A refinement of the moult-staging technique for Antarctic krill (Euphasia superba)

The moult-staging technique for euphausiids developed by Buchholz was examined experimentally to obtain estimates of the relative duration of each of the constituent stages. The method entailed removing uropods from indiviually maintainedEuphausia superba Dana on the day of moulting and for each day post-moult, and examining them microscopically to determine the moult stage. The krill were kept alive following uropod removal until the next moult so that the stage observed in the excised uropod could be referenced to both ends of the moult cycle for each individual examined. The proportion of the moult cycle occupied by each stage at 0°C was thereby calculated.     

Change in the gross biochemistry and mineral content accompanying the moult cycle in the Antarctic krill Euphausia superba

Concentrations of water, ash, protein, chitin, lipid, calcium, magnesium, sodium, potassium, strontium and copper were measured in individuals from a laboratory population of Antarctic krill, Euphausia superba Dana, over the course of a moult cycle. Significant changes in all variables were encountered. Total ash, lipid, calcium, magnesium and strontium all increased in concentration following moulting. Water, protein and copper concentrations all decreased following ecdysis and increased again towards the end of the moult cycle. The major ions sodium and potassium fluctuated around mean levels. Cast moults of E. superba were shown to be a drain on the ionic load of the krill, and the losses inherent in exuviation could account for much of the variation observed during the moult cycle.     

Blood sugars in relation to chitin synthesis during cuticle formation in Emerita asiatica

Blood sugars of the crustacean Emerita asiatica were studied during the moult cycle to examine their possible role in the synthesis of chitin, which takes place at the time of moulting. Blood sugars occur both in free state as well as bound with proteins, and show quantitative fluctuations in different phases of the moult cycle. The values of sugars were estimated in relation to total blood volume, to obviate the effects o absorption of water and consequent dilution of blood taking place during moulting. The data obtained suggest that the presence of glucosamine only during premoult stage may be due to resorption of chitin preparatory to the shedding of the cuticle. The fluctuations in the protein-bound blood sugars appear significant in the context of the synthesis of chitin, in view of the correlation seen between these and the chitin content. The above suggestion is supported by the observation that they are not involved in the nutritive metabolism of the crustacean. The protein-bound sugars do not appear to undergo further changes in the blood, as may be inferred by the absence of uridine diphosphate, and uridine diphosphate acetylglucosamine compounds, which have been suggested to be the more immediate precursors of chitin during the moult cycle of insects. It is suggested that protein-bound sugars may be transported, as such, to the epidermis, which may be the site of the final steps in chitin synthesis.     

Copper and zinc handling during the moult cycle of male and female shore crabs Carcinus maenas

Tissue concentrations and contents of copper and zinc were determined at 11 different stages of the moult cycle in male and female shore crabs Carcinus maenas. Metal concentrations in haemolymph, gills, midgut gland, muscle, and exoskeleton of males and haemolymph, gills, and midgut gland of females were determined, as were haemocyanin concentrations and haemolymph volumes (using ¹⁴C-inulin) in males. The changes in tissue Cu and Zn concentrations and contents that occur throughout the moult cycle can be attributed to muscle breakdown in late premoult, the period of starvation in late premoult and early postmoult, the resorption from and shedding of the old exoskeleton, and the dilution of the haemolymph caused by water uptake around the time of ecdysis. The present study demonstrates that whole-body Cu and Zn contents remain constant during a large part of the moult cycle of male and female C. maenas. This state of whole-body trace metal homeostasis is maintained in spite of major changes in tissue proportions and tissue Cu and Zn concentrations and contents. Previous studies have not carried out the necessary analysis to move from theoretical estimates to quantitative determination of the changes in tissue metal distribution associated with moulting in crustaceans; the data presented illustrate the necessity of measuring both tissue concentrations and contents of metals to avoid misinterpretation of either.     

