Host-parasite relation between the shore crab Carcinus maenas and Sacculina carcini (Rhizocephala): Identification and characterization of a specific fraction correlated with parasitism

Two protein fractions have been revealed in the blood of infested crabs. These fractions do not occur in healthy animals. Their relations are analyzed. Both present the same electrophoretic mobility and have common antigenic determinants. They are characterized in relation to the major serologic components of the hemolymph.     

Cryptic invasions of the crab Carcinus detected by molecular phylogeography

Coastal marine ecosystems world-wide are threatened by invasions of nonindigenous species. The ubiquity of marine sibling species identifiable only by genetic analysis suggests that many invasions are cryptic and therefore undetected, causing an underestimation of the actual number and impacts of invading species. We test this hypothesis with European crabs in the genus Carcinus that have invaded five regions globally. Partial 16S ribosomal RNA gene sequences confirm sibling species status of morphologically similar Atlantic C. maenas and Mediterranean C. aestuarii . Based on 16S rRNA haplotypes, crabs from California, New England and Tasmania were all C. maenas . However, we report the cryptic multiple invasion of both species in Japan and South Africa, where only C. aestuarii and C. maenas , respectively, were previously recognized.     

The capacity of crab megalopae to autotomize body appendages and the consequences upon their feeding ability–the price to pay to live another day

During the mass settlement events of brachyuran crabs, there is a significant chance of density-dependent injury in the megalopae (last larval stage) because cannibalism can occur by larger conspecifics. Laboratory observations revealed that the appendages that are more prone to injury are eyestalks, as well as first (P1) and fifth (P5) pereiopods. The ability of Carcinus maenas megalopae to autotomize these structures and the effect of such injuries in their feeding ability and metamorphosis were investigated. All tested specimens were able to autotomize one or both of their P1 and P5, but not their eyestalks. Megalopae missing a single P1, as well as one or both P5, were able to capture and ingest prey, as well as intact specimens. Megalopae with either P1 and P5 appendages or at least one damaged eyestalk failed to ingest sufficient food to reach the nutritional threshold required to successfully metamorphose.     

Spectral sensitivity of the cod,Gadus morhua L.

The spectral sensitivity of the cod was determined under both dark adapted and light adapted conditions in the laboratory. Cod were trained by cardiac conditioning to detect a difference in radiance between an image of spots and the background radiance of a screen. Thresholds for this response were measured for a range of different wavelengths, and expressed as quantum adjusted values. Electroretino‐graphic studies were also performed on the eyes of cod, and spectral sensitivity curves prepared. Under dark adapted conditions both the behavioural and e.r.g. derived curves showed greatest sensitivity in the blue/green at 490 nm, matching the absorption curve for rhodopsin. A secondary peak in the behaviourally derived curve in the green/yellow at 550 nm indicated that a population of yellow cones may be implicated with the rods in scotopic vision. Under light adapted conditions the behavioural curves showed a shift to the blue, perhaps indicating an adaption to the high red content of the illuminating source. The e.r.g. curve showed greatest sensitivity to blue/green, as in the scotopic experiments but with an enhanced response at 550 nm, indicating greater cone activity. It is suggested that there is complex interaction between rods and cones in the cod retina, both types of receptor being active over a wide range of light intensities.     

Physiological responses to emersion in the intertidal green crab,Carcinus maenas (L.)

The green shore crab, Carcinus maenas, undergoes on average 6?h periods of emersion during each low-tide cycle during the summer months. Under those conditions, the crab is cut off from its normal water environment and is exposed to potential stress from a suite of environmental and physiological changes: dehydration, compromised gas exchange and resultant internal hypoxia and hypercapnia, thermal stress, and ammonia toxicity. This study examined the comprehensive responses of the green crab in water and to a 6?h emersion period laboratory simulation of a tidal cycle followed by a 1?h re-immersion period, measuring indicators of dehydration, hemolymph osmolality, oxygen uptake, hemolymph acid–base status, heart and ventilatory rate, and hemolymph ammonia and ammonia excretion. Green crabs showed physiological responses of varying magnitude to 6?h of emersion. Individuals were found in the field exclusively under rocks and large clumps of seaweed where temperatures were approximately half those of exposed surfaces and relative humidity was about twice as high as ambient air. During emersion, crabs lost less than 5% of their wet weight, and hemolymph osmolality did not increase significantly. Oxygen uptake continued in air at about 50% of the control, aquatic values; and the gills continued to be ventilated by the scaphognathite, albeit at lower rates. Hemolymph lactate concentrations increased, indicating a shift to a greater reliance on anaerobic metabolism to support energetic needs. A slight acidosis developed in the hemolymph after 1?h of emersion, but it did not increase thereafter. Ammonia concentrations in the hemolymph were unchanged, as ammonia was volatilized by the gills and excreted into the air as NH₃ gas. These results show that the green crab copes with emersion by seeking refuge in microhabitats that mitigate the changes in the physical parameters of intertidal emersion. Physiologically, desiccation is avoided, cardio-respiratory processes are maintained at reduced levels, and hemolymph acid–base balance is minimally affected. Ammonia toxicity appears to be avoided by a shift to excreting NH₃ gas directly or indirectly to air.     

