Carcinus Maenas Research Articles

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.

Identification and Full Characterisation of Two Novel Crustacean Infecting Members of the Family Nudiviridae Provides Support for Two Subfamilies.

Multiple enveloped viruses with rod-shaped nucleocapsids have been described, infecting the epithelial cell nuclei within the hepatopancreas tubules of crustaceans. These bacilliform viruses share the ultrastructural characteristics of nudiviruses, a specific clade of viruses infecting arthropods. Using histology, electron microscopy and high throughput sequencing, we characterise two further bacilliform viruses from aquatic hosts, the brown shrimp (Crangon crangon) and the European shore crab (Carcinus maenas). We assembled the full double stranded, circular DNA genome sequences of these viruses (~113 and 132 kbp, respectively). Comparative genomics and phylogenetic analyses confirm that both belong within the family Nudiviridae but in separate clades representing nudiviruses found in freshwater and marine environments. We show that the three thymidine kinase (tk) genes present in all sequenced nudivirus genomes, thus far, were absent in the Crangon crangon nudivirus, suggesting there are twenty-eight core genes shared by all nudiviruses. Furthermore, the phylogenetic data no longer support the subdivision of the family Nudiviridae into four genera (Alphanudivirus to Deltanudivirus), as recently adopted by the International Committee on Taxonomy of Viruses (ICTV), but rather shows two main branches of the family that are further subdivided. Our data support a recent proposal to create two subfamilies within the family Nudiviridae, each subdivided into several genera.

Prey preferences, consumption rates and predation effects of Asian shore crabs (Hemigrapsus takanoi) in comparison to native shore crabs (Carcinus maenas) in northwestern Europe

The Asian brush-clawed shore crab Hemigrapsus takanoi was introduced to the northern Wadden Sea (southeastern North Sea) in 2009 and now represents one of the most abundant brachyuran crab species. Abundance studies revealed an increase of mean crab densities on mixed reefs of native blue mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) from 18 individuals m−2 in 2011 to 216 individuals m−2 in 2020. Despite its current high densities only little is known about the feeding habits of H. takanoi, its effects on prey populations and on the associated community in the newly invaded habitat. We summarize results of individual field and laboratory experiments that were conducted to assess feeding habits and consumption effects caused by Asian brush-clawed shore crabs and, additionally, compare the feeding ecology of H. takanoi with the one of the native shore crab Carcinus maenas. Field experiments manipulating crab densities revealed that both crab species affected the recruitment success of blue mussels, Pacific oysters and Australian barnacles (Austrominius modestus) with highest number of recruits at crab exclusion. However, endobenthic polychaetes within the reefs were differently affected. Only the native C. maenas caused a significant reduction in polychaete densities, whereas the introduced H. takanoi had no effect. Additional comparative laboratory studies revealed that single C. maenas consume more juvenile blue mussels than Asian brush-clawed shore crabs of the same size class. When offering amphipods as a mobile prey species, we found the same pattern with higher consumption rates by C. maenas than by H. takanoi. For Asian but not for native shore crabs, we detected a sex-dependent feeding behavior with male H. takanoi preferring blue mussels, while females consumed more amphipods. Considering mean crab densities and feeding behavior, our results suggest that despite lower consumption rates of single crabs, Asian brush-clawed shore crabs can cause stronger impacts on prey organisms than the native C. maenas, because H. takanoi exceeds their densities manifold. A strong impact of the invader on prey populations is supported by low amphipod occurrence at sites where H. takanoi density is high in the study area. Thus, the introduced Asian brush-clawed shore crab is an additional consumer with significant effects on the associated community of mixed reefs of mussels and oysters in the Wadden Sea.

Wasted Biomaterials from Crustaceans as a Compliant Natural Product Regarding Microbiological, Antibacterial Properties and Heavy Metal Content for Reuse in Blue Bioeconomy: A Preliminary Study.

The compliance of crab shells traditionally used as a complex natural product for agricultural soil amendment with modern biofertilizers’ quality and safety requirements was investigated. Shells waste from the Blue crab, Callinectes sapidus and the Green crab, Carcinus aestuarii were tested for macronutrients, heavy metals, bacteria content, and antimicrobial properties. Such information is crucial for further utilization of the biogenic powders for any composite formulation in added-value by-products. The calcium carbonate-rich hard tissue yield was 52.13% ± 0.015 (mean ± S.D.) and 64.71% ± 0.144 from the blue and green crabs, respectively. The contents of Pb, Ni, Zn, Cr (VI), and Cu were several orders of magnitude below the prescribed limit by EU biofertilizer legislation, with Fe, Mn (not prescribed), and As being the most abundant. The content of As and Cd from the material considered here was within limits. The shells contain no colony-forming units of Salmonella spp. and compliant levels of Escherichia coli; moreover, the shell micro-powder showed dose-dependent growth inhibition of Pseudomonas aeruginosa and Staphylococcus aureus. In summary, the waste crab shells present a complex natural product as plant biofertilizer following the circular economy concepts.

