Carcinus Maenas Research Articles

Larval development of the brush-clawed shore crab Hemigrapsus takanoi Asakura & Watanabe, 2005 (Decapoda, Brachyura, Varunidae)

AbstractThe brush-clawed shore crab Hemigrapsus takanoi is a native species from the Western Pacific and an invader of the European Atlantic coast from northern Spain to southern Denmark. Despite the increasing concern about its rapid expansion, little is known about the early stages in its life history. In the present study, the larval morphology of H. takanoi is described and illustrated from specimens obtained in the laboratory from its type locality, Tokyo Bay, Japan. Its larval development follows the pattern of Varunidae, that involves five zoeae and one megalopa. The morphological characters of the larvae of H. takanoi are compared with those of the other known Hemigrapsus species of the North Pacific. In addition, to facilitate an early detection of the invasive species of Varunidae inhabiting European Atlantic waters, a summary of the key characters to identify their larval stages is included.

Variation in juvenile stages and success of male acquisition in Danish and French populations of the parasitic barnacle Sacculina carcini (Cirripedia: Rhizocephala) parasitizing the shore crab Carcinus maenas

ABSTRACTPopulation and developmental characteristics of the rhizocephalan parasite Sacculina carcini were studied in the Limfjord, Denmark and at Roscoff, France. The frequency of juvenile externae in the Limfjord was higher during summer (69.8% of all externae) than during winter (43%). At Roscoff, 62.6% of externae were juvenile in May-June, but only 8.4% in September. The percentage of juveniles with settled males in the Limfjord was higher in summer (20.7% of all juveniles) compared to winter (6.7%). Juveniles at Roscoff in summer had less success in male acquisition (18.0%). The mean number of settled male cyprids per juvenile externa was 0.56 in summer and 0.12 during winter in the Limfjord, but only 0.27 in the summer at Roscoff. Laboratory kept virgin externae invaded by male cyprids ceased to attract additional males within 5–6 days after the first male settlement and then grew into adults within 3 weeks. Externae without males, kept in isolation, did not grow or show any other signs of maturation. Our results confirm and extend previous data on the role of males and their effect on externa development in S. carcini, and show that the success of male acquisition is susceptible to both seasonal and regional variation.

Improving the efficiency of the Fukui trap as a capture tool for the invasive European green crab (Carcinus maenas) in Newfoundland, Canada.

The European green crab (Carcinus maenas) is a crustacean species native to European and North African coastlines that has become one of the world’s most successful marine invasive species. Targeted fishing programs aimed at removing green crabs from invaded ecosystems commonly use Fukui multi-species marine traps. Improving the efficiency of these traps would improve the ability to respond to green crab invasions. In this study, we developed four distinct trap modifications that were designed to facilitate the successful capture of green crabs, with the goal of improving the performance of the Fukui trap. We tested these modifications in situ during the summer of 2016 at two locations in Placentia Bay, Newfoundland. We discovered that three of our modified Fukui trap designs caught significantly more green crabs than the standard Fukui trap, increasing catch-per-unit-effort (CPUE) by as much as 81%. We conclude that our top-performing modifications have great potential for widespread use with existing Fukui traps that are being used for green crab removal efforts.

Improved camouflage through ontogenetic colour change confers reduced detection risk in shore crabs.

Animals from many taxa, from snakes and crabs to caterpillars and lobsters, change appearance with age, but the reasons why this occurs are rarely tested.We show the importance that ontogenetic changes in coloration have on the camouflage of the green shore crabs (Carcinus maenas), known for their remarkable phenotypic variation and plasticity in colour and pattern.In controlled conditions, we reared juvenile crabs of two shades, pale or dark, on two background types simulating different habitats for 10 weeks.In contrast to expectations for reversible colour change, crabs did not tune their background match to specific microhabitats, but instead, and regardless of treatment, all developed a uniform dark green phenotype. This parallels changes in shore crab appearance with age observed in the field.Next, we undertook a citizen science experiment at the Natural History Museum London, where human subjects (“predators”) searched for crabs representing natural colour variation from different habitats, simulating predator vision.In concert, crabs were not hardest to find against their original habitat, but instead, the dark green phenotype was hardest to detect against all backgrounds.The evolution of camouflage can be better understood by acknowledging that the optimal phenotype to hide from predators may change over the life history of many animals, including the utilization of a generalist camouflage strategy. A plain language summary is available for this article.

