European Green Crab Carcinus Maenas Research Articles

Range extension of invasive Cancer irroratus and native Carcinus maenas polewards in the Ascophyllum-dominated intertidal zone in north-west Iceland

Abstract The rocky intertidal zone of sheltered shores in Breiðafjörður, north-west Iceland is dominated by monospecific stands of canopy-forming brown algae Ascophyllum nodosum, which provide habitat for mobile organisms and has been subjected to long-standing rotational harvesting. We investigated the assemblage composition of little-studied mobile brachyuran crabs in this area, to track distributional shifts in a native species responding to climate change and extent of occupancy of the intertidal by a primarily subtidal invasive non-native species. Potential interactive effects of seaweed harvesting were explored. Breiðafjörður was compared with two reference sites in Faxaflói, south-west Iceland. The study revealed clear poleward expansion of the native European green crab Carcinus maenas in the region, displacing the native spider crab Hyas araneus particularly at mid-shore levels. The invasive non-native Atlantic rock crab Cancer irroratus had negligible occupancy in the intertidal zone, indicating limited effects on the intertidal crab assemblage, composition, and abundance. The current harvesting regime of A. nodosum in Breiðafjörður did not affect the composition and abundance of the brachyuran crab assemblage in the rocky intertidal zone. H. araneus is likely being squeezed by displacement subtidally by C. irroratus, and intertidally by C. maenas. Overall, we provide insights into the potential interactions between climate change, invasive species, and human activities in the rocky intertidal zone.

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.

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.

Feeding, agonistic and cooperative behavioural responses of shallow-water benthic marine scavengers

ABSTRACT Baited remote underwater video station (BRUVS) investigations of benthic scavenging by fish and invertebrates were conducted in an Irish sea lough. Mackerel (Scomber scombrus) baits were deployed under natural light during the day and under dim red light at night. Ethograms for feeding mechanisms and agonistic behaviours were established for four abundant scavengers (two crabs: the harbour crab Liocarcinus depurator, and the European green crab Carcinus maenas; two fish: the shanny Lipophrys pholis, and the small-spotted catshark Scyliorhinus canicula). Crabs’ feeding mechanisms were similar, with differences reflecting their morphologies. Feeding bouts lasted minutes/tens of minutes. Intraspecific agonistic responses were mild and did not result in mutilation or mortality. Feeding mechanisms on macerated baits focussed on ‘chewing’ (combined use of chelipeds and mouthparts to feed continuously); agonistic behaviour was reduced, especially at night when balls of crabs showed ‘cooperative feeding’. Fish feeding bouts lasted for a few seconds in all cases. Shannies showed anticipatory agonistic behaviour (bait ‘guarding’ and ‘patrolling’ by large shannies) before bait maceration. Catsharks exhibited no intraspecific agonistic behaviour but removed large bait morsels by ‘biting’, ‘chewing’ and ‘spinning’. The common prawns Palaemon serratus only scavenged at night and were invisible to other scavengers; they showed no agonistic behaviours. Kleptoparasitism amongst the scavenger guild was common but intra-community predation was extremely rare. Phoretic feeding on bait scraps by red-speckled anemones (Anthopleura ballii) attached to the carapaces of the edible crab Cancer pagurus was observed.

Predatory ability and abundance forecast the ecological impacts of two aquatic invasive species

Characterising interspecific interaction strengths, combined with population abundances of prey and their novel predators, is critical to develop predictive invasion ecology. This is especially true of aquatic invasive species, which can pose a significant threat to the structure and stability of the ecosystems to which they are introduced. Here, we investigated consumer-resource dynamics of two globally-established aquatic invasive species, European green crab (Carcinus maenas) and brown trout (Salmo trutta). We explored the mediating effect of prey density on predatory impact in these invaders relative to functionally analogous native rock crab (Cancer irroratus) and Atlantic salmon (Salmo salar), respectively, feeding on shared prey (Mytilus sp. and Tenebrio molitor, respectively). We subsequently combined feeding rates with each predator’s regional abundance to forecast relative ecological impacts. All predators demonstrated potentially destabilising Type II functional responses towards prey, with native rock crab and invasive brown trout exhibiting greater per capita impacts relative to their trophic analogues. Functional Response Ratios (attack rates divided by handling times) were higher for both invasive species, reflecting greater overall per capita effects compared to natives. Impact projections that incorporated predator abundances with per capita effects predicted severe impacts by European green crabs. However, brown trout, despite possessing higher per capita effects than Atlantic salmon, are projected to have low impact owing to currently low abundances in the sampled watershed. Should brown trout density increase sixfold, we predict it would exert higher impact than Atlantic salmon. Such impact-forecasting metrics and methods are thus vital tools to assist in the determination of current and future adverse impacts associated with aquatic invasive species.

