Effects of endogenous and some exogenous factors on the activity of the juvenile banana prawn Penaeus merguiensis

In conditions of alternating light and dark, juvenile Penaeus merguiensis de Man are more active during the dark phase. The rhythm persists in continuous dim red light, but not in continuous bright white light. The period of circadian rhythm shown in continuous dim red light varies between individuals from 22.75 to 26.0 h, with a mean of 23.8 h. The response of prawns to an artificially produced tidal situation is mediated by the presence or absence of water flow. No endogenous component of this tidal rhythm was demonstrated. There is an irregular short-term rhythm (period 2 to 3 h). It is suggested that this allows starved prawns to conserve energy.     

Photoperiodic control of growth and segment proliferation by Nereis (Neanthes) virens in relation to state of maturity and season

The effects of two fixed photoperiodic regimes on the rate of somatic growth and segment proliferation in the semelparous polychaete Nereis (Neanthes) virens Sars has been investigated. The two photoperiods (16 h light:8 h dark and 8 h light:16 h dark, hereafter LD 16:8 and LD 8:16) were close to the extremes experienced naturally by N. (N.) virens in the course of a year. The experiments were carried out during the ambient winter and all worms (including four-setiger larvae raised out of season) showed elevated feeding, growth and enhanced segment-proliferation rates when reared under LD 16:8, compared to worms reared under LD 8:16. The rate of replacement of lost segments after caudal ablation was also higher under LD 16:8. The number of segments present when the segment proliferation rate had fallen to zero was higher in individuals grown from birth under LD 16:8 compared to those grown under LD 8:16. Feeding activity showed a degree of spontaneous recovery under LD 8:16 from January onwards, but remained lower than under LD 16:8. This difference continued into the following spring, and was not attributable to differences in sexual maturity. We conclude that the rate of feeding in N. (N.) virens and other indicators of somatic growth rate such as rates of caudal regeneration and segment proliferation are directly influenced by the photoperiod, but that the seasonal cycle of growth also includes a circa-annual component modifying the response to static photoperiods according to the time of year. Received: 20 October 1998 / Accepted: 4 February 1999     

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.     

Biomineralization markers during early shell formation in the European abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>, Linnaeus

Larval shell formation was investigated in the European abalone Haliotis tuberculata. Stages of mineralization as well as enzymatic and endocrine biomarkers were monitored throughout larval development, from hatching to post-larval stages. Polarized light microscopy and infrared spectroscopy analyses revealed the presence of crystallized calcium carbonate arranged in aragonite polymorphs from the late trochophore stage. A correlation between the main steps of shell formation and enzymatic activities of alkaline phosphatase and carbonic anhydrase was seen. The variations of these biologic activities were related to the onset of mineralization, the rapid shell growth, and the switch from larval to juvenile shell following metamorphosis. Furthermore, a strong increase in the level of calcitonin gene-related molecules was measured in post-larvae, suggesting that endocrine control takes place after metamorphosis. The changes measured for the three biomineralization markers together with mineralogical analysis allowed us to correlate physiologic mechanisms with early steps of abalone shell formation.     

Endogenous control of timing of metamorphosis in megalopae of the shore crab Carcinus maenas

Batches of hundreds of freshly collected megalopae of the shore crab Carcinus maenas (L.) showed persistent circatidal rhythms of moulting to the juvenile crab stage when maintained in constant laboratory conditions. Peaks of moulting occurred around expected times of high tides, with few megalopae moulting at other times. In larvae collected offshore, the highest tidally-timed peak of metamorphosis occurred during the second to fifth expected times of high tide, and metamorphosis of 50% of each batch took about 22 h or longer. In contrast, in larvae collected at the water's edge, 70% metamorphosed during the first expected episode of high tide, within 6 to 8 h after collection. However, although inshore megalopae moulted before offshore ones, the tidal timing of moulting remained unaltered whether megalopae were collected at neaps or springs, from the water's edge or farther offshore, in the presence or absence of natural substratum, and under various light–dark and salinity regimes. Metamorphosis of C. maenas megalopae around the times of high tides may enhance settlement into the upper intertidal zone. Early juveniles of the crab apparently prefer that zone as they are most abundant there and, unlike adults, do not undertake up-and-down-shore migration with tides. The present finding demonstrates, for the first time, endogenous physiological timing of circatidal periodicity in the metamorphic moult of crab megalopae, suggesting that endogenous factors, as well as exogenous ones should be taken into account in considering the process of settlement by crab megalopae. Received: 21 February 1996 / Accepted: 27 November 1996     

