Maja Brachydactyla Research Articles

Effects of different natural or prepared diets on growth and survival of juvenile spider crabs, Maja brachydactyla (Balss, 1922)

The effects of different diets (natural or pellets) on growth, survival, and moulting interval of juvenile spider crabs, weighing between 0.011–1.56 g and up to 17.6 mm in carapace length, were tested over a period of 90 days. During experiment I, five diets were tested: (1) frozen shrimp—Paleomonetes sp., (2) fresh mussels—Mytilus sp., (3) white fish fillets—Merlucius merlucius, (4) blue fish fillets—Sardina pilchardus, and (5) commercial crustacean pellets. Spider crabs fed fresh mussels grew larger (0.98 ± 0.69 g) and had higher growth rates (4.0 ± 0.7 %BWd−1) compared to the other four diets. The crabs fed shrimp pellet and frozen shrimp grew to intermediate sizes and were smaller than the ones fed fresh mussels, but they were larger than spider crabs fed either blue or white fish fillets (0.46 ± 0.63 and 0.26 ± 0.13 g, respectively) compared to the ones fed white fish fillets (0.12 ± 0.04) and blue fish fillets (0.04 ± 0.02 g). The spider crabs fed blue fish fillets only lasted until day 60 of the experiment, after this day none of the 20 fed this diet were left. During experiment II, two diets were tested: (1) white and blue fish fillets and (2) commercial fish pellet. There were no differences in growth both in weight or carapace length (2.9 ± 1.8 and 2.1 ± 1.5 g in weight, and 18.9 ± 5.0 and 17.7 ± 3.3 mm, respectively) at the end of the experiment. Similarly, there were no differences in growth rates in weight between the two diets (1.2 ± 0.4 and 0.9 ± 0.3 %BWd−1, respectively) or in carapace length (0.4 ± 0.1 and 0.4 ± 0.2 %BWd−1, respectively). Fresh mussel appears to be a very good diet to culture the early stages of this species, while shrimp pellets also deliver acceptable results. On the contrary, frozen shrimp, fish fillets either from blue or white species (much higher lipid content in the blue species), and fish pellets were found to be bad diets for the culture of the early stages of M. brachydactyla.

Growth, survival and biochemical composition of spider crab Maja brachydactyla (Balss, 1922) (Decapoda: Majidae) larvae reared under different stocking densities, prey:larva ratios and diets

The spider crab Maja brachydactyla is overexploited on the NW coast of Spain. Aquaculture of this species can be the solution to the problem, and consequently, several attempts of intensive larval rearing have been conducted. However, most of the studies already published do not provide enough zoo technical data, especially in terms of larval and prey densities or the nutritional quality of diets used for rearing.Three experiments were carried out to evaluate the conditions for intensive larval rearing of M. brachydactyla. Larval stocking density (10, 50 and 100 larvae L−1), prey:larva ratio (15, 30 and 60 enriched Artemia larva−1) and diet (enriched Artemia, non-enriched Artemia and polychaete supplement) effects on growth and survival of this species were studied. For larval culture nine, 35 L, 150 μm mesh-bottomed PVC cylinders (triplicates for each treatment and larval stage) connected to a recirculation unit, were used. Temperature and salinity were kept constant at 18 °C and 36‰ respectively. A 12 to 18 day trial was conducted for each experiment and samples of larvae were collected at each larval stage (zoea I, zoea II, megalopa) in the inter-molt phase and at first juvenile. Survival, carapace length and width, dry weight (DW), and proximate biochemical content (protein, carbohydrates and total lipid) as well as lipid class composition were determined.Stocking densities of 100 larvae L−1 resulted in higher growth in DW and higher content in lipids and protein for zoea I (ZI) and zoea II (ZII) than 10 larvae L−1. However, survival decreased with increasing stocking density.The use of 60 preys larva−1 produced larvae with significantly higher DW and protein content, especially at ZII stage, than lower prey densities. Survival rate obtained feeding 60 preys larva−1 up to the megalopa stage was almost two-fold (42.2%) the rate obtained using 15 preys larva−1 (24.8%).Larvae fed on enriched Artemia (EA) showed an increase in weight up to megalopa (518.9±26.5 μg) in contrast to larvae fed on non-enriched prey (A) (467.9±6.9 μg). Variation in DW correlated with the total lipid content (L) of the larvae (LEA=70.1±37.5 μg ind−1; LA=28.9±3.2 μg ind−1) especially in terms of neutral lipids. The use of an initial density of at least 50 larvae L−1 and 60 enriched Artemia larva−1 can be considered the most adequate rearing parameters in order to obtain good results in growth and survival of M. brachydactyla.

