Point Of Reserve Saturation Research Articles

Nutritional vulnerability of early zoeal stages of the ornamental shrimp Lysmata ankeri (Decapoda: Caridea)

Abstract The evaluation of the effects of early starvation and feeding on survival and growth in the early stages of the life cycle of ornamental marine caridean shrimp species is fundamental to establish adequate feeding protocols in their culture. In this study, we determine the nutritional vulnerability in the early larval stages of ornamental shrimp Lysmata ankeri exposed to different periods of starvation or feeding. The larvae were separated into three groups (zoea I-ZI, zoea II with ZI fed, and zoea II with ZI unfed) and subjected to two experiments: (1) point-of-no-return (PNR), comprising one or two days of initial starvation followed by feeding; and (2) point-of-reserve-saturation (PRS), comprising one or two days of initial feeding followed by starvation. Each experiment was still composed of two control groups: continuous feeding and continuous starvation. Larvae tolerated some periods of starvation, with a high PNR value (2.00) and low PRS (0.50). Longer periods of starvation influenced both growth and survival rates in zoea II stages. The nutritional vulnerability index for zoea I was 0.25, which represents a low dependence on food supply. In this study, it was observed that ornamental shrimp L. ankeri larvae hatch with energy reserves, presenting facultative primary lecithotrophy, in which they are able to moult from zoea I to zoea II using such reserves in the absence of food. In this sense, the early larvae stages (zoeas I and II) can tolerate a certain period of starvation, indicating the great potential of this species for aquaculture.

Nutritional vulnerability of early zoeal stages of the invasive shrimp Lysmata vittata (Decapoda: Caridea) in the Atlantic Ocean

AbstractLysmata vittata is considered an invasive shrimp in the Atlantic Ocean and some characteristics might have contributed to its invasive success, such as its larval nutritional vulnerability during the early stages of development. The objective of this study was to evaluate the early larval stages of the shrimp L. vittata. Ovigerous specimens were captured in an estuarine region of north-eastern Brazil. Zoeae were assigned to two experiments: (1) the point of no return (PNR), consisting of treatments with an increasing number of days of starvation and subsequent days of feeding; and (2) the point of reserve saturation (PRS), consisting of treatments with an increasing number of days of feeding and subsequent days of starvation. Two control groups were considered: continuous starvation (CS) and continuous feeding (CF). Nutritional vulnerability was estimated by the time when 50% of the initially starved larvae (PNR50) lost the ability to moult to the next stage, when 50% of the initially fed larvae (PRS50) were capable of moulting to the next stage. In the CF, the mean development time (±SD) of the larvae that reached stage III was 4.36 ± 0.74 days with a mortality of 70%, and the mean carapace length (±SD) was 0.61 ± 0.04 mm CL. The PNR50 and PRS50 were 2.42 ± 0.14 and 1.32 ± 0.83 days, respectively. The nutritional vulnerability index (PRS50/PNR50 = 0.54) indicates that L. vittata presents intermediate dependence on exogenous food during the early larval stages, which might help our understanding of the invasive potential of this species in the Atlantic Ocean.

Impacts of nutritional stress on the survival and developmental time to metamorphosis in megalopa larvae of the exploited mangrove crab, Ucides cordatus (Ucididae)

ABSTRACTTemporal variation in food availability may affect the early life-history stages of many decapod crustaceans in the pelagic environment. Here, we investigated whether temporary food restrictions affect the survival and developmental period in the last larval stage (i.e. megalopa) of the mangrove crab Ucides cordatus. We further examined whether the prior nutritional history experienced during the megalopal life affects the body size (carapace width) of the first juvenile crab stage of this species. Megalopae were subjected to five different periods (1, 3, 5, 7, and 9 days) of initial starvation followed by constant feeding (‘Point of No Return’ experiment), or initial feeding with subsequent food deprivation (‘Point of Reserve Saturation’ experiment). They were also starved or fed (Artemia sp. nauplii) constantly in two control groups. Our results showed that U. cordatus megalopae may tolerate only one day without food, but need to feed for at least three, five or seven days at the beginning of their development to avoid a significantly lower survival and/or a delay in larval metamorphosis when compared to larvae fed constantly. However, megalopae initially fed from one to seven days may produce juveniles of smaller body size than those larvae fed for nine days or constantly.