Metabarcoding, direct stomach observation and stable isotope analysis reveal a highly diverse diet for the invasive green crab in Atlantic Patagonia

The European green crab Carcinus maenas and its sister species C. aestuarii are highly invasive species causing damage to coastal ecosystems and contributing to severe economic losses worldwide. C. maenas was first detected at the Atlantic Patagonian coast in 2001. In this work, we studied the diet of the green crab in a recently invaded location in Golfo Nuevo, using three complementary techniques: direct stomach observation, metabarcoding of gut content and stable isotope analysis. Direct stomach observation and metabarcoding showed that green crabs have a broad omnivorous diet, ingesting most of the phyla present in the study area. Gut content metabarcoding allowed a detailed description of algal diversity and revealed other taxa that went unnoticed in the visual stomach analysis. Stable isotope analysis showed that the major contribution to the crabs' diet was from the phytoplankton chain (by bivalve consumption) and not directly from algae. This study approach combining three complementary techniques also allowed us to detect some differences in the diet between sexes, which suggests that male and female crabs are not as ecologically equivalent as previously thought. Besides, we detected sequences corresponding to C. aestuarii suggesting that the green crab Patagonian population is a hybrid of both sister species. These findings are key to understanding the impacts green crabs can have on the local ecosystem.

Ocean Indicators Predict Range Expansion of an Introduced Species: Invasion History of the European Green Crab Carcinus maenas on the North American Pacific Coast

An introduced population of European green crabs Carcinus maenas (Linneaus, 1758) was established in San Francisco Bay prior to 1991. Their subsequent northern range expansion is linked to larval transport in the Davidson Current to northern California (1993), southern Oregon (approximately 1996), the Oregon and Washington coastal estuaries and the west coast of Vancouver Island, British Columbia (1998). Range expansions through larval transport to the central British Columbia coast occurred before 2010, to Haida Gwaii in 2020, and into the inland Salish Sea in 2015 and 2016. Both the range expansions of C. maenas and local abundance are strongly linked to oceanic factors during their larval development. These include (1) strong northward flow of coastal waters during winter; (2) warm surface water temperatures (>10°C for larval development); and (3) coastal circulation patterns that keep larvae close to shore, where they can be carried by wind and tidal currents into estuaries and embayments to settle. The strongest year classes and largest range expansions occurred during the last two major El Niño events. The 1997 to 1998 El Niño resulted in the colonization of embayments in Oregon, coastal Washington, and on the west coast of Vancouver Island, while the El Niño of 2015 to 2016 and the Pacific Warm Blob are linked to the range expansion into the Salish Sea. More local range expansions along the west coast of Vancouver Island, to the central British Columbia Coast, to Haida Gwaii, and inside the Salish Sea occurred during non-El Niño years.

Balanced polymorphism fuels rapid selection in an invasive crab despite high gene flow and low genetic diversity.

Adaptation across environmental gradients has been demonstrated in numerous systems with extensive dispersal, despite high gene flow and consequently low genetic structure. The speed and mechanisms by which such adaptation occurs remain poorly resolved, but are critical to understanding species spread and persistence in a changing world. Here, we investigate these mechanisms in the European green crab Carcinus maenas, a globally distributed invader. We focus on a northwestern Pacific population that spread across >12degrees of latitude in 10years from a single source, following its introduction <35years ago. Using six locations spanning >1500km, we examine genetic structure using 9376single nucleotide polymorphisms (SNPs). We find high connectivity among five locations, with significant structure between these locations and an enclosed lagoon with limited connectivity to the coast. Among the five highly connected locations, the only structure observed was a cline driven by a handful of SNPs strongly associated with latitude and winter temperature. These SNPs are almost exclusively found in a large cluster of genes in strong linkage disequilibrium that was previously identified as a candidate for cold tolerance adaptation in this species. This region may represent a balanced polymorphism that evolved to promote rapid adaptation in variable environments despite high gene flow, and which now contributes to successful invasion and spread in a novel environment. This research suggests an answer to the paradox of genetically depauperate yet successful invaders: populations may be able to adapt via a few variants of large effect despite low overall diversity.

