Carcinus Maenas Research Articles

Role of estuarine habitats for the feeding ecology of the European eel (Anguilla anguilla L.).

This study aims to characterize and compare the feeding ecology of the European eels (Anguilla anguilla L.) during the continental phase (i.e. yellow and silver) along a salinity gradient (i.e. lower, middle and upper) in six northern France estuaries (i.e. brackish water). The diet and stable isotopic (i.e. δ15N and δ13C values) compositions of eels collected with a fyke net in six estuaries (Slack, Wimereux, Liane, Canche, Authie and Somme estuaries) located along the French coast of the eastern English Channel per season over a year were described by combining gut content and stable isotope analyses. Eel guts were dominated by typical BW prey, Malacostraca and Actinopterygii (54% and 40%, respectively), with the gammare Gammarus zaddachi and the green crab Carcinus maenas (38% and 14%, respectively), and smaller yellow eels of A. anguilla and juvenile European flounder, Platichthys flesus (19% and 14%, respectively) being the most frequently found in their guts. The δ13C values of a majority of eels confirmed the sea- and brackish water-specific carbon resources. Dietary and isotopic niche revealed no clear change between total length, silvering stages and seasons, but a significant difference between salinity gradients and estuaries. Eels δ13C values showed significant enrichment from upper to lower along the estuaries while the δ15N values showed an inverse effect, with the lowest values in the lower part and highest in the upper part. Higher variability in δ13C values in larger estuaries suggested that eels feed on a wide range of food sources than in smaller estuaries. While eels in the smaller estuaries fed mainly on Actinopterygii prey, eels in the larger ones had a lower trophic level (i.e. δ15N values) and fed mainly on Malacostraca prey. This spatial difference in dietary and isotopic niche is discussed in relation to biological structure of eel and environmental variables.

THE SPECIES COMPOSITION IN CATCHES OF GILL-NET IN THE COASTAL AND INSHORE AREA OF BENTRE PROVINCE, VIETNAM

and analyzed. The result of study shows that 105 species belonging to 77 genera and 42 orders have been encountered. In which, demersal fish with 45 species (42.9%), 21 species of pelagic fish (20.0%); 18 species of reef-associated fish (17.1%); shrimps with 14 species (13.3%); crabs with 4 species (3.8%); 2 species of cephalopods (1.9%) and 1 species of seahorse crab (1.0%). In terms of catch composition, the croaker (Sciaenidae), the lizardfishs (Synodontidae) and Anchovies (Engraulidae) dominated with yields up to 60% of the total catch. In terms of species with high economic value and dominant in catches were Bombay duck (Harpadon nehereus), Sodier croaker (Nibea soldado) and Green mub crab (Scylla paramamosain) which were play an important economic species and high proportion of the total income.

Mr. and Mrs. Crab: How Can We Tell Them Apart?

Male and female mud crabs may look alike at first glance, but clear differences in physical characteristics exist. These variations between sexes are known as sexual dimorphism. Sexual dimorphism may help species to survive in their environments. We found that three mud crab species (orange, green, and purple mud crabs) showed similar patterns of sexual dimorphism. Males generally have larger body and claw sizes, whereas females have larger abdomens. Orange mud crabs also have a unique body shape variation compared to green and purple mud crabs. All mud crabs have spines along the top edge of their shells, and scientists have numbered these spines to identify them. Unlike the green and purple species, orange mud crabs are wider at spine 8 than spine 9. Sexual dimorphism in crabs might be linked to how they reproduce and where they live.

Exercise and emersion in air, and recovery in seawater in the green crab (Carcinus maenas): metabolic, acid-base, cardio-ventilatory and ionoregulatory responses.