Physiological and biochemical changes during lecithotrophic larval development and early juvenile growth in the northern stone crab,Lithodes maja (Decapoda: Anomura)

Larvae of the northern stone crab, Lithodes maja L., were reared in the laboratory from hatching to the second crab stage. complete larval development (at constant 9°C) lasted about 7 wk, invariably consisting of three pelagic zoeal stages and a semibenthic Megalopa; only two zoeal stages have been described in the literature. All larval stages are lecithotrophic. First feeding was consistently observed only after metamorphosis, in the first juvenile crab stage. In short intervals (every 1 to 5 d), developmental changes in biomass, B (expressed as: dry weight, W; carbon, C; nitrogen, N; hydrogen, H) and oxygen consumption (respiration, R) were measured in larvae and early juveniles; additionally, protein and carbohydrates were measured, but only in the zoeal stages and early Megalopa. Unusually high C contents (varying between 56 and 61% of W in eggs and freshly hatched Zoea I larvae from 12 different females) and high C:N weight ratios (8 to 11) indicate enhanced initial lipid stores, which are utilized as the major metabolic substrate during both embryonic and lecithotrophic larval development. Predominant degradation of lipids is shown indirectly; the C:N ratio decreased significantly, from 10 (at hatching) to 6 (at metamorphosis), while larval protein decreased only little, from ca. 55% of W (at hatching) to 48% (in the Megalopa). From hatching to metamorphosis, about 27% of the initially present W, 48% of C, 18% of N, and 52% of H were lost. This decrease in larval biomass can be described as an exponential function of development time. The major part of these losses were associated with metabolic energy requirements, while exuvial losses were comparably small. In each of the zoeal stages, only about 1 to 2% of late premoult (LPM) B was shed with the exuvia. The Megalopa, which produces a much thicker, calcified exoskeleton, lost 20% of LPM W, but only 5 to 8% of organic constituents (C, N, H). Much higher exuvial losses were measured in the Crab I stage (51% in W, 21% in C, 5% in N, and 7% in H). Maximum respiration was found in the actively swimming zoeal stages, a minimum in the predominantly benthic, mostly inactive Megalopa. The Crab I stage exhibits also a sluggish behaviour and low R, in spite of beginning food uptake and growth. Immediately after metamorphosis, the juvenile crab gained rapidly in W, in particular in its C fraction. A transitorily steep increase in the C:N ratio indicates a replenishment of partially depleted lipid stores, but also a rapid initial increase of inorganic C in the heavily calcified exoskeleton. Instantaneous rates of growth, assimilation, and net growth efficiency (K ₂) were high during the initial (postmoult) phase in the first juvenile crab stage (C-specific growth rate: 6% d^-1; K ₂:70%), but decreased towards zero values during laterstages of the moulting cycle; metabolism remained practically constant during the Crab I stage. Entirely lecithotrophic larval development from hatching to metamorphosis in L. maja is considered an adaptation to seasonally short and limited planktonic food production in subarctic regions of the northern Atlantic.     

Patterns of larval and early juvenile growth in a semiterrestrial crab, Armases angustipes (Decapoda: Sesarmidae): comparison with a congener with abbreviated development

In a semiterrestrial and estuarine tropical crab, Armases angustipes Dana (Grapsoidea: Sesarmidae), changes in biomass (measured as dry mass, W; carbon, C; nitrogen, N; and hydrogen, H; per individual) and relative elemental composition (C, N, H, in percent of W; C:N mass ratio) were studied during development from an early egg stage through hatching, the complete larval phase, metamorphosis and the first juvenile crab stage (CI). In the megalopa and CI, growth was measured also within the moulting cycle, and biomass and elemental composition were determined in cast exuviae. From an early egg stage to the freshly hatched larva, A. angustipes lost about 20% of W, 29% of C, 5% of N and 32% of H. Proportionally higher losses in C than in N were reflected also in a significantly decreasing C:N mass ratio (from 5.02 to 3.74). These results indicate that lipids mobilised from yolk reserves represented the principal metabolic substrate for embryonic energy production, while proteins were catabolised at a much lower rate. The present data of growth and exuviation are compared with previously published data from a congener, A. miersii Rathbun, which has an abbreviated and facultatively lecithotrophic mode of larval development (with three instead of four zoeal stages; stages I and II in principle independent of food). When growth is measured as an increase in the final (premoult) biomass of successive developmental stages, both species show an exponential pattern. Within the moulting cycles of the megalopa and the first juvenile, both species show parabola-shaped growth curves, with a rapid biomass increase in postmoult and intermoult stages, and losses in the premoult phase. Thus, the two Armases species show, in general, similar patterns of larval and early juvenile growth. However, the initial size of eggs and larvae is about four times larger in A. miersii, and its biomass remains higher throughout the period of larval and early juvenile development. A. angustipes is able to partially make up for this difference, as it has an additional zoeal stage, and its megalopa and CI stages show higher relative biomass increments (in percent of initial values). Due to this compensatory growth pattern, A. angustipes reaches in its CI stage about half the biomass of a juvenile A. miersii. When exuvial losses of megalopae and juveniles are compared between these two species, A. miersii shows higher biomass losses per individual (corresponding with its larger size), but lower relative losses (C, N, H, in percent of late premoult body mass or in percent of previously achieved growth increments). Differences in larval and early juvenile growth and in the exuvial losses of megalopae and juveniles of these two congeners are discussed in relation to their differential ecology, life history and reproductive strategy.     

