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.     

Moulting and reproduction of the spiny lobster Jasus edwardsii (Decapoda: Palinuridae) in northern New Zealand

Aspects of moulting and reproduction of a primarily adult population of the spiny lobster Jasus edwardsii (Hutton) (Palinuridae) were investigated in the field and at an adjacent laboratory in northeast New Zealand from 1982 to 1986. Most males moulted in October/November, ensuring they were in intermoult stage at mating. Females moulted in late April–June, 2 to 3 mo later than females from more southern latitudes. For individual females the specific timing of ecdysis and mating and the length of the interval between them were related to size. Larger females (125 to 135 mm carapace length), tended to moult earlier and wait longer (up to 38 d) before mating, but did so prior to smaller females (95 to 105 mm carapace length, CL) which moulted later, but mated within as few as 9 d. These differences are explained equally well by size-dependent growth processes and by social or chemical inhibition by larger females. Most spiny lobsters (93 to 131 mm CL) moulted at night at depths <10 m. No clear reasons for these behaviours could be found. Eggs were incubated for 101 to 116 d by females in the study population, 70% of the time recorded for more southern areas, these differences probably being related to differences in water temperature. A consequence of earlier female moulting and egg-laying, and longer egg-incubation periods with increasing latitude is that the majority of J. edwardsii larvae hatch in September–November.     

Growth and elemental composition (C,N, H) in Inachus dorsettensis (Decapoda: Majidae) larvae reared in the laboratory

Larvae of the spider crab Inachus dorsettensis were reared in the laboratory at constant 12 °C. Development lasted 8 to 10 d in the Zoea I, 10 to 12 d in the Zoea II and 14 to 20 d in the megalopa stage. During this time, larval growth was measured in samples taken every 2 to 4 d as dry wt (W), carbon (C), nitrogen (N), and hydrogen (H); energy content (E) was calculated from C. Biomass and energy (per individual) increased in each larval stage as a parabola-shaped function of age, which could be fitted by a power equation. C, H, and E show a higher percentage gain (relative to the initial values at hatching) than W or N, suggesting that proportionally more lipid than protein is accumulated during larval development. There are cyclical changes in the relative (per unit of W) biomass and energy figures, corresponding to the larval moult cycles: immediately after each ecdysis all these values decrease, presumably due to rapid uptake of water and minerals, then they increase again due to tissue growth and remain high until the next moulting occurs. Cyclical changes in the C/N ratio suggest that proportionally more lipid than protein is accumulated during the initial (postmoult) phase of the moult cycle, followed by a period of balanced or protein-dominated gain during the intermoult and premoult phases. These patterns of growth and elemental composition observed during the complete larval development and in single moult cycles of I. dorsettensis are compared with those described in the literature for other decapod species. This comparison suggests a high degree of similarity in biochemical composition and growth characteristics of larval decapod crustaceans.     

Developmental changes in body weight and elemental composition of laboratory-reared larvae of the red frog crab,Ranina ranina (Decapoda: Brachyura)

Ranina ranina larvae were reared at 29°C from hatching to the megalopa stage to measure daily changes in body weight, water content and elemental composition. Energy, estimated from carbon content, was also examined. The water content was 85 to 92% of body weight immediately after ecdysis but decreased with days after ecdysis. Gains in body weight, carbon, nitrogen, hydrogen and energy during each instar ranged from 52 to 245% and increased with instar after instar II (body weight and carbon), instar III (hydrogen and energy), and instar IV (nitrogen). Cumulative gains of these elements from hatching to 2 d before metamorphosis into megalopa ranged from 11 567% (carbon) to 12 209% (energy). Most cumulative gains (57 to 59%) in elemental composition were contributed by instar VII. Carbon, nitrogen and hydrogen content in body weight decreased to a minimum on the day of ecdysis and increased on the subsequent days. C:N ratios after instar IV were lowest on the day after ecdysis and reached a plateau by the second day. Energy, estimated as J mg^-1 dry weight (DW), decreased with instar and within a molt cycle, and was at a minimum on the day after ecdysis. Gains in elemental composition could be described by an exponential function of days after hatching and by a quadratic function in each instar.     