In nature, the green crab exhibits emersion and terrestrial activity at low tide. Treadmill exercise in air (20-23°C) of crabs acclimated to 32ppt seawater (13°C) revealed an inverse relationship between velocity and duration: 2.0 body lengths (BL) s-1 was sustainable for several minutes, and 0.25BLs-1 was sustainable for long periods. Fatigue was not due to dehydration. Physiological responses over an 18h recovery in seawater after near-exhaustive exercise (0.25BLs-1, 1 h) in air were compared with responses after quiet emersion (1 h) in air. Exercising crabs exhibited transient scaphognathite slowing and progressive increases in heart rate, whereas emersed crabs exhibited persistent inhibition of ventilation and transient heart slowing. Upon return to seawater, all these rates increased above both control and treatment levels. Post-exercise disturbances were more marked and/or longer lasting (e.g. EPOC, hyperventilation, tachycardia, metabolic acidosis, lactate elevation, ionic disturbances) than those after simple air exposure. However, an increase in net acidic equivalent excretion to the environment occurred after emersion but not after exercise. Instead, post-exercise crabs relied on carapace buffering, signalled by elevated haemolymph Ca2+ and Mg2+. Prolonged lowering of haemolymph PCO2associated with hyperventilation also played a key role in acid-base recovery. EPOC after exercise was 3-fold greater than after emersion, sufficient to support resting ṀO2for >14 h. This reflected clearance of a large lactate load, likely by glycogen re-synthesis rather than oxidation. We conclude that the amphibious green crab uses a combination of aquatic and terrestrial strategies to support exercise in air, emersion in air and recovery in seawater.

Predicting ecological impacts of the invasive brush-clawed shore crab under environmental change

Globally, the number of invasive non-indigenous species is continually rising, representing a major driver of biodiversity declines and a growing socio-economic burden. Hemigrapsus takanoi, the Japanese brush-clawed shore crab, is a highly successful invader in European seas. However, the ecological consequences of this invasion have remained unexamined under environmental changes—such as climatic warming and desalination, which are projected in the Baltic Sea—impeding impact prediction and management. Recently, the comparative functional response (resource use across resource densities) has been pioneered as a reliable approach to quantify and predict the ecological impacts of invasive non-indigenous species under environmental contexts. This study investigated the functional response of H. takanoi factorially between different crab sexes and under environmental conditions predicted for the Baltic Sea in the contexts of climate warming (16 and 22 °C) and desalination (15 and 10), towards blue mussel Mytilus edulis prey provided at different densities. Hemigrapsus takanoi displayed a potentially population-destabilising Type II functional response (i.e. inversely-density dependent) towards mussel prey under all environmental conditions, characterised by high feeding rates at low prey densities that could extirpate prey populations—notwithstanding high in-field abundances of M. edulis. Males exhibited higher feeding rates than females under all environmental conditions. Higher temperatures reduced the feeding rate of male H. takanoi, but did not affect the feeding rate of females. Salinity did not have a clear effect on feeding rates for either sex. These results provide insights into interactions between biological invasions and climate change, with future warming potentially lessening the impacts of this rapidly spreading marine invader, depending on the underlying population demographics and abundances.

Fatty acid-based index development in estuarine organisms to pinpoint environmental contamination

Estuaries have long been preferred areas of human settlement, where multiple anthropogenic activities take place, which have contributed to a significant decrease in environmental quality of these ecosystems. Accordingly, environmental monitoring and management have long relied on the development of tools that summarize and simplify complex information and provide direct interpretation of quality status. Here, the fatty acid profiles of three abundant estuarine species, namely Hediste diversicolor, Carcinus maenas and Pomatoschistus microps, were used to develop and validate a multimetric index, based on the Euclidean dissimilarities of profiles between sites, in response to contamination gradient in a large urban estuary. Spatial differences were generally related to unsaturated fatty acids (mono- and polyunsaturated, of the n−3 and n−6 series) in all species, albeit more pronounced in P. microps. Multivariate models returned high classification accuracies for the three sampled sites, varying from 73.3% in the invertebrate species to 100.0% in the fish species. Results show the applicability of the developed FA-based index, particularly due to the easy of communication, for managers and the public alike, but also highlight the need for prior validation on species suitability or sensitivity to depict environmental contamination.

Brachyuran crabs (Crustacea, Decapoda) from the remote oceanic Archipelago Trindade and Martin Vaz, South Atlantic Ocean.