Impact of an ecological factor on the costs of resource acquisition: fighting and metabolic physiology of crabs

1. Current game theory models and recent experimental evidence suggests that the strategy an animal adopts in agonistic encounters is determined by individual state. Therefore manipulation of an individual's state should elicit different behavioural responses. In this paper, mechanisms are examined that underlie state-dependent strategies using Shore Crabs, Carcinus maenas , and how, by altering the environment, behaviour and physiology are affected.
2. Fights were staged between pairs of male crabs under normoxic and severely hypoxic (<15 torr) conditions to determine if the metabolic costs of fighting and resource acquisition are affected by water P _O2. After fighting, blood and tissue samples from each crab were taken and analysed for metabolites associated with anaerobiosis ( L -lactate, glucose and glycogen).
3. The spectrum of behavioural acts performed during contests was unaffected by hypoxic conditions. However, fight duration was significantly shorter in the hypoxic treatment.
4. The phenomenon of being of a larger relative size and winning had a greater influence in the contests staged under hypoxia with 93% of the victors being of a larger size compared to 78% in normoxic conditions. Fight duration and intensity had no relationship with relative size in either treatments.
5. The accumulation of L -lactate was significantly greater in the blood and tissues of crabs after fighting under hypoxia than in normoxic conditions. In addition, there was greater glycolytic activity in the tissues of these crabs, shown by elevated concentrations of glucose in the blood and increased breakdown of glycogen.
6. This study demonstrates that the internal state of the crabs altered the length of time they were willing to engage in fighting and that fighting was energetically more expensive under hypoxic conditions.     

Mise en Evidence de la Carcinine Synthétase, une Nouvelle Enzyme Catalysant le Métabolisme de l''Histamine dans le Systeme Nerveux Central de Carcinus maenas

Carcinine biosynthesis was induced in vitro from its two components, beta-alanine and histamine. The reaction was catalyzed by muscle, heart, and CNS extracts from Carcinus maenas. The specific activity of the enzyme, carcinine synthetase, was 15 times higher in CNS than in other organs. Only CNS extracts induced biosynthesis of carcinine from histidine, and only in the presence of pyridoxal-5'-phosphate. Hence the seat of carcinine biosynthesis seems to be the CNS. It is highly probable that in the CNS, histidine is transformed into histamine, which is then catabolized into carcinine. The latter would then be transported and accumulated in the cardiac tissue. Thus histamine--the metabolism of which takes place totally within the CNS--would be implicated as a participant in the neuronal activity of Carcinus maenas. Carcinine synthetase is a soluble enzyme that requires the presence of ATP, beta-alanine, and histamine. Mg2+ and dithiothreitol are also essential for activity. Optimum pH is approximately 7.6. Carcinine synthetase differs from carnosine synthetase and gamma-glutamylhistamine synthetase in that it does not catalyze synthesis of beta-alanylhistidine or gamma-glutamylhistamine.     

Characterization of microsatellite loci in the European green crab (Carcinus maenas)

Carcinus maenas (Decapoda: Portunidae) has proven a highly successful invasive marine species whose potential economic and ecological impacts are of great concern worldwide. Here, we characterize 14 polymorphic microsatellite loci in C. maenas and its sister species Carcinus aestuarii. These markers will prove useful for fine‐scale genetic analyses of native and introduced populations, for assessment of the sources and routes of invasion and for evaluation of post‐invasion population dynamics.     