Decapod crustaceans associated with the snakelock anemone <i>Anemonia sulcata</i>. Living there or just passing by?

The present work identifies the decapod crustaceans that associate with Anemonia sulcata on the southwestern Atlantic coast of Portugal and characterises their host use pattern. It determines whether the anemone is monopolised by any species, resulting in the exclusion of conspecifics or other decapods and, under laboratory conditions, it evaluates the degree of association between each species and A. sulcata. From all sampled anemones, 79% harboured at least 1 decapod crustacean, with the majority displaying either one or two specimens (32 and 24%, respectively). The most abundant species were the shrimp Periclimenes sagittifer and the crab Inachus phalangium (representing 36 and 31% of collected specimens, respectively), which displayed lasting associations and were commonly recorded among the tentacles of the host. The species Eualus occultus, E. complex cranchii, Clibanarius erythropus, Maja brachydactyla, Pilumnus hirtellus and Polybius (Necora) puber displayed short-term associations, were mainly present on the substratum near the base, and avoided the tentacles of A. sulcata. Periclimenes sagittifer and I. phalangium were only recorded alone or in heterosexual pairs, appearing to efficiently defend their host against conspecifics. The majority of recorded species only seem to temporarily associate with A. sulcata, in order to seek protection from predators when other shelters are unavailable.

Congener-specific accumulation and trophic transfer of polychlorinated biphenyls in spider crab food webs revealed by stable isotope analysis

Polychlorobiphenyls (PCB) and stable isotopes ( δ 15N and δ 13C) were analyzed in the spider crab ( Maja brachydactyla) food web from the Iroise Sea (Western Brittany) and the Seine Bay (Eastern English Channel). PCB concentrations were all significantly higher in organisms from the Seine Bay than those from the Iroise Sea. PCB patterns were strongly related to the feeding mode of the species, and increased influence of higher chlorinated congeners was highlighted with trophic position of the organisms. PCB concentrations (lipid normalized) were significantly related to the isotopically derived trophic level (TL) in spider crab food webs. The highest trophic magnification factors (TMFs) were calculated for the congeners with 2,4,5-substitution, and were lower in the Seine Bay compared to the Iroise Sea. The confrontation of PCB and TL data also revealed biotransformation capacity of decapod crustaceans for specific congeners based on structure–activity relations.

Ovarian maturation of the multi-spawning spider crab Maja brachydactyla (Decapoda: Majidae) with special reference to yolk formation

In the study of the reproductive biology of the spider crab Maja brachydactyla, the morphology of the female reproductive system and yolk formation have long been overlooked. Females spawn two or three times during their annual reproductive cycle in northern Spain (Galicia). The ovaries consist of two lobes. The right and left lobes are connected by a small cross-lobe at the level of the heart and merge at the posterior edge. Before merging, the ovaries descend to the ventral part of the body, joining the spermathecae in the vagina, which opens through a chitin tube to the gonopore, located in the sternite, at the level of the third walking leg. No morphological changes have been observed between either the different parts of the ovaries or the different annual spawning periods. At the start of vitellogenesis, the oocyte of M. brachydactyla is characterized by a large number of vesicles in the cytoplasm. These vesicles are surrounded by a unit membrane whose size increases as the oocyte matures and contain fine granular material including a variable number of ovoid, electron-dense granules. The vesicles are of diverse origin, although most of them develop directly from the mitochondria and the Golgi complex (endogenous phase of vitellogenesis). In a subsequent phase, a series of substances (principally lipoproteins) are incorporated into the ooplasma by means of micropinocytosis. These substances are also involved in yolk formation (exogenous phase of vitellogenesis). During vitellogenesis in M. brachydactyla, mitochondria play the most important role since they are not only the energetic centre of the cellule, but they also act as containers of high-energy reserve substances: the yolk granules.