Energetics,moult cycle and ecdysteroid titers in spider crab (Hyas araneus) larvae starved after the D0 threshold

Zoea I larvae of Hyas araneus L. (Decapoda: Brachyura: Majidae) were dredged in January 1986 from the German Bight and reared in the laboratory at constant 12°C, until they reached the transition of stages C/D₀ of the moult cycle (4 d after hatching). This developmental stage had previously been found to correspond with the point of reserve saturation (PRS) which allows autonomous (food-independent) development through the rest of the moult cycle and hence, was termed the D₀ threshold. One part of the larvae was continually fed (control), another group was starved from the D₀ threshold until moulting to the zoea II instar. In these two experimental groups, as well as in the two groups of zoea II larvae obtained from the different feeding conditions, the course of the moult cycle, biomass (dry weight, W; carbon, C; nitrogen, N; hydrogen, H; energy, E; the latter estimated from C), and ecdysteroid titers (measured with a radio-immuno-assay as ecdysone equivalents) were investigated. When the larvae reached the PRS, they had gained 90% in W, 72% in C, 32% in N, 53% in H, and 65% in E, since hatching, corresponding to an accumulation of 87% of final W and 62 to 69% of C, N, and H reached later, at the end of the mould cycle in the control. The period of starvation caused a 2.5-d delay of the moult cycle, mainly in late premoult, and significant losses of biomass and energy. Starved and fed larvae secreted similar amounts of moulting hormone per individual, but with a reduced rate in the starved group, thus causing developmental delay. Zoea II larvae moulting after starvation contained less than half of the control biomass and energy, and even less than a freshly hatched zoea I. Growth rate was only slightly enhanced in these zoea II larvae as compared to the fed control, but losses of biomass, mainly of lipids, were partly compensated by a 4-d prolongation of their moult cycle, chiefly (3 d) in stage C. Biomass curves were almost parallel in the two experimental groups of zoea II larvae, with significantly higher values in the control during all stages of the moult cycle. However, similar relative proportions (74 to 89%) of late premoult biomass and energy were reached at the D₀ threshold, regardless of different feeding history and initial or final values in a given group. The ecdysteroid titer curve of the zoea II which had moulted from starved zoea I was very similar to that in control larvae, but with a 3-d delay in the occurrence of premoult peak concentration (in both groups in stage D₁). Regulation and coordination of moult cycle, ecdysteroid titers, and growth in the larval development of decapod crustaceans are discussed, with special reference to the D₀ threshold.     

Two distinct forms of the chitin-degrading enzyme N-acetyl-β-d-glucosaminidase in the Antarctic krill: specialists in digestion and moult

In the Antarctic krill Euphausia superba two forms of the chitinolytic enzyme N-acetyl-β-d-glucosaminidase (NAGase, EC 3.2.1.52) have been described, previously identified as NAGase B and NAGase C. Here, we demonstrate the organ-specific distribution and physiological relevance of both forms using a polyclonal antibody preparation which allows them to be distinguished immunologically. While NAGase B was localized in the integument and displayed a pattern of activity related to the moult cycle, the activity of NAGase C was independent of the moult cycle and was predominantly found in the gastrointestinal tract. Accordingly, NAGase B played a significant role in chitin degradation during the krill's moult, whereas NAGase C participated in the digestion of chitin-containing dietary components. Chromatographic elution profiles of isolated organs confirmed the immunological results by displaying characteristic organ-specific patterns in NAGase activity. The molecular characteristics of the moulting form, NAGase B, may further indicate a vesicular transport of moulting enzymes from the epidermis into the ecdysial space. Based on our results we develop a hypothesis explaining the concurrent processes of simultaneous chitin degradation and chitin synthesis occurring during moult. Received: 30 December 1998 / Accepted: 23 April 1999     

