eel. The blocking effect of dams on the potential invasion of freshwater systems by the blue crab was limited (13%). Our study highlights the need to study the upstream migration of the blue crab within its non‐native range, since it could involve serious impacts in reachable river and stream habitats.

Soft-Shell Production of the Invasive Atlantic Blue Crab Callinectes sapidus in the Lesina Lagoon (SE Italy): A First Assessment

The current invasion of the Mediterranean Sea by the Atlantic blue crab Callinectes sapidus requires the implementation of effective strategies of control and management. In native areas, the species is highly appreciated as a hard- and soft-shell seafood, and hard-shell fisheries are developing in a number of invaded countries. Here, to verify alternative approaches for enhancing the commercial value of the species, we carried out a pilot experiment to test a flow-through system for the production of soft-shell blue crabs. Fifty crabs were collected in the Lesina lagoon (Adriatic Sea, Italy) and inspected for the coloration of the line on the distal edge of the fifth pereiopod. Accordingly, they were grouped into three groups showing no, white, and red lines, symptomatic of the progression of the pre-molt phase, and maintained for 31 days in a flow-through pond system. The overall mortality rate determined during the trial was similar across the three groups and ranged between 10 and 20%, indicating that the flow-through system was effective for rearing the crabs. In addition, the molting rate was 10%, 65%, and 85% for individuals at an early, intermediate, and advanced pre-molt stage, confirming that the line coloration can be used as an effective indicator of the advancement of the molting process. Our study provides the first contribution towards the introduction in the Mediterranean fishery sector of novel procedures and practices for the production of soft-shell blue crabs, which may represent a cost-effective strategy to enhance the capture and commercialization of this invasive species as a high-quality and valuable shellfish product.

Evidence for a male bias in Atlantic blue crab pot‐based sampling

AbstractObjectiveThe Atlantic blue crab Callinectes sapidus (hereafter, “blue crab”) is an ecologically and economically important species that supports one of the highest valued commercial fisheries in coastal South Carolina, USA. Researchers at the South Carolina Department of Natural Resources conduct multiple surveys to monitor the status of the blue crab by using a variety of gear configurations. Demographic characterizations can often be influenced by sampling gear‐related biases.MethodsWe compared blue crab sex ratios between passive, pot‐based sampling and active, trawl‐based sampling in the fall across three estuaries and for year‐round sampling in a single estuary (Ashley River, South Carolina).ResultDuring the fall, there was a difference of 20.1% between the percentage of males collected in pot‐based sampling (73.5%) and the percentage of males in trawl‐based sampling (53.4%). Furthermore, an overall male bias of 23.0% was observed for year‐round sampling in the Ashley River; however, this bias was only significant in certain months.ConclusionOur findings suggest that although particular sampling gears may have specific advantages, such as greater suitability to effectively sample certain habitats, the resulting characterizations of blue crab population demographics can differ among gear types. Recognizing gear‐related biases is important for ensuring that field surveys are representative of population demographics, particularly when sex‐specific modeling approaches are used as part of stock assessments to determine population status.

Early life stages of the invasive Atlantic blue crab Callinectes sapidus in the Western Mediterranean Sea

The early life cycle of the Atlantic blue crab Callinectes sapidus includes seven zoeal stages that develop in coastal waters, and a later megalopal stage that colonizes estuaries. Although these stages have been largely studied in native ecosystems, very little is known about larval patterns in smaller-scale, invaded, estuarine environments such as those available in the Mediterranean Sea. The general aim of this study is to assess the distribution and abundance of early life stages of C. sapidus in the communication channels of the Albufera lagoon with the Mediterranean Sea, and in adjacent coastal waters. Different sampling methods were employed to target each life stage. (1) For zoeae, planktonic tows were conducted using a 300 μm manta net along 200 m transects parallel to the coastline at distances of 300, 1000 and 3000 m from the shore. (2) A small and manageable passive collector model was used to capture megalopae and juveniles in estuarine areas. This system was first tested from 2020 to 2021 in a single channel, with a weekly sampling frequency, and two more channels were added in 2022. Additionally, intensive daily sampling was conducted in one of the channels from September to November 2022 during the settlement peak. Results showed that zoeae of C. sapidus were more abundant in August 2021, at 1000 m from the coast, and appear to have a disjoint temporal distribution with zoeae of other crab species. Megalopae and juveniles were more abundant from September to November at all sampling sites and times. In 2022, collectors featured a dominance of megalopae at two of the sites (ca. 73%), while the site with the lowest salinity showed a dominance of juveniles (84%). For megalopae, comparative results from the intensive and the regular sampling campaigns showed that time of residence within collectors is just a single day. For juveniles, higher numbers were detected with increased deployment time, suggesting a need for enhanced habitat complexity.