Nutritional vulnerability in zoeal stages of the yellowline arrow crab Stenorhynchus seticornis (Brachyura: Majoidea)

Knowledge of the critical points in larval stages is essential to evaluate the physiological state of the larvae in their natural environment. This study investigated the nutritional vulnerability index (NVI) of the first (ZI) and second (ZII) zoeal stages of Stenorhynchus seticornis. Zoeae were assigned to two experiments: (1) point of no return (PNR), consisting of treatments with increasing days of starvation and subsequent days of feeding; and (2) point of reserve saturation (PRS), consisting of treatments with increasing days of feeding and subsequent days of starvation. There were two control groups: continuous starvation (CS) and continuous feeding (CF). Mortality was used to estimate the time when 50% of initially starved larvae (PNR50) lost the ability to moult to the next stage and when 50% of initially fed larvae (PRS50) were capable of moulting to the next stage. The mean (±s.d.) development time of ZI and ZII under CF was 4.4±1.2 and 5.1±1.8 days respectively. Mortality in the CF groups was 30 and 52% for ZI and ZII respectively. For ZI, PNR50 and PRS50 were 1.0±0.0 and 2.1±1.0 days respectively. The estimated NVI for ZI was 2.2, which indicates that S. seticornis depends on exogenous food and is considered planktotrophic during the first larval stage.

Effects of temporary starvation and feeding on the survival and developmental time to metamorphosis in megalopa larvae of two Neotropical mangrove crab species, genus Sesarma (Sesarmidae)

Temporal variation in pelagic food supply may affect the larval development and recruitment success of many decapod crustaceans in marine coastal ecosystems. In the present study, we experimentally investigated the degree of nutritional vulnerability in megalopa larvae of two sesarmid crab species (Sesarma curacaoense and S. rectum) subjected to different conditions of nutritional stress. In the laboratory, Sesarma megalopae were initially starved for up to 9days followed by a constant feeding period in one experiment (i.e., point of no return), or they were fed at the beginning of their development for up to 9days followed by a continuous period of food deprivation in a second experiment (i.e., point of reserve saturation). Megalopae were also constantly reared in the absence and presence of food (Artemia sp. nauplii) in two control groups. The larval response to the different experimental conditions was evaluated through the percentage of survival (=% metamorphosed larvae), developmental time to metamorphosis, and Nutritional Vulnerability Index (= PRS50/PNR50). All megalopae died when reared under constant starvation whereas 100% of the larvae metamorphosed into the first juvenile crab stage after 13.1±4.4days (S. curacaoense) or 12.4±1.2days (S. rectum) when continuously fed. In the first experiment, the starvation periods did not affect the mean developmental time of the megalopae through metamorphosis (13.6±4.3days) of S. curacaoense and only those larvae initially starved for 7days presented the lowest percentage of metamorphosis to juvenile crab (73%). In S. rectum, by contrast, megalopae starved from 5 to 9days exhibited lower percentages of metamorphosis (≤86%) compared to larvae starved for 1 or 3days or those constantly fed. Furthermore, megalopae starved for 7 and 9days delayed by 1.6 and 3.5days their metamorphosis, respectively, compared to larvae constantly fed. In the second experiment, the Sesarma megalopae initially fed for only 1day presented lower percentages of metamorphosis (≤73%) than megalopae fed for 3 or more days or continually (≥93%). The mean developmental time to metamorphosis was shorter with 1day (8.1±0.7days in S. curacaoense) or 3days (11.3±1.6days in S. rectum) of temporary feeding. The estimated values of the PNR50 and PRS50 indices were respectively 7.34 and 0.93days for S. curacaoense and 9.01 and 1.78days for S. rectum. These values provided a Nutritional Vulnerability Index of 0.13 for S. curacaoense and 0.2 for S. rectum, indicating a reduced dependence on exogenous food by the megalopae of these two sesarmid crab species. This starvation tolerance associated with a short megalopal development should increase the likelihood of successful survival into the benthic life phase and avoid latent effects of the larval nutritional stress and/or delayed metamorphosis on early juvenile performance of both Sesarma species.