Blood sugar metabolism during moulting in the isopod crustacean Ligia exotica

Blood sugar metabolism of the isopod Ligia exotica Roux was studied in relation to chitin synthesis during the moult cycle. The blood sugars were found to occur free, as well as bound with blood proteins, during all moult stages, as in Emerita asiatica. The variety of free blood sugars is smaller in L. exotica; it comprises only glucose and glucose-6-phosphate. The protein-bound blood sugars are glucose and glucosamine. The blood-volume values do not differ markedly during the moult cycle. Estimations of blood sugars showed a marked rise of sugar levels in the blood during the premoult phase, and a subsequent fall during the freshmoult phase, when chitin is actively synthesised. The chitin values also showed a definite correlation with the blood-sugar values. The increased resorption of chitin during the premoult stage, and its liberation into the blood stream as glucosamine, is indicative of its reutilisation in chitin synthesis as in E. asiatica and the genus Cecropia. As more immediate precursors of chitin, such as uridine diphosphate and uridine diphophate acetylglucosamine compounds, were absent in the blood, a thorough biochemical study of the epidermis is suggested to locate the intermediate precursors of chitin which are possibly derived from blood sugars.     

Ovarian development and spawning in relation to the moult cycle in Northern krill, Meganyctiphanes norvegica (Crustacea: Euphausiacea), along a climatic gradient

Adaptive processes linked to reproduction were studied comparatively for three populations of Northern krill, Meganyctiphanes norvegica (M. Sars, 1857), sampled during winter and summer cruises in the Clyde Sea (W Scotland), the Kattegat (E Denmark), and the Ligurian Sea (NW Mediterranean). The aim was to investigate the functional relationship between egg production and moulting under contrasted climatic and environmental conditions. A staging system for female sexual development established for live krill was complemented by a histological study of the ovary at various developmental steps. During the reproductive season, all adult female krill were engaged in cyclical egg production. During experiments, female krill released one batch of mature oocytes in one or two spawning events. The ovary of postspawn female krill still contained developing oocytes for another egg batch. In the non-reproductive period, all female krill had a resting ovary. Ovarian structure and pattern of egg production were identical in the three populations, but seasonal timing of egg production was different. The model proposed for the Ligurian population of the annual cycle of ovarian development can be extended to the other two populations, taking into account the seasonal characteristics of each site. Random field samples were staged simultaneously for moult cycle and for sexual development. Moult stages and the seasonal variation of the intermoult period were studied for the Kattegat population using multi-year data and compared to data obtained during summer/winter cruises in the Clyde and the Ligurian Sea. At the three sites, intermoult period was shorter and temperature-dependent during the reproductive period, concurrent with the season of greatest food availability. During most of the year and the period of sexual rest, moulting activity was reduced. The relationship between spawning and the moult cycle was studied comparatively for the three populations. Eggs were released during the premoult phase of a “spawning moult cycle”, in one or two spawnings associated with apolysis and Moult Stage D1, respectively. Yolk accumulation for the next egg batch was completed during an alternating “vitellogenic moult cycle”. A model for the timing of cyclical egg production in relation to moulting, as proposed for the Kattegat, can be extended to the other populations, taking into account intermoult period variation with temperature. Temperature appeared to be the principal environmental factor controlling growth (through moulting) and egg production during the reproductive season, in connection with favourable trophic conditions. Received: 22 December 1997 / Accepted: 29 August 1998     

Population dynamics of the commensal spider crab Inachus phalangium (Decapoda: Maiidae)

The ecology of the spider crab Inachus phalangium (Fabricius, 1775) (Decapoda: Maiidae) was studied in the field. I. phalangium inhabits the sublittoral on the sea anemone Anemonia sulcata Pennant. From July 1981 to April 1984 in the Mediterranean (Banyuls sur Mer, southern France) more than 3000 anemones were examined and ca 1800 I. phalangium were found on them. The population dynamics' generation cycles, reproductive activities and the dynamics of the sex ratio were investigated. The density of juveniles (crabs before the pubertal moult) on anemones changed in a yearly cycle from low in the first six months to very high in the second six months. The first occasional young crabs of a generation appeared in March/April (3rd and 4th decapodite stages) on the anemones. Their density increased enormously in the following months. The generation grew gradually on the anemones and moulted into puberty in September-January. Density of adults (crabs after the pubertal moult) on anemones changed in a yearly cycle from low to high from the summer to winter months. A new adult generation was recruited every autumn through the pubertal moult and disappeared in the following summer. Female reproductive activity continued throughout the year. Females carried several broods in succession, but the frequency of breeding females fluctuated on a yearly cycle. The highest percentage of egg-carrying females, i.e. the peak of the reproductive season, lay in the first half of the year. The maximal life span of a generation, from the hatching of the first larvae to the disappearance of the last adults, lasted 1.5 to 2 years. Males moulted into puberty ca one month later than females. The moulting distribution of adult males had roughly the same course as in females. An adult male generation diet out about one to two months before the female generation. Life expectancy was therefore 14 to 17 months for females and 12 to 15 months for males. The sex ratio of juveniles shortly before the pubertal moult was balanced. The sex ratio of adults shifted from 1:1 at the beginning of the reproductive period to ca 1:9 in favour of females at its end.     