The validation case on invasive crustaceans of the LifeWatch ERIC Internal Joint Initiative: State of the art and next steps forward

LifeWatch ERIC, the e-Science European infrastructure for biodiversity and ecosystem research, launched an Internal Joint Initiative on Non-indigenous Species and Invasive Alien Species (NIS-IAS) as they are considered one of the major drivers of biodiversity and ecosystem change. Here, the case study focused on the trophic biogeography of invasive crustaceans is presented, describing the procedures, resources, and analytical web services implemented to investigate the trophic habits of these taxa by using carbon and nitrogen stable isotope data. The case study offers a number of analytical tools to determine the variability of the trophic position of invasive crustaceans in a spatially-explicit context and to model it as a function of relevant environmental predictors. Literature-based stable isotope data of the Atlantic blue crab Callinectes sapidus and of the Louisiana crayfish Procambarus clarkii have been used to evaluate the functionalities and outcomes of the workflow. The Tesseract Virtual Research Environment integrates all the analytical services offered by LifeWatch ERIC, including the ones developed for this case study, by means of a user-friendly interface. The analytical functions implemented for the crustacean workflow provide a proof of concept for future open e-science platforms focusing on NIS-IAS. The workflow conceptual structure can be adapted to a wide range of species, and can be further improved to support researchers in monitoring and predicting trophic-related impacts of NIS-IAS. In addition, it can support policymakers and stakeholders in the implementation of effective management and control measures to limit the negative effects of bioinvaders in recipient environments.

Free Pass Through the Pillars of Hercules? Genetic and Historical Insights Into the Recent Expansion of the Atlantic Blue Crab Callinectes sapidus to the West and the East of the Strait of Gibraltar

The invasive Atlantic blue crab Callinectes sapidus has considerably extended its distribution along the Gulf of Cadiz and Moroccan coasts in the northeast Atlantic. This could indicate a new introduction event in the Gulf of Cadiz from the native area, in case of detectable genetic differences from the Mediterranean Sea populations. To test this and reconstruct the invasion, we assessed the genetic structure of crabs in the Gulf of Cadiz and Alboran Sea. We used sequences of the mitochondrial gene cytochrome c oxidase subunit I (COI), in almost its full length (1511 basepairs), of 149 individuals from three sites along the Spanish Mediterranean coast, two in the Alboran Sea, and two in the Gulf of Cadiz. Our data reveal low genetic variability, with only two haplotypes (here referred to as CSWM1 and CSWM2), compared to its known high genetic diversity in the native range, indicating a strong founder effect in the study region. Here we document an inversion of haplotype predominance between regions, haplotype CSWM2 being dominant in most of the Spanish Mediterranean coast, but less frequent in the Gulf of Cadiz and Alboran Sea. This suggests a secondary introduction of propagules into the investigated area, rather than a new introduction from the native area, nor a natural westward expansion with environmental selection of one haplotype over the other. Further studies with additional populations would help to better unveil the history of yet another invasive species in the Gulf of Cadiz.

Diversity and Distribution of the Inland Water Decapods of Sicily (Crustacea, Malacostraca)

The current knowledge of Sicilian inland water decapod malacostracans is scarce and an updated synopsis on species distribution is lacking. Therefore, we reviewed the checklist and recent distribution of Sicilian inland water decapods based on published and unpublished records and novel observations with the aim of providing an exhaustive repository, also to be used as a sound baseline for future surveys. Overall, five native decapod species occur in the study area, i.e., the atyid shrimp Atyaephyra desmarestii, the palaemonid shrimps Palaemon adspersus, P. antennarius, and P. elegans, and the freshwater crab Potamon fluviatile, and their current local distributions are described. In addition, three alien species were recorded: the common yabby Cherax destructor and the red swamp crayfish Procambarus clarkii, strictly linked to inland waters, and the Atlantic blue crab Callinectes sapidus, a mainly marine species that can also colonise the lower stretches of rivers and coastal brackish waters. The collected data suggest the existence of a partial segregation of native versus non-native species, with the latter currently confined to coastal water bodies and the lower stretches of rivers. Moreover, the exclusively freshwater caridean A. desmarestii and P. antennarius show a parapatric distribution in the study area, which may suggest the existence of mutual exclusion phenomena. The results obtained raise some concerns about the effects of alien species on the native biota, and dedicated monitoring and management strategies should be implemented in order to better understand and mitigate their impact.