Carbon-nitrogen relations at whole-cell and free-amino-acid levels during batch growth of Isochrysis galbana (Prymnesiophyceae) under conditions of alternating light and dark

Isochrysis galbana Parke, Strain CCAP 927/1, was grown in ammonium-limited batch culture under a 12 h light: 12 h dark illumination cycle. Samples were taken every 12 h over the 26 d period from lag phase through exponential into stationary phase (no net carbon fixation), with more frequent sampling at points of interest. Exponential cell-specific growth rate was 0.3 to 0.4d^-1. Cell division occurred during the dark phase, while cell volume increase, ammonium uptake, and pigment synthesis occurred during the light. Stationary phase cells were small, and the lag phase was long (5 d) even though the C:N ratio had returned from 18 to 6.5 within 2 d, followed by synthesis of chlorophyll a. Net chlorophyll synthesis ceased within 4 d of exhaustion of the nitrogen source. The chlorophyll c: chlorophyll a ratio remained constant during increasing nitrogen deprivation. Biovolume and carotenoids correlated with carbon biomass. Levels of chlorophyll a correlated poorly with carbon fixation and carbon biomass once the nitrogen source had been exhausted. Except after the addition of ammonium to nitrogen-deprived cells (refeeding), the content of intracellular glutamine and the glutamine: glutamate ratio were low during the dark phase, rising to a plateau within the first 1 h of illumination. Refeeding of cells which had only just exhausted the extracellular nitrogen source resulted in a much smaller increase in glutamine than refeeding of nitrogen-starved (stationary-phase) cells. Nitrogen biomass correlated with the presence of an unidentified intracellular amine.     

Formation of initial daily increments in sagittal otoliths of reared and wild Sardina pilchardus yolk-sac larvae

Daily deposition of growth increments in sagittal otoliths of reared and wild Sardina pilchardus (Walbaum, 1792) larvae from hatching to complete yolk-sac absorption is reported. Increments laid down prior to hatching were observed. A distinct growth increment, 1 m wide and located 5 to 7 m from the focus is laid down on the day of hatching. Subsequently, narrower increments (<1 m) are laid down daily throughout the yolk-sac stage. Measurements were made on the maximum radius of the sagittal otoliths of two groups of larvae: 83 larvae reared from fertilized eggs sampled from Ría de Muros (NW Spain), and 239 wild individuals sampled along the northern coasts of the Iberian peninsula. Counting of daily ring increments can provide a direct and valid estimation of larval age without the necessity for later correction.     

Larval growth in the estuarine crab Chasmagnathus granulata: the importance of salinity experienced during embryonic development, and the initial larval biomass