Nucleic acids and growth of larval and early juvenile spider crab,Hyas araneus

The spider crabHyas araneus (L.) was collected from the North Sea in winter 1986–1987 and reared in the laboratory from hatching of the Zoea I (ZI) through the first juvenile instar (CI). Within a given moult cycle, individuals of the same age were sampled in intervals of 2 (ZI, ZII, CI) or 3 d (megalopa) for analysis of dry weight (W), carbon (C), nitrogen (N), hydrogen (H), protein, DNA, and RNA. Lipid was calculated from C. Biomass, growth rate and nucleic acid contents showed high variability during each moult cycle and between instars. Instantaneous growth rates of C were high in postmoult and intermoult, and low in the premoult period of each moult cycle. A shift was observed from high rates of lipid accumulation in the postmoult and intermoult stages to proportionally increasing protein accumulation during late premoult (ZI), or throughout a major part of the remaining moult cycle (in all other instars). DNA was accumulated throughout the ZI and ZII instars, but decreased in late premoult megalopa. It increased again from late intermoult through intermediate premoult in juveniles. RNA increased continuously during ZI and ZII, and decreased in the megalopa, almost to levels that had been found immediately after hatching. In juveniles, variation in RNA followed closely those in DNA. Cell multiplication (expressed by DNA increase) dominated over increase in cell size (defined by the C/DNA ratio) during the zoeal instars and in postmoult through early intermoult in the megalopa and CI. When specific (C-related) RNA values and RNA/DNA ratios were compared with instantaneous growth rates in C and N, no general correspondence was detected. The only significant relationship between specific RNA values and instantaneous C or N growth rates was found in the megalopa. The same held for the relationship between the RNA/DNA ratio and growth. Here, in addition to the megalopa, a correspondence with C growth was also found in the CI instar. Our results suggest that variation in nucleic acids may provide useful insights into mechanisms of growth on the cellular level (cell multiplication vs cell enlargement). However, lack of general correlation with variation in growth rates ofH. araneus larvae shows that the use of nucleic acids as a measure of growth is probably based upon too simplistic assumptions; it may not yield reliable predictions, when growth is associated with developmental events.     

Glycogen storage in relation to the moult cycle in the two crustaceansEmerita asiatica andLigia exotica

InEmerita asiatica, the quantitative fluctuations in the glycogen content of the hepatopancreas were markedly related to the moult cycle. The glycogen content of the hepatopancreas was maximum during premoult stages. It has been suggested that reserve glycogen, in addition to meeting general metabolic needs, may be especially involved in the genesis of the sugar precursors of chitin. The marked fall in the hepatopancreas glycogen values following moulting is probably due to its utilization in chitin synthesis during and immediately following moulting. InE. asiatica, the storage of glycogen was found to be meagre in muscles, and muscle glycogen had no bearing on chitin synthesis during moulting. InLigia exotica, glycogen is stored to a lesser extent than inE. asiatica, and was found in connective tissue and muscles. Significant fluctuations were noted in glycogen values correlated with the phases in the moult cycle when chitin synthesis took place. InL. exotica, the hepatopancreas does not serve as a storage depot for glycogen related to chitin synthesis.     