An individual-based dataset of carbon and nitrogen isotopic data of Callinectessapidus in invaded Mediterranean waters.

BackgroundThe characterisation of functional traits of non-indigenous and invasive species is crucial to assess their impact within invaded habitats. Successful biological invasions are often facilitated by the generalist diet of the invaders which can modify their trophic position and adapt to new ecosystems determining changes in their structure and functioning. Invasive crustaceans are an illustrative example of such mechanisms since their trophic habits can determine important ecological impacts on aquatic food webs. The Atlantic blue crab Callinectessapidus is currently established and considered invasive in the Mediterranean Sea where it has been recorded for the first time between 1947 and 1949. In the last decade, the blue crab colonised most of the eastern and central Mediterranean Sea and the Black Sea and it is currently widening its distribution towards the western region of the basin.New informationStable isotope analysis is increasingly used to investigate the trophic habits of invasive marine species. Here, we collated individual measures of the blue crab δ13C and δ15N values and of its potential invertebrate prey into a geo-referenced dataset. The dataset includes 360 records with 236 isotopic values of the blue crab and 224 isotopic data of potential prey collected from five countries and 12 locations between 2014 and 2019. This dataset allows the estimation of the trophic position of the blue crab within a variety of invaded ecosystems, as well as advanced quantitative comparisons of the main features of its isotopic niche.

A Comparison of Traditional and Locally Novel Fishing Gear for the Exploitation of the Invasive Atlantic Blue Crab in the Eastern Adriatic Sea

The Atlantic Blue Crab Callinectes sapidus has been recognized as invasive in the Mediterranean Sea, where it now provides a significant contribution to artisanal fisheries. In this study, we compared the efficiency, selectivity, and productivity of American wire crab traps and traditional fyke nets for the capture of Blue Crabs in a study conducted from June to December 2019 in the Parila Lagoon (River Neretva Estuary, Croatia). A total of 7707 specimens were caught in 15 wire traps, comprising 6959 males and 749 females. The total catch using 50 traditional fyke traps was 1451 crabs, of which 1211 were males and 240 were females. In general, wire crab traps showed a higher capture selectivity and economic performance compared to fyke nets. The catch per unit effort (CPUE) was 102.76 kg for the American wire crab trap and 5.96 kg for the traditional fyke net. The CPUE of gravid female Blue Crabs was lower for the wire traps than the fyke nets. Herein, the utility of crab traps as selective fishing gear for the capture of Blue Crabs, and management tools for control of the reproductive and recruitment phases of the crab, are discussed, with the perspective of future exploitation of the species as a commercially valuable shellfish product in the Mediterranean.

Size-weight relationships and condition factor of the invasive Atlantic blue crab Callinectes sapidus Rathbun, 1896 (Decapoda: Brachyura: Portunidae) from northern Tunisia: a preliminary investigation

Abstract We determined the condition factor and relative growth patterns of the newly established invasive Atlantic blue crab Callinectes sapidus in the Ghar El Melh Lagoon, northern Tunisia, central Mediterranean Sea using two biometric relationships: carapace width-weight and carapace length-weight. Crabs were sampled during winter and summer 2020. Growth coefficient (slope b) for width-weight relationship ranged from 2.037 to 3.008 according to sex and seasons, indicating an isometry to negative allometry growth patterns. Length-weight relationship, however, demonstrated isometry growth patterns, with the exception of the summer sample, which displayed a positive allometry. The allometry seems to be not affected by seasons, but sex demonstrated a strong effect for the width-weight relationship, as indicated by ANCOVA. The Fulton’s condition factor, however, showed significant variation between seasons, but not between sexes.

