Changes in contaminant bioaccumulation and biochemical responses of Carcinus maenas in response to ecosystem restoration measures.

Ballast water is a major vector for the transport of aquatic non-indigenous species among ecosystems worldwide. To comply with the International Convention for the Control and Management of Ships' Ballast Water and Sediments, vessels on international voyages commonly rely on Ballast Water Management Systems (BWMS) to meet the D-2 performance standard, often using ultraviolet (UV) irradiation as a key disinfection step. UV-light-emitting diodes (UV-LEDs) offer a mercury-free UV source with long lifespan and flexibility in wavelength selection; compared to conventional lamps, they are smaller in size and require no warm-up time. Yet, their effects on larger planktonic organisms (≥50μm) remain poorly understood. Here, we tested the effect of UV-C-LED (λ=265nm) on larvae of the invasive European green crab Carcinus maenas, assessing mortality, immobility, and respiration under three UV-C doses (40, 120, and 200mJ·cm-2). All UV-C treatments significantly reduced larval motility and respiration relative to controls, leading to increased mortality over time. Larvae required comparatively high doses (120-200mJ·cm-2) to reach substantial inactivation, relative to doses reported for bacterial and phytoplanktonic fractions. These results provide species- and life stage-specific UV-C thresholds for the ≥50μm size class and demonstrate the value of combining behavioural, lethal and physiological endpoints when validating UV-LED-based BWMS.

The European green crab (Carcinus maenas) is an intertidal crustacean that has extended its invasive range globally and is regarded as a major pest species for bivalves, impacting coastal food chains and aquacultures. Crabs primarily use chemosensory cues to sense their environment for feeding to avoid predation and to locate mates and induce mating. Consequently, known attractants including food baits are frequently employed in trapping and control efforts. Here, we investigate the effects of introducing a predatory fish odour to the environment and show that it elicits anti-predator behaviour in C. maenas. A 45% reduction in crab foraging and feeding behaviour was observed when predator odour was introduced compared with food control experiments. A further 23% reduction (68% reduction overall) in feeding behaviour was observed after crabs were exposed to (though housed separately from) the same seawater as the live predator for several days. This highlights the increased awareness or continuous stress of these habituated crabs towards predator odour. This study also presents potential for application as a deterrent in integrated pest management strategies for this global invader.

Ammonotelic animals excrete their toxic waste ammonia directly into the surrounding environment. To deal with conditions causing elevated hemolymph ammonia levels, such as feeding, an efficient ammonia excretion process must be in place to keep hemolymph ammonia levels within a tolerable range. Although the actual ammonia excretion mechanisms in fish and crustaceans have been investigated extensively, the intracellular regulation of these processes is more or less unknown. To investigate the involvement of the cAMP/PKA and cGMP/PKG pathway in the branchial excretion process, gills from osmoregulating green shore crabs, Carcinus maenas, were isolated and perfused with solutions containing either 200 or 500μmolL-1 NH4Cl, mimicking the hemolymph ammonia levels in the resting state and after feeding, respectively. Basolateral application of forskolin or 8-Bromo-cAMP caused a significant decrease in the ammonia excretion rate. Moreover, cAMP activation caused an increase in metabolically generated ammonia, of which the majority was now transported towards the hemolymph side and not, as seen under control conditions, into the environment. This suggests that cAMP/PKA pathway promotes a so far not described ammonia retention mechanism. In contrast, activating the cGMP/PKG pathway by 8-Bromo-cGMP resulted in an increase of the transbranchial ammonia excretion rate, which could be partially inhibited by the PKG blocker KT5823. Participation of branchial expressed nitric oxide synthase in cGMP synthesis via the soluble guanylyl cyclase is suggested due to the observed inhibitory effect after the application of L-NAME. This study opens a new venue of investigations regarding epithelial ammonia transport regulation in animal systems.

Repeated mild air exposure improves green mud crab (Scylla paramamosain) tolerance to stress: A transcriptomic study

Adult-juvenile interactions between decapod crustaceans in Atlantic Canada: Native rock crabs offer little biotic resistance against non-indigenous green crabs