Forty species of shore and shallow water brachyuran crabs are reported from the remote oceanic Archipelago Trindade and Martin Vaz (TMV), 11 of which were previously known from Trindade Island, 28 are recorded from the Archipelago for the first time, and one is a new species, Epialtus parvulus sp. nov. This brings the total known shore and shallow water decapod fauna of TMV to 99 species. The opportunity is taken here to elaborate on the taxonomy of the species reported from TMV. One new genus, Mecataleptodius, is recognized for two species, Cancer parvulus Fabricius, 1793, its type species, and Cataleptodius olsoni Manning Chace, 1990, endemic to Ascension Island. The following seven nominal species are synonymized: Acanthonyx dissimulatus Coelho in Coelho Torres, 1993; A. scutiformis (Dana, 1851a); Dromia gouveai Melo Campos Junior, 1999; Epialtus portoricensis Rathbun, 1923; Ranilia guinotae Melo Campos Junior, 1994; R. saldanhai H. Rodrigues da Costa, 1970; and Omalacantha garthi (Lemos de Castro, 1953). TMV is a subset of the western Atlantic crab fauna (23 species or 57.5%), also including 8 (20%) amphi-Atlantic species, 3 (7.5%) amphi-American, 3 (7.5%) endemic, 2 (5%) cosmopolitan, 1 (2.5%) known from both sides of the Atlantic and the Indo-West Pacific. The crab fauna of TMV, Ascension (AS) and Saint Helena (SH) are compared with one another as well as with that of the oceanic islands Fernando de Noronha (FN) and the Rocas Atoll (RA) by means of nonmetric multidimensional scaling (NMDS) applied to a dissimilarity matrix generated by Jaccards coefficient. TMV-FN-RA and AS-SH clustered into two distinct groups according to the composition of their crab fauna. The NMDS analysis ranked the species that cause segregation of the crab faunal assemblages among TMV, AS, and SH, while revealing a gradient in species composition between the two groups of islands (TMV-FN-RA and AS-SH) formed by the amphi-Atlantic species. Island isolation, age and size alone do not explain the existing differences in species richness among TMV, AS and SH. The taxonomic composition of the shallow water fauna in these islands is likely to have been determined by several variables that were interwoven differently along their evolutionary history.

Crustacean stomachs are crabby, but not caustic

There is a bag of hydrochloric acid inside each of us. To digest our food, our stomachs secrete stomach acid, which is powerful enough to dissolve bone and erode teeth. But not all animals are walking bags of caustic acid. Crustaceans’ stomachs are literally a thousand times less acidic than ours and are about the same pH as fresh rainwater. Crabs rely far less on stomach acid than we do, so Alex Quijada-Rodriguez, Dirk Weihrauch and colleagues at the University of Manitoba, Canada, studied crabs to find the consequences of using less stomach acid. When our stomach lining pumps in acid, it leaves our blood more alkaline, but if crustaceans use less stomach acid, does eating make them alkaline too?To investigate, Quijada-Rodriguez and colleagues fed green shore crabs (Carcinus maenas) a hearty meal of scallops and sampled the pH within and outside their stomachs. Yet, even while digesting their meal, the acidity of the crabs’ stomachs never changed. However, when the team tested samples of the crabs’ haemolymph (the crustacean equivalent of blood) after dining, they found something unexpected. Instead of becoming more alkaline, the haemolymph became more acidic.Being acidic is dangerous, whether you're a human or a crab. Acid impairs our hearts and brains, so animals keep a tight rein on their pH. Normally, crustaceans get rid of extra acid in the same way we do: they breathe it out. Our blood converts excess acid into carbon dioxide, which we exhale to reset our pH, and crabs do too. So Quijada-Rodriguez and colleagues sampled the crabs’ haemolymph after a meal to measure carbon dioxide, but things looked dire. Even 6 h after eating, carbon dioxide was ∼50% above normal. This means the crabs couldn't breathe out the carbon dioxide fast enough to reset their pH. Left unchecked, this build-up of acid could prove fatal. But, of course, crabs don't die after every meal. Surely, something else was expelling the acid.Acid is not the only by-product of digestion. Protein in the crabs’ diet produces ammonia, a toxic chemical used in household cleaners. And when the team checked ammonia concentrations in the crabs’ bodies after dining, the toxin doubled, and peaked at the same time as acid in their haemolymph. Yet, instead of compounding each other's toxicity, acid and ammonia may cancel each other out. The University of Manitoba team recorded how quickly acid and ammonia left the animals. Although the crabs secreted only a small amount of acid, they cleared ammonia at a much higher rate. However, ammonia appeared to carry acid away with it. Weihrauch's lab had previously shown that crustaceans secrete ammonia as a weak acid called ammonium. In essence, ammonia soaks up the crabs’ acidity before it's quickly thrown out. Just like us, after a messy meal, crabs use ammonia to clean house.We humans go through all the trouble of producing stomach acid – an acid so corrosive that laboratories like Quijada-Rodriguez's label it with ‘Danger!’ and lock it away in specially made safety cabinets. Perhaps in time, the team will clarify how crustaceans can digest without such extreme digestive systems, given that crabs’ stomachs are less acidic than the coffee I'm drinking now.