On the timing of moulting processes in reproductively active Northern krill Meganyctiphanes norvegica

The interactions between moult phasing, growth and environmental cues in Northern krill (Meganyctiphanes norvegica) were examined through analysing populations at seasonal, weekly, and daily timescales. The analyses were carried out on resident populations of krill found in three different neritic locations that experience similar environmental signals (the Clyde Sea, Scotland; the Kattegat, Denmark; Gullmarsfjord, Sweden). Seasonal analyses were carried out on the Clyde Sea population and showed that moulting frequency increased significantly moving from winter to summer. The proportion of moulting females in summer samples was often more than double the proportion of moulting males, suggesting that females had a comparatively shorter intermoult period (IMP). Weekly samples taken from the Kattegat showed a similar pattern. However, although the difference between the proportion of female and male moulters was significant in one week, it was not another, mainly because of the variability in the proportion of female moulters. Such variability in females was equally evident in the daily samples taken at Gullmarsfjord. It suggests that females have a shorter IMP (12.5 days) than males (18.4 days) and are more likely to moult in synchrony. Nevertheless, the daily samples revealed that males are also capable of moult synchronisation, although less frequently than females. Shortened IMPs in females were not a result of the abbreviation of specific moult stages. Accordingly, reproductive activity did not alter the course of the normal moult cycle. There was no significant difference between the total body lengths of males and females indicating that females achieve the same levels of growth despite moulting more frequently and having to provision the energy-rich ovaries. This is in contrast to most other crustaceans where the energy costs of reproduction reduce female growth. The fact that females were less abundant than males, probably by suffering a greater level of mortality, suggests that different behavioural strategies, particularly vertical migration regimes, were adopted by each sex to maximise growth and reproduction.     

Changes in physiology,structure and histochemistry occurring during the life-history of the sexually dimorphic isopod Dynamene bidentata (Crustacea: Peracarida)

The main food reserve of the intertidal hebivorous isopod Dynamene bidentata is lipid. Only algal-dwelling juveniles exhibit rhythms of oxygen consumption and defecation related to the tidal cycle. Males undergo the moult to maturity in the algal habitat and are, therefore, able to replenish their food reserves before entering upon a nonfeeding reproductive phase in empty barncle tests and erevices. Storage sites are increased at this moult so that males are able to survive on their food reserves for 2 breeding seasons. Females enter the reproductive habitat in the preovigerous stage and cease to feed. Lipid food reserves are largely used up in the formation of eggs and the final stage cuticle. Consequently, after the ovigerous moult, females are required to utilise lipoprotein-containing tissue as an energy source, and are able to survive only for a single breeding season. At the final moult, the posterior end of the male becomes highly thickened, rugose, and supplied with tegumental glands. These modifications are correlated with the need for self protection, and protection of the vulnerable females, against various physical and biological factors in the intertidal zone. There is a large increase in the dry weight of the brood over the period of incubation, and this is due mainly to the development of the exoskeleton at the last marsupial moult. The source of materials for the weight increase is attributable to a combination of factors, of which salt uptake probably plays the major part.     

Patterns of growth and triacylglycerol content in snow crab Chionoecetes opilio (Brachyura: Majidae) zoeal stages reared in the laboratory

Snow carb Chionoecetes opilio zoea I and zoea II larvae, hatched from females in a controlled mating experiment, were reared in the laboratory at 10.1 °C and 28.0 salinity, to resolve the patterns of growth (dry weight [DW]) and change in energy reserves (triacylglycerols [TAG]) within a given moult cycle. The patterns of growth and change in TAG reserves were similar in each zoeal stage. Following hatching or a moult, the zoeae entered a phase of rapid size increase, i.e. high daily growth rates (5.5 to 12.8% DWd^-1), for 1/3 to 2/5 of the duration of the moult cycle. During the same period, the zoeae accumulated TAG reserves until a maximum (TAG DW^-1) was reached at the end of the phase of rapid growth. The period of high growth rates and of TAG accumulation is interpreted as the required time for the zoeae to reach a point in development [i.e. point of reserves saturation (PRS); Anger and Dawirs (1981)] where sufficient growth and energy reserves allow moulting to the next stage. Following the phase of rapid growth and TAG accumulation, the zoeae entered a phase of low daily growth rates (0 to 1% DWd^-1) during which the TAG reserves decreased to a minimum at the end of the phase. Prior to, and during the moult to zoea II, a phase of negative growth was observed in the zoea I larvae. We conclude that measurement of zoeal size and TAG content, along with morphometric criteria (e.g. epidermal retraction), can be used to assess growth and nutritional condition of C. opilio zoeal stages from the sea.     