Polychlorinated biphenyl contamination of the spider crab (Maja brachydactyla): Influence of physiological and ecological processes

Maja brachydactyla is a decapod crustacean widely distributed along the Northeast Atlantic coasts. The main objective of this work was to establish the influence of ontogenic factors, such as growth, aging, seasonal migrations, and reproduction, on the contamination of this species by polychlorinated biphenyls (PCBs). Two populations were studied: One in the Seine Bay (Eastern English Channel), which is exposed to greatly contaminated discharges from the Seine River, and one in the Iroise Sea (Western Brittany), which is little contaminated by such man-made compounds. At both sampling areas, PCB analysis revealed concentrations in hepatopancreas that were 10- and 50-fold higher than concentrations in gonads and muscle, respectively. Levels of 2,2',4,4',5,5'-hexachlorobiphenyl (CB153) increased with the age of the spider crabs, whereas their seasonal migrations had no direct effect. No significant sex effect was observed with regards to CB153 levels, but adult females exhibited PCB fingerprints different from those of males, probably because of the influence of the reproductive cycle on enzymatic system activity. Finally, spawning gave rise to a higher CB153 decontamination of female body burdens for specimens from the Iroise Sea than for those from the Seine Bay.

Variability of stable isotope signatures ( δ13C and δ15N) in two spider crab populations ( Maja brachydactyla) in Western Europe

The ontogenic variations of nitrogen and carbon stable isotopic signatures ( δ 15N and δ 13C) were investigated in two spider crab ( Maja brachydactyla) populations inhabiting in different biotopes of Western Europe. The Iroise Sea population is localized in Western Brittany and characterized by a seasonal migration occurring on a large bathymetric and habitat gradient while the Seine Bay population, in the Eastern English Channel, remains in a more homogeneous environment during its migration. In the Iroise Sea population, δ 13C values increased significantly both with body size and age, revealing a shift towards “benthic-component” prey with spider crab growth. On the contrary, neither body size nor ageing gave rise to a significant trophic level change (derived from the δ 15N). In this M. brachydactyla population, the seasonal migrations from coastal waters in summer to offshore habitats in winter involved significant but slight differences in both δ 13C and δ 15N. In the Seine Bay population, low variations for both carbon and nitrogen were recorded related to either sex or size or seasonal migration. Thus, the δ 13C and δ 15N variability in the spider crab depends on the availability and diversity of prey in its different living habitats, as well as on the morphological aptitudes of individuals to feed on prey (individual's size).

Organochlorinated contaminants in decapod crustaceans from the coasts of Brittany and Normandy (France)

The contamination and distribution of organochlorinated compounds were considered in three crustacean species (edible crab, Cancer pagurus; spider crab, Maja brachydactyla; velvet swimming crab, Necora puber) from five sites along the coasts of Brittany and Normandy (Western and North-Western France). PCBs (16 single congeners), pp'-DDE and HCB were measured in hepatopancreas, gonads and muscle: in all, 175 samples were analysed. The spider crab was the only species found in the five sampling sites, thus enabling comparison between areas. Specimens from Antifer were much more contaminated (summation operator 16 PCBs in hepatopancreas=2000-4000 ng g(-1) dry weight) than those from other sites (50-1000 ng g(-1) d.w.). Among all the three species, the spider crab appeared more contaminated by PCBs than the edible crab, by a factor 2-3, probably in relation with specific differences in their life cycle. There was no difference due to the gender of the species. Within the different analysed tissues, contamination levels increased from muscle to gonads and hepatopancreas in relation with the fat content. A very similar PCB composition was observed in all samples, PCB fingerprints being characterised by the relative importance of the more persistent PCB congeners: CB153, 138, 180, 187, and 118. Finally, these results were compared to recent food regulations first of maximum marker PCB intake and secondly of maximum dioxin-like PCB intake. By considering the muscle, all samples were far below the regulatory limits; for hepatopancreas and gonads, however, some samples were unfit for human consumption.

