Shore Crab Carcinus Maenas Research Articles

Thermal performance of native and invasive crab species: investigating the invasion potential of Hemigrapsus takanoi in southern European Carcinus maenas’ habitats

Invasive species’ plasticity and latitudinal spread have become an increasing matter of concern in rapidly changing climate. The brush-clawed shore crab (Hemigrapsus takanoi), native along northwestern Pacific shores, has established dense populations in northern European coasts. Detrimental effects in natura have been reported, such as displacement of native species and competition for shelter, rasing concerns regarding shellfish early life stages and food webs-posing a threat to wild stocks’ recruitment and aquaculture. The species has not yet been observed in southern European countries (e.g., Portugal), where niche habitats such as harbours, mudflats, and lagoons reach higher temperatures than the invaded northern range. The aims of this study were to determine H. takanoi potential to acclimate to a southern thermal range, assess thermal performance, and identify potential competitive advantages over the native shore crab Carcinus maenas. This was accomplished through individual exposure to one of three treatments, resembling a southern European thermal range (17 °C, 21 °C, or 25 °C), for 30 days. H. takanoi thrived in temperatures as high as 25 °C, a realistic thermal scenario in Óbidos Lagoon (the biggest Portuguese lagoon)—while the native shore crab C. maenas underperformed at that treatment, showing lower survival, growth, and feed intake than H. takanoi. These results suggest that H. takanoi may be able to colonise southern and warmer European locations and have higher plasticity than the native species already inhabiting areas close to its upper thermal limits. Under global warming scenarios, inferences of further latitudinal spread and increased invaded range may also be taken to the invaded northern European habitats.

Artificial rockpools create habitat refugia on seawalls at high tide

Rockpools are fundamental habitats on natural rocky shores that provide refugia for marine life at low and high tide. Yet, artificial coastal structures lack the topographical complexity seen in these natural habitats. Eco-engineering, that may include the deployment of artificial rockpools, attempts to address the lack of suitable habitat on coastal infrastructure but most studies focus on species abundance metrics at low tide. It is important to understand how eco-engineering interventions may provide habitat at high tide compared to the surrounding artificial substrate.In this study, we demonstrate how groups of rockpools (1, 3 or 5 rockpools) add habitat complexity at high tide to a concrete seawall in Poole Harbour, UK. Between April and October 2022, eighteen GoPro cameras were deployed to record species richness and abundance in artificial rockpools and the adjacent concrete sea wall. Additionally, the length of time the most abundant fauna (the shanny fish Lipophrys pholis and the European shore crab Carcinus maenas) spent engaging in different behaviour (resting, feeding, moving) was recorded.Overall, there was no significant difference in the abundance and species richness of mobile fauna using the artificial rockpools versus the seawall. However, both the shanny and shore crab generally spent more time in the rockpools than on the seawall. Both crabs and shanny preferentially engaged in feeding behaviours on the seawall, which has been attributed to the high percentage cover of barnacle prey. Crabs and shanny spent more time resting in the rockpools than the seawall and the only reproductive behaviour observed occurred within the rockpools. Our work suggests that artificial rockpools support the habitat needs and multiple life history requirements of these species at high tide. Both the seawall and rockpools provide valuable resources, which further emphasises the need for variety in eco-engineering feature designs.

Dynamic visual noise has limited influence on the habitat selection and behavioural activity of crustaceans and cephalopods