Targeted Next Generation Sequencing improves detection and quantification of rare species from eDNA

Targeted species detection from eDNA is central to identifying and quantifying rare (i.e. invasive or endangered) species to inform conservation and resource management. Here we introduce a new targeted Next Generation Sequencing (tNGS) assay that shows improved detection relative to quantitative (q)PCR at low eDNA concentrations and increased precision to detect spatial variation in eDNA concentration related to species abundance. We compare the tNGS and qPCR methods using invasive European green crab (Carcinus maenas) in the northeast Pacific Ocean as a test case, and find that crab abundance measured by traditional trapping is significantly correlated with eDNA concentration across multiple sites for both methods. However, the tNGS assay outperformed qPCR in all tests: (1) increased precision of eDNA concentration estimation; (2) a 7-10% increase in detection probability at low abundance sites; and (3) greater power to detect spatial variation in eDNA concentration. The accuracy of predicting green crab abundance from eDNA concentration increased with the number of field replicates sampled and did not change appreciably over a tidal cycle. Green crab eDNA concentration behaving similarly to abundance measured from trapping demonstrates great promise for this tool to be implemented for early detection and routine monitoring surveys. The tNGS assay is easily accessible for surveying other species with existing qPCR assays and can thus be potentially important for detection and quantification of any species of high interest to management.

Effects of perceived competition and water temperature on the functional responses of invasive and native crabs

As the frequency of species introductions increases globally, the need for predicting the ecological impacts of invaders becomes ever more urgent. Functional responses, i.e. how resource uptake by consumers changes as a function of resource density, describe the species-specific ability to deplete resources under standardized conditions, and their shape has been used as a tool to predict the impact of non-native species. However, functional responses are usually derived from individuals foraging alone, which overlooks the important roles of intra- and interspecific interactions in shaping per capita consumption rates. We tested the extent to which the functional responses of invasive European green crabCarcinus maenasand native graceful rock crabMetacarcinus gracilisare affected by the perceived presence of con- and heterospecific individuals. Overall, crabs did not consume significantly more prey in the perceived presence of either a conspecific or novel heterospecific, but did demonstrate significantly higher attack rates in warmer water in the presence of a conspecific. Regardless of competitor type, green crabs consumed, on average, 16% more prey than the native crabs. This was largely due to their higher attack rate and lower prey handling time in warmer water. Green crab prey consumption increased significantly with increasing water temperature while that of the native crab species was unaffected (12 vs. 3.5% per 1°C increase, respectively). Higher maximum feeding rates are congruent with green crab impacts throughout their invaded range and suggest that green crabs might be undeterred from feeding in the presence of this co-occurring native crab species.

Rapid Adaptation to Temperature via a Potential Genomic Island of Divergence in the Invasive Green Crab, Carcinus maenas

Widespread species often adapt easily to novel conditions – both those found in new habitats and those generated by climate change. However, rapid adaptation may be hindered in the marine realm, where long-distance dispersal and consequently high gene flow are predicted to limit potential for local adaptation. Here, we use a highly dispersive invasive marine crab to test the nature and speed of adaptation to temperature in the sea. Using single nucleotide polymorphisms (SNPs) generated from cardiac transcriptome sequencing, we characterized six populations of the European green crab (Carcinus maenas) located across parallel thermal gradients in their native and invasive ranges. We compared SNP frequencies with local temperatures and previously generated data on cardiac heat and cold tolerance to identify candidate markers associated with population-level differences in thermal physiology. Of 10,790 SNPs, 104 were identified as frequency outliers, a signal that was strongly driven by association with temperature and/or cold tolerance. Seventy-two of these outlier markers, representing 28 different genes, were in a cluster of SNPs identified as a potential inversion polymorphism using linkage disequilibrium network analysis. This SNP cluster was unique in the data set, which was otherwise characterized by low levels of linkage disequilibrium, and markers in this cluster showed a significant enrichment of coding substitutions relative to the full SNP set. These 72 outlier SNPs appear to be transmitted as a unit, and represent a putative genomic island of divergence which varied in frequency with organismal cold tolerance. This relationship was strikingly similar across both native and invasive populations, all of which showed a very strong correlation with cold tolerance (R2 = 0.96 over all six populations). Notably, three of these populations have diverged recently (&amp;lt;100 years) and show little to no neutral divergence, suggesting that this genomic region may be responding to temperature on a relatively short time scale. This relationship indicates adaptation to temperature based on the action of a putative genomic island of divergence, perhaps partially explaining the extraordinary invasive ability of this species.

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.