A global occurrence database of the Atlantic blue crab Callinectes sapidus

The Atlantic blue crab Callinectes sapidus is a portunid native to the western Atlantic, from New England to Uruguay. The species was introduced in Europe in 1901 where it has become invasive; additionally, a significant northward expansion has been emphasized in its native range. Here we present a harmonized global compilation of C. sapidus occurrences from native and non-native distribution ranges derived from online databases (GBIF, BISON, OBIS, and iNaturalist) as well as from unpublished and published sources. The dataset consists of 40,388 geo-referenced occurrences, 39,824 from native and 564 from non-native ranges, recorded in 53 countries. The implementation of quality controls imposed a severe reduction, in particular from online databases, of the records selected for inclusion in the dataset. In addition, a technical validation procedure was used to flag entries showing identical coordinates but different year of record, in-land occurrences and those located close to the coast. Similarly, a flagging system identified entries outside the known distribution of the species, or associated with unsuccessful introductions.

Accelerated invasion of decapod crustaceans in the southernmost point of the Atlantic coast of Europe: A non-natives’ hot spot?

Observations of previously unrecorded non-native species in the Gulf of Cadiz (Spain), situated between the Atlantic Ocean and the Mediterranean Sea, have accelerated since 1980, and increased rapidly in the past 5 years. Four new records of decapod crustaceans have been detected in this region: the African snapping shrimp Alpheus sp., the West African cleaner shrimp Lysmata uncicornis, the Indo-West Pacific giant tiger prawn, Penaeus monodon, and the Atlantic blue crab Callinectes sapidus. The introduction and establishment of these species into the coastal waters of this region, the southernmost Atlantic coast of Spain may have been influenced by recent anthropogenic alteration of habitat, particularly estuaries and salt marshes, and by climate change facilitating the spread of warm water biota.

Using online questionnaires to assess marine bio-invasions: A demonstration with recreational fishers and the Atlantic blue crab Callinectes sapidus (Rathbun, 1986) along three Mediterranean countries

Marine bioinvasions require integrating monitoring tools with other complementary strategies. In this study, we collected information about the invasive alien crab Callinectes sapidus in Italy, Croatia and Montenegro, by means of online questionnaires administered to recreational fishers (n = 797). Our records matched the current distribution of the species: C. sapidus resulted far more common in the Adriatic/Ionian than in the Tyrrhenian/Ligurian sector. Most respondents rated the species as ‘occasional’ or ‘rare’. Moreover, the more C. sapidus was considered to be abundant, the more fishers tended to perceive it as a negative disturbance over fisheries and the environment. Our findings suggest that C. sapidus is more common than previously thought in most of the study area, and it could have reached the levels of a true invasions in the south-eastern Adriatic Sea. This experience demonstrates that online questionnaires can be appropriate tools to effectively engage stakeholders in alien species monitoring.

Expansion history of the blue crab (Callinectes sapidus Rathbun, 1896) in the Eastern Iberian Peninsula (Western Mediterranean Sea).

Expansion history of the blue crab (Callinectes sapidus Rathbun, 1896) in the Eastern Iberian Peninsula (Western Mediterranean Sea).

Individual and combined effects of low dissolved oxygen and low pH on survival of early stage larval blue crabs, Callinectes sapidus.

A large number of coastal ecosystems globally are subjected to concurrent hypoxic and acidified conditions that will likely intensify and expand with continued climate change. In temperate regions, the spawning of many important organisms including the Atlantic blue crab Callinectes sapidus occurs during the summer months when the severity of coastal hypoxia and acidification is the greatest. While the blue crab earliest larval stage can be exposed to co-occurring hypoxia and acidification observed in many coastal ecosystems, the effects of these concurrent stressors on larval blue crab survival is unknown. This study investigated the individual and combined consequences of low dissolved oxygen (DO) and low pH on blue crab larvae survival through a series of short-term experiments. During 14-day experiments with moderately hypoxic conditions (117–127 μM O2 or 3.74–4.06 mg L-1) and acidified conditions (pH on total scale of 7.16–7.33), low DO and low pH individually and significantly reduced larval survival by 60% and 49%, respectively, with the combination of stressors reducing survival by 87% compared to the control treatment (210–269 μM O2 or 6.72–8.61 mg L-1, 7.91–7.94 DO and pH, respectively). During 4-day experiments with lower DO levels (68–83 μM O2 or 2.18–2.62 mg L-1) and comparable pH levels of 7.29–7.39, low DO individually reduced survival by >90% compared to the control (261–267 μM O2 or 8.35–8.54 mg L-1, 7.92–7.97 DO and pH, respectively), whereas low pH had no effect and there was no interaction between stressors. Over a 4-day period, the DO threshold at which 50% of the larval blue crab population died (LC50) was 121 μM O2 (3.86 mgL-1). In 14-day experiments, the DO and pH effects were additive, yielding survival rates lower than the individual treatments, and significantly correlated with DO and pH concentrations. Collectively, these findings indicate that blue crab sensitivity to both low DO and low pH are acute within the larval stage, depend on the intensity and duration of exposure, and leads to mortality, thereby potentially contributing to the interannual variability and possible regional declines of this fishery.