After the Fall: Legacy Effects of Biogenic Structure on Wind-Generated Ecosystem Processes Following Mussel Bed Collapse

Blue mussels (Mytilus edulis) are ecosystem engineers with strong effects on species diversity and abundances. Mussel beds appear to be declining in the Gulf of Maine, apparently due to climate change and predation by the invasive green crab, Carcinus maenas. As mussels die, they create a legacy of large expanses of shell biogenic structure. In Maine, USA, we used bottom traps to examine effects of four bottom cover types (i.e., live mussels, whole shells, fragmented shells, bare sediment) and wind condition (i.e., days with high, intermediate, and low values) on flow-related ecosystem processes. Significant differences in transport of sediment, meiofauna, and macrofauna were found among cover types and days, with no significant interaction between the two factors. Wind condition had positive effects on transport. Shell hash, especially fragmented shells, had negative effects, possibly because it acted as bed armor to reduce wind-generated erosion and resuspension. Copepods had the greatest mobility and shortest turnover times (0.15 d), followed by nematodes (1.96 d) and the macrofauna dominant, Tubificoides benedeni (2.35 d). Shell legacy effects may play an important role in soft-bottom system responses to wind-generated ecosystem processes, particularly in collapsed mussel beds, with implications for recolonization, connectivity, and the creation and maintenance of spatial pattern.

Polymerase chain reaction as a promising tool for DNA-based diet studies of crustaceans

Abstract Studying the diet of crustaceans based on the direct visual inspection of the gut contents can be difficult because they can ingest only a portion of the prey and further crush it into very small pieces, making a very few food items identifiable. Here, the usefulness of molecular methods to identify the species present in the gut contents of two crustaceans, the shore crab Carcinus maenas and the brown shrimp Crangon crangon, was tested. Stomach contents were removed, and their total genomic DNA extracted followed by amplification (PCR) with four specific prey mtDNA primers. Since both crustaceans are opportunistic predators, preying upon around 40 different species, the study was restricted to common potential preys in the sampled area, the Minho Estuary (Portugal): the common goby Pomatoschistus microps, the ragworm Hediste diversicolor, the flounder Platichthys flesus and the peppery furrow shell Scrobicularia plana. After testing the most appropriate methodology for DNA extraction and PCR amplification to detect the presence of each potential prey with positive control samples, the same methodology was applied to the stomach content samples. The molecular methods allowed for detection of the presence of P. microps, P. flesus and H. diversicolor in the stomachs of both crustaceans. Therefore, once potential prey and their availability in the system are known, PCR technique can be an alternative tool to overcome some of the limitations of traditional methods in the study of the crustaceans’ diet, even when stomach contents include a great part of ‘detritus’. This study reflects also the need to develop more tools (primers) to improve the assessment of predator–prey interactions in aquatic ecosytems.

RADProc: A computationally efficient de novo locus assembler for population studies using RADseq data.

Restriction site-associated DNA sequencing (RADseq) is a powerful tool for genotyping of individuals, but the identification of loci and assignment of sequence reads is a crucial and often challenging step. The optimal parameter settings for a given de novo RADseq assembly vary between data sets and can be difficult and computationally expensive to determine. Here, we introduce RADProc, a software package that uses a graph data structure to represent all sequence reads and their similarity relationships. Storing sequence-comparison results in a graph eliminates unnecessary and redundant sequence similarity calculations. De novo locus formation for a given parameter set can be performed on the precomputed graph, making parameter sweeps far more efficient. RADProc also uses a clustering approach for faster nucleotide-distance calculation. The performance of RADProc compares favourably with that of the widely used Stacks software. The run-time comparisons between RADProc and Stacks for 32 different parameter settings using 20 green-crab (Carcinus maenas) samples showed that RADProc took as little as 2hr 40min compared to 78hr by Stacks, while 16 brown trout (Salmo trutta L.) samples were processed by RADProc and Stacks in 23 and 263hr, respectively. Comparisons of the de novo loci formed, and catalog built using both the methods demonstrate that the improvement in processing speeds achieved by RADProc does not affect much the actual loci formed and the results of downstream analyses based on those loci.