Effect of starvation on the nutritional condition of early zoea larvae of the red squat lobster Pleuroncodes monodon (Decapoda, Munididae)

One of the key factors affecting larval survival is food availability. This study investigated the influence of starvation on the nutritional condition of zoea I larvae of Pleuroncodes monodon. Experimental treatments with differential periods of starvation and subsequent feeding (point of no return: PNR) in addition to treatments with differential periods of feeding and subsequent starvation (point of reserve saturation: PRS) were used to quantify larval survival and the occurrence of lipid droplets in the hepatopancreas. Larval survival differed significantly depending on the starvation and feeding treatment administered. A high percentage of survival was found for the starvation treatment until day 1 (S1-PNR), for the feeding treatment until day 4 (F4-PRS), and for the continuously fed control groups (FC). Survival was minimal for the starvation treatment lasting until day 7 (S7-PNR) and for the continuously starved control groups (SC). In turn, similar tendencies were observed in the utilization of energy reserves; the lipid droplets significantly decreased throughout the PNR treatment, while the presence of lipid droplets gradually increased during the PRS treatment. All these larval condition parameters can be used in fishery models of population dynamics, which estimate the nutritional status of the offspring and their effects on survival.

Development and functional morphology of the mouthparts and foregut in larvae and post-larvae of Macrobrachium jelskii (Decapoda: Palaemonidae)

The morphology of the mouthparts and foregut of the larvae and post-larvae of Macrobrachium jelskii was investigated to determine their functional roles in feeding, in order to understand the larval feeding behaviour and the changes that occur during its development. The mouthparts and foregut of the zoea I and II are morphologically similar, rudimentary and non-functional in feeding. Only in the final larval stage, zoea III, do the external mouthparts and foregut become structurally more complex and thus likely to play a potential role in feeding. Two behavioral trials (point of no return, point of reserve saturation) evaluated the resistance to starvation in zoea I, II, and III. The results indicate that they have sufficient nutritional reserves to permit them to complete metamorphosis without feeding. Overall, our results suggest that the zoea I and II of Macrobrachium jelskii engage in obligate lecithotrophy and zoea III in facultative lecithotrophy.

Nutritional vulnerability of early zoea larvae of the crab Maja brachydactyla (Brachyura, Majidae)

We investigated the nutritional vulnerability of Zoeae I of the spider crab Maja brachydactyla in experimental treatments with differential periods of starvation. As response vari- ables, the moulting and survival rates, the point-of-reserve-saturation (PRS), the point-of-no- return (PNR), dry mass, elemental composition (carbon, hydrogen, nitrogen; CHN), hepatopan- creas lipid vacuoles and activities of digestive enzymes were measured. Average median time spans when 50% of the larvae reached PNR or PRS (PNR50 and PRS50) values were 2.8 and 1.9 d, respectively. In PNR treatments, complete mortality occurred only after extended initial starvation periods of ≥5 d, and in PRS treatments, Zoeae I were capable of completing the moulting cycle after a short initial feeding period (1 d). In continuously starved control larvae, the moulting cycle was arrested at the onset of apolysis. Concomitantly, considerable amounts of biomass were lost and the C:N ratio decreased, indicating lipid degradation during starvation. This effect was also microscopically visible as a decline of lipid vacuoles in the hepatopancreas. Feeding after previ- ous starvation periods of <7 d resulted in a re-establishment of the lipid vacuoles, indicating suc- cessful capture and ingestion of food, but this did not necessarily allow for completing the moult- ing cycle. In fed Zoea I larvae, digestive enzyme activities increased during the moulting cycle, while a significant decrease of enzyme activities occurred under starvation conditions. In newly moulted Zoeae II, biomass values and enzyme activities were linearly correlated with the duration of the feeding periods in Zoeae I. This study shows that biomass, elemental composition, the occurrence of lipid vacuoles in the hepatopancreas and activities of digestive enzymes are suitable indicators of the nutritional condition of early zoeal stages of M. brachydactyla.