The importance of salinity experienced during embryonic development and initial larval biomass on larval growth was studied in the South American estuarine crab Chasmagnathus granulata. Ovigerous females were maintained at three salinities (15, 20, and 32‰) from egg laying to hatching of zoea l. Larvae from all treatments were reared under constant conditions of photoperiod (12∶12), temperature (18°C), and salinity (first instar at 20‰, subsequent instars at 32‰). Biomass was measured as dry weight, carbon, and nitrogen content per individual at egg laying, hatching of zoea l, premoult zoea l, and zoea 4, and in 8-day-old megalopa. From hatching to premoult zoea 4, biomass was higher for larvae from prehatching salinities of 15 and 32‰. There was a significant positive correlation between biomass at hatching and at premoult zoea l and zoea 4. Accumulated biomass during zoeal stages tended to be higher for larvae from broods with higher biomass at hatching, although this trend was not always significant. Zoea 4 either directly metamorphosed to megalopa or moulted to zoea 5, following, respectively, a short or long developmental pathway. The proportion of zoea 4 that followed the long pathway was negatively correlated with biomass of zoeal stages. Biomass at hatching was correlated with biomass of megalopae developed through the short pathway, although it was not correlated with the accumulated biomass at this stage. Megalopae developed through the long pathway (i.e. metamorphosed from zoeae 5) had higher biomass than those from the short pathway. The present results suggest that prehatching salinity and initial egg and larval biomass can be very important for larval growth. Published online: 9 August 2002     

Cell cycle and toxin production in the benthic dinoflagellate Prorocentrum lima

Profiles of diarrhetic shellfish poisoning (DSP) toxins produced throughout the growth cycle and the cell cycle of the toxigenic marine dinoflagellate Prorocentrum lima were studied in triplicate unialgal batch cultures. Cells were pre-conditioned at 18 ± 1 °C, under a photon flux density (PFD) of 90 ± 5 μmol m⁻² s⁻¹ on a 14 h light:10 h dark photoperiod. In exponential growth phase, cultures were synchronized in darkness for 17 d. After dark synchronization, cultures were transferred back to the original photoperiod regime. Cells were harvested for DSP toxin analysis by LC-MS (liquid chromatography with mass spectrometry), and double-stranded (nuclear) DNA was quantified by flow cytometry. The cell populations became asynchronous within approximately 3 d after transition from darkness to the 14 h light:10 h dark photoperiod. This may be due to the prolonged division cycle (5 to 7 d) that is not tightly phased by the photoperiod. Unlike other planktonic Prorocentrum spp., cytokinesis in P. lima occurred early in the dark and ceased by “midnight”. Cellular levels of the four principal DSP toxins, okadaic acid (OA), OA C8-diol-ester (OA-D8), dinophysistoxin-1 (DTX1) and dinophysistoxin-4 (DTX4), ranged from 0.37 to 6.6, 0.02 to 1.5, 0.04 to 2.6, and 1.8 to 7.8 fmol cell⁻¹, respectively. No toxin production was evident during the extended period of dark synchronization nor during the initial period when NH₄ was consumed as the major nitrogen source. Soon after the cells were returned to the 14 h light:10 h dark cycle and they began to take up NO₃, cellular levels of all four toxins gradually increased. This increase in DSP toxins usually occurred in the light, marked by a rise in DTX4 levels that preceded an increase in the cellular concentration of OA and DTX1 (delayed by 3 to 6 h). Thus, DTX4 synthesis is initiated in the G1 phase of the cell cycle and persists into S phase (“morning” of the photoperiod), whereas OA and DTX1 production occurs later during S and G2 phases (“afternoon”). No toxin production was measured during cytokinesis, which happened early in the dark. The evidence indicates that toxin synthesis is restricted to the light period and is coupled to cell cycle events. Received: 3 September 1998 / Accepted: 30 March 1999     

Reproductive biology and early life history of the hermaphroditic feather star Dorometra sesokonis (Echinodermata: Crinoidea)

Reproduction and larval/post-larval development of the one of the smallest known comatulid Dorometra sesokonis were studied on the coral reefs of Sesoko-jima Island, Okinawa, Japan. Breeding individuals were found every month from May 2003 to April 2004 indicating continuous reproduction. Individuals possessed both mature ovaries and testes, and were therefore characterized as simultaneous hermaphrodites. This species was observed to be an external brooder in which the embryos developed on the surface of parental genital pinnules until the doliolaria larval stage, and subsequently released doliolariae settled on substrata within 4 days after hatching. Larvae then metamorphosed into the post-larval cystidean stage, which lasted for more than a month. The reproductive features of this species are unique among crinoids, and, together with juvenile morphological features observed in adults, can be interpreted as adaptations to their cryptic habitat, which is subject to frequent natural disturbances.     

