Carcinus Maenas Research Articles

Artificial light at night alters predation on colour-polymorphic camouflaged prey

Artificial light at night (ALAN) disrupts biological processes across taxa and at all levels of organisation. Despite growing interest in this globally pervasive sensory pollutant, its impact on colour-guided processes remains largely unexplored. This is especially concerning given the rapid transition in recent years away from narrow-spectrum lighting and towards broad-spectrum options such as white LEDs, which are rich in the short wavelengths of light to which many taxa are particularly sensitive. Camouflage is particularly likely to be disrupted by broader spectra of ALAN due to changes in conspicuousness in background matching prey, which may alter prey recognition in visually guided predators. We simulated natural intensities of moonlight with and without ALAN, using both broad-spectrum (‘white’) ALAN and ALAN filtered to remove the characteristic short (blue) wavelength peak of broad-spectrum LEDs to test whether filtering might mitigate their effects. We tested how exposure to these light treatments impacted predator-prey interactions, using the intertidal crab Carcinus maenas and contrasting colour morphs of the colour-polymorphic snail Littorina obtusata as a model system. Exposure to broad-spectrum ALAN reduced overall predation and reversed the pattern of colour-based prey selection observed under control conditions. Snails were 55 % less likely to be attacked under broad-spectrum ALAN than in control conditions, with likelihood decreasing over 70 % for yellow snails. Yellow snails were over 26 % more likely to be attacked than brown ones under control conditions, but brown snails were over 40 % more likely to be attacked than yellow ones under broad-spectrum ALAN. Exposure to filtered ALAN removed any significant colour-based difference in prey recognition. Our results demonstrate that spectral composition is a crucial aspect of ALAN as a sensory pollutant, capable of instigating profound changes in predator-prey interactions that could drive changes in population demography and increase morphological homogeneity in species that depend on colour polymorphism for camouflage.

Horizon scanning for potentially invasive non-native marine species to inform trans-boundary conservation management – Example of the northern Gulf of Mexico

Prevention of non-native species introductions and establishment is essential to avoid adverse impacts of invasive species in marine environments. To identify potential new invasive species and inform non-native species management options for the northern Gulf of Mexico (Alabama, Mississippi, Louisiana, Texas), 138 marine species were risk screened for current and future climate conditions using the Aquatic Species Invasiveness Screening Kit. Species were risk-ranked as low, medium, high, and very high risk based on separate (calibrated) thresholds for fishes, tunicates, and invertebrates. In the basic screening, 15 fishes, two tunicates, and 26 invertebrates were classified as high or very high risk under current climate conditions. Whereas, under future climate conditions, 16 fishes, three tunicates, and 33 invertebrates were classified as high or very high risk. Very high risk species included: California scorpionfish Scorpaena guttata, red scorpionfish Scorpaena scrofa, purple whelk Rapana venosa, and Santo Domingo false mussel Mytilopsis sallei under both current and future climates, with weedy scorpionfish Rhinopias frondosa, Papuan scorpionfish Scorpaenopsis papuensis, daggertooth pike conger Muraenesox cinereus, yellowfin scorpionfish Scorpaenopsis neglecta, tassled scorpionfish Scorpaenopsis oxycephalus, brush-clawed shore crab Hemigrapsus takanoi, honeycomb oyster Hyotissa hyotis, carinate rock shell Indothais lacera, and Asian green mussel Perna viridis under climate change conditions only. This study provides evidence to inform trans-boundary management plans across the five Gulf of Mexico states to prevent, detect, and respond rapidly to new species arrivals.

Trophic ecophysiology of the native green shore crab, Carcinus maenas, and the invasive Asian shore crab, Hemigrapsus sanguineus, in the rocky intertidal of Helgoland (North Sea)