Neither historical climate nor contemporary range fully explain the extant patterns of molecular diversity in marine species

AbstractAimIntraspecific diversity is a significant component of adaptive potential, and thus, it is important to identify the evolutionary processes that have and will continue to shape the molecular diversity of natural populations. This study aims to untangle the possible drivers of intraspecific molecular diversity by testing whether patterns of historical climatic stability or contemporary range position correlate with molecular diversity.LocationSouth African coastline.TaxaThe cape urchin (Parechinus angulosus), common shore crab (Cyclograpsus punctatus) and granular limpet (Scutellastra granularis).MethodsSpecies distributions were hindcasted to the Last Glacial Maximum to assess the biogeography of the study species. Linear models were built to compare the relationships between historical climatic stability or contemporary distributional ranges with extant genetic (mtDNA) and genomic (SNP) diversity.ResultsWe found large differences in the historical ranges among species and time periods. Regions of higher habitat stability corresponded to regions of higher molecular diversity, but historical climatic variability was not a predictor of molecular diversity within linear models. Lower genetic diversity values, and higher genetic differentiation, were detected in edge populations, but this was not consistent across marker type or species.Main conclusionsBoth historical and contemporary processes are potentially driving patterns of diversity, but a large portion of the variation in molecular diversity remains unexplained. Our findings suggest that marine species within cool‐temperate bioregions in the Southern Hemisphere may have more complex biogeographic and evolutionary histories than terrestrial taxa and/or coastal species within northern, formerly glaciated regions.

Do microplastic contaminated seafood consumption pose a potential risk to human health?

Microplastics are present in all parts of the ocean and can have deleterious effects on marine resources. The aim of this work was to map the presence of microplastics in commercial marine species such as bivalves (mussels Mytilus galloprovincialis and clams Scrobicularia plana), crabs (Carcinus maenas) as well as fish (Mullus surmuletus) to relate microplastics levels to pollution sources, assess possible impact on marine food chains and on human health. These species were collected from several sites of the Ria Formosa lagoon and along the south coast of Portugal. A quantitative assessment (number, size and color) and typology of microplastics were made in these species. Only one green fragment of polypropylene was detected in the gills of the crabs, while a blue polyethylene fragment was detected in the hepatopancreas of the mullets. Moreover, no microplastics were present in S. plana nor in the crabs whole soft tissues. Among mussels, 86% of microplastics were present from all sites and the number, size and color were site specific. Mussels from the west side of the coast (Sites 1–3) had the highest levels of MPs per mussel and per weight compared to the other sites, probably related to the impact of touristic activity, fishing gears, fresh water and sewage effluents along with the hydrodynamics of the area.

Symbionts of invasive and native crabs, in Argentina: The most recently invaded area on the Southwestern Atlantic coastline

Biological invasions have the capacity to introduce non-native parasites. This study aimed to determine whether the invasive green crab population, Carcinus spp., on the Southwestern Atlantic coast of Argentina harbours any symbionts, and whether these may spillover or spillback between native crabs, Cyrtograpsus altimanus and C. angulatus. Macroscopy, histology, and molecular analyses of some parasites were used to describe and compare their diversity across the three species of crab. We also evaluated the susceptibility of invasive Carcinus spp. to a native digenean, Maritrema madrynense, via experimental infections (exposure and cohabitation).Our results revealed that the green crab pathobiome included similar symbiotic groups to native crabs. This included putative viral, bacterial, and protozoan parasites. Haplosporidium-like observations were recorded in all crab species, and a single green crab was found to be parasitized by an Agmasoma-like microsporidium. Metagenomic analysis of one individual revealed additional symbiotic diversity (46 bacteria, 5 eukaryotic species). The green crabs were infected by more microparasite taxa than the native crabs (5:3). Wild populations of Carcinus spp. were free of metazoan parasites and are shown not to be susceptible to M. madryense under experimental conditions.Our results suggest a reduction/escape of macroparasites (trematode Maritrema madrynense; acanthocephalan Profilicollis chasmagnathi) in invasive Carcinus spp. compared to their native competitors.