Moulting patterns drive within-individual variations of stable isotopes and mercury in seabird body feathers: implications for monitoring of the marine environment

One major limitation in the use of body feathers of seabirds as a monitoring tool of the trophic structure and contamination levels of marine ecosystems is the degree of heterogeneity in feather chemical composition within individuals. Here, we tested the hypothesis that moulting patterns drive body feather heterogeneity, with synchronous moult minimizing within-individual variations, in contrast to asynchronous feather growth. Chicks of white-chinned petrels Procellaria aequinoctialis (representative of bird chicks) and adults of king penguins Aptenodytes patagonicus (representative of adult penguins) that moult their body feathers synchronously showed very low within-individual variations in their feather δ¹³C and δ¹⁵N values and mercury (Hg) concentrations. By contrast, body feathers of adults of Antarctic prions Pachyptila desolata (representative of adult seabirds with asynchronous feather growth during a protracted moult) presented much higher within-individual variances for the three parameters. These findings have three important implications for birds presenting a synchronous body moult. (1) They suggest that all body feathers from the same individual have identical δ¹³C and δ¹⁵N values and Hg content. (2) They predict negligible within-individual variations in the body feather values of other useful stable isotopes, such as δ²H and δ³⁴S, as well as in the concentrations of other compounds that are deposited in the keratin structure. (3) Analysis of one or any number of pooled body feathers is equally representative of the individual. In conclusion, we recommend that long-term routine monitoring investigations focus on birds presenting synchronous rather than asynchronous moult of body feathers both in marine and terrestrial environments. This means targeting chicks rather than adults and, for seabirds, penguins rather than adults of flying species.     

Ultrastructure of the integument of a pelagic Crustacean: moult cycle related studies on the Antarctic krill,Euphausia superba

The ultrastructure of euphausiid integument was examined in relation to the moult cycle and supplemented by investigations of chitinase activity in the integument and content of N-acetyl--D-glucosamine in the hemolymph. The Antarctic krill, Euphausia superba was collected in 1983 in Admiralty Bay, King George Island, Antarctica. Some specimens of the Northern krill, Meganyctiphanes norvegica, from the Danish Kattegat served for comparison. As a major aim of the study, the moult staging system developed for living tissue could be verified by ultrastructural findings. Under experimental high production conditions of the Antarctic summer, no period of rest or intermoult between post- and premoult was observed in subadult E. superba. Neither was a resting phase seen at the cellular level, the epidermis remained active. The epidermal gland cells did not show any cyclical changes, and the organelles of protein synthesis were generally well developed in all moult stages. In order to follow the physiological course of events, structural and biochemical methods were combined and showed as a result that the last moult stage before ecdysis is characterized by massive cuticular resorption. The epicuticle remained ultrastructurally unchanged before and after ecdysis, even though its permeability should alter at ecdysis. The existence of muscle insertions which connect the old and the new cuticle across the exuvial space suggests an answer to the question why E. superba is hardly impaired in swimming almost up to the time of ecdysis.Dedicated to Professor Dr. H. Leonhardt on the occasion of his 70th birthday     

Functional cytology of the hepatopancreas of Penaeus semisulcatus (Crustacea: Decapoda) during the moult cycle

In the shrimp Penaeus semisulcatus, the digestive gland functions as the main site for the digestion, absorption and storage of nutrients and metals during the feeding stages of intermoult and for the mobilization of reserves during the non-feeding stages of pre-and post-moult. These different activities are reflected directly in the cytology of the gland. All the epithelial cells show marked fluctuations in frequency and changes in structure, form and function which occur in phase with the moult cycle. The shrimp were collected offshore from Kuwait in 1980.     