Abstract Biological invasion is one of the major threats to biodiversity, ecosystem health and services worldwide. In marine ecosystems, invasions are difficult to monitor and control, thus management strategies that can enhance biotic resistance are the key to tackling invasion risks. However, the biotic resistance of marine ecosystems is poorly understood with respect to the influencing factors and regulating mechanisms. We used an individual‐based modelling approach to predict the potential risks of a biological invasion event from an ecosystem perspective, and tested how fishing as a driving factor of ecosystem structure can alter biotic resistance. We considered a species of high invasive risk globally, European green crab ( Carcinus maenas ) as an example, and evaluated its invasion risk in a heavily exploited ecosystem Haizhou Bay, China. Further, we illustrated the role of fishery management to improve biotic resistance in order to inform the development of resistance‐enhancing strategies. We found the Haizhou Bay ecosystem would be vulnerable to the invasion of the green crab, while reducing fishing intensity by half could effectively enhance its biotic resistance by decreasing the invasion success rate by up to 52%. Alternatively, the reduced predation pressure experienced by juvenile C. maenas would largely contribute to successful invasions. Fishing activities could regulate the predation pressure by changing predator biomass and trophic links within the ecosystem, and thereby alter the biotic resistance to invasion. We further designed a range of simplified management strategies that controlled the fishing efforts on selected predators and illustrated their effectiveness to enhance biotic resistance. These strategies could mediate the trade‐offs between fisheries production and ecosystem management to a certain degree. Synthesis and applications. We validated the predation‐based hypothesis of biotic resistance in marine ecosystems and illustrated that fishery management can enhance biotic resistance by changing ecosystem structure. Based on this mechanism, fishery management strategies could simultaneously enhance biotic resistance and reduce management conflicts. We proposed an IBM‐based framework as a comprehensive assessment tool that holds significant potential for developing precautionary management strategies.

Biological invasions are reshaping coastal ecosystems, yet invader performance in aquaculture-influenced salt marsh habitats remains poorly resolved. We conducted an 18-month survey (January 2023-July 2024) at two contrasting salt marsh sites in the Bay of Cádiz, Spain, to compare the invasive Atlantic blue crab (Callinectes sapidus) with the native European green crab (Carcinus maenas). Monthly fyke-net sampling was paired with concurrent prey assessments and water-column measurements. We captured 168 C. sapidus and 1086 C. maenas individuals. Mean abundance (individuals net-1 24h-1) was higher for C. sapidus at the Fish site (1.83±0.36) and for C. maenas at the Oyster site (16.28±1.91). Biomass (ash free dry mass, g) was higher for C. sapidus at the Fish site (11.63±2.08 vs 4.58±1.15 at the Oyster site) and for C. maenas at the Oyster site (10.53±1.22 vs 1.12±0.43 at the Fish site). Body sizes mirrored these patterns (C. sapidus at Fish site: +14.5mm carapace width, +5.9mm carapace length relative to Oyster site; C. maenas at the Oyster site: +2.7mm carapace width, +2.3mm carapace length versus the Fish site; p<0.05). Seasonal peaks differed (C. sapidus: late spring-early summer; C. maenas: winter-spring), with a winter non detection of C. sapidus. Linear mixed-effects models showed that C. sapidus abundance increased under warmer, macroinfauna-rich conditions, whereas C. maenas was more abundant in cooler, more turbid waters with higher availability of fish and hyperbenthic prey. These patterns suggest thermal-prey pathways in aquaculture-modified salt marshes and provide cues for targeted monitoring, removal, and future management.

Multi-tissue transcriptome analyses provide insights into habituation of handling stress in green mud crab (Scylla paramamosain)

Understanding the effects of climate change on the physiology of marine species, particularly during their early life stages (larvae and juveniles), is essential for predicting population dynamics. Carcinus maenas is a widely distributed species of significant ecological and economic importance. This experimental study investigates the effects of warming on the early life stages of the European green crab, C. maenas, through two complementary experiments: (1) larval development and survival were assessed under three temperature regimes—approximately 18.5 °C (representing the annual average Portuguese seawater temperature between 1980 and 2020, used as the control), and two projected climate change scenarios: RCP 4.5 (+1.5 °C) and RCP 8.5 (+3.5 °C), and (2) juvenile survival and growth were monitored in mesocosms from early settlement to sexual maturity. Results indicated that larval mortality exceeded 90 % across all treatments, with 75 % occurring within the first 8 days (95 % CI: 7–8), and that warming enhanced larval survival, with the RCP 4.5 scenario yielding the highest survival rates compared with the control. Additionally, warming also reduced the pelagic larval duration, which declined from 27 (±2) days at 18.5 °C to 16 (±1) days at 22 °C. Similarly, the duration of the megalopa (settlement) stage decreased from 10 to 6 days. Therefore, despite high mortality, accelerated development under warming may enhance population resilience. Juvenile mortality was also high, with 50 % of settled individuals dying within the first 50 (95 % CI: 31–46) days, and differences in growth and survival between sexes were observed: females reached sexual maturity faster than males 83 ± 12 and 109 ± 20 days, respectively. Moreover, only 24 % (95 % CI: 16–34) of the settled females reached sexual maturity, compared to just 9 % of males (95 % CI: 5–18). These results indicate that C. maenas reach reproductive maturity within six months. The biological data reveal a fast growth increment, high larval and juvenile mortality, and suggest that projected climate change scenarios through the end of the century will have a limited impact on the species' population dynamics and recruitment. • Larval mortality rates exceeded 90 % across all temperature treatments. • Warming accelerated larval development and increased survival. • Juvenile mortality was high, with 50 % dying within the first 50 days. • Juveniles reached sexual maturity in less than four months. • Females reached sexual maturity faster than males.