Can the timing and duration of planktonic larval development contribute to invasion success? A case study comparing range expansion in the European green crab, Carcinus maenas, and the native lined shore crab, Pachygrapsus crassipes, in the northeast Pacific

Can the timing and duration of planktonic larval development contribute to invasion success? A case study comparing range expansion in the European green crab, Carcinus maenas, and the native lined shore crab, Pachygrapsus crassipes, in the northeast Pacific

Microbial Consortium Associated with Crustacean Shells Composting.

Soil microbes play an essential role in the biodegradation of crustacean shells, which is the process of sustainable bioconversion to chitin derivatives ultimately resulting in the promotion of plant growth properties. While a number of microorganisms with chitinolytic properties have been characterized, little is known about the microbial taxa that participate in this process either by active chitin degradation or by facilitation of this activity through nutritional cooperation and composting with the chitinolytic microorganisms. In this study, we evaluated the transformation of the soil microbiome triggered by close approximation to the green crab shell surface. Our data indicate that the microbial community associated with green crab shell matter undergoes significant specialized changes, which was reflected in a decreased fungal and bacterial Shannon diversity and evenness and in a dramatic alteration in the community composition. The relative abundance of several bacterial and fungal genera including bacteria Flavobacterium, Clostridium, Pseudomonas, and Sanguibacter and fungi Mortierella, Mycochlamys, and Talaromyces were increased with approximation to the shell surface. Association with the shell triggered significant changes in microbial cooperation that incorporate microorganisms that were previously reported to be involved in chitin degradation as well as ones with no reported chitinolytic activity. Our study indicates that the biodegradation of crab shells in soil incorporates a consortium of microorganisms that might provide a more efficient way for bioconversion.

Pathology and genetic connectedness of the mangrove crab (Aratus pisonii) – a foundation for understanding mangrove disease ecology

Mangrove forests are productive ecosystems, acting as a sink for CO2, a habitat for a diverse array of terrestrial and marine species, and as a natural barrier to coastline erosion. The species that reside within mangrove ecosystems have important roles to play, including litter decomposition and the recycling of nutrients. Crustacea are important detritivores in such ecosystems and understanding their limitations (i.e. disease) is an important endeavour when considering the larger ecological services provided.Histology and metagenomics were used to identify viral (Nudiviridae, Alphaflexiviridae), bacterial (Paracoccus sp., 'Candidatus Gracilibacteria sp.’, and Pseudoalteromonas sp.), protozoan, fungal, and metazoan diversity that compose the symbiome of the mangrove crab, Aratus pisonii. The symbiotic groups were observed at varying prevalence under histology: nudivirus (6.5%), putative gut epithelial virus (3.2%), ciliated protozoa (35.5%), gonad fungus (3.2%), gill ectoparasitic metazoan (6.5%). Metagenomic analysis of one specimen exhibiting a nudivirus infection provided the complete host mitochondrial genome (15,642 bp), nudivirus genome (108,981 bp), and the genome of a Cassava common mosaic virus isolate (6387 bp). Our phylogenetic analyses group the novel nudivirus with the Gammanudivirus and protein similarity searches indicate that Carcinus maenas nudivrius is the most similar to the new isolate. The mitochondrial genome were used to mine short fragments used in population genetic studies to gauge an idea of diversity in this host species across the USA, Caribbean, and central and southern America.This study report several new symbionts based on their pathology, taxonomy, and genomics (where available) and discuss what effect they may have on the crab population. The role of mangrove crabs from a OneHealth perspective were explored, since their pathobiome includes cassava-infecting viruses. Finally, given that this species is abundant in mangrove forests and now boasts a well-described pathogen profile, we posit that A. pisonii is a valuable model system for understanding mangrove disease ecology.