AbstractEnvironments contain various forms of noise that can interfere with the ability of animal sensory systems to perceive information. One ubiquitous type of visual noise in shallow aquatic habitats is caustic flicker (or caustics), consisting of dynamically moving light patterns caused by the refraction of light when passing through the water's rippling surface. While some teleost fish avoid environments with caustic noise (where their prey can be more difficult to detect), it remains untested whether caustics affect the habitat selection of invertebrates. In the present study, we ask whether three invertebrate species, the shore crab Carcinus maenas, the brown shrimp Crangon crangon, and the common cuttlefish Sepia officinalis, prefer or avoid associating with environments with caustic noise, and whether caustics affect their behavioural activity and habitat exploration. To do this, we exposed the three species in binary choice experiments to different simulated caustic noise levels varying in their temporal (speed) and spatial (definition) components. Neither of the three tested invertebrate species spent more or less time in environments with higher caustic noise levels. While we also found no evidence that caustics affected the behavioural activity and exploration of Ca. maenas and S. officinalis, the brown shrimp Cr. crangon reduced its activity with increasing spatial caustic noise. However, all obtained effect sizes in this study were small, suggesting that caustic noise only minimally affects invertebrate behaviour. Overall, our results show that, unlike in teleost fish, caustics have limited influence on the habitat selection, exploration, and activity of crustaceans and cephalopods.

On their way to the north: larval performance of Hemigrapsus sanguineus invasive on the European coast—a comparison with the native European population of Carcinus maenas

The Asian shore crab Hemigrapsus sanguineus has become invasive in North Europe and it co-occurs and competes with the native European shore crab Carcinus maenas. Both species develop through a feeding and dispersive larval phase characterised by several zoeal and a settling megalopa stage. Larvae of marine crabs are vulnerable to food limitation and warming has the potential to exacerbate the negative effects of food limitation on survival and growth. We quantified the combined effects of temperature and food limitation on larval performance (survival and growth) of H. sanguineus and we compared our results with those reported on performance of C. maenas larvae, under the same experimental design and methodology. Larvae from four females of H. sanguineus collected on Helgoland (North Sea) were experimentally reared from hatching to megalopa, at four temperatures (range 15–24 °C) and two food conditions (permanent vs. daily limited access to food). Larval survival of H. sanguineus was low at 15 °C and increased with temperature, in contrast to the high survival reported for C. maenas larvae in the range 15–24 °C. Food limitation reduced survival and body mass of H. sanguineus larvae at all temperatures, but without evidence of the exacerbating effect caused by high temperatures and reported for C. maenas. By contrast, high temperature (24 °C) mitigated the negative effect of food limitation on body mass on H. sanguineus larvae. Advantages of H. sanguineus over C. maenas appear especially under the increased temperatures expected from climate change.

Extracellular vesicle signatures and protein citrullination are modified in shore crabs (Carcinus maenas) infected with Hematodinium sp

ABSTRACT Epizootiologists recurrently encounter symbionts and pathobionts in the haemolymph (blood equivalent) of shellfish. One such group is the dinoflagellate genus Hematodinium, which contains several species that cause debilitating disease in decapod crustaceans. The shore crab Carcinus maenas acts as a mobile reservoir of microparasites, including Hematodinium sp., thereby posing a risk to other co-located commercially important species, e.g. velvet crabs (Necora puber). Despite the widespread prevalence and documented seasonality of Hematodinium infection dynamics, there is a knowledge gap regarding host-pathogen antibiosis, namely, how Hematodinium avoids the host’s immune defences. Herein, we interrogated the haemolymph of Hematodinium-positive and Hematodinium-negative crabs for extracellular vesicle (EV) profiles (a proxy for cellular communication), alongside proteomic signatures for post-translational citrullination/deimination performed by arginine deiminases, which can infer a pathologic state. Circulating EV numbers in parasitized crab haemolymph were reduced significantly, accompanied by smaller EV modal size profiles (albeit non-significantly) when compared to Hematodinium-negative controls. Differences were observed for citrullinated/deiminated target proteins in the haemolymph between the parasitized and control crabs, with fewer hits identified overall in the former. Three deiminated proteins specific to parasitized crab haemolymph were actin, Down syndrome cell adhesion molecule (DSCAM), and nitric oxide synthase – factors that contribute to innate immunity. We report, for the first time, Hematodinium sp. could interfere with EV biogenesis, and that protein deimination is a putative mechanism of immune-modulation in crustacean-Hematodinium interactions.

Resistance to white spot syndrome virus in the European shore crab is associated with suppressed virion trafficking and heightened immune responses.