Laboratory comparison of American lobster,Homarus americanus,foraging responses to invasive green crab,Carcinus maenas,and two traditional finfish baits

The American Lobster (Homarus americanus) is trapped primarily with finfish baits that are becoming more costly and difficult to acquire as stocks dwindle. Thus, alternative bait options should be considered. We made video recordings of lobster foraging responses in the laboratory to compare the attractiveness of the invasive green crab (Carcinus maenas) bait, two traditional finfish baits and an inert control. Solitary lobsters approached and handled all three biological baits with similar latencies and spent similar time in contact with the biological baits. In contrast, lobsters took longer to approach and handle, and spent significantly less time in contact with control bait. As green crabs were statistically indistinguishable in attractiveness from traditional baits in our laboratory setting, we suggest field trials should test this alternate bait in circumstances more directly relevant to the fishery.     

Temperature and growth in Carcinus maenas L. (Decapoda: Portunidae) larvae reared in the laboratory from hatching through metamorphosis

Larvae of Carcinus maenas L. were reared in the laboratory from hatching through metamorphosis at 9, 12, and 18°C. Dry weight (DW) and elemental contents of carbon (C), nitrogen (N), and hydrogen (H) were analysed at short intervals through successive larval moulting cycles (four zoea-stages, megalopa), and newly metamorphosed crabs. C. maenas larvae grew significantly during all instars, at all temperatures tested. Biomass (DW, C, N, H) and energy (Joule) slightly declined shortly before ecdysis in zoea stages. This terminal decrease was more distinct in the megalopa stage, where ≈39 and 83% of the maximum energy attained, was lost at 12 and 18°C, respectively. Changes of biomass and energy in successive moult cycles showed best fits to quadratic equations, whereas their maximum in successive larval instars formed exponential sequences with time. Due to parabolic growth curves, biomass and energy accumulation within single instars were discussed as maximum (MG) and effective growth (EG), considering gain both at times of maximum biomass, and shortly before ecdysis. Metamorphosing larvae achieved EG with 1137% (DW), 1195% (C), 1108% (N), 1395% (H), 1339% (Joule) at 12°C, and 1140% (DW), 1099% (C), 1133% (N), 1225% (H), 1107% (Joule) at 18°C, relative to newly hatched zoea-1. Ash content and inorganic C in newly hatched zoea-1, were 29.4% and 5.5% ash, respectively. The stoichiometric C H N method of Gnaiger & Bitterlich was used to assess protein, lipid, and carbohydrate compositions. Obviously proteins formed the major part of larval biomass (>50% DW). C: N ratios indicate that more lipid than protein was built up shortly after moulting, but relatively more protein was subsequently accumulated. Temperature effects on larval growth (MG, EG), growth rates (GR), and gross growth efficiencies (K₁) were discussed. C. maenas zoea stages accumulated energy and biomass with higher efficiencies at 18 than at 12°C. Megalopa growth seemed to be limited at 18°C, showing lower K₁ values than at 12°C. N was accumulated with higher efficiencies than C in all larval stages. Characteristic variations in larval K₁ values between premoult and ecdysis were discussed. Cumulative gross growth efficiencies (MG-related) were calculated as ≈11 and 10%, at 12 and 18°C, respectively.     

Effect of environmental temperature on the phospholipid metabolism of gill mitochondria of Carcinus maenas

The different types of phospholipids extracted from gill mitochondria of crab Carcinus maenas have been analysed and it was found that a significant increase of the phosphatidylethanolamine (PE) content and a concomitant decrease of the phosphatidylcholine (PC) amount are present in animals living in low temperatures. The incorporation of [³H]ethanolamine in total phospholipids, PE and PC, was demonstrated in gill mitochondria and a thermal alteration of the in vivo exchange of PE between mitochondria and 10,000 g supernatant is suggested by the kinetics of the incorporation. It is suggested that the conversion of PE to PC by N-methylation is very low in crab gills. There is a marked action of acclimation temperature on the gills-hemolymph exchange of PC and PE. It is postulated that the changes reported at the level of the PE → PC conversion by N-methylation and in phospholipid exchange between hemolymph and gills could be implicated in adapting the organism to seasonal fluctuations of environmental temperatures.     

Lipid composition of tissues of marine crustaceans

Analyses of lipids and fatty acids from various tissues isolated from two crabs (Eriocheir sinensis and Carcinus maenas) and the lobster (Homarus vulgaris) were made by TLC and GLC. Phospholipids, cholesterol and triglycerides were the main fats found in all three invertebrates. Fatty acids obtained from the total lipids extracted from different tissues of these marine animals contain relatively large amounts of long-chain polyunsaturated fatty acids (principally 20:5 and 22:6). Polyunsaturated fatty acids are mainly incorporated into phospholipids and especially into phosphatidylethanolamine.     