Corrigendum to: Evidence of complete gastric mill ossicle loss at ecdysis in the European green crab Carcinus maenas (Linnaeus, 1758) (Decapoda: Brachyura: Carcinidae)

Corrigendum to: Evidence of complete gastric mill ossicle loss at ecdysis in the European green crab Carcinus maenas (Linnaeus, 1758) (Decapoda: Brachyura: Carcinidae)

Seasonal lipid storage and dietary preferences of native European vs. invasive Asian shore crabs

The invasive Asian shore crab Hemigrapsus sanguineus and the native European green crab Carcinus maenas share intertidal habitats along European North Atlantic shores and may compete for food. We evaluated the energy-storing capacities of the 2 species and determined their dietary preferences by means of lipid analysis and fatty acid trophic marker indices. Specimens of both sexes and various sizes were sampled in the rocky intertidal of the island of Helgoland (North Sea) in April, June, August, and October 2015. Total lipids of the midgut glands were significantly higher in H. sanguineus than in C. maenas and followed a distinct seasonal cycle in both sexes (ca. 20−50% of dry mass, DM). The lower lipid contents of C. maenas (ca. 20% of DM) remained at a similar level throughout the seasons. The seasonal differences in the females of H. sanguineus may be due to higher reproductive output and, consequently, lipid turnover, but remain unexplained in males. Trophic indices for Bacillariophyceae, Chlorophyta, and especially Phaeophyceae were higher in H. sanguineus than in C. maenas, suggesting a higher degree of herbivory of the invader. In contrast, the Rhodophyta index was higher in C. maenas. Thus, competition for food between the 2 species will probably be low in habitats rich in macroalgae. The ability of H. sanguineus to utilize mainly energy-poor algae but accumulate high-energy reserves may be an advantage for successfully establishing persistent populations in new habitats.

Invasive versus native brachyuran crabs in a European rocky intertidal: respiratory performance and energy expenditures

The invasive Asian shore crab Hemigrapsus sanguineus is now the second most abundant intertidal crab in the North Sea after the native European green crab Carcinus maenas. To compare their respiratory performance and energy expenditures, we measured standard respiration rates of both species from around the island of Helgoland, North Sea, Germany (54°11′N, 7°53′E) in 2015. Oxygen consumption was recorded in a flow-through setup between 5 and 20 °C. At lower temperatures, H. sanguineus had similar respiration rates as C. maenas, but approximately twofold higher rates at higher temperatures. Numerical models for the calculation of individual respiration rates were established and applied to the entire intertidal populations around Helgoland to compare the energy expenditures of both species. Abundance and biomass data recorded in August 2014 showed that H. sanguineus reached values as high as 21 and 59%, respectively, compared to those of C. maenas. Based on these data and the numerical respiration models, the energy expenditures of both populations were calculated for the whole year 2014. The H. sanguineus population reached, depending on the assumed diet of both species (complete herbivory versus complete carnivory), 86–135% of the expenditure value of C. maenas. As population densities of H. sanguineus are likely to increase in the North Sea, the energy expenditure of the invader and thus its impact on the energy flux in the intertidal habitat will further increase. Whether this will lead to an impact on the local intertidal community depends on species-specific dietary preferences and remains to be investigated.

Color Phase—Specific Ion Regulation of the European Green CrabCarcinus maenasin an Oscillating Salinity Environment

The physiology of ion regulation in the highly invasive European green crab Carcinus maenas has been widely studied, but mostly in constant salinity conditions, and not in context of their molt cycle-dependent sternite coloration. The ventral sternites are typically green after molting, and turn red through prolonged intermolt, with a concurrent decrease in stress tolerance. In this study, whole animal and molecular physiology was evaluated at constant low salinity (12), and oscillating salinity (12–32 every 6 h). Performance in three whole animal measures revealed that the green phase is more tolerant than the red phase, and that females are more tolerant than the respective males under both salinity conditions. These differences result from larger increases in expression of the drivers behind ion transport (Na /K -ATPase, cytoplasmic carbonic anhydrase) in green phase and female crabs. Low salinity exposure resulted in increased expression of these markers compared with oscillating salinity, demonstrating that low salinity is more strenuous, as more cellular regulation is required. This agrees with the crabs' natural environmental conditions where prolonged low salinity is rarely experienced. These findings are presented in context of a crab population survey conducted from May 2012 through November 2016 in southern Maine, USA. Female and red phase crabs were found at higher proportions in the intertidal than previously reported. In addition, gravid females were found year round, which is indicative of continuous reproduction. The data demonstrate the necessity to evaluate C. maenas in an ecologically relevant context with respect to color phase within each invasive population to truly understand the invasive capabilities of this species and to better inform management strategies.

A microstructural study of the pleon-holding mechanism in Carcinus maenas (Decapoda, Brachyura, Portunoidea, Carcinidae) of different sizes.