All decapod crustaceans are considered potentially susceptible to White Spot Syndrome Virus (WSSV) infection, but the degree of White Spot Disease (WSD) susceptibility varies widely between species. The European shore crab Carcinus maenas can be infected with the virus for long periods of time without signs of disease. Given the high mortality rate of susceptible species, the differential susceptibility of these resistant hosts offers an opportunity to investigate mechanisms of disease resistance. Here, the temporal transcriptional responses (mRNA and miRNA) of C. maenas following WSSV injection were analysed and compared to a previously published dataset for the highly WSSV susceptible Penaeus vannamei to identify key genes, processes and pathways contributing to increased WSD resistance. We show that, in contrast to P. vannamei, the transcriptional response during the first 2 days following WSSV injection in C. maenas is limited. During the later time points (7 days onwards), two groups of crabs were identified, a recalcitrant group where no replication of the virus occurred, and a group where significant viral replication occurred, with the transcriptional profiles of the latter group resembling those of WSSV-susceptible species. We identify key differences in the molecular responses of these groups to WSSV injection. We propose that increased WSD resistance in C. maenas may result from impaired WSSV endocytosis due to the inhibition of internal vesicle budding by dynamin-1, and a delay in movement to the nucleus caused by the downregulation of cytoskeletal transcripts required for WSSV cytoskeleton docking, during early stages of the infection. This response allows resistant hosts greater time to fine-tune immune responses associated with miRNA expression, apoptosis and the melanisation cascade to defend against, and clear, invading WSSV. These findings suggest that the initial stages of infection are key to resistance to WSSV in the crab and highlight possible pathways that could be targeted in farmed crustacean to enhance resistance to WSD.

Sanderlings Feed on a Diverse Spectrum of Prey Worldwide but Primarily Rely on Brown Shrimp in the Wadden Sea

Knowing what birds eat is fundamental to understand the ecology and distribution of individuals and populations. Often, diet is assessed based on field observations and excrement analyses, which has previously been the case for Sanderling Calidris alba. This may have biased their known diets towards large prey with indigestible body parts that can still be recognized in faeces or regurgitations. A literature review of Sanderling diet worldwide showed that Sanderlings exploit a large diversity of prey. We carried out DNA metabarcoding on Sanderling faeces to get a complete view of their diet in the Wadden Sea during staging and moult from late July to early October. Given the diversity of available prey in the Wadden Sea, it was remarkable that 94% of the samples contained Brown Shrimp Crangon crangon which, next to the Shore Crab Carcinus maenas, were also the most abundant species in the samples. This study shows that whereas Sanderling can feed on a large variety of invertebrates, in the Wadden Sea during southward staging they primarily rely on Brown Shrimp

New insights into the evolution of portunoid swimming crabs (Portunoidea, Heterotremata, Brachyura) and the brachyuran axial skeleton

Portunoidea (Heterotremata) is a morphologically disparate taxon of true crabs (Brachyura) best-known for many of its representatives being considered “swimming crabs”. The term “swimming crab”, however, sometimes refers to a distinct taxon (traditionally to Portunidae within Portunoidea), and sometimes to a certain morphotype in which the 5th pereiopod (P5) has a specific shape that facilitates swimming. We use the term “P5-swimming crab” or “P5-swimmer” herein, not only to restrict it to the morphotype, but also to distinguish the swimming in question from other kinds of swimming in Brachyura. The evolution of P5-swimming crabs has not yet been satisfactorily investigated. In particular, it is not known whether the morphotype evolved several times independently in different lineages of Portunoidea or whether it evolved only once and was lost in several lineages. Ours is the first approach combining molecular with morphological data to result in a new phylogenetic positioning of some members of Portunoidea. For the first time, data from the axial skeleton and extrinsic musculature are used. Morphological examinations reveal that the axial skeleton and extrinsic musculature in P5-swimming crabs are more diverse than previously thought, with the exception of the P5 anterior coxa muscle, which originates at the median plate in all P5-swimmers. Ancestral state reconstructions based on parsimony reveal that the stem species of Portunoidea already showed the morphotype of a P5-swimming crab, but with a long merus which probably resulted in less effective P5-swimming than in extant P5-swimming crab species with a short merus. Several other extant taxa represent a reversal of the P5-swimmer morphotype to varying degrees, with some extant species showing a complete reversal of unambiguous P5-swimming crab character states—one example being the well-known common shore crab Carcinus maenas. The absence of a connection between interosternite 7/8 and the sella turcica (the secondary loss of the “brachyuran sella turcica”) in the stem species of Heterotremata, resulting in a junction plate which forms a cavity that offers room and attachment sites for the P5 extrinsic musculature is uncovered as preadaptation to the P5-swimmer morphotype in Heterotremata. This preadaptation is missing in Podotremata and Thoracotremata, the other two traditional main taxa of Brachyura.