In vivo effects of serotonin and fluoxetine on cardio-ventilatory functions in the shore crab Carcinus maenas (L. 1758)

Serotonin (5-HT) takes a key position in regulating vital functions, such as cardio-ventilatory activity, locomotion and behaviour. Selective serotonin reuptake inhibitors (SSRIs) modulate the serotonergic system and thus affect these functions. Rhythmic behaviours, such as cardio-ventilatory activity, are controlled by central pattern generators, which in turn are regulated by 5-HT. In crustaceans, 5-HT also regulates the synthesis and secretion of crustacean hyperglycaemic hormone, a pleiotropic hormone involved in the mobilisation and release of glucose into the haemolymph, thus stimulating the animal’s activity. As a matter of consequence, SSRIs may affect cardio-ventilatory activity. In order to examine how the SSRIs affect fundamental physiological parameters based on rhythmic behaviours in decapods, cardio-respiratory activity in the shore crab Carcinus maenas was assessed after pericardial injection of a single dose of either 0.5 μM, 0.75 μM or 1 μM fluoxetine, respectively. Simultaneous recordings of heart and scaphognathite movements in both brachial chambers were conducted by measuring impedance changes in the respective body compartments. Injection of 5-HT had an immediate effect on cardio-ventilatory activities and strongly upregulated both cardiac and ventilatory activities. Fluoxetine showed similar effects, entailing moderate tachycardia and increased ventilation rates. Compared to 5-HT, these effects were delayed in time and much less pronounced. Metabolism of fluoxetine into the active compound nor-fluoxetine might account for the delayed action, whereas compensatory regulation of cardio-ventilatory frequencies and amplitudes are likely to explain the attenuation of the responses compared to the strong and immediate increase by 5-HT. Overall, the results suggest increased 5-HT levels in invertebrates following fluoxetine exposure, which are able to disturb physiological functions regulated by 5-HT, such as cardiac and respiratory activity.

Effects of dietary phospholipids levels on growth performance, lipid metabolism, and antioxidant capacity of the early juvenile green mud crab,Scylla paramamosain(Estampador)

Four iso-nitrogenous and iso-lipidic diets were designed to investigate the effects of dietary phospholipids (PL) levels (with 0%, 1%, 2%, and 4% PL supplementation) on growth performance, lipid metabolism, and antioxidant capacity in early juvenile green mud crab (Scylla paramamosain). There were three replicates of 28 crabs (initial body weight from 42.02 to 42.44 mg) for each diet treatment, and growth trial lasted for 8 weeks. At the end of the growth trial, there was no significant difference in survival among all treatments. Crabs fed diet with 2% PL obtained highest weight gain (WG) and specific growth rate than other crabs. The molting frequency was not affected by different dietary PL addition. Besides, the contents of whole body lipid and long chain highly unsaturated fatty acids significantly increased with elevating dietary PL levels. In the hepatopancreas, crabs fed diet with 0% PL had significantly higher malondialdehyde concentration than other crabs. And crabs fed diet with 2% PL obtained significantly higher superoxide dismutase activity than crabs fed diets with 0% and 4% PL. Moreover, the mRNA expression of Na+/K+-ATPase was significantly down-regulated with dietary PL supplementation over 2%. Based on the second order polynomial regression analysis of WG, 2.37% dietary PL level was the optimal demand for early juvenile S. paramamosain. Moreover, we found crabs fed diet with 2% PL obtained better antioxidant capacity than other crabs.

Population dynamics and development of the rhizocephalan Sacculina carcini, parasitic on the shore crab Carcinus maenas.