Trophic flexibility of the Atlantic blue crab Callinectes sapidus in invaded coastal systems of the Apulia region (SE Italy): A stable isotope analysis

The Atlantic blue crab Callinectes sapidus is recognized as an Invasive Alien Species in the Mediterranean Sea. However, its trophic role and feeding flexibility in invaded benthic food webs have been addressed only recently. Here, field samplings were conducted in winter and summer in five coastal systems of the Apulia region (SE Italy), three located on the Ionian Sea (Mar Piccolo, Torre Colimena, and Spunderati) and two on the Adriatic Sea (Acquatina and Alimini Grande). Captured blue crabs were weighed and had their δ13C and δ15N isotopic signatures measured; their trophic level (TL) was estimated using the mussel Mytilus galloprovincialis as isotopic baseline.C. sapidus abundances varied greatly across systems and seasons, and in Adriatic systems the species was not collected in winter. Trophic levels showed significant spatial and temporal variations, although with no general pattern. In winter, the Mar Piccolo population showed the highest TL values; the lowest estimates were in Torre Colimena and Spunderati, where crabs showed δ13C signatures significantly higher than mussels, suggesting the contribution of 13C-enriched plant material in the diet. In summer, with the exception of the Mar Piccolo, Ionian populations increased their trophic level; both Adriatic populations were characterized by the lowest TL estimates. The analysis performed at the individual scale further indicated body weight-related changes in trophic level. For the Torre Colimena population, in particular, a hump-shaped pattern was observed in both seasons. The present study highlighted a considerable spatial and temporal trophic flexibility of C. sapidus at the population scale, while at the individual scale size-related shifts in trophic level were observed. The ability of the blue crab to vary its energy sources in relation with season, local environmental conditions, and ontogenetic stage is emphasized, suggesting that it may represent a key determinant of its invasion success.

The trophic position of the Atlantic blue crab Callinectes sapidus Rathbun 1896 in the food web of Parila Lagoon (South Eastern Adriatic, Croatia): a first assessment using stable isotopes.

The Atlantic blue crab Callinectes sapidus is to date widely distributed in the Mediterranean Sea, where is recognized as an Invasive Alien Species. Noticeably, while records of its occurrence are increasing, quantitative information on its functional role in the benthic food webs of invaded coastal habitats are scarce.Here, carbon and nitrogen isotopic signatures were measured in C. sapidus and other representative taxa of the benthic flora and fauna sampled in summer in the Parila Lagoon, a coastal basin located in the Neretva River estuary area (Croatia). d15N values of individual blue crab specimens were used to calculate their trophic position (TP) , using the filter feeder mussel Mytilus galloprovincialis as the isotopic baseline. In general, the isotopic signature of C. sapidus was comparable with those characterizing invertebrate and fish predators (e.g., Hexaplex trunculus, Gobius niger). An average trophic position of 3.73 was estimated for the blue crab population. However, a considerable inter-individual variation was observed in TP values, significantly related with the size of the specimens. Interestingly, a hump-shaped quadratic polynomial resulted the best fitting model for the data, characterized for small-size individuals by a positive body size-TP relationship, leveling or even turning negative for larger adult crabs. The interplay between environmental factors and ontogenetic diet shifts in determining the trophic position of the blue crab and, ultimately, its ecological impact on the benthic community of the Parila Lagoon is discussed.