Body condition and energy content of the shore crab Carcinus maenas L. in a temperate coastal system: the cost of barnacle epibiosis

The impact of barnacle epibionts on the condition of the shore crab Carcinus maenas was studied for the western Wadden Sea population. Approximately 39% of the crabs were fouled with the barnacle Balanus crenatus. Although the morphological Fulton’s K condition decreased by 5.8% in fouled crabs, Linear Mixed-Effects Models (LMM) showed that only the energetic condition of the crabs was significantly affected by fouling. The energy density of fouled crabs was consistently poorer (4.1% in AFDW; 8.7% in dry weight) than that of non-fouled crabs, especially in females and green forms in dry weight (12.8% and 11.4% reduction, respectively). Cumulative infection with Sacculina carcini, detected in 4.5% of the fouled crabs, additionally reduced by 14.3% the energy density in dry weight and almost to half of the total energy of the fouled crabs. Impacts of energy density reduction on crabs’ growth and reproduction are discussed.

Boom and bust: Simulating the effects of climate change on the population dynamics of a global invader near the edge of its native range

Despite the increasing awareness of climate change, few studies have used the Intergovernmental Panel on Climate Change (IPCC) scenarios to simulate the effects of climate change on estuarine populations of crustaceans. The objective of this study was to investigate the effects of temperature and salinity fluctuations on the population dynamics of the shore crab Carcinus maenas at the southern edge of its native range. To this end, a population dynamics model was developed based on experimental and literature data on the biology, ecology and physiology of the species. Results showed that the shore crab will be more affected by changes in temperature than in salinity. The parameter sensitivity analysis revealed that the larval phase of the species is the most sensitive stage of the shore crab life cycle. Three IPCC scenarios (SSP1-2.6, SSP2-4.5, and SSP3-8.5) were used to simulate the effects of temperature increase on the population of C. maenas in the near- (2040), mid- (2060), and long-term (2100). Two scenarios of drought conditions accompanied by the estimated salinity change were also simulated (10 % and 40 % drought). Results suggested that slight increases in temperature (up to 2 °C) lead to a strong increase on the density of C. maenas in the mid-term, while further temperature increases lead to a decline or local extinction of the shore crab population at the southern edge of its distribution range. Results indicated that a salinity increase in the estuary had a negative effect on the shore crab population. Given the importance of the species to temperate coastal ecosystems, both population increase and local extinction are likely to have significant impacts on estuarine communities and food webs, with unknown ecological and socioeconomic consequences.

Sacculina carcini impact on energy content of the shore crab Carcinus maenas L.