Haemocyanin concentration of juvenile lobsters (Homarus gammarus) in relation to moulting cycle and feeding conditions

Groups of laboratory-reared, juvenile lobsters (Homarus gammarus, 40–50 g wet weight) were given different types of food (shrimp, mixed invertebrates and pellets, bivalves, starved) for a period of 22 wk. Haemocyanin concentration was measured weekly, moult stage and moultings noted. Haemocyanin concentration decreased rapidly in the starved group (from 0.8–0.6 to 0.2 mM). The group fed with bivalves showed a small decline with time, to 0.5–0.3 mM at the end of the period, indicating a deficient diet. The haemocyanin in the other groups did not change significantly during the experiment. Moultings decreased in frequency and the intermoult period was prolonged when the quality of food was decreased, and in the starved group moulting ceased completely after 1.5 months. Haemocyanin concentration was lowest immediately after moult and increased gradually through stages C and D. Lobsters that were starved or maintained on the bivalve diet did not reach the same premoult haemocyanin levels as those fed with shrimps and mixed food.     

Gender- and oxygen-related irrigation behaviour of the decapod Nephrops norvegicus

The Norway lobster Nephrops norvegicus (L.) inhabits burrows in muddy clay sediments (e.g. on the Swedish west coast), where an autumnal oxygen deficiency in the bottom water can occur. Our experiments investigated whether the irrigation of the burrows would reflect a behavioural adaptation to hypoxia, and whether any gender differences of such behaviour exist. Irrigation is performed by the pleopods which may compensate for a decreasing oxygen tension. Pleopod activity (total number of strokes per sampling time), associated with oxygen concentration and gender, was studied in N. norvegicus kept in artificial burrows resembling their natural habitat. Male and female lobsters were separately exposed to either normoxia (70% oxygen saturation) or hypoxia (30% oxygen saturation). A sexual difference in behaviour was found, where females irrigated the burrow less than males during normoxia. Females showed a significant increase of pleopod activity in hypoxia compared with normoxic conditions, which was not displayed by the males probably due to the degree of individual variation found. However, when only males were studied during progressive hypoxia (from 60 to 5% oxygen saturation), following any changes of irrigational behaviour, a significant increase of accumulated pleopod activity occurred. A major increase of pleopod activity appeared between 60 and 50% oxygen saturation, below which the activity remained high until a critical point (<10% saturation, 11 °C, 33 psu) where irrigation dropped to a level close to that of normoxic values. Activity sessions during hypoxia were longer and had a higher stroke rate than during normoxia. Received: 22 October 1997 / Accepted: 26 February 1998     

Interactions between haemolymph chemistry and condition in the southern rock lobster, Jasus edwardsii

A haemolymph colour index is developed in an attempt to improve the resolution of serum protein data in the characterisation of temporal and spatial changes in the condition and growth of a wild population of Jasus edwardsii. The index can be used as an indicator of nutritional condition if combined with conventional moult staging techniques. Lobsters and haemolymph samples were collected from two high- and two low-growth sites over two fishing seasons. Haemolymph samples were analysed for serum protein and astaxanthin level and categorised according to colour, that is, "pigment stage" (PS). Moult stage data were collected and abdominal and hepatopancreatic tissue analysed for percent dry weight. Haemolymph colour changes from light blue-grey, through beige, to deep orange during the moult cycle. These changes were explained with reference to the major pigment, astaxanthin, which increased from 0.135 mg/l (ǂ.054, n=38) at PS 1 (early intermoult) to 2.670 mg/l (ǂ.599, n=12) at PS 4.5 (late premoult). There were significant increases in percent abdominal and hepatopancreatic dry tissue weight over the moult cycle (Kruskal-Wallis non-parametric ANOVA, P<0.05), especially during intermoult. Serum protein levels increased concomitantly and were significantly correlated with percent dry weight of both tissues (abdomen: r²=0.78, n=871, P<0.001; hepatopancreas: r²=0.64, n=864, P<0.001) There were also significant differences between sites in both PS-specific serum protein and percent dry tissue. Lobster condition differed significantly between sites, probably as a result of temperature-mediated effects on growth rate. The addition of haemolymph pigment to the serum protein index allows the differentiation of lobsters at the beginning, middle and end of intermoult.