Buoyancy in Porcellana platycheles

Intermoult Porcellana platycheles (Pennant) are slow moving, crawling crabs, incapable of swimming upwards from the substrate. Newly moulted porcelain crabs, however, are capable of effective upward swimming. An increased efficiency of tail-fan propulsion in newly moulted crabs was thought unlikely, and it was suspected that newly moulted P. platycheles were more buoyant than intermoult crabs. Results are presented to show that this is the case, and calculations were performed which indicate that fluid uptake at moult is insufficient to produce the observed increase in buoyancy. It is concluded that loss of heavy minerals and scleroprotein at moult cause the increased buoyancy. The adaptive significance of the enhanced swimming ability in newly moulted crabs is thought to lie in an improved ability to escape predation by intertidal fish and crabs.     

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.     

The influence of per offspring investment (POI) and starvation on larval developmental plasticity within the palaemonid shrimp,Palaemonetes varians

At the inter-specific level, per offspring investment (POI), degree of abbreviated development, and lecithotrophic potential all increase with increasing latitude and freshwater penetration among crustaceans. These traits are considered adaptations to conditions of decreasing growth potential. We hypothesise that this relationship between POI and abbreviated development also occurs at the intra-specific level. We studied the caridean shrimp, Palaemonetes varians, to investigate the hypothesis that under food-limited conditions, higher POI enables development through fewer larval instars. Under starvation stress, larvae from broods of greater POI (measured as hatchling brood average dry weight, DW) generally developed through fewer larval instars. With increasing starvation period, larval development time increased, whilst larval growth rate, juvenile DW, juvenile carbon mass, and juvenile carbon:nitrogen (C:N) ratio all decreased. Larval development time generally decreased with increasing brood average dry weight. In contrast, larval growth rate, juvenile DW, juvenile carbon mass, and juvenile C:N ratio all increased with increasing larval brood average DW. The relationship between POI and larval instar number (abbreviation of development) reported here is consistent with that at the inter-specific level and supports the concept that macro-ecological trends in development modes at the inter-specific level may be driven by selection occurring on POI at the intra-specific level.     

Elemental composition (C,N, H) and energy in the development of Pagurus bernhardus (Decapoda: Pagurida) megalopa

No differences in development time and mortality were detected between starved and fed laboratory raised megalopa of Pagurus bernhardus. The average time of development in 138 megalopa was determined as 7.3±0.1 (95% CI) days. During megalopa development P. bernhardus loses about 7% in dry weight (DW), 17% in carbon (C), 6% in nitrogen (N) and 17% in hydrogen (H). During development C/N ratio and individual energy content descend about 14 and 22% respectively. Weight specific energy content decreases by 17% in the first 3 d and remains constant at 12.3±0.3 (95% CI) J·(mg DW)^-1 thereafter. About another 25% in individual energy content was lost by molting to crabs. The measured compounds do not follow a steady decrease. The possibility is discussed that a period of low energy cost (about the first half of development) alternates with times of higher energy expenditure mainly based on lipids. A fixed physiological program different from starvation capability is indicated for P. bernhardus megalopae. By comparing megalopae hatched in two different seasons and years reference is given to the variability in growth pattern.     

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.     

Lipid components as a measure of nutritional condition in fish larvae (Pleuragramma antarcticum) in East Antarctica

Pleuragramma antarcticum is a key component of the neritic assemblages in the Antarctic coastal waters. Larvae of this species were sampled from 2008 to 2011 in the Dumont d’Urville Sea (East Antarctica). The lipid class composition [triacylglycerols (TAG), cholesterol (Chol) and polar lipids (PL)] of larvae was measured to assess the larval condition. The total amount of lipids was linearly related to the quantity of structural polar lipids, suggesting that growth is favored over lipid storage. The TAG:Chol ratio showed interannual variability in the condition of fish larvae, probably related to prey availability. Nevertheless, the essential fatty acids composition of polar lipids illustrates that larvae with low levels of TAG:Chol could be either growing or under starvation. Only the combination of a low TAG:Chol ratio and low polar lipids content, which can also be mobilized during starvation periods, allowed identification of larvae in poor condition. This lipid condition index should be of great assistance to evaluate the probability of survival of P. antarcticum larvae in long-term monitoring. It has widespread applicability and should also be useful in the diagnosis of nutritional condition in other species.     