Starvation resistance and metabolic response to food deprivation and recovery feeding in Fenneropenaeus chinensis juveniles

Starvation resistance in the juveniles of Chinese shrimp, Fenneropenaeus chinensis Osbeck, was studied by point-of-no-return (PNR) and point-of-reserve-saturation (PRS) experiments. Changes in oxygen consumption rate, ammonia-N excretion rate, and oxygen consumed to nitrogen excreted (O:N) ratio were investigated immediately before and after the period of recovery feeding for each regime to assess metabolic response during starvation and refeeding. There was a significant change in survival rate and wet weight of test shrimp throughout the PNR and PRS experiments (P < 0.05). The estimated PNR and PRS for F. chinensis juveniles could be directly calculated from the selected equations as PNR50 = 7.86 days, PNR100 = 21.42 days, PRS0 = 1.16 days, and PRS50 = 11.75 days. A decrease in metabolic rate during starvation as a means of conserving energy was found in F. chinensis juveniles. Furthermore, although F. chinensis juveniles only utilized protein as an energy source during starvation, they showed a shift from pure protein during starvation to an equal utilization of protein and lipid or a lipid-carbohydrate mixture during later satiate feeding. The results in the present study indicate that F. chinensis juveniles have the ability to withstand and recover from relatively prolonged starvation after longer initial feeding periods. The knowledge derived from the understanding of starvation resistance and the corresponding metabolic response of F. chinensis juveniles will be useful in the design of feeding regimes in this species.

Effect of starvation during late megalopa stage of Mithraculus forceps (Brachyura: Majidae) on larval duration, synchronism of metamorphosis, survival to juvenile, and newly metamorphosed juvenile size

Larval resistance to temporary starvation is considered a key factor for successful development in the wild. Subjecting larvae to temporary starvation during early and/or late development is occasionally used in larviculture to reduce production costs.Mithraculus forceps is a popular species in the marine aquarium industry for their ability to control nuisance algae in aquarium tanks; a larval culture methodology was previously proposed in order to avoid collection from the wild. In an attempt to reduce production/feeding costs of M. forceps larval culture (two zoea stages and a megalopa), larvae (megalopa stage) were starved after 7 and 8 days post-hatch (DPH); starvation treatments were compared with those of the control treatment where larvae were fed continuously. No differences were found in survival to juvenile, metamorphosis synchronism or larval duration between the treatments, which suggest that at least by day 7 DPH, megalopae have already achieved the point-of-reserve-saturation (PRS) and are able to successfully metamorphose to crab stage without feeding (facultative lecithotrophic); newly metamorphosed juveniles are slightly smaller (particularly the ones starved after 7DPH). This flexible way of development might be very advantageous in the wild and might allow the reduction of costs of larval culture in captivity.

Effects of prehatching salinity and initial larval biomass on survival and duration of development in the zoea 1 of the estuarine crab, Chasmagnathus granulata, under nutritional stress

The effects of individual larval biomass, and salinity experienced during embryogenesis (i.e., prehatching salinity) on starvation tolerance and growth of zoea 1 of the estuarine crab ( Chasmagnathus granulata) were evaluated in laboratory experiments. Freshly hatched zoeae 1 were obtained from broods maintained at three salinities (15‰, 20‰ and 32‰), and cultured at 20‰ under different initial feeding periods and subsequent food deprivation (“point of reserve saturation” experiment: PRS) or under initial periods of food deprivation and subsequent feeding (point of no return experiment: PNR). Another group of larvae were used for determination of biomass (dry weight, carbon, and nitrogen) of zoea 1. Larval survival and duration of development depended on the length of feeding period: no larvae reached the second instar under complete starvation; survival was higher and duration of development shorter as the feeding period lengthened. After different initial feeding periods (PRS experiment), zoeae 1 that hatched from eggs incubated at the prehatching salinities of 15‰ and 20‰ showed higher survival and shorter duration of development than those at 32‰. Prehatching salinity also affected the amount of reserves accumulated during the first 2 days after hatching, with larvae from 15‰ and 20‰ showing the highest percentage of total accumulation of carbon and nitrogen. Initial larval biomass did not affect survival, but it had a slight effect on duration of development, with larger larvae (in terms of biomass) developing faster. After different initial starvation periods (PNR experiment), prehatching salinity did not affect survival, but it affected duration of development: larvae from 15‰ and 20‰ reached the second instar earlier. Variability in survival and duration of development was explained in part by among-brood variability in initial larval biomass: larvae with higher biomass showed higher survival and shorter duration of development. Thus, C. granulata, survival and duration of development under food stress depend on the interaction between environmental conditions experienced before and after hatching (pre- and posthatching factors, respectively).