The brachyuran crabs Carcinus maenas and Hemigrapsus sanguineus belong to the most ´successful´ invaders along the oceans coasts. In 2009, H. sanguineus appeared at the rocky intertidal of the island of Helgoland in the North Sea, where it encounters the native Green shore crab, C. maenas. H. sanguineus established a self-sustaining population, approaching in numbers and biomass that of C. maenas. Both species are considered to be opportunistic omnivores with variable food preferences and, thus, are potential competitors for food. To evaluate the intrinsic properties of either species to utilize food, we analyzed their stomach content, the morphology of the gastric mills, which shred the ingested food, the activities of digestive enzymes during a seasonal cycle, and the stable isotope ratios. A huge share of the stomach contents was macerated and, thus, could not be identified. The shares of animal food and algae food were almost equal in C. maenas but algae food dominated over animal food in H. sanguineus. The gastric mill of C. maenas shows blunt medial tooth and rounded lateral teeth, which indicates efficient grinding of a carnivorous diet. In contrast, the gastric mill of H. sanguineus shows sharp ridges, which facilitate cutting of algal food. The activities of the proteolytic enzymes trypsin and leucine-aminopeptidase were almost equal in both species with slightly higher activities in C. maenas in summer. The activities of the carbohydrases laminarinase and amylase dominated in H. sanguineus during all seasons. Stable isotope ratios indicate a higher degree of carnivory in C. maenas. The morphological and biochemical features indicate that C. maenas is better suited to utilize animal food and H. sanguineus algal food. Upon scarcity of animal food or severe competition with C. maenas, H. sanguineus may be able to increase the amount of algal food and to utilize it efficiently.

On the rebound: removal programs yield local-scale benefits but do not sustainably suppress populations of invasive European green crabs (Carcinus maenas)

On the rebound: removal programs yield local-scale benefits but do not sustainably suppress populations of invasive European green crabs (Carcinus maenas)

Thermal acclimation and habitat-dependent differences in temperature robustness of a crustacean motor circuit.

At the cellular level, acute temperature changes alter ionic conductances, ion channel kinetics, and the activity of entire neuronal circuits. This can result in severe consequences for neural function, animal behavior and survival. In poikilothermic animals, and particularly in aquatic species whose core temperature equals the surrounding water temperature, neurons experience rather rapid and wide-ranging temperature fluctuations. Recent work on pattern generating neural circuits in the crustacean stomatogastric nervous system have demonstrated that neuronal circuits can exhibit an intrinsic robustness to temperature fluctuations. However, considering the increased warming of the oceans and recurring heatwaves due to climate change, the question arises whether this intrinsic robustness can acclimate to changing environmental conditions, and whether it differs between species and ocean habitats. We address these questions using the pyloric pattern generating circuits in the stomatogastric nervous system of two crab species, Hemigrapsus sanguineus and Carcinus maenas that have seen a worldwide expansion in recent decades. Consistent with their history as invasive species, we find that pyloric activity showed a broad temperature robustness (>30°C). Moreover, the temperature-robust range was dependent on habitat temperature in both species. Warm-acclimating animals shifted the critical temperature at which circuit activity breaks down to higher temperatures. This came at the cost of robustness against cold stimuli in H. sanguineus, but not in C. maenas. Comparing the temperature responses of C. maenas from a cold latitude (the North Sea) to those from a warm latitude (Spain) demonstrated that similar shifts in robustness occurred in natural environments. Our results thus demonstrate that neuronal temperature robustness correlates with, and responds to, environmental temperature conditions, potentially preparing animals for changing ecological conditions and shifting habitats.

Investigating the impact of introduced crabs on the distribution and morphology of littorinid snails: Implications for the survival of the snail Littorina saxatilis

Introduced species can have profound impacts on communities by displacing and consuming native organisms. The intertidal communities in the Gulf of Maine have been radically altered through a suite of invasions in the early 1800s, including the herbivorous snail Littorina littorea and the omnivorous European green crab Carcinus maenas leading to morphological and distributional changes in two native gastropod grazers (Littorina saxatilis and Littorina obtusata). Green crabs and native cancrid crabs occupy the mid to low intertidal zones, leaving the high intertidal zones relatively free from crab predation pressure. However, a more recent invasion in the 1980s by the intertidal omnivorous Asian shore crab Hemigrapsus sanguineus, has eliminated this predator-free zone in the high intertidal. This invasion is of particular concern to populations of L. saxatilis, which were relegated to the high intertidal through combined competition and predation pressure by L. littorea and C. maenas. In order to quantify the potential impact of H. sanguineus on native snails, we conducted both field and lab experiments, testing the susceptibility of different sized snails to predation by introduced crabs. Additionally, we measured the distribution, abundance, and morphology of intertidal snails and crabs. Smaller snails of all species were the most susceptible to predation, although susceptibility differed among snail species and predation capabilities differed among crab species. L. saxatilis was the most vulnerable snail species to predation, with 73 and 64% of the population susceptible to large H. sanguineus and small C. maenas, respectively, while >96% of the L. littorea population was resistant to predation. L. saxatilis has been relegated to the high intertidal where there is high abiotic stress and poor-quality food, but until the invasion of H. sanguineus, there was little predation risk. This added predation pressure may further threaten populations of L. saxatilis, especially as the upper intertidal becomes more hostile with increasing temperatures and possible species introductions.