Effect of Predator Exclusion on Softshell Clam (Mya arenaria L.) Recruitment

Despite estimates of very high (>99.9%) pre-settlement mortality, the extremely large numbers of eggs released into the plankton means that there are abundant post-larval softshell clams (Mya arenaria) available to settle and populate intertidal flats. Many seemingly suitable flats remain devoid of clams, presumably due to post-settlement predation. Predator exclusion/clam recruitment boxes (wooden frames covered top and bottom with a fine plastic screening) were set on a mudflat in Salem Harbor, Salem, MA from April to November 2019. Clam larvae were able to settle through the screen into the boxes but large (>1.9 mm) predators such as European green crabs (Carcinus maenas) and milky ribbon worms (Cerebratulus lacteus) were excluded. At the end of the study, four of five boxes contained between 121 and 290 juvenile softshell clams ranging in size from 7 mm to 32 mm shell length. A bimodal frequency distribution of sizes likely illustrates an early summer (June) set represented by a larger size grouping followed by a second late-summer set represented by a smaller size grouping. Small green crabs (9–46 mm carapace width) found in all five boxes must have grown from extremely small stage 1 crabs that were able to settle or crawl through the screening as recently settled individuals. Resulting empty clam shells could be paired to yield the equivalent of additional clams, making the total number per box between 147 and 417 individuals. No clams were found in samples outside of the boxes, indicating that the absence of a clam population on the mudflat is due to post-settlement predation and not pre-settlement mortality.

Niche separation between two dominant crustacean predators in European estuarine soft-bottom habitats

Epibenthic predators in estuarine shallow soft-bottom environments are generally considered to have broad ecological niches with a wide overlap. This allows them to cope with abundant but highly variable prey communities. The assessment of trophic relationships in shallow soft-bottom habitats is, however, challenging and often complicated by the bias and low resolution of the analytical tools available to study diet in relatively small invertebrates. This study investigates niche overlap between two dominant epibenthic predators in European estuarine soft-bottom environments, the brown shrimp (Crangon crangon L.) and the European green crab (Carcinus maenas L.), by means of trophic DNA-metabarcoding with universal primers for cytochrome c oxidase I (COI). Results show differences in diet composition between the two predators, despite the fact that both species are opportunistic generalists with a high overlap in prey items (218 overlapping Molecular Taxonomic Units). The European green crab showed a richer, more even, and more geographically consistent diet than the brown shrimp, with fairly balanced consumption of algal, arthropod, annelid and mollusc food items. The brown shrimp instead preferred arthropods and annelids, and showed more spatial variation in diet. The observed niche separation could be linked to behavioural variation between the two predators, with European green crab showing more active movements over shallow soft-bottom environments compared to the brown shrimp, which regularly stays buried in the sediment, ambushing its prey. An accurate understanding of the trophic ecology of these estuarine crustaceans is important to capitalise on their role as sentinel organisms since their diet reflects local diversity and can result in toxin bioaccumulation. This study provides new insights in the predator–prey relationships and food web dynamics in European estuaries and highlights the importance of trophic DNA-metabarcoding to study marine food webs.

Tracking an invasion front with environmental DNA.