Effects of starvation on intermolt development in Calanus finmarchicus copepodites: a comparison between theoretical models and field studies

Campbell et al . (Deep Sea Research II, 48 (2001) 531) have shown that there was a localized starvation event affecting Calanus finmarchicus on the southern flank of Georges Bank in April 1997. Growth and molting rates of this dominant copepod were reduced. We have used the morphology of tooth development in field-collected samples to show that this starvation affected animals living continuously in the field, as well as those in Campbell et al .'s experimental tanks. Assuming a point of reserve saturation (PRS) response of Calanus to food limitation, and correspondence between PRS and advance from the postmolt jaw facies, the proportion of individuals with postmolt jaws should increase in all copepodite stages under starvation. Individuals that have developed past PRS should molt to the next stage, acquiring postmolt facies. Thus, the fraction of postmolt jaws should increase, while the fraction of jaws in later phases should decrease. This was observed for a drifter-marked station over five days. Numerical simulations of jaw phase distributions expected under full nutrition, and both total and patchy starvation were generated from individual-based models of development. Proportions of copepodites in postmolt phase do not increase with full nutrition. A simulation of a total starvation event showed a marked increase in postmolts during food limitation, but the increase was more extreme than the field data. A modification of the starvation simulation, representing patchy feeding conditions, matched the level of increase of postmolt individuals in all stages that was observed in the field samples.

Efecto de períodos de ayuno en el crecimiento de la zoea I de Petrolisthes violaceus (Guérin, 1831) (Decapoda: Anomura: Porcellanidae)

The present study describes consequences of starvation upon growth (wet and dry weight) and survival of zoea I - larvae of Petrolisthes violaceus, a common species of the Chilean intertidal belt. The experimental design included five groups (1-5 days after hatching without food, respectively) as well as one starvation treatment and one control (larvae were fed daily). Food (Artemia franciscana) consisted in 15 nauplii per ml. Temperature was kept at 19°C and salinity at 34/oo.The larvae which were fed daily achieved the highest biomass increase, gaining 94.7% of its initial dry weight. In other experiments (2-5 days of initial feeding) a slight biomass increase was observed. Larvae fed only one day and those under starvation conditions lost biomass: starved larvae a continuos biomass decrease up to 18.9% of its initial dry weight. The Point of Reserve Saturation was at 4 days. The first zoeal stage of P. violaceus demostrated a low starvation resistance, since zoea I was not capable to complete the molt cycle in the absence or with brief periods (1-3 days) of food. Furthermore, larvae molted only when they inceased their initial body weight by more then half (55.4%). Our results suggest that larvae of P. violaceus possess a high capacity of assimilation since they start loosing biomass not before two days of starvation.This capacity may permit to compensate the biomass loss caused by food deprivation.

Starvation resistance in larvae of a semiterrestrial crab, Sesarma curacaoense (Decapoda: Grapsidae)