The impact of Sacculina carcini infection on the nutritional status of the shore crab Carcinus maenas was investigated in the western Dutch Wadden Sea for a period of 20 months. About 3.3% of the population was sacculinized, i.e. externally infected with S. carcini and only 0.7% presented scars of previous infection. The results of mixed linear models showed that sacculinized and non-sacculinized crabs had similar morphometric condition, while the energy density of parasitized crabs (externa excluded) was significantly reduced by about 4.3% overall, and by up to 5.8% in crabs under 40 mm carapace width. However, when Sacculina externa was included in the energy determinations, the difference in energy density decreased to 1.2%, while total energy content of the pair infected crab-parasite including externa was 30.8% higher than non-sacculinized crabs of similar size. The total energy content of ovigerous females (eggs included) was even higher, near doubling the energy of similar-sized crabs. The same way, total energy content of Sacculina externa was about 4 times lower than total energy of egg mass. The results suggest that the rhizocephalan parasite is efficient in consuming the energy that the host may allocate for growth and maintenance, but require future studies to disentangle the impact of the degree of internal infection and the implications for the dynamics of the population.

The role of tidal acclimation on the physiological responses of the green shore crab, Carcinus maenas, to thermal stress

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, and thus we currently know little about how acclimation to cyclic emersion-immersion influences the ability of intertidal organisms to cope with fluctuations in environmental conditions. In the present study, the green shore crab Carcinus maenas was acclimated to either a simulated tidal regime of continuous emersion-immersion (tidal) or to permanently submerged conditions (non-tidal). Aquatic oxygen consumption was assessed when crabs were exposed to cooling (15 °C - 5 °C) or warming (15 °C - 25 °C) regimes. Tidal crabs had lower levels of oxygen consumption over the 15 °C - 20 °C range. During acute thermal stress, the Q10 values of non-tidal crabs increased as the temperature declined to 5 °C, whereas tidal crabs maintained relatively consistent Q10 values across the temperature range (5 °C–25 C). These changes in oxygen consumption were paralleled by changes in haematological parameters. Tidal crabs had higher levels of haemocyanin which may have augmented oxygen delivery to the tissues and buffered acid-base imbalances. Surprisingly lactate levels were higher in tidal crabs, these appeared unconnected to anaerobic metabolism, but may have been an important metabolic fuel for tidal crabs. These results suggest that acclimation to a simulated tidal cycle may result in different physiological responses to environmental stressors and as such is an important consideration when assessing the responses of intertidal animals in a laboratory setting.

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.

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.

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.

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.

Anthropogenic underwater vibrations are sensed and stressful for the shore crab Carcinus maenas

Acoustic pollution in aquatic environments has increased with adverse effects on many aquatic organisms. However, little work has been done considering the effects of the vibratory component of acoustic stimuli, which can be transmitted in the substrate and propagated into the aquatic medium. Benthic marine organisms, including many invertebrates, are capable of sensing seabed vibration, yet the responses they trigger on organism have received little attention. This study investigates the impact of underwater vibration on the physiology and behaviour of a ubiquitous inhabitant of coastal areas of the northern hemisphere, the shore crab Carcinus maenas. We developed a novel vibratory apparatus with geophones supported on a softly sprung frame to induce a seabed vibration of 20 Hz frequency, as observed during dredging, piling and other anthropogenic activities. The geophone internal mass caused the frame to vibrate in a controlled manner. Our results show that transition from ambient to anthropogenic vibrations induced an increase in activity and antennae beats in shore crabs, indicating perception of the vibratory stimulus and a higher stress level. There was also a trend on sex-specific responses to anthropogenic vibration, with males showing a higher activity level than females. However, no effect of anthropogenic vibrations was found upon oxygen consumption. These results show that anthropogenic underwater vibration induces behavioural responses in Carcinus maenas. This highlights the importance of evaluating man-made vibratory activities on coastal invertebrates and the necessity of evaluating anthropogenic effects on both sexes.