Data from environmental DNA (eDNA) may revolutionize environmental monitoring and management, providing increased detection sensitivity at reduced cost and survey effort. However, eDNA data are rarely used in decision-making contexts, mainly due to uncertainty around (1) data interpretation and (2) whether and how molecular tools dovetail with existing management efforts. We address these challenges by jointly modeling eDNA detection via qPCR and traditional trap data to estimate the density of invasive European green crab (Carcinus maenas), a species for which, historically, baited traps have been used for both detection and control. Our analytical framework simultaneously quantifies uncertainty in both detection methods and provides a robust way of integrating different data streams into management processes. Moreover, the joint model makes clear the marginal information benefit of adding eDNA (or any other) additional data type to an existing monitoring program, offering a path to optimizing sampling efforts for species of management interest. Here, we document green crab eDNA beyond the previously known invasion front and find that the value of eDNA data dramatically increases with low population densities and low traditional sampling effort, as is often the case at leading-edge locations. We also highlight the detection limits of the molecular assay used in this study, as well as scenarios under which eDNA sampling is unlikely to improve existing management efforts.

Challenges in eDNA detection of the invasive European green crab, Carcinus maenas

The early detection of invasive species is essential to cease the spread of the species before it can cause irreversible damage to the environment. The analysis of environmental DNA (eDNA) has emerged as a non-harmful method to detect the presence of a species before visual detection and is a promising approach to monitor invasive species. Few studies have investigated the use of eDNA for arthropods, as their exoskeleton is expected to limit the release of eDNA into the environment. We tested published primers for the invasive European green crab, Carcinus maenas, in the Gulf of Maine and found them not species-specific enough for reliable use outside of the area for which they were designed for. We then designed new primers, tested them against a broad range of local faunal species, and validated these primers in a field study. We demonstrate that eDNA analyses can be used for crustaceans with an exoskeleton and suggest that primers and probe sequences must be tested on local fauna at each location of use to ensure no positive amplification of these other species.

Assessing the potential for invasive species introductions and secondary spread using vessel movements in maritime ports

Global shipping facilitates the introduction of invasive species and parasites via ballast water and hull fouling. Regional management of invasives may be strengthened by identifying the major routes in a network, to allow for targeted ship inspections. This study used cargo shipping records to establish the connectivity of shipping routes between ports in Ireland and other nations. 9291 records were analysed, investigating vessel residence and journey times. On average, vessels spent up to five days in port and less than five days at sea. However, there was strong variation, with general cargo ships recording up to 13 days in port. A horizon scan for species likely to invade in Ireland was incorporated for five species and their associated parasites: American razor clam, Asian shore crab, Brush clawed shore crab, Chinese mitten crab and American slipper limpet. Routes of concern are highlighted and a general framework for effective management is outlined.

Tradeoffs associated with autotomy and regeneration and their potential role in the evolution of regenerative abilities

Abstract The capacity of certain animals to regrow a lost appendage has been exploited as a powerful tool to study development. As a result, we now understand many of the proximate details of the regeneration process. Ironically, despite being one of the oldest studied developmental phenomena, regeneration is not often considered in the context of natural selection and evolution. Why do select species retain the capacity to shed and regrow body parts, whereas more derived lineages do not? We conducted a comprehensive study on the costs and benefits of autotomy and regeneration on Hemigrapsus nudus, the purple shore crab. In the realms of feeding and locomotion, regeneration restored fitness to what it otherwise would have been; autotomized animals showed decreases in feeding and locomotion, but regenerated animals performed no differently than intact crabs. However, for fecundity and male–male competition, regenerated animals had the lowest fitness compared with control and autotomized crabs. Our results raise the intriguing possibility that tradeoffs associated with reproduction may have led to the loss of regenerative abilities in derived lineages such as mammals and birds. Future work on the hundreds of species that regenerate lost body parts will reveal if and how this hypothesis can address the pervasive speculation plaguing the ultimate causes of regenerative losses.

Hematodinium sp. infection does not drive collateral disease contraction in a crustacean host.