Prey preferences of invasive (Hemigrapsus sanguineus, H. takanoi) and native (Carcinus maenas) intertidal crabs in the European Wadden Sea

AbstractInvasive predators can have wide-ranging effects on invaded ecosystems and identifying the prey spectra and preferences of invaders are important steps in assessing their potential impacts on native biota. In this study, we investigated prey preferences of two invasive crab species (Hemigrapsus sanguineus and Hemigrapsus takanoi) that recently invaded Europe's shores and compared them with preferences of native shore crabs (Carcinus maenas) of similar size. In laboratory experiments, all three crab species preferred animal over algal prey. In general, sessile mussels (Mytilus edulis) were preferred over motile amphipods (Gammarus locusta) by all three crab species but amphipod predation was lower in the invasive compared with the native crabs. For the two invasive crab species, this pattern was the same in treatments where prey was offered separately (no-choice treatments) or simultaneously (choice treatments), while for the native crabs, mussel preference disappeared in choice treatments. The general preference of mussels by all three crab species suggests that local invasions of crabs most likely lead to increased competition among crabs. In addition, given that local densities of invasive crabs are often much higher than those of native crabs, predation pressure on native mussels can be expected to strongly increase at invaded sites. In contrast, local predation pressure on amphipods may be less affected by the crab invasions. Further field studies are needed to establish the magnitude of competition and predation pressure exerted by the invaders under natural conditions.

Long‐term study reveals top‐down effect of crabs on a California salt marsh

AbstractConsumers can structure plant communities and may function as keystone species or ecosystem engineers. In salt marshes, the prevailing paradigm has shifted in recent decades from nearly complete focus on bottom‐up processes to inclusion of top‐down effects. Although the number of studies investigating top‐down control continues to climb, few experiments span multiple years, so temporal variability in or long‐term impacts of consumers have not been well characterized. In addition, while top‐down control has been found to be common in Western and Eastern Atlantic and Western Pacific salt marshes, our study is one of the first to experimentally consider top‐down control of salt marsh plants in the Eastern Pacific. We conducted a five‐year field experiment along eroding creekbank edges of a California salt marsh in which we manipulated densities of the shore crab, Pachygrapsus crassipes, and tracked marsh responses over time. Our results demonstrate that, through both consumption and engineering activities, this superabundant crab is regulating marsh vegetation and soil structure. Experimentally reducing crab abundance enhanced vegetation biomass and sediment bulk density. Moreover, root biomass and bulk density—factors known to increase marsh resilience to erosion and sea‐level rise—decreased linearly with increasing burrow density. Our long‐term study uniquely revealed that burrows can persist for years after crab abundances are reduced and that plant responses from grazer exclusions gradually strengthen over time, likely due to the relatively slow growth of woody perennial foundational plants. Since shore crabs are abundant throughout the marsh in most major estuaries within the range of the species (from Baja California, Mexico to Oregon, USA), we hypothesize that this species is exerting significant, yet underappreciated top‐down control and modifying the sediment properties of many West Coast salt marshes.

Acclimation to tidal conditions alters the physiological responses of the green shore crab, Carcinus maenas, to subsequent emersion.

Animals inhabiting the intertidal zone are exposed to abrupt changes in environmental conditions associated with the rise and fall of the tide. For convenience, the majority of laboratory studies on intertidal organisms have acclimated individuals to permanently submerged conditions in seawater tanks. In this study, green shore crabs, Carcinus maenas, were acclimated to either a simulated tidal regime of continuous emersion-immersion ('tidal') or to permanently submerged conditions ('non-tidal') to assess their physiological responses to subsequent emersion. Tidal crabs exhibited an endogenous rhythm of oxygen consumption during continuous submersion with lower oxygen consumption during periods of anticipated emersion, which was not detected in non-tidal crabs. During emersion, tidal crabs were able to buffer apparent changes in acid-base balance and exhibited no change in venous pH, whereas non-tidal crabs developed an acidosis associated with a rise in lactate levels. These results indicate that tidal crabs were better able to sustain aerobic metabolism and had lower metabolic costs during emersion than non-tidal crabs. It is likely that the elevated levels of haemocyanin exhibited by tidal crabs allowed them to maintain oxygen transport and buffer pH changes during emersion. This suggests that acclimation of C. maenas to submerged conditions results in a loss of important physiological mechanisms that enable it to tolerate emersion. The results of this study show that caution must be taken when acclimating intertidal organisms to submerged conditions in the laboratory, as it may abolish important physiological responses and adaptations that are critical to their performance when exposed to air.