Effects of handling during experimental procedures on stress indices in the green shore crab, Carcinus maenas (L)

ABSTRACT Stress due to handling is often an unavoidable feature of experimental investigations. In some cases, appropriate settling times are not considered, and as such, physiological responses caused by handling may become additive with those of experimental treatments. This study investigated the effect of different handling procedures on the acute physiological responses of green shore crab (Carcinus maenas). Handling, such as would occur during transport around a research facility or transfer during experimental procedure, was designated as light (10 min emersion) or severe (10 min emersion with shaking). Oxygen consumption (MO2) and haemolymph glucose and haemolymph L-lactate concentrations were elevated post-handling, the magnitude of the change related to the severity of handling stress. Glucose and L-lactate concentrations peaked within 1 h and returned to basal levels within 6 h, but MO2 remained elevated for 10 h, reflecting the additional energy required to oxidize L-lactate and replenish energy reserves. Differences between light and severe handling treatments showed that vibration (shaking) was a major contributor to the stress response, rather than the experimental emersion. This was confirmed in a second experiment where crabs were handled without emersion, and MO2 remained elevated for 14 h. In this experiment, the most pronounced increase in MO2 and metabolic parameters occurred in crabs that were physically touched and moved rapidly from the holding to experimental tanks. Here the touch, as well as vibration and visual stimuli, provoked a fight-flight response in the crabs. Stress responses were also evident in crabs gently transferred by containers. The fact that transferring crabs with no physical touching and minimal visual and vibrational stimuli still evoked a stress response, albeit less pronounced, supports a recommendation that crustaceans should be left to settle in the apparatus for at least 12 h after handling before experimental procedures are initiated.

The Effect of Turbidity on Functional Responses of European Shore Crab

Understanding the mechanisms of the natural environment that affect the interaction between consumers and resources is the key to understanding the stability and function of ecosystems. Although the effects of many environmental factors on predator-prey interactions have been well studied, turbidity in aquatic ecosystems is not one of them. Turbidity is ubiquitous and can be important because it is related to water pollution and can significantly reduce visibility of both predator and prey. In this study, the effect of turbidity on the interaction between the shore crab Carcinus maenas and the gammarid amphibians Echinogammarus marinus is studied. The functional response of the predator (crab) under different turbidity levels (consumption rate under different prey (shrimp) densities) was quantified, and it was found that turbidity increased the search speed and handling time. In zero turbidity, that is, completely clear water, the performance of the predator (crab) is not as good as the performance under low turbidity conditions. This may be caused by many reasons, such as the crab is get used to low turbidity conditions because they live at the bottom of intertidal and they will stir up sand at the bottom when they are moving. However, in order to better understand how the interaction between consumers and resources responds to turbidity, more research is needed.

Ontogeny of osmoregulation of the Asian shore crab Hemigrapsus sanguineus at an invaded site of Europe.

We studied the ontogeny of osmoregulation of the Asian shore crab Hemigrapsus sanguineus at an invaded area in the North Sea. H. sanguineus is native to Japan and China but has successfully invaded the Atlantic coast of North America and Europe. In the invaded areas, H. sanguineus is becoming a keystone species as driver of community structure and the adults compete with the shore crab Carcinus maenas. Strong osmoregulatory abilities may confer the potential to use and invade coastal areas already earlier in the life cycle. We reared larvae and first juveniles at 24°C in seawater from hatching to intermoult of each developmental stage (zoea I-V, megalopa, crab I). We exposed each stage to a range of salinities (0–39 ppt) for 24 h, and then we quantified haemolymph osmolality, using nano-osmometry. In addition, we quantified osmolality in field-collected adults after acclimation to the test salinities for 6 days. Larvae of H. sanguineus were able to hyper-osmoregulate at low salinities (15 and 20 ppt) over the complete larval development, although the capacity was reduced at the zoeal stage V; at higher salinities (25–39 ppt), all larval stages were osmoconformers. The capacity to slightly hypo-regulate at high salinity appeared in the first juvenile. Adults were able to hyper-osmoregulate at low salinities and hypo-regulate at concentrated seawater (39 ppt). H. sanguineus showed a strong capacity to osmoregulate as compared to its native competitor C. maenas, which only hyper-regulates at the first and last larval stages and does not hypo-regulate at the juvenile-adult stages. The capacity of H. sanguineus to osmoregulate over most of the life cycle should underpin the potential to invade empty niches in the coastal zone (characterized by low salinity and high temperatures). Osmoregulation abilities over the whole life cycle also constitute a strong competitive advantage over C. maenas.