Host, pathogen, and environment are determinants of the disease triangle, the latter being a key driver of disease outcomes and persistence within a community. The dinoflagellate genus Hematodinium is detrimental to crustaceans globally - considered to suppress the innate defences of hosts, making them more susceptible to co-infections. Evidence supporting immune suppression is largely anecdotal and sourced from diffuse accounts of compromised decapods. We used a population of shore crabs (Carcinus maenas), where Hematodinium sp. is endemic, to determine the extent of collateral infections across two distinct environments (open-water, semi-closed dock). Using a multi-resource approach (PCR, histology, haematology, population genetics, eDNA), we identified 162 Hematodinium-positive crabs and size/sex-matched these to 162 Hematodinium-free crabs out of 1191 analysed. Crabs were interrogated for known additional disease-causing agents; haplosporidians, microsporidians, mikrocytids, Vibrio spp., fungi, Sacculina, trematodes, and haemolymph bacterial loads. We found no significant differences in occurrence, severity, or composition of collateral infections between Hematodinium-positive and Hematodinium-free crabs at either site, but crucially, we recorded site-restricted blends of pathogens. We found no gross signs of host cell immune reactivity towards Hematodinium in the presence or absence of other pathogens. We contend Hematodinium sp. is not the proximal driver of co-infections in shore crabs, which suggests an evolutionary drive towards latency in this environmentally plastic host.

Postprandial nitrogen and acid-base regulation in the seawater acclimated green crab, Carcinus maenas

The effects of feeding (meal of 3% of body mass) on acid-base and nitrogen homeostasis were investigated in the seawater acclimated green shore crab, Carcinus maenas. Feeding did not change gastric fluid pH (~pH 6); however, feeding was associated with a respiratory acidosis. Hemolymph HCO3− did not increase during this acidosis, although titratable and net acid efflux changed from an uptake to an excretion. Feeding affected the crabs' nitrogen homeostasis causing a substantial increase in hemolymph ammonia and urea concentrations after six hours. At this point, hemolymph urea accounted for ~1/3 of nitrogenous waste accumulated within the hemolymph, suggesting a potential role in ammonia detoxification. The postprandial increase in hemolymph ammonia coincided with an 18-fold increase in ammonia excretion rates that accounted for the majority of net acid excreted by the crabs. Urea excretion rates did not increase after feeding; however, branchial urease activity increased, implying that the gills may possess a mechanism to form excretable ammonia through the catabolism of urea. Our results demonstrate that despite an acidic gastric compartment, C. maenas does not experience a postprandial alkaline tide and that any feeding related acid-base challenges are primarily derived from metabolic acid production. Our findings also indicate that unlike the bicarbonate buffering acid-base compensatory response induced by hypercapnia and emersion, acid-base challenges upon feeding are compensated through changes in the excretion of acid equivalents, mainly in the form of ammonia.

Seascape genomics identify adaptive barriers correlated to tidal amplitude in the shore crab Carcinus maenas.

Most marine invertebrates disperse during a planktonic larval stage that may drift for weeks with ocean currents. A challenge for larvae of coastal species is to return to coastal nursery habitats. Shore crab (Carcinus maenas L.) larvae are known to show tidal rhythmicity in vertical migration in tidal areas and circadian rhythmicity in microtidal areas, which seems to increase successful coastal settlement. We studied genome‐wide differentiation based on 24,000 single nucleotide polymorphisms of 12 native populations of shore crab sampled from a large tidal amplitude gradient from macrotidal (~8 m) to microtidal (~0.2 m). Dispersal and recruitment success of larvae was assessed with a Lagrangian biophysical model, which showed a strong effect of larval behaviour on long‐term connectivity, and dispersal barriers that partly coincided with different tidal environments. The genetic population structure showed a subdivision of the samples into three clusters, which represent micro‐, meso‐ and macrotidal areas. The genetic differentiation was mostly driven by 0.5% outlier loci, which showed strong allelic clines located at the limits between the three tidal areas. Demographic modelling suggested that the two genetic barriers have different origins. Differential gene expression of two clock genes (cyc and pdp1) further highlighted phenotypic differences among genetic clusters that are potentially linked to the differences in larval behaviour. Taken together, our seascape genomic study suggests that tidal regime acts as a strong selection force on shore crab population structure, consistent with larval behaviour affecting dispersal and recruitment success.