Consumers that are not 'ideal' or 'free' can still approach the ideal free distribution using simple patch-leaving rules

1.  The ideal free distribution (IFD) has been widely used to determine whether consumers distribute themselves optimally. However, this theory is based on three assumptions that are clearly violated in many systems. The theory assumes that all individuals know the quality of each available site, are equally free to move between all sites, and have equal competitive abilities.
2.  I examine the utility of this theory to predict the distribution of the invasive European green crab Carcinus maenas , a species that likely violates all of these assumptions. I demonstrate three main findings.
3.  First, understanding how density-dependent interference and size alter individual foraging behaviour is important for understanding the density and biomass distribution of C. maenas in invaded habitats.
4.  Second, once behavioural mechanisms of crab foraging are accurately included in the model, the IFD does a good job of predicting the distribution of C. maenas , even though C. maenas violates the theory's fundamental assumptions.
5.  Third, C. maenas ' distribution can be obtained using simple decision rules and reasonable movement patterns.     

Potential of active excretion of ammonia in three different haline species of crabs

Isolated perfused gills of stenohaline crabs Cancer pagurus adapted to seawater, brackish water-adapted euryhaline shore crabs Carcinus maenas and freshwater-adapted extremely euryhaline Chinese crabs Eriocheir sinensis were tested for their capacity to excrete ammonia. Gills were perfused with haemolymph-like salines and bathed with salines equal in adaptation osmolality. Applying 100 μmol · l⁻¹ NH₄Cl in the perfusion saline and concentrations of NH₄Cl in the bath that were stepwise increased from 0 to 4000 μmol · l⁻¹ allowed us to measure transbranchial fluxes of ammonia along an outwardly as well as various inwardly directed gradients. The gills of all three crab species were capable – to different extents – of active excretion of ammonia against an inwardly directed gradient. Of the three crab species, the gills of Cancer pagurus revealed the highest capacity for active excretion of ammonia, being able to excrete it from the haemolymph (100 μmol · l⁻¹ NH⁺ ₄) through the gill epithelium against ambient concentrations of up to 800 μmol · l⁻¹, i.e. against an eightfold gradient. Carcinus maenas and E. sinensis were able to actively excrete ammonia against approximately fourfold gradients. Within the three crab species, the gills of E. sinensis exhibited the greatest capacity to resist influx at very high external concentrations of up to 4000 μmol · l⁻¹. We consider the observed capacities for excretion of ammonia against the gradient as ecologically meaningful. These benthic crustaceans protect themselves by burying themselves in the sediment, where, in contrast to the water column, concentrations of ammonia have previously been reported that greatly increase haemolymph levels. Electrophysiological results indicate that the permeabilities of the gill epithelia are a clue to understanding the species-specific differences in active excretion of ammonia. During the invasion of brackish water and freshwater, the permeabilities of the body surfaces greatly decreased. The gills of marine Cancer pagurus exibited the greatest permeability (ca. 250 mS cm⁻²), thus representing practically no influx barrier for ions including NH⁺ ₄. We therefore assume that C. pagurus had to develop the strongest mechanism of active excretion of ammonia to counteract influx. On the other hand, freshwater-adapted E. sinensis exhibited the lowest ion permeability (ca. 4 mS cm⁻²) which may reduce passive NH⁺ ₄ influxes at high ambient levels. Accepted: 14 October 1998     

Genetic patterns across multiple introductions of the globally invasive crab genus Carcinus

The European green crab Carcinus maenas is one of the world's most successful aquatic invaders, having established populations on every continent with temperate shores. Here we describe patterns of genetic diversity across both the native and introduced ranges of C. maenas and its sister species, C. aestuarii, including all known non‐native populations. The global data set includes sequences from the mitochondrial cytochrome c oxidase subunit I gene, as well as multilocus genotype data from nine polymorphic nuclear microsatellite loci. Combined phylogeographic and population genetic analyses clarify the global colonization history of C. maenas, providing evidence of multiple invasions to Atlantic North America and South Africa, secondary invasions to the northeastern Pacific, Tasmania, and Argentina, and a strong likelihood of C. maenas × C. aestuarii hybrids in South Africa and Japan. Successful C. maenas invasions vary broadly in the degree to which they retain genetic diversity, although populations with the least variation typically derive from secondary invasions or from introductions that occurred more than 100 years ago.