The ecologically important shore crab Carcinus maenas is commonly infected in its native range by the rhizocephalan Sacculina carcini. However, several aspects of this host-parasite interaction are poorly understood. Here, we analyse data from approximately 60000 Danish crabs to unravel factors governing infection patterns in time and space, and according to host sex and size. Female crabs were more frequently infected (12.6%) than males (7.9%). Sites with high salinity supported the highest infection prevalence. Infection prevalence peaked in summer (10 to 15%) and winter (20 to 35%) due in part to emergence of virginal externae in summer (main outbreak) and autumn (minor outbreak) preceded by peaks in crabs with lost externa (scars). Younger externae and scars dominated among males, whereas adult externae were most frequent among females. Infection prevalence increased with size in females but decreased in males, and modified (feminized) males showed lower scar frequency than unmodified ones. Modified males occurred frequently among the smaller size classes, whereas unmodified males dominated the larger size classes. Externa size was positively related to host size in both genders (same linear relationship). Molecular analyses suggested that hosts below 16 mm in carapace width do not become infected. Dissections of infected hosts revealed marked reduction of ovaries, whereas testes were unaffected by sacculinization. Our study demonstrates great spatio-temporal variation in infection prevalence mainly related to the parasite's life history. S. carcini appears capable of infecting all host sizes except the smallest. Owing to incomplete feminization of males, infections are rapidly lost from the larger and highly profitable male hosts.

Multifunctional behaviour in a sandy shore crab enhances performance in extreme intertidal environments.

Soft sediment shores in the tropics are highly dynamic environments, where behavioural patterns of organisms are constrained by tidal conditions, and environmental temperatures during an organisms' activity periods can exceed their thermal tolerance levels. In such extreme habitats, behavioural responses to environmental changes are key to survival, driving differential performance. We investigated sponging behaviour (water uptake from sediments) of the deposit-feeding crab, Scopimera intermedia, on tropical sandy shores to determine its thermoregulatory function. The thermal physiology of the crabs and their habitat conditions were quantified by measuring thermal performance curves and recording environmental temperatures during the crabs' activity periods. Environmental temperatures were combined with experimental data to investigate the role of sponging on the thermal performances of the crabs by simulating field body temperatures. Sponging rate was strongly and positively correlated with feeding rate, as sponging replenishes water for flotation feeding. Sponging, however, also reduced body temperatures on average by 1.3°C. Simulated populations of crabs which were unable to sponge had more variable body temperatures, which exceeded the critical thermal maximum of the crabs (~ 39°C) nearly 2000 times more often than crabs able to sponge. Sponging is, therefore, a multifunctional behavioural trait important for both feeding and thermoregulation. The evolution of such multifunctional traits is likely to be a widespread, but overlooked phenomenon in intertidal species, as maintaining a functional body temperature is energetically costly in habitats where environmental conditions fluctuate strongly such as on tropical shores.

Potential of recovered proteins from invasive green crabs (Carcinus maenas) as a functional food ingredient

Invasive green crabs contain high-quality proteins that have potential as functional ingredients in formulated foods. This study evaluated the functional properties and compositional characteristics of green crab proteins recovered by isoelectric solubilization/precipitation (ISP). Mechanically separated green crab mince (control) was solubilized at pH 2 (PP2) and pH 10 (PP10), then proteins were precipitated at pH 5.5 and subsequently dried. Yield of recovered protein powder was approximately 1.5 times higher for PP2 than for PP10. Compared with the control (230 g kg-1 ), ash content was reduced in PP2 (54 g kg-1 ) and PP10 (23 g kg-1 ) samples. PP2 contained predominantly large-molecular-weight proteins, while small-molecular-weight proteins were distributed in PP10. With regard to functional properties, at pH 7 and 8, solubility of PP10 was significantly higher than that of PP2. At pH 7.5, PP10 exhibited significantly higher emulsifying activity (1482 m2 g-1 ) than PP2 (858 m2 g-1 ) and the control (958 m2 g-1 ). PP2 showed statistically higher gelation activity and had higher L* value than PP10 and the control. The results indicate that recovered green crab proteins have functional properties potentially useful for formulated foods, and that these functional properties can be modified by the solubilization pH during the recovery process. © 2018 Society of Chemical Industry.