Implications of Warming on the Morphometric and Reproductive Traits of the Green Crab, Carcinus maenas

Understanding the relationship between environmental temperature and the biological traits of organisms is fundamental to inferring the potential impacts of climate change. In the case of marine poikilotherm species, seawater temperature is one of the main driving forces of biological processes, with consequences at higher levels of organization such as population and ecosystem. In this study, we analysed differences in maximum carapace width (CWmax), size at maturation, relative size at maturation, and duration of the reproductive season for the green crab (Carcinus maenas) along a temperature gradient. An extensive review of bibliographic data was performed on studies published between 1962 and 2020, gathering C. maenas data from 55 different populations, spread over 20 degrees of latitude and 14.2 °C of sea surface temperature (SST). In addition, green crab data were collected at five different lagoons and estuaries along the continental Portuguese coast. The relationship between average SST and CWmax, age of maturation, reduction of size at maturation, and duration of egg bearing was analysed to understand the role of SST in driving variation in these C. maenas characteristics across a latitudinal gradient. There was a significant relationship between SST and CWmax for males and SST and CW of females at maturation, respectively. The results extrapolate for each local projected temperature increase caused by climate change and suggest an effect on the morphometric and reproductive traits of C. maenas across regions. These changes comprise an overall reduction in C. maenas body size, an enlargement of the reproductive season, a shortening in the duration of larval developmental time, and a decrease in the relative size of crabs at maturation. Secondary consequences on the fecundity and connectivity of populations are discussed.

The impact of food availability on risk-induced trait responses in prey

Abstract Prey respond to predation risk by altering their morphology, physiology, and behavior, responses that may come at a cost to prey foraging and growth. However, their perception of risk may depend upon the environmental context in which the interaction occurs. Here, we examined how food availability influenced prey’s responses to a nonlethal but free-ranging predator. We used an experimental mesocosm set-up of an intertidal system of green crab (Carcinus maenas) predators and dogwhelk snail (Nucella lapillus) prey, with blue mussels as the basal resource. We measured individual Nucella risk-aversion behavior (summed value of their habitat use) and their growth throughout the 28-day experiment. We found that when Nucella were exposed to predation risk, they had greater risk-aversion behavior when food was available as compared to when food was not. We also found that risk-aversion behavior increased over time in all treatments but that individuals exposed to predation risk with food always had greater risk-aversion behavior. Nucella had significantly more growth when provided with food as compared to without. In treatments with food, snails exposed to predation risk had significantly reduced growth compared to those not exposed to risk. In treatments without food, predation risk had no effect on growth. Our results support the hypothesis that greater resource availability significantly increases individual risk responses and the costs of risk avoidance, thus food magnifies risk-induced non-consumptive effects. They provide insights into context-based predation risk effects and how individuals may prioritize safety versus foraging depending upon perceived risk, food availability, and the costs of responding.