Physiologische anpassungen eines marinen insekts. I. Die zeitliche steuerung der entwicklung

The Baltic populations of Clunio marinus (Chironomidae, Diptera) differ from their Atlantic counterparts in three ways: they neither pupate nor hatch in synchrony with a lunar rhythm; they live in a permanently submersed habitat; the structures of their gelatinous egg-masses are different. C. marinus produces two generations each year. The spring generation, which hibernates in the 4th larval stage, hatches in May; the summer generation hatches at the end of July or beginning of August; hatching periods last only a few days. In the laboratory, a permanent short-day period (8 h light, 16 h dark; LD 8:16) induces larval quiescence (oligopause), which can be terminated by long-day conditions (ca. LD 16:8). If larval populations are exposed to continuous light (LL) for 4 days every 30 days, particularly large numbers of imagos hatch about the time of the next LL-period. Increased illumination may influence the time of hatching. Raising the temperature for a few days does not affect hatching. The roles of photoperiod, illumination and temperature are discussed with regard to the temporal programming of development and the start of mass hatching in the natural habitat.

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Herrn Professor Dr. D. Neumann danke ich für die Anregung und Betreuung dieser Arbeit, die Teil einer Dissertation ist.

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Communicated by O. Kinne, Hamburg     

Can photoperiod manipulation affect gonad development of a boreo-arctic echinoid (Strongylocentrotus droebachiensis) following exposure in the wild after the autumnal equinox?

A laboratory experiment was conducted in the winter of 2003–2004 to assess the effect of varying photoperiod regime on consumption rate, assimilation rate, absorption efficiency, and gonad development of the green sea urchin, Strongylocentrotus droebachiensis. Adult individuals were collected from the wild after they had been exposed to the ambient autumn photoperiod cue (which is the extraneous trigger thought to elicit gametogenesis in this species) and placed at ambient temperature for 12 weeks under five different photoperiod regimes: (1) 24 h light:0 h dark=“0D”, (2) 16 h light:8 h dark=“8D”, (3) 8 h light:16 h dark=“16D”, (4) 0 h light:24 h dark=“24D”, and (5) ambient photoperiod (range: 10.50–15.25 h dark). Urchins in these five treatments were fed ad libitum with bull kelp, Nereocystis luetkeana. A sixth treatment consisted of starved individuals held under 0D conditions. Various gonad factors including gonad index, percent gonad water, gonad colour (CIE lightness or L*, CIE hue or a*, and CIE chroma or b*), percent area occupation of the gonad by various cell types (nutritive phagocytes, spermatozoa, and secondary oocytes/ova), and stage of development were assessed at the beginning of the experiment and at weeks 4, 8, and 12 of the study. Consumption and assimilation rates were assessed at weeks 4 and 12 and absorption efficiency at week 12 of the experiment. Urchins were predominantly in the growing and premature stages at the beginning of the experiment, but by week 4 at least 20% of individuals in all treatments receiving food were classified as mature. Spawning occurred during all these treatments between weeks 4 and 8, as evidenced by significant decreases in spermatozoa and secondary oocytes/ova and a significant decrease in percent gonad water, but was not accompanied by major declines in gonad indices. Greater than 90% of individuals in all five of the fed treatments were in the recovering and growing stages at the end of the experiment. The 16D treatment had by far the greatest percentage of urchins in the growing stage. In contrast, individuals that were starved were predominantly in the mature stage at weeks 4, 8, and 12, with only ~30% reaching the spawning stage by the end of the experiment. Photoperiod significantly affected gonad indices at the termination of the experiment with gonad index being the highest in the 16D treatment; this was significantly greater than in the 8D and ambient treatments. Photoperiod did not significantly affect gonad percent water, gonad lightness, or gonad hue. Gonad chroma was significantly affected by photoperiod, urchins held under ambient conditions having significantly lower b* readings than individuals in any other treatment. Photoperiod had little or no affect on consumption rate, assimilation rate, or absorption efficiency. Thus, differences among treatments in regards to gonad index, gonad chroma, and stage of development cannot be attributed to variations in feeding, absorption, or assimilation. The results of this experiment indicate that once gametogenesis is initiated, photoperiod manipulation cannot prevent ultimate spawning. However, photoperiod regime can affect the rate at which urchins move through the various stages of the gametogenic cycle. Urchins placed on short days under artificial lighting (16D) moved through the spawning stage into recovering and growing stages the fastest. This photoperiod regime also produced the highest gonad index at the end of the experiment. Since the commercial urchin market prefers large gonads in the growing and premature stages (i.e. before the mature stage is reached and gonads start leaking sperm and eggs), short day-lengths under artificial lighting (16D) appear to be the best photoperiod conditions for optimizing marketability.     

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.     