Sex, size, and prey caloric value affect diet specialization and consumption of an invasive prey by a native predator.

Escaping the control of natural enemies is thought to heavily influence the establishment success and impact of non-native species. Here, we examined how the profitability of alternative prey in combination with the presence of a competitor and predator aggressive behavior explain individual differences in diet specialization and the consumption of the invasive green porcelain crab Petrolisthes armatus by the native mud crab predator Panopeus herbstii. Results from bomb calorimetry estimates show that invasive P. armatus has high caloric value relative to alternative native prey. Laboratory assays indicated that specialization and consumption of invasive P. armatus was mostly exhibited by large, female P. herbstii, but the presence of a competitor and predator aggressiveness did not influence diet and the consumption of P. armatus. Thus, intrinsic factors (e.g., sex and body size) seem to explain consumption of P. armatus and dietary specialization in P. herbstii, more generally. Although there are still many predator individuals that do not consume P. armatus, the proportion of individuals that have begun to specialize on P. armatus suggests that for some, it has become more profitable relative to alternative native prey. Given the high caloric value of P. armatus, we suggest that it is likely that differences in the cost of its consumption, including attack, capture, and handling times relative to alternative prey, determine its net profitability to individual predators.

A temperate labrid fish demonstrates compensatory mechanisms to feed at torpor‐inducing temperatures

AbstractTemperature can have profound impacts on fitness‐related activities in fishes. Feeding is an ecologically relevant task which is controlled by muscle function. Consequently, in ectotherms, muscle function and feeding kinematics can be altered by temperature. This study investigated the effect of decreasing temperature on the feeding kinematics of the northern most labrid in the Western Atlantic. During winter, cunner (Tautogolabrus adspersus) enter a state of extended torpor in order to conserve energy when water temperatures drop below ~10°C. We hypothesized that feeding kinematics would be slower at lower temperatures especially those associated with torpor (≤10°C). Additionally, we hypothesized that prey type will elicit different feeding behaviors. Feeding events on sandworms and Asian shore crabs were recorded at 5, 10, 15 and 20°C. Fish held at 5°C had slower opening and closing jaw velocities while using more ram than the other temperature treatments. No differences were detected between prey types. For both prey types, the temperature treatment which consistently induced torpor (5°C) slowed oral jaw movements, which likely forced cunner to rely more on ram than suction to capture prey. Torpor temperatures appeared to have less of an effect on feeding than on metabolic rate, steady swimming capabilities and muscle function, suggesting some compensatory mechanisms of feeding musculature in cunner.

DNA metabarcoding unveils multiscale trophic variation in a widespread coastal opportunist.

A thorough understanding of ecological networks relies on comprehensive information on trophic relationships among species. Since unpicking the diet of many organisms is unattainable using traditional morphology‐based approaches, the application of high‐throughput sequencing methods represents a rapid and powerful way forward. Here, we assessed the application of DNA metabarcoding with nearly universal primers for the mitochondrial marker cytochrome c oxidase I in defining the trophic ecology of adult brown shrimp, Crangon crangon, in six European estuaries. The exact trophic role of this abundant and widespread coastal benthic species is somewhat controversial, while information on geographical variation remains scant. Results revealed a highly opportunistic behaviour. Shrimp stomach contents contained hundreds of taxa (>1,000 molecular operational taxonomic units), of which 291 were identified as distinct species, belonging to 35 phyla. Only twenty ascertained species had a mean relative abundance of more than 0.5%. Predominant species included other abundant coastal and estuarine taxa, including the shore crab Carcinus maenas and the amphipod Corophium volutator. Jacobs’ selectivity index estimates based on DNA extracted from both shrimp stomachs and sediment samples were used to assess the shrimp's trophic niche indicating a generalist diet, dominated by crustaceans, polychaetes and fish. Spatial variation in diet composition, at regional and local scales, confirmed the highly flexible nature of this trophic opportunist. Furthermore, the detection of a prevalent, possibly endoparasitic fungus (Purpureocillium lilacinum) in the shrimp's stomach demonstrates the wide range of questions that can be addressed using metabarcoding, towards a more robust reconstruction of ecological networks.