Growth at Moult, Intermoult Period, and Moulting Seasonality of the Spider Crab Maja Brachydactyla: Combining Information from Mark-Recapture and Experimental Studies

Abstract Growth at moult (for both the prepubertal and terminal moults), and moulting seasonality in the spider crab Maja brachydactyla in the Ria de A Coruna (NW Spain) was quantified within a mark-recapture experiment. Crabs 70-130 mm carapace length (CL) underwent a mean increase at moult of 32.4% from their pre-moult size, with no significant differences between sexes or moult types. Generalised Linear Models (GLMs) were used to construct growth models, employing a combination of information from the mark-recapture study and previous studies performed in laboratory and extensive culture to characterize driving factors. The first model revealed that study method growth did not differ between males and females. However, the effects of the study method (mark-recapture, laboratory, and extensive culture), the pre-moult CL and the interaction between them were significant. The smallest-sized crabs underwent a greater increase in size in the laboratory and culture studies, while the largest individuals unde...

Assessment of methods to estimate abundance and population structure of the spider crab Maja brachydactyla in soft substrates

A good sampling method for collecting data on the abundance, spatial and demographic structure of a marine population would enable a researcher to: (1) obtain unbiased abundance estimates (absolute or relative), (2) accurately represent the spatial and demographic structure, and (3) obtain enough samples at a reasonable cost to analyze size-frequency distributions and other demographic parameters. Different methods for estimating the abundance and population structure of the spider crab Maja brachydactyla in the Ría de A Coruña (NW Spain) were assessed. Sampling was carried out with different procedures—tangle-nets, beam trawls, diving and traps. The use of tangle-nets caused serious problems as both the specimens sampled and the gear itself were damaged. These nets also provided less spatial resolution of the small-scale distribution of organisms. Sampling by means of diving in this area was unviable due to limited visibility, high turbulence and strong currents. The catches obtained during monthly samplings using traps and beam trawls in the same area during one yearly cycle (June 1998–June 1999) were compared. Trap catches were much higher, in terms of actual quantities and catch per unit of effort (CPUE), although the seasonal pattern was similar with both methods. A significant linear relationship was found between the trap and beam trawl catches: CPUE traps = 3.34 + 3.987CPUE trawl ( R 2 = 0.54, p = 0.02). The beam trawl catches contained a higher proportion of very small crabs (specimens < 60 mm carapace length, CL, comprised 23% of the total catch taken by beam trawling, compared to only 0.7% when traps were used), and very few large specimens (CL > 130 mm), especially adults. The catchability of adult crabs using the beam trawl accounted for only 12% as compared to that of traps. The fishing area of a trap was estimated to be 1440 m 2 for juveniles (CL = 70 mm). A comparison of these two sampling methods in terms of cost-effective sampling (in days) showed that the beam trawl is almost four times as expensive as the traps, for the same number of organisms collected.

Effect of lipid removal on carbon and nitrogen stable isotope ratios in crustacean tissues

The analysis of tissue's naturally occurring stable carbon and nitrogen isotope ratios is a useful tool to delineate trophic relationships. However, the interpretation of δ 13C and δ 15N is complicated by the influence of multiple factors such as the tissue-specific lipid content. The aim of this work was to evaluate the effects of lipid extraction on δ 13C and δ 15N compositions in muscle, hepatopancreas and gonads of a marine decapod crustacean, the spider crab Maja brachydactyla. Samples were analyzed for stable isotopes before and after lipid removal, using a derived Soxhlet extraction method. Differences in δ 13C and δ 15N were measured among tissues before and after treatment. Lipid extraction of muscle did not have a significant effect on either δ 13C or δ 15N. By contrast, ecologically significant shifts for both carbon and nitrogen stable isotopes ratios (+ 2.9 ± 0.8‰ for δ 13C, and + 1.2 ± 0.7‰ for δ 15N) were noticed in the hepatopancreas. In regard to gonads, lipid extraction led to a shift only on δ 13C (+ 1.3 ± 0.3‰). Finally, the derived Soxhlet extraction method removed the lipid influence for δ 13C, and had an effect on δ 15N composition for lipid-rich samples. We recommend this treatment for carbon stable isotope studies on decapod crustacean lipid-rich tissues.