Differential analysis of the haemolymph proteome of Carcinus maenas parasitized by Sacculina carcini (Cirripeda, Rhizocephala) reveals potential mechanisms of parasite control

Sacculina carcini is an endoparasite of the green crab, Carcinus maenas. This parasite induces behavioural changes in its host and affects its metabolism by inhibiting moulting and reproduction. Using a proteomic approach in mass spectrometry, we studied the haemolymph proteomes of healthy and parasitized wild green crabs from Brittany, France to identify proteins that are differentially expressed as a consequence of parasitization. We also investigated specific proteins involved in reproduction, moulting, and immunity. We detected 77 proteins for females and 53 proteins for males that were differentially present between the healthy and parasitized crabs, some of which were sex-specific. Detection of these differentially expressed proteins suggests that the parasite can inhibit and promote different aspects of the immune response of the host. Sacculina appears to inhibit host melanisation for self-protection, while promoting the presence of immune factors, such as antimicrobial peptides to cope with possible bacterial superinfections. Moreover, one protein, juvenile hormone esterase-like carboxylesterase, was 17-times more abundant in parasitized crabs than in healthy crabs and may be responsible for inhibiting moulting and reproduction in parasitized crabs, thus ensuring the success of Sacculina reproduction.

Macro and microscopic maturation stage key of green crab (Carcinus maenas, Linnaeus 1758): Reproductive cycle and differences among estuarine systems

Gonadal histology is a helpful tool to validate species' macroscopic maturity stages in fisheries biology. Regardless of the many studies on Carcinus maenas, there are still few concerning gonads tissue histology and description of maturity stages. In Portugal, information regarding this species' biology to help support the regulation of crab fisheries, including the minimum landing size, has not yet been defined. In this work, the macro and microscopic characteristics of the reproductive cycle of C. maenas, oogenesis, and spermatogenesis development stages along the Portuguese coast are described, and a new macroscopic scale based on the histological analyses is suggested. During 2019 and 2020, adult C. maenas (both males and females) were collected from the Ria de Aveiro estuary, Rio Sado estuary, and Ria Formosa lagoon, respectively, North, Center, and South Portugal. No-significant differences (P > 0.05) were observed in carapace width and individual weight between all systems. Significant differences (P < 0.05) were observed in gonad weight, gonadosomatic index, and Fulton's condition index between the Rio Sado estuary and Ria Formosa lagoon. Furthermore, significant differences (P < 0.05) in the oocyte diameter between the northern and southernmost locations suggest a geographic variation related to the local environmental conditions of each system. Principal component analysis (PCA) revealed maturity stage and carapace width an association, and a similar morphometry between Ria de Aveiro and Ria Formosa. Temperature was correlated to both maturity stage and carapace width in Ria de Aveiro and Ria Formosa. From the histological analysis and based on microscopic criteria, it was observed that females previously classified within the late macroscopic development stage 2 should be considered mature, so a classification change in the current ovary's developmental stage is proposed. These findings can allow fisheries researchers to reclassify the estimations of maturity ogives and help support the regulation of this species' fishery. The proposed macroscopic scale was validated by histological analyses and can be used elsewhere.

Identification and functional analysis of endoplasmic reticulum oxidoreductase 1 (ERO1) from the green mud crab Scylla paramamosain: The first evidence of ERO1 involved in invertebrate immune response.

Endoplasmic reticulum oxidoreductase 1 (ERO1) is an important mediator in regulating disulfide bond formation and maintaining endoplasmic reticulum homeostasis. Its activity is transcriptionally regulated by the unfolded protein response (UPR) in the endoplasmic reticulum, which is known to be essential in immunity. However, whether ERO1 is involved in innate immunity in invertebrates remains unclear. In the present study, two subtypes of ERO1 from Scylla paramamosain were first identified and characterized. Sequence analysis revealed the conserved ERO1 domain and the oxidative capacity assay verified the oxidative capacity of SpERO1 recombinant protein. Moreover, SpERO1s were found to be ubiquitously expressed in all the tested tissues, with the highest expression observed in hemocytes. Two SpERO1s exhibited distinct expression patterns in response to Vibrio alginolyticus and White Spot Syndrome Virus (WSSV). Importantly, the downregulation of the expression of immune factors upon bacterial challenge in SpERO1-silenced crabs was observed. These results provided an initial foundation for further investigations into the role of ERO1 in the innate immunity of invertebrates.

The role of octopamine and crustacean hyperglycemic hormone (CHH) in branchial acid-base regulation in the European green crab, Carcinus maenas.