Impaired larval development at low salinities could limit the spread of the non-native crab Hemigrapsus takanoi in the Baltic Sea

The Asian shore crab Hemigrapsus takanoi, native to the northwest Pacific Ocean, was recently discovered in Kiel Fjord (southwestern Baltic Sea). In laboratory experiments, we tested the salinity tolerance of H. takanoi across 8 levels (0 to 35) and across 3 life history stages (larvae, juveniles and adults) to assess its potential to invade the brackish Baltic Sea. Larval development at different salinities was monitored from hatching to the megalopa stage, while survival and feeding of juveniles and adults were assessed over 17 d. Larvae of H. takanoi were able to complete their development to megalopa at salinities ≥ 20 and the time needed after hatch to reach this stage did not differ between salinities of 20, 25, 30 and 35. At a salinity of 15, larvae still reached the last zoea stage (zoea V), but development to the megalopa stage was not completed. All juveniles and adults survived at salinities from 5 to 35. Feeding rates of juveniles increased with increasing salinity across the entire salinity range. However, feeding rates of adults reached their maximum between salinities of 15 and 35. Our results indicate that both juveniles and adults of H. takanoi are euryhaline and can tolerate a wide range of salinities, at least for the time period tested (2 wk). However, larval development was impaired at salinities lower than 20, which may prevent the spread of H. takanoi into the Baltic Proper.

Predation risk increases in estuarine bivalves stressed by low salinity

Salinity drops in estuaries after heavy rains are expected to increase in frequency and intensity over the next decades, with physiological and ecological consequences for the inhabitant organisms. It was investigated whether low salinity stress increases predation risk on three relevant commercial bivalves in Europe. In laboratory, juveniles of Venerupis corrugata, Cerastoderma edule, and the introduced Ruditapes philippinarum were subjected to low salinities (5, 10 and control 35) during two consecutive days and, afterwards, exposed to one of two common predators in the shellfish beds: the shore crab Carcinus maenas and the gastropod Bolinus brandaris, a non-indigenous species present in some Galician shellfish beds. Two types of choice experiment were done: one offering each predator one prey species previously exposed to one of the three salinities, and the other offering each predator the three prey species at the same time, previously exposed to one of the three salinities. Consumption of both predators and predatory behaviour of C. maenas (handling time, rejections, consumption rate) were measured. Predation rates and foraging behaviour differed, with B. brandaris being more generalist than C. maenas. Still, both predators consumed significantly more stressed (salinity 5 and 10) than non-stressed prey. The overall consumption of the native species C. edule and V. corrugata was greater than that of R. philippinarum, likely due to their vulnerability to low salinity and physical traits (e.g., thinner shell, valve gape). Increasing precipitations can alter salinity gradients in shellfish beds, and thus affect the population dynamics of harvested bivalves via predator–prey interactions.

Do predators have a role to play in wetland ecosystem functioning? An experimental study in New England salt marshes.

The historical ecological paradigm of wetland ecosystems emphasized the role of physical or “bottom‐up” factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or “top‐down” factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent.

Effect of size on concentrations and cadmium inducibility of metallothionein in the shore crab Carcinus maenas

Metallothionein (MT) plays an important role in protecting organisms from the adverse effects of Cd, Hg, Zn and Cu. Investigations on mammals show variations in metallothionein concentrations and inducibility with age. This has never been investigated in invertebrates, and we determined the concentrations and inducibility of metallothionein in gills and midgut gland of different size classes of shore crabs from uncontaminated areas. Metallothionein concentrations in gills and midgut gland ranged between 30 and 40 μg g−1 dry weight with no differences among the different size classes. Concentrations of cadmium, copper and zinc in the midgut gland increased with increasing size of the crabs when the concentrations were expressed on a dry weight basis; water content in the midgut gland increased with the size and only the cadmium concentration increased with size when concentrations were expressed on wet weight basis. There was an inverse relationship between metallothionein and both copper and cadmium concentrations. Smaller crabs exposed to 1 mg Cd L−1 accumulated higher concentrations of cadmium in midgut gland and gills than larger ones and metallothionein concentrations in the midgut gland were higher in the smaller crabs. However, the increase in metallothionein concentration per accumulated unit of cadmium showed a linear increase with the size of the crabs. The ratio [Cd]midgut/[Cd]gills decreased with the size of the crabs. The overall conclusion is that baseline metallothionein concentrations do not change with age in shore crabs, but that the inducibility of metallothionein upon cadmium challenge does.