Starvation resistance in the larvae of a semiterrestrial grapsid crab, Sesarma curacaoense De Man, 1892, was studied by point-of-no-return (PNR) and point-of-reserve-saturation (PRS) experiments. S. curacaoense shows an abbreviated larval development (only two zoeal stages) and a high degree of lecithotrophy. In complete absence of food, larval development is possible from hatching to the megalopa stage. Thus, no PNR or PRS can be given for individual zoeal stages of this species. However, late effects of early starvation indicate that lecithotrophy is only facultative in S. curacaoense zoeae: food is not essential but will be eaten when available. The endotrophic potential decreases from the first to the last larval stage: while the zoea I is entirely independent of external food sources, the zoea II shows increasingly delayed development after increased periods of initial food deprivation, and the megalopa can develop independent of food only if the preceding zoeal stages were fed continuously. Besides ontogenetic changes, significant variability was observed also in starvation resistance of larvae originating from different females. In an experiment with a particularly starvation-resistant hatch, development in the zoea II was accelerated during continuous lack of food or when starvation followed brief initial feeding periods. This effect was interpreted as a mechanism which should be specific to facultative lecithotrophy: starvation may induce a change in energy partitioning, from a preference for growth (uptake and accumulation of additional energy reserves) to accelerated development (mobilization of internal reserves, rapid termination of the planktonic larval phase). Enhanced starvation resistance in S. curacaoense zoeae compared with that in most planktotrophic marine decapod larvae is considered an adaptation that allows for retention of the larvae within a nutritionally unstable environment where the adult populations live. These ontogenetic traits corroborate the assumption that S. curacaoense may be the closest relative of an ancestral Sesarma species from which adaptive radiation of endemic Jamaican freshwater and terrestrial crabs began.

Developmental biology of Armases miersii (Grapsidae), a crab breeding in supratidal rock pools. I. Facultative lecithotrophy of larval stages

Starvation resistance in the larvae of a grapsid crab, Armases miersii, that breeds in supratidal rock pools in Jamaica was examined by point-of-no-return (PNR) and point-of-reserve- saturation (PRS) experiments. A. miersii shows an abbreviation of larval development (only 3 zoeal stages) and a high degree of lecithotrophy in the zoea I and II stages. In complete absence of food, larval development is possible from hatching to the zoea III stage. The potential for endotrophic development decreases during ontogeny: the zoea I is, in principle, entirely independent of food, without significant effects of starvation on survival; the zoea II shows significantly higher mortality under continued lack of food (since hatching) and delayed development after initial temporary starvation; the zoea III can also develop independently of food, but only if the preceding stages were fed continuously. Hence, no PNR or PRS can be given for individual zoeal stages of this species. Late effects of early feeding or starvation indicate that lecithotrophy in A. miersii is only facultative, i.e. food is not essential in the beginning of larval life, but it will be taken up when available. Conspicuous intraspecific variability in the degree of lecithotrophy was observed in larvae originating from 2 different females. In a hatch with particularly high endotrophic potential (but not in nutritionally more vulnerable larvae), development was significantly faster under starvation. This effect is interpreted as a change in energy partitioning: lack of food may induce a signal for switching from growth (accumulation of exogenous energy) to rapid mobilization of internal reserves (accelerated development, termination of the nutritionally vulnerable planktonic larval phase). Feeding after initial starvation may cause inverse effects, i.e. slower development, replacement of utilized reserves, and accumulation of additional energy for later stages. This switching should occur only in facultatively lecithotrophic larvae that have sufficient internal energy reserves to allow for this opportunistic bioenergetic strategy. Compared with most planktotrophic marine decapod larvae, the zoeal stages of A. miersii show higher starvation resistance and endotrophic potential. These ontogenetic traits are considered adaptations to breeding and larval development in a short-lived, nutritionally unpredictable habitat.

Nutritional requirements and starvation resistance in larvae of the brachyuran crabs Sesarma cinereum (Bosc) and S. reticulatum (Say)

Nutritional requirements during zoeal development of Sesarma cinereum (Bosc) and S. reticulatum (Say) were compared. Both species were raised in the laboratory from hatching to the megalopa on two diets: Artemia nauplii and the rotifer Brachionus plicatilis Muller. Although both species demonstrated a delay in development when fed rotifers, only S. cinereum showed greatly reduced survival. Continuously starved S. cinereum zoeae died during the first zoeal stage, while 17.5% of S. reticulatum larvae successfully molted to Z 2 under starvation conditions. We examined starvation resistance in the Z 1 of S. cinereum and the Z 1 and 3 (terminal zoea) of S. reticulatum by pount-of-no-return (PNR) and point-of-reserve saturation (PRS) experiments. The greater starvation resistance in S. reticulatum is correlated with significantly higher lipid content in their larvae as compared to S. cinereum larvae. The high ndegre of “nutritional flexibility” shown by developing S. reticulatum larvae may be related to other life history traits that characterize its abbreviated larval development.