Pyridine is a by-product of several industrial processes and is traditionally extracted from coal tar. In October 2021, a mass stranding of dead, twitching and moribund crustaceans, including edible crabs and lobsters, were observed off the northeast coast of England leading to speculation that pyridine released from dredging was the causal agent. This led to campaign groups asking for a cessation of dredging activity in the Tees estuary until the matter had been resolved. Over the past few years, considerable debate and scepticism have remained among the UK press and the public regarding the potential role of pyridine in this event. To determine the effects of pyridine on juvenile common shore crabs (Carcinus maenus) we conducted a four-day static renewal exposure experiment with the nominal concentrations 1, 10, 100 and 1000 µg/L pyridine hydrochloride. Mortality was recorded and novel activity behaviours (Mean Pixel Difference (MSD)) measured using a Zantiks LT machine after 2 h, 24 h, 48 h, 72 h and 96 h. Concentrations were chosen as below those reported to be lethal but represent some environmentally relevant concentrations recorded in the area over the past decade. No mortality was recorded following four-day exposure at concentrations up to 1 mg/L. There was no significant effect of pyridine exposure on the distance travelled by the juvenile crabs during the experiment. Pyridine did not significantly affect the activity of the crabs, as recorded by the MSD analysis. However, there was an interaction between light and exposure where individuals in the highest exposure concentration were significantly more active during light phases of the experiment. No obvious twitching or erratic limb movement was observed over the course of the experiment. This research highlights the minimal effects that pyridine, has on crab movements and activity at environmentally relevant concentrations. This research supports the opinion that pyridine was an unlikely casual factor in the mass mortality event in crustaceans in 2021. Furthermore, we highlight the promising use of MSD for subtle behavioural movement analysis in ecotoxicology.

Body size is one of the most important traits governing individual‐level demographic rates and modulating population‐level processes. Multiple size‐dependent demographic rates can simultaneously change population structure, so distinguishing their individual contributions to overall population dynamics remains a challenge.Disentangling size‐dependent harvest rates from other demographic rates is critical for assessing the impact of removal on populations of invasive species. Inference about invasive populations can be difficult, however, as observations are often collected opportunistically as part of removal programs, rather than experimentally designed. Yet accurate inference is essential for understanding the feasibility of population suppression and optimising management decisions.We develop an integrated integral projection model (IPM2) that leverages the strengths of the integrated population model and integral projection model to enable inference about complex, size‐structured demographic rates from imperfect observations. We apply the IPM2 in the context of invasive European green crab (Carcinus maenas), a species for which individual body size strongly regulates both the observation‐generating process and latent, population dynamics.The IPM2 facilitates the distinct estimation of green crab size‐structured harvest and natural mortality rates, parameters for which no explicit data is collected and that are unidentifiable in component datasets of the integrated population model. The model represents how the green crab population changes over time, providing the first estimates of size‐structured abundance of this high‐priority species.By forecasting the stable size distribution and equilibrium population size under varying removal efforts, we demonstrate that extremely high levels of removal effort can reduce the equilibrium green crab population size. Yet these high mortality rates also shift the stable size distribution and increase the equilibrium abundance of smaller crabs, since size‐selective removal alters intraspecific interactions. The ecological outcome of this shift in size structure will be variable, as green crab size modulates only some of its interactions with other species. These results highlight the value of the IPM2 framework for inferring complex population dynamics with information needs that outpace information in individual observational datasets, providing a path forward for accurate assessment of conservation programs.

The mitochondrial genome of Grapsus adscensionis (Osbeck, 1765), a rocky shore crab distributed across the Macaronesian archipelagos and the eastern Atlantic, was sequenced and annotated for the first time. The circular mitogenome is 15,553 bp in length and comprises 13 protein-coding genes (PCGs), 22 tRNAs, two rRNAs, and a non-coding control region. It exhibits a strong AT bias, with negative AT- and GC-skews. Gene arrangement and composition are consistent with other brachyuran crabs. These findings provide novel molecular data for the species, representing the third mitogenome published for the genus Grapsus, and contribute to a better understanding of brachyuran evolutionary relationships.