Effects of climate variability on an estuarine green crab Carcinus maenas population

The increase in frequency and intensity of extreme climate events over the last few decades has been leading to profound changes in estuarine and marine ecosystems worldwide, with strong implications for the species inhabiting these ecosystems as well as for the services provided by them. In this study, we analysed the effects of climate variability on the temporal and spatial variations in population dynamics of the green crab Carcinus maenas in the Mondego estuary (Portugal), between 2003 and 2018. In this 15-year period, a greater recruitment of C. maenas was observed during drought periods, periods which was matched by an increase in secondary production. Ontogenic stage segregation was also observed, with juveniles being found mainly in the further upriver areas of the estuary. The estuarine population was mainly composed of the green morphotype, with the orange and red morphotypes present in more downstream areas of the estuary. Redundancy analysis (RDA) showed high spatial and temporal variability of C. maenas in the estuary which was related with environmental changes over the 15-year period. A correlation between C. maenas biological features and several local-scale (salinity and river runoff) and large-scale (North Atlantic Oscillation index and Eastern Atlantic pattern) environmental variables was identified through cumulative sums analysis (CUSUM), indicating a strong environmental control on C. maenas population dynamics. This paper shows the importance of relatively long-term datasets to unravel the effects of extreme weather events due to climate change on key epibenthic estuarine species, and also how they might cope with a changing marine environment.

Relationship between ocean ecosystem indicators and year class strength of the invasive European green crab (Carcinus maenas)

The annual abundance of the non-native European green crab, Carcinus maenas, in Oregon estuaries varies greatly with ocean conditions. Average numbers were high following the 1997–1998 El Niño, decreased and remained low (<0.3 per trap) until they increased (>2 per trap) following the extended anomalous warming in 2014–2016. The year class strength of young crabs is strongly linked to ocean indicators during their planktonic larval development. Many of the same physical and biological ecosystem indicators used in salmon forecasting are also correlated with green crabs, but in the opposite direction. While cold ocean conditions benefit salmon, warm ocean indicators are positively linked to green crab year class strength. Among the best indicators for green crab year class strength are winter water temperatures, the sign of the Pacific Decadal Oscillation index, the day of physical and biological spring transitions, and negative biomass anomalies of northern copepods. These correlations suggest that green crabs need (1) warm winters (temperature > 10 °C), which enable larvae to complete their development in the near-shore, (2) strong northward flow of coastal waters during winter, which allows larvae to be transported from established populations to the south and (3) coastal circulation patterns that keep larvae close to shore, where they can be carried by wind and tidal currents into estuaries to settle. By using a relatively simple stoplight approach of ranking indicators, we were able to explain 69% of the inter-annual variability in green crab year class strength, while a quantitative metric of a combination of indicators explained 64% of the variability. Recruitment in 2018 and 2019 exceeded what was expected from the suite of ocean indicators. We discuss the possible role of additional larval sources, from the north or from local estuaries, that may have contributed to the increased recruitment during these years. If breeding populations of green crabs in Oregon and Washington continue to build, the relationships between ocean conditions and recruitment we have developed based solely on larval sources from the south could be greatly underestimating recruitment in the future.

Polybrominated diphenyl ethers and their methoxylated congeners in Douro river estuary biota: Seasonal occurrence and risk assessment

Especially added on many industrial and domestic products as flame retardants (FRs), polybrominated diphenyl ethers (PBDEs) are among the chemicals of high environmental concern because of their potential harmfulness for environmental and human health. Seafood consumption is considered the main source of PBDEs and their methoxylated congeners (MeO-BDEs) for humans. The present study aims to investigate the seasonal occurrence of six PBDEs and eight MeO-BDEs congeners using Douro river biota (different trophic levels) as sentinels, as well as to evaluate the human exposure risk to PBDEs through seafood consumption. Biota samples (n = 273) were collected from one of the most important Portuguese estuaries in the north-western coast of Portugal at four different seasons (2019–2020). The analyses were performed by an environmental-friendly extraction procedure followed by Gas Chromatography coupled to a triple quadrupole detector (GC–MS/MS). PBDEs were detected in all seafood samples analysed, with means ranging from 0.02 ng g−1 ww (flounder in autumn) to 3.75 ng g−1 ww (mussel in winter). Levels of lower-brominated PBDE congeners were significantly higher than higher-brominated ones in all seasons (p < 0.01). MeO-BDEs ranged from 0.001 ng g−1 ww (grey mullet in summer) to 5.66 ng g−1 ww (green crab in spring). Crabs and mussels presented the highest means of PBDEs and MeO-BDEs. Regarding the health risk assessment of the studied PBDE congeners (47, 99, and 153), consumption of Douro river fish is not a case of concern for consumers.