Ontogenetic variation in metabolism, biochemical composition and energy content during the early life stages of Farfantepenaeus paulensis (Crustacea: Decapoda: Penaeidae)

Dry weight (DW), oxygen consumption, ammonia-N excretion, proximate biochemical composition (total protein, carbohydrate, lipid, water and ash), and energy content (estimated from biochemical composition and by wet combustion) were determined in early developmental stages of cultured Farfantepenaeus paulensis. Pooled samples from embryonic, larval and postlarval stages (at 26 ± 1 °C and 34 ± 1‰) were used for measurements. The study focused on physiological and biochemical processes during transitional periods of ontogeny, such as hatching, lecithotrophic and planktotrophic stages, metamorphosis, and the attainment of a benthic existence in postlarva. DW showed higher increment between protozoea I (PZ I) and mysis I (M I) than in the next mysid and postlarval stages. Individual rates of oxygen consumption and ammonia-N excretion increased, while weight-specific rates presented significant reduction throughout development. Higher weight-specific oxygen consumption was registered in nauplius III (N III) and PZ I, following a decrease in subsequent stages. Postlarval stages PL V–VI and PL X–XII exhibited the lowest values among the stages studied. Weight-specific excretion was high in N III and protozoeal stages, with maximum values in PZ II, while the following stages were marked by lower rates. O:N ratios indicated higher protein catabolism in the stages between egg and M I and a shift to more lipid utilization close to metamorphosis. Water content was higher in the protozoeal stages and decreased afterwards. Higher percentages of protein, lipid and carbohydrate (%DW) were observed in egg and nauplius stages. Protein and lipid decreased from the egg through the naupliar and protozoeal stages, rising again in mysis stages. Lipid content (%DW) decreased in PL V–VI and PL X–XII. Lipid:protein ratios showed an increase of the importance of lipid between PZ III and M II. Carbohydrates represented a minor fraction of body composition, and ash percentages increased from egg to a maximum in PZ II, decreasing in subsequent stages. Energy content determined by wet combustion or calculated by energy equivalents presented the same trend throughout development, varying similarly to protein. Protein was the main energy contributor to body energy in all stages, while the importance of lipid was higher in egg and early naupliar stages. Trends observed in metabolic rates and body composition may be associated to morphological and behavioral changes during the early stages of penaeid development, such as the transition from herbivory to omnivory, and the adoption of a benthic existence. Different ontogenetic energy strategies contribute to succeed through such diverse type of development. Received: 4 July 2000 / Accepted: 6 December 2000     

Lipid-class composition of organs and tissues of the tiger prawnPanaeus esculentus during the moulting cycle and during starvation

Neutral lipid and phospholipid fractions and their component lipid classes in the digestive gland, abdominal muscle, epidermis and cuticle ofPenaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985–1987, and were fed on a standard, semi-purified diet. The digestive gland appears to be a major site of lipid synthesis, storage and mobilisation in preparation for moulting. Neutral lipid, 59 to 80% of which was triacylglycerol, was the larger fraction. It accumulated during early premoult, mainly due to the increase in triacylglycerol. The digestive gland contained only 18% of the total body lipid, or 8% of body lipid as triacylglycerol. Thus, the reserve lipid available for energy production is very small. Digestive gland triacylglycerol was markedly depleted after 4 d starvation and was almost completely absent after 8 d. In the other tissues, the major fraction was phospholipid, of which over 50% was phosphatidylcholine and up to 20% phoshatidylethanolamine; cholesterol was the major class in the neutral lipid fraction and appeared to be very stable. Most of this lipid was probably a component of cellular membranes. The lipid composition of muscle changed very little during the moulting cycle: total lipid levels in the epidermis were high in late premoult and early postmoult, when new cuticle is being secreted, but the proportions of the component lipids were closely similar. Cuticle lipid, together with other major components, was resorbed from the old cuticle prior to ecdysis, but the cuticle phospholipids appeared to be labile at all moult stages. The total of all lipids in fedP. esculentus was about 3.6% dry weight, of which about 70% was phospholipid. Earlier research had shown that when digestive gland lipid is exhausted after a short period of starvation, muscle is metabolised for energy. The present research showed that in the remaining muscle only about 13% of lipid was lost after 21 d starvation, mostly as phosphatidylcholine. This is in keeping with the need to maintain this tissue in a functional state. In contrast, epidermal lipid levels were markedly reduced after only 4 d starvation and the proportions of phospholipids changed significantly. This sensitivity of the cuticle lipids to starvation may be the cause of delayed moulting, which is characteristic of poor nutrition.     

Permanence of Euscorpius carpathicus (L.) larvae on the mother's back (Scorpiones,Chatidae)

Summary The tendency of Euscorpius carpathicus larvae to remain on immobilized live or dried scorpions of the same or different species (Euscorpius flavicaudis) has been tested. Dried scorpions are less attractive than live ones, which are equally attractive regardless of species, sex or reproductive phase. The larvae find old (one year) dried specimens less attractive than freshly or recently (15 days) killed females, which are equally as attractive as live mothers (Table 1). A substratum treated with a chloroform extract of the mother's cuticle is consistently preferred by the larvae. The maternal behaviour (tolerating the larvae on the back) usually disappears about a week after the moult of the larvae, but it can be protracted if they are continually replaced by younger larvae (Table 2). The survival rate of larvae on live mothers is higher than on dried specimens.     