Crustaceans' endocrinology is a vastly understudied area of research. The major focus of the studies on this topic to date has been on the molting cycle (and in particular, the role of crustacean hyperglycemic hormone (CHH)), as well as the role of other hormones in facilitating physiological phenotypic adjustments to salinity changes. Additionally, while many recent studies have been conducted on the acclimation and adaptation capacity of crustaceans to a changing environment, only few have investigated internal hormonal balance especially with respect to an endocrine response to environmental challenges. Consequently, our study aimed to identify and characterize endocrine components of acid-base regulation in the European green crab, Carcinus maenas. We show that both the biogenic amine octopamine (OCT) and the CHH are regulatory components of branchial acid-base regulation. While OCT suppressed branchial proton excretion, CHH seemed to promote it. Both hormones were also capable of enhancing branchial ammonia excretion. Furthermore, mRNA abundance for branchial receptors (OCT-R), or G-protein receptor activated soluble guanylate cyclase (sGC1b), are affected by environmental change such as elevated pCO2 (hypercapnia) and high environmental ammonia (HEA). Our findings support a role for both OCT and CHH in the general maintenance of steady-state acid-base maintenance in the gill, as well as regulating the acid-base response to environmental challenges that C. maenas encounters on a regular basis in the habitats it dwells in and more so in the future ocean.

A novel method for quantifying the attractiveness of lobster trap baits

We developed a new method for quantifying the attractiveness of bait in traps used for crustacean fisheries by using accelerometers in bait containers to assess the amount of time animals spend interacting with the baits. We validated our approach in the laboratory by using time-lapse video recordings to verify that the accelerometry data accurately reflected when, and how much, American lobsters (Homarus americanus) interacted with bait. We then conducted a field experiment comparing traps baited with traditional herring, crushed green crabs (Carcinus maenas), or an inert control. We found that during 48-h trap sets, the number of minutes in which the accelerometers recorded movements of the bait bags was correlated with lobster catch. Although the traps baited with herring did not catch significantly more lobsters than traps baited with crushed green crabs, the accelerometer data revealed differences in bait attractiveness over time. Lobsters interacted less with the green crab bait on the second day of the set, while no such decline was observed with the herring bait. This technique is inexpensive, easy to use, and the data obtained can be more rapidly analyzed than the video data traditionally used for these types of studies, making it well suited for future work on bait choice and attractiveness.

Past energy allocation overwhelms current energy stresses in determining energy allocation trade-offs.

Regeneration of lost appendages is a gradual process in many species, spreading energetic costs of regeneration through time. Energy allocated to the regeneration of lost appendages cannot be used for other purposes and, therefore, commonly elicits energetic trade-offs in biological processes. We used limb loss in the Asian shore crab Hemigrapsus sanguineus to compare the strength of energetic trade-offs resulting from historic limb losses that have been partially regenerated versus current injuries that have not yet been repaired. Consistent with previous studies, we show that limb loss and regeneration results in trade-offs that reduce reproduction, energy storage, and growth. As may be expected, we show that trade-offs in these metrics from historic limb losses far outweigh trade-offs from current limb losses, and correlate directly with the degree of historic limb loss that has been regenerated. As regenerating limbs get closer to their normal size, these historical injuries get harder to detect, despite the continued allocation of additional resources to limb development. Our results demonstrate the importance of and a method for identifying historic appendage losses and of quantifying the amount of regeneration that has already occurred, as opposed to assessing only current injury, to accurately assess the strength of energetic trade-offs in animals recovering from nonlethal injury.

New records of rarely reported species in the Mediterranean Sea (July 2023)