TIMING AND SEASONALITY OF THE TERMINAL MOLT AND MATING MIGRATION IN THE SPIDER CRAB, MAJA BRACHYDACTYLA: EVIDENCE OF ALTERNATIVE MATING STRATEGIES

Timing and synchronization at individual and population levels of the processes related to the terminal molt, gonad maturation, accumulation of energy reserves and migration in the spider crab Maja brachydactyla are analyzed. Also, the intra and intersexual variability is established. Two hypotheses are tested to explain the temporal and population variability: (1) physiological hypothesis: males and females begin migration when they reach the appropriate physiological stage (the optimum level of energy reserves) and (2) mating opportunities hypothesis: the timing of the migration maximize mating opportunities and mate quality. Our results show that males carry out the terminal molt before females, the former having a peak in July and the latter in August. The onset of gonad maturity in females occurs between two and three months after they have reached morphometric maturity (starting in October), coinciding with the period prior to and during the mating migration to deep waters. In an analysis of the spermathecae of primiparous females, it was found that practically no mating activity occurred in shallow waters, whereas the first copulations took place in the migration corridor. However, probably most of the mating activity occurs in deep mating grounds. Males reached gonad maturity prior to morphometric maturity. No differences were observed in the physiological status (muscle, gonad and hepatopancreas relative mass) between migrating and nonmigrating crabs, which is a clear indication that the physiological hypothesis does not hold true for this species. A higher percentage of postmolt crabs were caught in the migration corridor than in shallow waters. The physiological condition improved over time in males and females in the specimens caught in the shallow area as well as in the migration corridor. Therefore, the crabs that start migrating first did so in poorer physiological condition. Moreover, the early migrators had a significantly lower mean size than the late migrators. Our results suggest that variability within populations and between sexes are related to the different reproductive strategies and not to a physiological limitation. Thus, the poor-quality males (with a reduced competitive ability) would migrate at the beginning of the season to maximize the mating opportunities that would not be feasible if they had to compete with the late migrators, which are larger in size and in better physiological condition. Sperm competition is not clear in M. brachydactyla, but all evidences point at last male preference for fertilization of eggs.

Identification and characterization of microsatellite loci in the spiny spider crab Maja brachydactyla

The spiny spider crab Maja brachydactyla in an important fishery resource throughout its distribution range (Northeast Atlantic). Here we describe the isolation of nine microsatellite loci for this species. These new markers were tested in 20 crabs from NW Spain. The number of alleles ranged from 3 to 20 and expected heterozigosity from 0.57 to 0.95. All loci followed Hardy–Weinberg expectations except mMb33 and mMb307, which could be affected by null alleles. Some of these loci seem to be better fitted by a multi-step substitution process.

Variability in the onset of hatching of Maja brachydactyla Balss, 1922 (Brachyura: Majidae) in the English Channel in relation to sea temperature

Summary Long-term monitoring of zooplankton and temperature has been carried out at the nuclear power station of Flamanville (west coast of Cotentin, English Channel, France) since 1977. Zooplankton sampling and temperature measurements took place at fortnightly intervals, particularly during the spring and summer. In addition, daily records of water temperature were recorded since 1986. The seasonal appearance of Maja brachydactyla Balss, 1922 first stage zoeae in the plankton outside the thermal plume near to the power station can greatly vary from year-to-year. Earliest observations have occurred in early June whilst latest observations were made at the end of July. During the period of study, temperature records display a warming trend whilst hatching is gradually recorded earlier in the season. An analysis of year-to-year variability in temperature and hatching date reveals that early hatching is related to higher winter-spring sea temperature. Cumulated temperature (degree-days) has been calculated for different periods (during winter and spring) to detect the time at which temperature may influence the date of initial occurrence of first zoeal stage. There is no relationship with January temperatures whilst a strong correlation is observed for the period ranging from early February to the end of May. Based on regression analysis, a predictive model of timing of zoeae appearance in the plankton is constructed. The model can predict timing of zoeae appearance from mean temperature recorded from February 1st to March10th.