Differential timing of larval starvation effects on filtration rate and growth in juvenile Crepidula onyx

This study demonstrates that the timing of larval starvation did not only determine the larval quality (shell length, lipid content, and RNA:DNA ratio) and the juvenile performance (growth and filtration rates), but also determine how the latent effects of larval starvation were mediated in Crepidula onyx. The juveniles developed from larvae that had experienced starvation in the first two days of larval life had reduced growth and lower filtration rates than those developed from larvae that had not been starved. Lower filtration rates explained the observed latent effects of early larval starvation on reduced juvenile growth. Starvation late in larval life caused a reduction in shell length, lipid content, and RNA:DNA ratio of larvae at metamorphosis; juveniles developed from these larvae performed poorly in terms of growth in shell length and total organic carbon content because of “depletion of energy reserves” at metamorphosis. Results of this study indicate that even exposure to the same kind of larval stress (starvation) for the same period of time (2 days) can cause different juvenile responses through different mechanisms if larvae are exposed to the stress at different stages of the larval life.     

Changes of respiration and biomass of spider crab (Hyas araneus) larvae during starvation

The influence of starvation on respiration (R), dry weight (W), carbon (C), nitrogen (N), hydrogen (H), and energy content (E; calculated fromC) of spider crab (Hyas araneus L.) larvae was studied in the laboratory. In all larval stages (zoea I and II, megalopa)W increased during postmoult, independent of food, and decreased subsequently. The final reduction inW after continued starvation increased from stage to stage (9, 13, and 20% respectively), but it was always much lower than the decrease inC (44 to 52%),N (42 to 46%),H (50 to 58%), andE (53 to 62%). Individual (R) and weight-specific respiration rates (QO ₂) were reduced by 83 to 88%. The time-dependence of these reductions in metabolism and biomass as well as the rates of change in all parameters studied were described with non-linear regression models and differential equations, respectively. Rates and total amounts of energy lost during starvation were independently calculated fromC andR values, and similar results were mostly obtained. Only in the megalopa stage was there a conspicuous difference between the two estimates: higher losses were calculated fromR. This shows that further (biochemical) data are required for a more complete understanding of the energetics of this stage. Estimates of total protein (fromN) and lipid (fromC) suggest that both constituents serve as metabolic substrates during starvation, but most of the energy originates from the breakdown of protein.Supported by the Deutsche Forschungsgemeinschaft (An 145/1-1)     

Elemental (C, N and P) analysis of metamorphosing bonefish (Albula sp.) leptocephali: relationship to catabolism of endogenous organic compounds, tissue remodeling, and feeding ecology

Whole-body carbon (C), nitrogen (N) and phosphorus (P) content, and stable-isotope composition (¹³C:¹²C and ¹⁵N:¹⁴N), were followed during metamorphosis of bonefish (Albula sp.) larvae (leptocephali). Metamorphosing larvae depend entirely on endogenous carbon compounds (some of which contain N and P) as an energy source. Two fundamental questions are (1) Do the demands of extensive tissue remodeling during metamorphosis require the efficient retention of N and P during the catabolism of carbon compounds? (2) What effect does the lack of feeding have on stable-isotope composition? Our results showed that both C and N decreased by ～35 to 40%, reflecting the utilization of neutral lipid (triacylglycerols) and N-containing compounds (phosphatidylethanolamine and keratan sulfate glycosaminoglycan) as energy sources, and indicating that larvae have little or no capacity to retain N. Evidence suggested that collagen breakdown, measured as a loss of hydroxyproline content, also contributed to N loss. Stable-isotope ratios, expressed as ¹³C and ¹⁵N, showed no statistically significant differences in early and advanced metamorphosing larvae. In contrast to C and N, phosphorus was conserved during metamorphosis and most probably is utilized in the increased bone mineralization occurring in advanced larvae. We show, however, that advanced larvae are P-limited and that normal ossification is dependent upon a supply of exogenous P obtained after the resumption of feeding. The N:P ratio of 12.3 in early larvae decreased to 8.1 in advanced larvae owing to the conservation of P as N was lost. The mean ¹⁵N value in early metamorphic larvae (11.6‰) is consistent with results from other studies, and provides further support for the view that premetamorphic leptocephali feed at a very low trophic level.     