This Collective Article presents new information about the occurrence of 23 marine taxa that belong to five Phyla: two Chlorophyta, one Annelida, six Mollusca, three Arthropoda, eleven Chordata (one Ascidiacea, one Elasmobranchii and nine Teleostei) and extending from the Western Mediterranean to the Levantine Sea. All these records were reported from nine countries from the western to the eastern Mediterranean Sea, with a broad biogeographical coverage as follows: Spain: first records of the sacoglossans Cyerce graeca and Placida tardyi for the Alboran Sea and first records of the nudibranch Marionia gemmii for the Mediterranean waters of Spain; first records of nudibranch Algarvia alba in the Mediterranean Sea. Italy: First report of the long-legged crab Paragalene longicrura, a further new Mediterranean record of the rare offshore rockfish Pontinus kuhlii, first documented record of the spiny butterfly ray Gymnura altavela in Sardinia (Tyrrhenian Sea), new record of the red‐spotted wrasse Lappanella fasciata from the Messina Strait, first documented record of the rarely observed brown moray Gymnothorax unicolor in the Ionian coast, first record of the colonial ascidian Botrylloides israeliensis, first record of the Morocco dentex Dentex maroccanus, first record of mottled shore crab Pachygrapsus maurus and of an adult specimen of barracudina Lestidiops sphyrenoides in the Adriatic Sea, and further new Mediterranean records of Ross worm Sabellaria spinulosa along the same coast. Tunisia: second record of smalleye squaretail Tetragonurus cuvieri from the African Mediterranean coast. Slovenia: first records of the sea slug Trapania graeffei and Melanochlamys wildpretii, with the last one also representing the northernmost finding of this species. Croatia: northernmost record of the endangered twaite shad Alosa fallax in the Adriatic coast. Albania: first records of the Mediterranean spearfish Tetrapturus belone. Türkiye: first record from the Aegean coasts for Türkiye of the green macroalgae Cladophora battersii and Valonia aegagropila. Israel: first record of the skeleton shrimp Caprella acanthifera in the Southeastern Mediterranean Sea. Syria: first record of the Smooth grenadier Nezumia aequalis from Syrian marine waters.

Interspecies and spatial differences in the shell microbiome of Atlantic rock crab Cancer irrotatus and European green crab Carcinus maenas from Atlantic Canada

IntroductionThe native Atlantic rock crab (Cancer irrotatus) and the invasive European green crab (Carcinus maenas) are commercially and ecologically important crustacean species in Atlantic Canada. The importance of microbiomes for host health and ecology has been recognized in many species, although very few studies have focused on crustaceans or their external shell microbiome. This is the first-ever study to characterize and analyze the microbial communities associated with the external carapace of C. irrotatus and C. maenas.MethodsMicrobiome samples were collected from three locations in Atlantic Canada, processed using standard 16S Illumina MiSeq PE250 sequencing and analyzed with the open-access QIIME2 software.ResultsTaxonomic classification of the microbial compositions, as well as alpha- and beta diversities, reveal that the shell microbiome differs by host species between C. irrotatus and C. maenas sampled from the same location and between C. irrotatus sampled from different locations. Interestingly, the differences are greater between species at the same location than between locations for the same species.DiscussionThese are the first-ever results showing that the crustacean shell microbiome not only depends on geographical factors but also on intrinsic factors specific to the host species. This implies that crustaceans exert some impact on their shell microbiome, potentially selecting beneficial taxa. These are important findings that could elucidate contributing factors of crustacean shell diseases that are still poorly understood.

The population dynamics of Carcinus maenas (Crustacea: Portunoidea) in a coastal lagoon (Portugal, SW)

The green crab (Carcinus maenas) population was investigated in a coastal lagoon (Santo André) located on the southwest coast of Portugal. This study assessed the spatial-temporal variability of green crab abundance in the lagoon and its relationship with environmental variables. Experimental fishing was used to collect data on abundance, size structure and other demographic characteristics. Sampling was conducted monthly in 2019 at five sites, using fyke nets. From a total of 15063 individuals collected, 3898 were analysed. The highest catches were obtained in winter and at sites closer to the sea. The population was male-biased (58.70% of males and 41.30% of females), with an average carapace width of 48.81 mm for males and 40.79 mm for females. Ovigerous females were most abundant in December and January, and 50% were sexually mature at 45.11 mm. Based on data from the experimental fishing and fishermen’s logbooks, the estimated annual catch of green crab ranged from 1873 to 3354 kg/ha, confirming the potential value of its fishery in the lagoon. This resource can be exploited for multiple purposes, including its meat or shell waste, thus contributing to the circular economy. Considering that green crab is a bycatch of the eel fishery, fishing regulations need to be modified to safeguard the stocks of both species.