Mushroom bodies and reniform bodies coexisting in crabs cannot both be homologs of the insect mushroom body.

In one species of shore crab (Brachyura, Varunidae), a center that supports long-term visual habituation and that matches the reniform body's morphology has been claimed as a homolog of the insect mushroom body despite lacking traits that define it as such. The discovery in a related species of shore crab of a mushroom body possessing those defining traits renders that interpretation unsound. Two phenotypically distinct, coexisting centers cannot both be homologs of the insect mushroom body. The present commentary outlines the history of research leading to misidentification of the reniform body as a mushroom body. One conclusion is that if both centers support learning and memory, this would be viewed as a novel and fascinating attribute of the pancrustacean brain.

The ecological impacts of multiple environmental stressors on coastal biofilm bacteria.

Ecological communities are increasingly exposed to multiple interacting stressors. For example, warming directly affects the physiology of organisms, eutrophication stimulates the base of the food web, and harvesting larger organisms for human consumption dampens top-down control. These stressors often combine in the natural environment with unpredictable results. Bacterial communities in coastal ecosystems underpin marine food webs and provide many important ecosystem services (e.g. nutrient cycling and carbon fixation). Yet, how microbial communities will respond to a changing climate remains uncertain. Thus, we used marine mesocosms to examine the impacts of warming, nutrient enrichment, and altered top-predator population size structure (common shore crab) on coastal microbial biofilm communities in a crossed experimental design. Warming increased bacterial α-diversity (18% increase in species richness and 67% increase in evenness), but this was countered by a decrease in α-diversity with nutrient enrichment (14% and 21% decrease for species richness and evenness, respectively). Thus, we show some effects of these stressors could cancel each other out under climate change scenarios. Warming and top-predator population size structure both affected bacterial biofilm community composition, with warming increasing the abundance of bacteria capable of increased mineralization of dissolved and particulate organic matter, such as Flavobacteriia, Sphingobacteriia, and Cytophagia. However, the community shifts observed with warming depended on top-predator population size structure, with Sphingobacteriia increasing with smaller crabs and Cytophagia increasing with larger crabs. These changes could alter the balance between mineralization and carbon sequestration in coastal ecosystems, leading to a positive feedback loop between warming and CO2 production. Our results highlight the potential for warming to disrupt microbial communities and biogeochemical cycling in coastal ecosystems, and the importance of studying these effects in combination with other environmental stressors.

Physiological basis of interactive responses to temperature and salinity in coastal marine invertebrate: Implications for responses to warming.

Developing physiological mechanistic models to predict species’ responses to climate‐driven environmental variables remains a key endeavor in ecology. Such approaches are challenging, because they require linking physiological processes with fitness and contraction or expansion in species’ distributions. We explore those links for coastal marine species, occurring in regions of freshwater influence (ROFIs) and exposed to changes in temperature and salinity. First, we evaluated the effect of temperature on hemolymph osmolality and on the expression of genes relevant for osmoregulation in larvae of the shore crab Carcinus maenas. We then discuss and develop a hypothetical model linking osmoregulation, fitness, and species expansion/contraction toward or away from ROFIs. In C. maenas, high temperature led to a threefold increase in the capacity to osmoregulate in the first and last larval stages (i.e., those more likely to experience low salinities). This result matched the known pattern of survival for larval stages where the negative effect of low salinity on survival is mitigated at high temperatures (abbreviated as TMLS). Because gene expression levels did not change at low salinity nor at high temperatures, we hypothesize that the increase in osmoregulatory capacity (OC) at high temperature should involve post‐translational processes. Further analysis of data suggested that TMLS occurs in C. maenas larvae due to the combination of increased osmoregulation (a physiological mechanism) and a reduced developmental period (a phenological mechanisms) when exposed to high temperatures. Based on information from the literature, we propose a model for C. maenas and other coastal species showing the contribution of osmoregulation and phenological mechanisms toward changes in range distribution under coastal warming. In species where the OC increases with temperature (e.g., C. maenas larvae), osmoregulation should contribute toward expansion if temperature increases; by contrast in those species where osmoregulation is weaker at high temperature, the contribution should be toward range contraction.