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

Salinity tolerance of the invasive blue crab Callinectes sapidus: From global to local, a new tool for implementing management strategy

The latest report from the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) raises concerns about the global proliferation of non-native species (NIS) driven by increasing temperatures. In 2023, the invasive blue crab Callinectes sapidus experienced a significant range expansion in the French Mediterranean lagoons, now present in over 20 lagoons and numerous estuaries with different invasion gradients. It has been established that this species is eurytherm (tolerates a wide range of temperatures; 0-40 °C), rendering temperature a non-limiting factor for its proliferation. On the other hand, salinity is a critical factor to consider, as C. sapidus requires brackish water for copulation and saline water for egg maturation. In this study, we present the salinity tolerance of C. sapidus using the metabolic performance to define the tolerance of the species to a large range of salinities (13 levels from 0 to 65 psu). Results showed that C. sapidus tolerates a large range of salinities with a minimum critical threshold (CTmin) at 0 psu, an optimum at 18.5 psu, and a CTmax at 62.4 psu. Using the performance curve equation, we applied the curve to real salinity data measured each month in 2023 in 20 lagoons invaded. Using this approach, we were able to map, on a fine spatial scale, the distribution of suitable habitats for C. sapidus in the year 2023. Additionally, we have developed a tool to prioritize the lagoons based on their suitability, thereby providing a decision-making framework for management measures in each lagoon. It emerged that 50 % of lagoons were priority areas, 10 % were intermediate and 40 % required monitoring. On the basis of this approach, we can respond to European regulations to help decision-makers implement action plans and/or early detection programs for invasive species management.

Opportunistic omnivory impairs the use of the Atlantic blue crab Callinectes sapidus as a trace metal biomonitor in invaded Mediterranean coastal waters

The contribution of non-indigenous species to the transfer of contaminants in invaded food webs represents an active research area. Here we measured trace metals and CN stable isotopes in five populations of the invasive Atlantic blue crab Callinectes sapidus and in baseline bivalve species from Spain, Italy and Greece. They were used to estimate trophic transfer effects and the trophic position and isotopic niche of C. sapidus. Maximum trophic transfer effects occurred where the crab showed the largest isotopic niches and highest trophic positions; furthermore, the consistency of trace metal profiles between bivalves and crabs co-varied with the trophic position of the latters. Omnivory may influence the success of an invasive species, but also limit its effectiveness for biomonitoring. However, our results indicated that stable isotopes analysis provides a clarifying background where to cast patterns of contamination of the blue crab as well as of other omnivorous biomonitor species.

The Blue Treasure: Comprehensive Biorefinery of Blue Crab (Callinectes sapidus)

The blue crab, Callinectes sapidus (Rathbun, 1896), has become an invading species in the Mediterranean region, almost completely replacing native species within a few years and causing significant loss to local production. In some areas, there is an urgent need to propose new supply chains based on blue crab exploitation, where the potential valorisation routes for unsaleable blue crab and waste play an important role. The final purpose is to transform a threat into a treasure, towards a more sustainable world. In addition to applications in food industries, the considerable quantity of bioactive compounds in by-products, such as polysaccharides, proteins, amino acids, carotenoids, and chitin, needs to be capitalised by means of efficacious strategies and appropriate management. Crab exoskeleton can also be exploited as a carbonaceous material with applications in several fields, including medicine. Blue crab bioactive molecules have been widely recognised for having antioxidant, anticancer, antidiabetic, anti-inflammatory, and antimicrobial properties. Due to these functional and distinctive activities, such high-value components could be employed in various industries such as food-feed-pharma and cosmetics. Recycling and reusing these underutilised but economically valuable waste or by-products could help to reduce the environmental impacts of the whole supply chain from the perspective of the circular economy.

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.

Non-indigenous aquatic fauna in transitional waters from the Spanish Mediterranean coast: A comprehensive assessment

Understanding drivers of spatial variation in non-indigenous species (NIS) is a key goal in invasion biology, but comprehensive assessments providing high-resolution data are extremely scarce. Anthropogenic modifications to transitional waters facilitate the invasion of NIS where they cause both ecological and economic important damage. By screening validated data sources, we conducted a comprehensive assessment of non-indigenous aquatic fauna in Spanish Mediterranean transitional waters (30 sites), as well as assessed introduction pathways, native regions, NIS assemblage patterns and temporal introduction rate. One hundred and twenty-nine NIS were inventoried, with 72 % established and more than half listed before 1980. Two intentional (release, escape) and two unintentional (contaminant, stowaway) introduction pathways were dominant. Recorded NIS originated mostly from North America and Asia. A clear nested pattern in NIS assemblages was observed across sites, suggesting secondary spread from the most invaded waters placed in the northern regions. Our updated inventory should be pivotal for designing prevention protocols and informing specific management plans on non-indigenous fauna in transitional waters.

A horizon scan exercise for aquatic invasive alien species in Iberian inland waters

As the number of introduced species keeps increasing unabatedly, identifying and prioritising current and potential Invasive Alien Species (IAS) has become essential to manage them. Horizon Scanning (HS), defined as an exploration of potential threats, is considered a fundamental component of IAS management. By combining scientific knowledge on taxa with expert opinion, we identified the most relevant aquatic IAS in the Iberian Peninsula, i.e., those with the greatest geographic extent (or probability of introduction), severe ecological, economic and human health impacts, greatest difficulty and acceptability of management. We highlighted the 126 most relevant IAS already present in Iberian inland waters (i.e., Concern list) and 89 with a high probability of being introduced in the near future (i.e., Alert list), of which 24 and 10 IAS, respectively, were considered as a management priority after receiving the highest scores in the expert assessment (i.e., top-ranked IAS). In both lists, aquatic IAS belonging to the four thematic groups (plants, freshwater invertebrates, estuarine invertebrates, and vertebrates) were identified as having been introduced through various pathways from different regions of the world and classified according to their main functional feeding groups. Also, the latest update of the list of IAS of Union concern pursuant to Regulation (EU) No 1143/2014 includes only 12 top-ranked IAS identified for the Iberian Peninsula, while the national lists incorporate the vast majority of them. This fact underlines the great importance of taxa prioritisation exercises at biogeographical scales as a step prior to risk analyses and their inclusion in national lists. This HS provides a robust assessment and a cost-effective strategy for decision-makers and stakeholders to prioritise the use of limited resources for IAS prevention and management. Although applied at a transnational level in a European biodiversity hotspot, this approach is designed for potential application at any geographical or administrative scale, including the continental one.

Euryhaline Aliens Invading Italian Inland Waters: The Case of the Atlantic Blue Crab Callinectes sapidus Rathbun, 1896

Alien invasive species represent a major threat in Italian freshwaters. Despite national and European regulations aimed at the control and prevention of new invasive species, the number of allochthonous species is increasing and so is the rate of spread. One of the most widespread invasive animals in coastal areas of the Mediterranean Sea is the blue crab Callinectes sapidus, a native of the Western Atlantic from Nova Scotia to Argentina. The species is euryhaline, and besides coastal waters, it is also commonly recorded in upper estuaries and lower reaches of rivers. Considering its fast adaptability and invasiveness, the main purpose of this work is to assess whether its biological plasticity and invasive capability may represent, in addition to marine and coastal habitats, also a potential threat for inland waters. Samples were collected in seven sites distributed between Southern and Central Italy. The new records are herein presented, starting from the original introduction by ballast waters and the actual westward migration in inland waters of Latium and Tuscany. In addition, the threat to biodiversity is also discussed, considering the blue crab aggressiveness toward both vertebrates and invertebrates, which may limit the distribution of native freshwater fish and macrofauna.