Larval development of Pilumnoides perlatus (Brachyura: Xanthidae) under laboratory conditions

Larvae of the xanthid crab Pilumnoides perlatus (Poeppig, 1836) have been reared in the laboratory at 3 different temperatures (10.2°, 15° and 20°C) from hatching to megalopa stage. The 5 zoea stages and the megalopa, as well as the setation of the functional appendages are described and illustrated. The main characteristics useful to differentiate the larval stages of P. perlatus from those of Homalaspis plana, the other Chilean species of the same family so far reared, are discussed. Data on duration of zoea development, length of moulting intervals, and mortality at the 3 test temperatures are also given.This study was partially supported by the Chilean National Commission for Scientific and Technological Research (CONICYT).     

Kinetics of light-intensity adaptation in a marine planktonic diatom

The marine planktonic diatom Thalassiosira weisflogii was grown in turbidostat culture under both continuous and 12 hL: 12 hD illumination regimes in order to study the kinetics of adaptation to growth-irradiance levels. In both illumination regimes adaptation to a higher growth-irradiance level was accompanied by an increase in cell division rates and a decrease in chlorophyll a cell^-1. The rates of adaptation for both processes, derived from first order kinetic analysis, equaled each other in each experiment. The results suggest that during the transition from low-to-high growth-irradiance levels chlorophyll a is diluted by cell division and is not actively degraded. Introduction of a light/dark cycle lowered the rate of adaptation. In transitions from high-to-low growth-irradiance levels there was a sharp drop in growth rates and a slow increase in chlorophyll a cell^-1 under both continuous and intermittent illumination. In the 12 hL:12hD cycle there was a circadian rhythm in chlorophyll a cell^-1, where cellular chlorophyll contents increased during the light cycle and decreased during the dark cycle. This circadian rhythm was distinctly different from light intensity adaptation. For kinetic analysis of light intensity adaptation in a 12 hL: 12 hD cycle, the circadian periodicity was separated from the light intensity response by subjecting the data to a Kaiser window optimization digital filter. Kinetic parameters for light-intensity adaptation were resolved from the filtered data. The kinetics of lightintensity adaptation of marine phytoplankton are discussed in relation to their spatial variations and time scales of mixing.This research was performed at Brookhaven National Laboratory under the auspices of the United States Department of Energy under Contract No. DE-AC02-76 CH00016     

Observations sur le développement larvaire de Meganyctiphanes norvegica (Crustacea: Euphausiacea) au laboratoire

Larvae of Meganyctiphanes norvegica (M. Sars), caught with a plankton net, were reared in the laboratory from the calyptopis phase onwards, under different temperature and trophic conditions. Eyestalk ablation was performed on the first furciliae. Data are presented on growth, moulting rate and ontogenesis of the larvae as a function of the varying experimental conditions, and on larval morphology, pigmentation and diet. Recent modifications of larval nomenclature in euphausiids are discussed.

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Observations sur le développement larvaire de Meganyctiphanes norvegica (Crustacea: Euphausiacea) au laboratoire

     

Field estimates of growth and mortality of juvenile banana prawns (Penaeus merguiensis)

Postlarval and juvenile Penaeus merguiensis de Man from the Embley River estuary on the north-eastern Gulf of Carpentaria were sampled every 2 wk from September 1986 until August 1989, using a small beam trawl. Settlement of planktonic postlarvae peaked during the pre-wet season (October to December), and declined through the wet season (January to March). Using length-frequency analysis between 12 and 14 cohorts of juvenile prawns were identified each year. Length-frequency analysis and modal progression were used to derive growth rates during the estuarine phase of the life cycle. Growth rates, which could be described by a linear model, ranged from 0.63 to 1.65 mm CL (carapace length) wk^-1. Growth rates were positively influenced by water temperature and negatively influenced by prawn density. Salinity had no effect on growth rates. Prawns spent between 6 and 20 wk in the Embley River before emigrating offshore from the estuary. Weekly instantaneous rates of natural mortality (M) ranged from 0.23 to 0.94, and in general were lowest during the dry season (July to September) and highest during the pre-wet and wet seasons. Only temperature significantly influenced mortality rates, with mortality rates increasing with temperature. By projecting juvenile growth rates forward through time, we established which cohorts contributed to the offshore fishery each year. In 1987 and 1988 the April fishery consisted of prawns which had settled in the river before the end of January each year. Slow growth rates during the pre-wet season of 1988 meant that only cohorts that were settled before early December 1988 contributed to the fishery in April 1989. Whether a cohort contributes to the fishery depends on the settlement date, water temperature and prawn density.     

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.