Effects of the invasive green crab (Carcinus maenas) on American lobster (Homarus americanus): Food acquisition and trapping behaviour

The American lobster (Homarus americanus) is the most commercially important crustacean species in Eastern Canada. Fishery landings in Placentia Bay, Newfoundland have decreased steadily following the cod moratorium in 1992, with another noticeable drop in 2002 when the first invasion of the European green crab (Carcinus maenas) was likely to have happened. The effect of green crabs on the food consumption and catchability of lobsters was quantified in relation to crab density (n = 0, 1, 5, 25) and water temperature (4 °C, 12 °C). Food acquisition and behavioural responses of lobsters were unaffected by the water temperature or crab densities of 1 to 25 animals. However, when a lobster was pitted against 150 crabs they were unable to obtain any food and the crabs consumed all the food within 8 min. In contrast to lobsters, the green crabs consumed more food at the higher temperature because they were more active. As crab density increased the number of agonistic interactions and retreat behaviours increased at both temperatures, and crabs were more likely to retreat from a lobster than vice versa. The effects of green crabs on the catchability of lobsters around a baited trap was also investigated when crabs were freely mobile outside the trap or contained within the trap. Lobsters were more likely to approach and enter the trap at 12 °C than at 4 °C, however, they were also more likely to escape. Lobsters were less likely to approach or enter a trap if they interacted with crabs outside the trap. The present results suggest that interactions between green crabs and adult lobsters may influence lobster catch rates in Newfoundland.

Invasion dynamics: interactions between the European Green Crab Carcinus maenas and the Asian Shore Crab Hemigrapsus sanguineus

As ecosystems are increasingly inhabited by multiple invasive species, interactions among exotic species have the potential to negatively impact native communities and habitats, often in counterintuitive ways. In rocky intertidal habitats along southern New England, the recently introduced Asian Shore Crab, Hemigrapsus sanguineus, has been implicated in the displacement of the more established invasive European Green Crab, Carcinus maenas. We coupled faunal sampling with two field experiments to examine whether H. sanguineus is also displacing C. maenas in the Gulf of Maine. First, we investigated natural recruitment of the two species across an elevation gradient, using cage exclusion units to manipulate predator access. Excluding H. sanguineus adults significantly increased the density of C. maenas recruits, but not conspecific recruit density. Next, to simulate the transition that occurred from pre-invasion to the establishment of H. sanguineus, we conducted a predator inclusion experiment manipulating the density of adult H. sanguineus to examine the effects on C. maenas and conspecific recruit densities. In contrast to the previous experiment, we found that the density of H. sanguineus included in cages negatively affected conspecific recruit density but had no effect on C. maenas recruit density. We hypothesize that juxtaposing results from the two experiments may be a consequence of the considerably greater abundance of C. maenas recruits relative to H. sanguineus recruits during the first experiment. Our work highlights the importance of considering the multitude of factors that influence competitive and intraguild predation interactions, including density-dependent effects, ontogeny and life history characteristics.

Sensitivity to near-future CO2 conditions in marine crabs depends on their compensatory capacities for salinity change