ABSTRACT Invasive predators are a large concern throughout invaded ranges as they commonly compete with native predators and overconsume prey items. European green crabs ( Carcinus maenas ) have a long history of causing the decline of native species populations, many of which are important fishery species, and damaging ecosystems on the Atlantic coast of North America. These invasive crabs are expected to have similar impacts on the Pacific coast of North America. Comparing the predatory capabilities of green crabs with the native red rock crab ( Cancer productus ) on an abundant native bivalve species ( Leukoma staminea , littleneck clam) will help predict how increased predation pressure due to an introduced predator might affect local prey populations. In‐laboratory predator–prey experiments were conducted to examine the behaviour and capabilities of both red rock crabs and green crabs preying upon the littleneck clam. Most red rock crabs broke into clams quickly, typically in less than 10 min, whereas green crabs were unable to damage any size class of bivalve despite overlapping in crusher chelae size with the native crabs. Successful attacks resulted in stereotypic predation traces (consistent in shape and repetitively caused by predatory attack) that are commonly found in the field. Green crabs and red rock crabs utilized different attack strategies while grappling. Because green crabs grappled the clams, in some cases for extensive periods of time, it is probable that they recognise L. staminea as a prey item. Fully‐grown L. staminea are likely in a size refuge from green crab predation. Future work should investigate the interactions between European green crabs and younger, smaller, size‐classes of Leukoma staminea .

Tributyrin enhances growth and intestinal health in green mud crab (Scylla paramamosain) through butyrate-driven metabolic regulation.

The first report of Hematodinium perezi genotype I infection of Chinese mitten crab (Eriocheir sinensis) from the River Thames, UK.

ABSTRACTThe cognitive abilities of canids are increasingly recognized, though insights from noncaptive populations are comparatively rare. Recently, recurring damage to crab traps used by Haíɫzaqv Nation Guardians to control a European Green Crab invasion was investigated with remote cameras. A wolf was recorded emerging from the water carrying a crab trap buoy, then sequentially pulling the attached line up the beach until an initially submerged trap emerged from the water. The wolf then extracted the bait cup from within and consumed the bait. The recorded behavior, combined with similarly extracted and damaged traps nearby, suggests a sophisticated understanding of the trap and sophisticated cognition more broadly. This observation raises questions about the context and origins of the behavior and prompts consideration of our relationship with this cognitively complex species.

Invasive species are reshaping aquatic ecosystems worldwide at an accelerating pace, with profound ecological and economic impacts. Many crustacean species have demonstrated invasive potential or are already well-established invaders. The green shore crab, Carcinus maenas, native to Europe and North Africa, is one of the most successful global marine invaders and is now present on six continents. Although the role of genomics in invasion science is increasingly recognized, genomic resources for brachyuran crabs remain limited, including the notable absence of a reference genome for C. maenas. Here we report on a de novo whole genome assembly of C. maenas via long-read Oxford Nanopore Technology sequencing. The assembly spans 1.09 Gbp across 21,887 scaffolds (NG50 = 13 Mbp) with a BUSCO completeness of 98.4%, providing a high-quality resource for future genomic analyses. We provide a detailed protocol for obtaining high-quality DNA to successfully sequence brachyuran crabs using a long-read approach. This new resource expands available genomic data for the species-rich infraorder Brachyura, and provides a valuable foundation for understanding the genetic factors underlying the global invasion success of C. maenas, supporting future research in marine invasion genomics.

Surveillance of European green crab (Carcinus maenas) and monitoring of three native crab species using different environmental DNA collection methods

Abstract A majority of marine benthic macroinvertebrate and fish species have planktonic larval stages that disperse in the water column from days to months. However, the adaptive significance of pelagic larvae, and whether predation is higher in the pelagic or the benthic environment, is still debated, partly due to a lack of studies assessing larval predation in offshore, pelagic habitats. Here we assess predation mortality on shore crab megalopae ( Carcinus maenas ) using tethering techniques in the eastern North Sea, comparing diel differences in predation rates in five different benthic and pelagic habitats, tethering close to 900 megalopae over a 2‐year period. Our results showed that relative predation rates on shore crab megalopae were up to 10 times higher in shallow benthic nursery habitats (0.5–4 m depth; 23–58% 6 h −1 ) compared to nearshore and offshore pelagic habitats (10–100 m depth; 5–7% 6 h −1 ). This pattern was consistent both during day and night conditions in both years, and also in a 24‐h experiment when the periods of dusk and dawn were included. The higher predation rates in shallow benthic areas were likely a direct effect of an estimated 3 to 4 orders of magnitude higher abundance of potential predators in this habitat compared to the pelagic environment. By demonstrating an order of magnitude lower predation rates in a pelagic offshore environment for the first time, the study provides new support that planktonic larvae may be an adaptation to use pelagic environments as a spatial refuge from high predation rates in shallow nursery habitats.