Morphometric and gonad maturity in the spider crab Maja brachydactyla: a comparison of methods for estimating size at maturity in species with determinate growth

Abstract Ontogenetic changes in the relative growth of males and females of the spider crab Maja brachydactyla, a species with terminal moult and determinate growth, were analysed and related to their reproductive (maturity) status. Based on the allometry of cheliped size, two morphometric groups of males separated juvenile and adult phases. Juvenile males also showed two growth phases, immature (smaller ones, without spermatophores) and adolescent (with spermatophores). Size at gonad maturity in males (estimated as CL50) was 96.2 mm carapace length (CL). Histological analysis of males showed that &gt;60% of morphometric juveniles and 100% of morphometric adults had spermatophores in the gonad. Females begin to develop gonads 2–3 months after the terminal moult. Size at morphometric maturity was estimated comparing two methodologies: the size at 50% maturity (CL50) and the median size of adult cohorts (CLM). In all cases the CLM size at maturity was greater than that resulting from the CL50 method, and, in contrast to the CL50 method, CLM was greater for females in all cases. Therefore, CLM reflects better the real size at maturity for M. brachydactyla. Owing to spatial segregation of adults and juveniles and the availability of morphological and morphometric methods to estimate maturity status, we suggest a combination of spatial closures and direct protection of juvenile habitat as management strategies alternative to minimum landing sizes.

Toxicity of Organic Compounds to Marine Invertebrate Embryos and Larvae: A Comparison Between the Sea Urchin Embryogenesis Bioassay and Alternative Test Species

This study investigated the toxic effects of the insecticides lindane and chlorpyrifos, the herbicide diuron, the organometallic antifoulant tributyltin (TBT), and the surfactant sodium dodecyl sulfate (SDS) on the early life stages of Paracentrotus lividus (Echinodermata, Euechinoidea), Ciona intestinalis (Chordata, Ascidiacea), Maja squinado and Palaemon serratus (Arthropoda, Crustacea) in laboratory acute toxicity tests. The assays studied embryogenesis success from fertilized egg to normal larvae in P. lividus (48 h incubation at 20 degrees C) and C. intestinalis (24 h incubation at 20 degrees C), and larval mortality at 24 and 48 h in M. squinado and P. serratus. For P. lividus, the median effective concentrations (EC50) reducing percentages of normal larvae by 50% were: 350 microg l(-1) for chlorpyrifos, 5500 microg l(-1) for diuron, 4277 microg l(-1) for SDS, and 0.309 microg l(-1) for TBT. For C. intestinalis, the EC50 values affecting embryogenesis success were 5666 microg l(-1) for chlorpyrifos, 24,397 microg (l-1) for diuron, 4412 microg l(-1) for lindane, 5145 microg I(-1) for SDS, and 7.1 microg l(-1) for TBT. The median lethal concentrations (LC50) for M. squinado larval survival were 0.84 microg l(-1) (24 h) and 0.79 microg l(-1) (48 h) for chlorpyrifos, 2.23 microg(l(-1) (24 h) and 2.18 microg l(-1) (48 h) for lindane, and 687 microg l(-1) (48 h) for SDS. For P. serratus the LC50 values obtained were 0.35 microg l(-1) (24 h) and 0.22 microg l(-1) (48 h) for chlorpyrifos, 3011 microg l(-1) (24 h) and 3044 microg l(-1) (48 h) for diuron, 5.20 microg l(-1) (24 h) and 5.59 microg l(-1) (48 h) for lindane, and 22.30 microg l(-1) (24 h) and 17.52 microg l(-1) (48 h) for TBT. Decapod larvae, as expected, were markedly more sensitive to the insecticides than sea urchins and ascidians, and SDS was the least toxic compound tested for these organisms. Lowest observed effect concentrations (LOEC) of TBT for sea urchin and ascidian embryos, chlorpyrifos and lindane for crustacean larvae, and SDS, were similar to those found in many coastal areas indicating that there would be a risk to invertebrate embryos and larvae from exposure in the field to these pollutants.

Amino acid composition of early stages of cephalopods and effect of amino acid dietary treatments on Octopus vulgaris paralarvae