Assessment of the nutritional condition of larval and early juvenile tuna and Spanish mackerel (Pisces: Scombridae) in the Panamá Bight

The nutritional condition of first-feeding and late larval/early juvenile scombrids was investigated in waters of the northwestern Panamá Bight from May through early November 1988. Wild-caught larvae and juveniles of three taxa, black skipjack tuna (Euthynnus lineatus), bullet and/or frigate tuna (Auxis spp.) and sierra (Scomberomorus sierra), were examined histologically to determine nutritional condition. The incidence of malnourishment in wild-caught preflexion (first feeding—prior to notochord flexion) larvae of all taxa was high. Starvation rates for E. lineatus and Auxis spp. preflexion larvae ranged from 62 to 63% d^-1, while the percentage of larvae actually dying of starvation was estimated at 41 to 43% d^-1. The nutritional point-of-no-return for preflexion larvae was estimated at 1 to 2 d maximum. The cellular condition of liver hepatocytes, particularly the relative amount of vacuolation related to storage of glycogen and lipid, proved to be a sensitive indicator of nutritional condition. In laboratory trials, late larval (postflexion) and early juvenile black skipjack exhibited a nutritional point-of-no-return of 2 to 3 d. Although postflexion larvae were moderately vulnerable to malnourishment in laboratory trials, <13% of wild-caught postflexion larvae exhibited even mild nutritional stress, and no postflexion larvae or juveniles showed signs of severe malnourishment. This pattern of starvation incidence suggests that tropical scombrids undergo stagespecific starvation mortality. Preflexion larvae can suffer significant daily losses due to starvation, while postflexion larvae and early juveniles seem to experience a rapid improvement in feeding ability and/or food availability.     

Escape speeds of marine fish larvae during early development and starvation

Response rates to tactile stimulation and subsequent escape speeds were measured using a video-recording system during early development and starvation of fish larvae. The species studied included the yolk-sac larvae of Clyde and Baltic herring (Clupea harengus L.), cod (Gadus morhua L.), flounder (Platichthys flesus L.) and older larvae of Clyde herring. The proportion of larvae responding (response rate) was initially about 20 to 25% in herring and 35 to 40% in cod and flounder using a probe, but about 70 to 80% using the sucking action of a pipette in all species except flounder. Both response rates and escape speeds (mean and maximum) tended to peak 1 to 2 d before the PNR (point-of-no-return, when 50% of larvae are too weak to feed), then decreased slowly during further starvation. An inter-species comparison showed that the highest recorded mean escape speeds (measured over a period of 200 ms) and highest maximum escape speeds (over 20 ms) ranged from 5.7 to 8.6 BL/s (body lengths/s) and 12.1 to 16.1 BL/s, respectively. The larvae made directional responses away from the stimulus only when they developed and reached the feeding stage.     

Growth and reproduction of Pycnogonum litorale (Pycnogonida) under laboratory conditions

The complete life cycle of Pycnogonum litorale Ström was observed under laboratory conditions. At 15?°C and a 16?h light:8?h dark photocycle, the duration of embryonic development from oviposition to egg-hatching varied from 32 to 111?d. The onset of egg hatching ranged from 32 to 81?d after oviposition in different egg batches, and the period between the first and the last hatch within a single egg batch varied between 16 and 57?d. The larval period, consisting of five larval instars, lasted between 66 and 113?d. Juvenile development required seven (exceptionally 8 or 9) moults and lasted between 263 and 400?d. The average interval between successive moults in juveniles increased with increasing size from 24 to 82?d. Though females did not moult more often than their male conspecifics, they reached a size from 8.5 to 11.0?mm (average 10.1?mm) while adult males measured only 7.0 to 8.5?mm (average 7.7?mm). At low temperatures (2?°C) moulting was almost completely inhibited. After raising the temperature to 6?°C, the moulting frequency increased to a rate almost as high as at a constant temperature of 15?°C. Moulting was also retarded by starvation and accelerated by subsequent feeding. Adults lived for up to 9?years without further moults, with several periods of mating and oviposition at irregular intervals. In combination with previous long-term field observations, the present results provide a more complete picture of the life cycle of P. litorale in a natural habitat. The great variation in the duration of the different developmental stages, the ability to survive periods of cold and starvation, and the longevity of the adults are important for the survival of pycnogonid populations under changing environmental conditions.     

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.