The D 0 threshold: a critical point in the larval development of decapod crustaceans

In prior studies, critical points have been found in the interaction between exogenous (food) and endogenous (hormonal) control of the larval development of decapod crustaceans. One of them was termed “point of reserve saturation” (PRS). If it has been passed under conditions of sufficient availability of food, decapod larvae may complete their moulting cycle and develop, independent of food, to the next instar. In the present investigation the PRS and the moulting cycle were studied simultaneously in first instar larvae of nine decapod species belonging to eight families and four higher taxa (Caridea, Macrura, Anomura, and Brachyura). The experimental results suggest that the PRS was in general near the transition between stages C and D 0 of Drach's classification system, independent of the species, instar duration, and temperature. When temperature was kept constant throughout the experiment, the critical point was reached after one third to one half of total time of first instar development. If postmoult and intermoult (stages A–C) were prolonged by lower initial temperature, the PRS was delayed but found again near the C D 0 transition. If starvation began before the PRS, the reserves accumulated from food did not allow successful development to the second instar. Depending on the time of initial feeding, the moulting cycle was arrested at one of the two following critical points 1. (1) immediately before or at the beginning of premoult (late C-early D 0) 2. (2) immediately before or at ecdysis (D 3-E). The developmental periods from stage A through C and from D 0 to D 3 or D 4 were potentially autonomous sequences. These results corroborate the hypothesis that critical points in development of decapod larvae exist and can be characterized by distinct morphological and hormonal conditions. One of them is the “D 0 threshold”, the other may be termed “exuviation threshold”. Suspension of the moulting cycle by lack of food is much less likely in all other moulting stages. Frequent exceptions to this rule were found only in lobster Homarus gammarus L. larvae, in which the critical points may be less fixed. The probable basis of the D 0 threshold is discussed, and it is suggested that a threshold concentration of sterols or other essential substances accumulated from food sets the PRS and thus initiates potentially autonomous development through the premoult stages of the moulting cycle.

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.

Relative accuracy of some methods of harmonic analysis of tides : Dos Santos Franco A., 1965. Int. Hydrogr. Rev., 42 (2): 149–158.

In prior studies, critical points have been found in the interaction between exogenous (food) and endogenous (hormonal) control of the larval development of decapod crustaceans. One of them was termed “point of reserve saturation” (PRS). If it has been passed under conditions of sufficient availability of food, decapod larvae may complete their moulting cycle and develop, independent of food, to the next instar. In the present investigation the PRS and the moulting cycle were studied simultaneously in first instar larvae of nine decapod species belonging to eight families and four higher taxa (Caridea, Macrura, Anomura, and Brachyura). The experimental results suggest that the PRS was in general near the transition between stages C and D0 of Drach's classification system, independent of the species, instar duration, and temperature. When temperature was kept constant throughout the experiment, the critical point was reached after one third to one half of total time of first instar development. If postmoult and intermoult (stages A–C) were prolonged by lower initial temperature, the PRS was delayed but found again near the CD0 transition. If starvation began before the PRS, the reserves accumulated from food did not allow successful development to the second instar. Depending on the time of initial feeding, the moulting cycle was arrested at one of the two following critical points 1.(1) immediately before or at the beginning of premoult (late C-early D0)2.(2) immediately before or at ecdysis (D3-E). The developmental periods from stage A through C and from D0 to D3 or D4 were potentially autonomous sequences. These results corroborate the hypothesis that critical points in development of decapod larvae exist and can be characterized by distinct morphological and hormonal conditions. One of them is the “D0 threshold”, the other may be termed “exuviation threshold”. Suspension of the moulting cycle by lack of food is much less likely in all other moulting stages. Frequent exceptions to this rule were found only in lobster Homarus gammarus L. larvae, in which the critical points may be less fixed. The probable basis of the D0 threshold is discussed, and it is suggested that a threshold concentration of sterols or other essential substances accumulated from food sets the PRS and thus initiates potentially autonomous development through the premoult stages of the moulting cycle.