During the present study, we aimed to provide a first look at the amino acid composition of the early stages of cephalopods and follow possible effects of certain dietary treatments. Amino acid profiles of cuttlefish Sepia officinalis, squid Loligo vulgaris and octopus, Octopus vulgaris hatchlings and wild juveniles of L. vulgaris and O. vulgaris were analysed. Cephalopod hatchlings showed high fractions of non-protein nitrogen (NPN), from 25% to 38% of the dry weight. Lysine, leucine and arginine represented half of the total content of essential amino acids (EAA), and glutamate and aspartate represented also nearly half of the non-essential amino acids (NEAA). In O. vulgaris, a general tendency for a decrease in the level of EAA from mature ovary and eggs to hatchlings was observed. Hatchlings after 4 days of fasting lost 28% of their dry weight and the level of EAA and NEAA decreased in both the total content and free forms. Free proline after 2 days of fasting and free tyrosine at 4 days of fasting were not detected. Comparison of the total EAA profiles of preys showed few differences between enriched Artemia nauplii and hatching crab zoeae ( Pagurus prideaux and Maja squinado). The enriched Artemia nauplii EAA profiles showed no differences with the EAA profiles of O. vulgaris paralarvae during first 10 days of culture, except for histidine. Present results confirm the positive capacity for amino acid uptake from seawater by early stages of cephalopods. In the three species analysed, radiolabelled phenylalanine was incorporated in inverse relation to body size. After 10 days of culture, O. vulgaris paralarvae showed a tendency to increase the levels of total and free amino acids in the groups receiving a daily amino acids solution. At 20 days of age, the O. vulgaris cultures that received the amino acids solution had survivals that on average were three times that of the control group. However, the supposed beneficial effects of the amino acids solution remained unclear, as the dry weight of these paralarvae was equal or lower to that of paralarvae from the control group. In wild O. vulgaris juveniles, the percentage of protein and total amino acids increased with the dry weight of the individuals. These juvenile biochemical changes were associated with strong morphometric changes in body proportions after settlement with the development of the muscular, protein-rich arm crown.

Aggregating Behaviour of the Spider Crab Maja Squinado in Shallow Waters

Abstract A year's monitoring of a population of Maja squinado in Galicia, NW Spain, revealed the seasonal formation of pods. From September to November 1994, we analysed samples from five pods located in two areas near the coast, Mexilloeira and O Carreiro, as well as specimens living in isolation in the same area. These pods were made up mainly of juveniles, except for the aggregation detected in September in O Carreiro, where 72% of the animals were adults. The sex ratio was around 1:1 in juveniles, with a predominance of females in the adult population. No differences were found in the proportion of juveniles vs. adults, sex ratio, size range, or intermoult stage between animals in pods and isolated specimens. The arrangement of the animals in the pod as well as the large number of specimens in the premoult or postmoult stage would suggest that these pods serve as a form of protection.

The Completed Life Cycle of the Octopus (Octopus vulgaris, Cuvier) under Culture Conditions: Paralarval Rearing using Artemia and Zoeae, and First Data on Juvenile Growth up to 8 Months of Age

This paper shows innovating results on Octopus vulgaris Cuvier 1797 growth under culture conditions during the whole life cycle. Experiments were conducted at the Spanish Institute of Oceanography of Vigo (Spain). Using mean water temperature of 22.5°C, salinity of 35‰ and adult Artemia (1–4 mm of total length) along with a diet complement of Maja squinado zoeae as living prey, it was possible to obtain a 31.5% paralarval survival at day 40 after hatching. At this age, paralarvae had reached a dry weight of 9.5 mg, 23 suckers per arm, and they began the settlement process. First results on juvenile growth showed that they reached 0.5–0.6 kg at the age of 6 months after hatching, and 2 months later, they attained weights ranging between 1.4 and 1.8 kg. Mean temperature of the ongrowing process was 18°C.

Moult cycle and growth ofMaja squinado(Decapoda: Majidae) in coastal habitats of Galicia, north-west Spain

Over the course of the moult cycle ofMaja squinado, the spider crab changes in the hardness and colour of the carapace were assessed and used as methods to identify the intermoult stage in each individual. This intermoult staging was later verified by means of the microscopic observation of the maxilla. These staging techniques made it possible for the prompt identification of the principal intermoult stages—postmoult, intermoult and premoult. In 90% of the cases analysed, there was a correlation between the presence of an underlying carapace and a pink colour of the abdominal vein in crabs in advanced premoult stages.The seasonality of the moult was studied based on the number of specimens in the postmoult stage. There were two main moulting periods—the first occurring in April, and the second, longer period was between July and November. A hypothetical growth model was established and growth rates were determined by length–frequency distribution analyses. Three groups of juveniles and one group of adults were identified. The adults were only found among the population between July and October. In both males and females, the moult increment rate was lower in terminal moults (mean=22%) than in juvenile or prepubertal moults (mean=27%).