Within the Brachyura there are a variety of specialized holding mechanisms, which facilitate the close attachment of the highly reduced pleon underneath the cephalothorax. The most common mechanism in eubrachyurans, known as the press-button, consists of a sternal protrusion and a corresponding pleonal socket. Reports on the microstructural properties of the surface of these holding structures are scarce and patchy. In this study, the European Green Crab Carcinus maenas, is used as model to describe the microstructure of a typical press-button mechanism with the use of scanning electron microscopy and light microscopic histology. A highly tuberculate cuticle and an apical ridge on the sternal knob are found in juveniles of both sexes. The microstructures are lost in adult males. In adult females, the holding structures themselves are reduced, but never completely lost. These findings show that C. maenas does not undergo a single "final puberty moult," after which all juvenile characteristics are lost, as previously assumed. Further comparison of the morphology of juveniles to another species indicates a close resemblance of the holding structures at this stage. Therefore, the use of the microstructure of the pleon-holding mechanism for phylogenetic analysis is restricted to adult specimens.

Lifting Barriers to Range Expansion: the European Green CrabCarcinus maenas(Linnaeus, 1758) Enters the Salish Sea

Although the European green crab Carcinus maenas has persisted in Oregon and Washington coastal estuaries, and thrived in the inlets of the west coast of British Columbia since 1998, populations of this species had not established themselves in the inner Salish Sea, between southern Vancouver Island, the mainland, and Puget Sound. It has been hypothesized that the Strait of Juan de Fuca acts as a semipermeable barrier preventing C. maenas larvae from entering this inland sea. Most years, the water is too cold ( 2.5°C above average) from the fall of 2013 to 2015 would have allowed larvae to survive alongshore transport off the coasts of Oregon, Washington, and southern British Columbia. Reversals of the estuarine current in the Strait of Juan de Fuca forced by strong southerly winds associated with major storms along the outer coast in late October 2014 and 2015 could have transported the warm ocean water and larvae inward through the strait and, with the aid of local winds and tidal currents, into the inner Salish Sea. Preferential inward transport would have been with the Olympic Peninsula Countercurrent that forms along the U.S. side of the channel.

Metabolic costs of capital energy storage in a small-bodied ectotherm.

Reproduction is energetically financed using strategies that fall along a continuum from animals that rely on stored energy acquired prior to reproduction (i.e., capital breeders) to those that rely on energy acquired during reproduction (i.e., income breeders). Energy storage incurs a metabolic cost. However, previous studies suggest that this cost may be minimal for small‐bodied ectotherms. Here I test this assumption. I use a laboratory feeding experiment with the European green crab Carcinus maenas to establish individuals with different amounts of energy storage. I then demonstrate that differences in energy storage account for 26% of the variation in basal metabolic costs. The magnitudes of these costs for any individual crab vary through time depending on the amount of energy it has stored, as well as on temperature‐dependent metabolism. I use previously established relationships between temperature‐ and mass‐dependent metabolic rates, combined with a feasible annual pattern of energy storage in the Gulf of Maine and annual sea surface temperature patterns in this region, to estimate potential annual metabolic costs expected for mature female green crabs. Results indicate that energy storage should incur an ~8% increase in metabolic costs for female crabs, relative to a hypothetical crab that did not store any energy. Translated into feeding, for a medium‐sized mature female (45 mm carapace width), this requires the consumption of an additional ~156 mussels annually to support the metabolic cost of energy storage. These results indicate, contrary to previous assumptions, that the cost of energy storage for small‐bodied ectotherms may represent a considerable portion of their basic operating energy budget. An inability to meet these additional costs of energy storage may help explain the recent decline of green crabs in the Gulf of Maine where reduced prey availability and increased consumer competition have combined to hamper green crab foraging success in recent years.

Local Knowledge of Distribution of European Green Crab (Carcinus maenas) in Southern Nova Scotian Coastal Waters

Local knowledge is making important contributions to environmental management. Improving understanding of local knowledge that is in the early stages of development may be useful towards management of novel species or understanding other contemporary events. In this study we interviewed Nova Scotian fishermen with experience with a recently arrived invasive species, the European green crab (Carcinus maenas), to evaluate their knowledge of its local distribution. Ten participants who had either fished green crab or experienced it as a by-catch were interviewed. Environmental, temporal and internal population factors that were frequently associated with green crab distributions were reported by participants. Environmental factors described included primarily depth, vegetation, biotic interactions and bottom type. Furthermore, interactions with temporal factors (e.g. tidal and seasonal changes) as well as internal-population factors (e.g. sex and age) were observed by a number of participants. Internal factors were described more frequently among participants with more experience and more direct associations with green crab. Local knowledge illustrates not only a nascent understanding of this species’ distribution, but realization of internal population structure and temporal variations, which may help to refine management strategies. This study illustrates the potential for local knowledge to form and develop, even around relatively recent environmental events.