Maternal influence on the larval morphometry of the brush-clawed shore crab Hemigrapsus takanoi (Decapoda: Brachyura)

The morphology of larvae is a key factor influencing their behaviour, performance and ultimately their survival. There is evidence indicating a significant morphological variability among broods, and that this may be related to the size or conditions of the mother. However, this maternal influence is not consistent across decapod crustaceans. Using 35 broods from different mothers of the crab Hemigrapsus takanoi collected in the same locality of inner Tokyo Bay and at the same time, we tested the hypothesis that there is a positive relationship between the size of the mother and the progeny’s morphology. Our results indicate that different patterns in the length of the lateral, rostral and dorsal spines differentiated two distinct morphogroups of larvae. These morphogroups were linked to the size of the mother, showing that larger mothers produced bigger larvae with longer carapace spines. It is possible that larger size and longer spines can influence swimming performance and predator avoidance, respectively. These relationships should be tested in future experimental studies.

Aliens eating aliens: an introduced amphipod as a potential prey of an invasive rocky shore crab in laboratory experiments

Behavioural interactions between introduced predators and introduced prey are still largely underestimated. The present work takes advantage of the co-occurrence of two introduced species, the Asian shore crab Hemigrapsus sanguineus and the amphipod Ptilohyale littoralis, respectively first recorded on rocky shores along the French coast of the eastern English Channel in 2005 and 2016. In this context, the predation by male and female H. sanguineus on P. littoralis was examined under controlled laboratory conditions, by presenting either juveniles of the blue mussel Mytilus edulis or adult P. littoralis to H. sanguineus. We subsequently assessed the potential prey preference of the Asian shore crab for P. littoralis and M. edulis by presenting the two prey items simultaneously in the same proportion. In the absence of choice, male H. sanguineus preyed significantly more on M. edulis than P. littoralis. In contrast, females preyed significantly less on M. edulis than P. littoralis; however, male and female H. sanguineus consumed similar numbers of P. littoralis. When choice was possible between P. littoralis and M. edulis, the crab did not exhibit preference strictosensu for any type of prey. These results suggest that the Asian shore crab cannot be considered as a naive predator when confronted to a newly introduced prey. Our results also suggest that the amphipod P. littoralis did not exhibit any effective antipredator response towards the crab. These observations nevertheless warrant further work on the effects of abiotic factors (e.g. temperature) as well as other biotic interactions (e.g. presence of other prey or predators for H. sanguineus) may have on the observed prey-predator interactions between H. sanguineus and M. edulis and P. littoralis.

Detection of non-ribosomal and polyketide biosynthetic genes in bacteria from green mud crab Scylla serrata gut microbiome and their antagonistic activities

Multi-modular enzyme complexes known as non-ribosomal peptide synthetases (NRPSs) and polyketide synthetases (PKSs) have been widely reported in bacteria that produce secondary bioactive metabolites such as non-ribosomal peptides (NRPs) and polyketides (PKs), respectively. These NRPS/PKS pathways contribute to synthesizing several antibiotics, such as vancomycin, rifamycin, and bleomycin, which are vital in human medicine. The present study aimed to isolate gut-associated bacteria from mud crab Scylla serrata, and detect NRPS and PKS gene clusters associated with it. This study included 36 bacterial isolates from five mud crab gut samples. Biosynthetic gene clusters (NRPS and PKS), were detected by PCR using degenerative primers specific to these genes. Three isolates (FKP2–4, FKP4–1, and FKP2–16) were positive for NRPS and two for PKS (FKP2–4 and FKP4–1) genes. The isolates were subjected to 16S rRNA gene amplification and sequenced. In silico analysis of the sequences using the Basic Local Alignment Search Tool (BLAST) identified the isolates FKP2–4, FKP4–1, and FKP2–16 as Acinetobacter variabilis, Vagococcus fluvialis, and Staphylococcus arlettae, respectively, after comparing with the existing sequences available in the National Center for Biotechnology Information (NCBI) database. Compared to the control, it was observed that these isolates exhibited intriguing antagonistic activities against Escherichia coli and Staphylococcus aureus. However, these isolates failed to show significant activity against Candida albicans. Exopolysaccharide production by the isolated organisms was tested using Zobell marine agar (ZMA) with 5% sucrose, but none of the colonies were mucoid or slimy.