Marine crabs inhabit shallow coastal/estuarine habitats particularly sensitive to climate change, and yet we know very little about the diversity of their responses to environmental change. We report the effects of a rarely studied, but increasingly prevalent, combination of environmental factors, that of near-future pCO2 (~1000 µatm) and a physiologically relevant 20% reduction in salinity. We focused on two crab species with differing abilities to cope with natural salinity change, and revealed via physiological and molecular studies that salinity had an overriding effect on ion exchange in the osmoregulating shore crab, Carcinus maenas. This species was unaffected by elevated CO2, and was able to hyper-osmoregulate and maintain haemolymph pH homeostasis for at least one year. By contrast, the commercially important edible crab, Cancer pagurus, an osmoconformer, had limited ion-transporting capacities, which were unresponsive to dilute seawater. Elevated CO2 disrupted haemolymph pH homeostasis, but there was some respite in dilute seawater due to a salinity-induced metabolic alkalosis (increase in HCO3− at constant pCO2). Ultimately, Cancer pagurus was poorly equipped to compensate for change, and exposures were limited to 9 months. Failure to understand the full spectrum of species-related vulnerabilities could lead to erroneous predictions of the impacts of a changing marine climate.

Spatial and Temporal Associations Between Native Crabs and the Invading Green Porcelain Crab, Petrolisthes armatus, Throughout Its Northernmost Invaded Range

Increasing ocean temperatures have led to poleward range expansions of many marine organisms. The green porcelain crab, Petrolisthes armatus, was first reported on intertidal oyster reefs near Charleston, South Carolina in the mid-1990s, an expansion from its tropical to sub-tropical native range. In order to investigate the relative abundances of this introduced crab and a portion of the native crab community, resident crab assemblages were sampled on intertidal oyster reefs across four seasons from 2015 to 2016. Sampling occurred at five locations extending from Savannah, Georgia where P. armatus is now well-established, to Wilmington, North Carolina, where its inter-annual presence is intermittent. Petrolisthes armatus was the numerically dominant crab species at all locations except Wilmington, where the species was not collected in the winter. Differences between northern and southern sample locations in the taxonomic composition of crab assemblages were most pronounced in the summer (June–September) and fall (October–January), with dissimilarities largely attributed to high abundances of P. armatus at southern locations. Crab abundances of all species peaked in the summer and were lowest in the winter (February–March). Petrolisthes armatus was less abundant toward the northern range edge, whereas native crabs did not differ in abundance throughout the sampling range. Throughout the study area, adult P. armatus sex ratios shifted from unbiased or female-biased in the summer to male-biased in the fall. Adults were collected in the spring (April–June), indicating they had overwintered. While native crab densities (Panopeus herbstii, Eurypanopeus depressus) stayed relatively constant across locations, P. armatus densities varied greatly, suggesting that resources, such as shelter and food, are not limiting factors for the coexistence of these native and invading crabs.

A lipidomic perspective on the embryogenesis of two commercially important crabs, Carcinus maenas and Necora puber

Lipids play a central role in the metabolism of most organisms. These molecules are paramount during reproduction, when females transfer their internal lipid reserves to build-up oocytes' yolk. The aim of the present study was to understand neutral lipid (NL) dynamics during the embryogenesis of two commercially important crabs, Carcinus maenas (Linnaeus, 1758) and Necora puber (Linnaeus, 1767), using electrospray ionization mass spectrometry (ESI–MS) and tandem MS (ESI–MS/MS). Total lipid extracts were fractionated into NLs and polar lipids (PLs). Triacylglycerol (TAG) profile of NL and fatty acid (FA) profiles of both NLs and PLs were determined in two different embryonic stages: newly-extruded embryos (stage 1, a proxy of maternal investment) and ready-to-hatch embryos (stage 3, a proxy of newly-hatched larvae). In total, 16 molecular species of TAGs and their fatty acyl composition were identified, for the first time in marine invertebrate embryos. During embryogenesis, TAGs bearing C14 to C18 saturated and monounsaturated FAs were preferentially consumed, while TAGs with longer carbon chains and polyunsaturated FAs were selectively retained in the late embryonic stage of both crab species. The analysis of FA profiles revealed that energetic FAs were associated with NLs, while essential FAs were more abundant in PLs. These results evidence the different functions of NLs and PLs as energetic and structural lipids, respectively. The novel approach used in our study provides an unprecedented level of information of lipid dynamics at the molecular level, opening new perspectives in the study of maternal investment and embryogenesis in marine invertabrates.