Description: The Amazon River prawn, Macrobrachium amazonicum (Heller 1862), has an extremely large geographic range, comprising estuarine and fully limnic inland populations, which are hydrologically (and thus also genetically) isolated from each other. Significant variations in adult ecology, physiology, sex-specific growth, and reproduction suggest an at least incipient speciation. The biology of populations from central Amazonia and from the Atlantic and Caribbean coasts of South America has been studied both in the field and laboratory, while next to nothing is known about the life history of populations living in the upper La Plata (Paraguay and Paraná) river system. In an experimental investigation with shrimps from the Pantanal (upper Paraguay basin, southwestern Brazil), we quantified larval biomass and biochemical composition at hatching, and studied patterns of early larval feeding and growth. Unlike the larvae from the Amazon estuary, those from the Pantanal can successfully develop in freshwater, although slightly brackish conditions (5 ) are more favourable. In both populations, the larvae hatch with conspicuous fat reserves remaining from the egg yolk, the first zoeal stage (Z I) is completely non-feeding, the Z II is facultatively lecithotrophic, and the Z III still shows a strong tolerance of food limitation. However, Pantanal larvae survived in complete absence of food (at constant 29°C) for maximally 8-9 d, while estuarine larvae died only after 14-15 d, in some cases successfully developing even the Zoea IV stage. These patterns of early larval starvation tolerance are in contrast to inverse differences in larval size and dry mass (W) at hatching. Pantanal larvae were on average larger (3.3 vs 2.6 mm body length), showing also significantly higher W (79 vs 58 µg) and higher contents of C (39 vs 29 µg), N (8.7 vs 5.8 µg), and protein (30 vs 20 µg) per individual. On the other hand, the difference observed in larval starvation tolerance is congruent with a significantly lower lipid content at hatching in the Pantanal larvae (9 vs 15% of dry mass, W). Within their lipid fraction, they showed a higher percentage of unsaturated fatty acids (typical of structural lipids), while estuarine larvae contained larger amounts of saturates (typical energy reserves). The moulting pattern through the early larval stages (Z I-VI) is in both populations a linear function of time (with ecdyses on average every 2 d), but the pattern of increase in W (an exponential function of the number of moults) indicates a much steeper growth rate in the Pantanal larvae compared to those from the Amazon estuary. Our lipid data indicate that the early larval stages of an estuarine population are well adapted to conditions of food limitation, which should occur during the downstream transport towards coastal marine waters. The Pantanal larvae, by contrast, develop in highly productive lentic inland waters, where large body size and a strong musculature (indicated by high protein contents) should facilitate their role as planktonic predators, allowing for fast growth. Initial independence from food as well as a preference for oligohaline conditions may be interpreted as ancestral traits that have persisted in this limnic clade with presumably coastal marine origin. Altogether, consistent ontogenetic differences between shrimps originating from inland and estuarine waters, respectively, are hardly compatible with the population concept, suggesting that M. amazonicum represents a complex of closely related, but separate species.

Description: The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (〉4000 km across) in northern and central South America, comprising estuarine and fully limnic inland populations, which are hydrologically isolated from each other. Significant variations in ecology, physiology, reproduction, and larval development suggest an at least incipient allopatric speciation due to limited genetic exchange. In a comparative experimental investigation with shrimps from the Pantanal (upper Paraguay River basin) and the Amazon delta, respectively, we measured larval body size, dry weight (W), biochemical (total protein; lipid; fatty acids, FA), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN) at hatching. All these early larval traits are relevant for the degree of developmental dependence on planktonic food sources. Various consistent differences were observed between the two populations: Newly hatched larvae produced by shrimps from the Amazon delta were significantly smaller and showed lower values of W, CHN, protein, and unsaturated FA compared to those from the Pantanal. On the other hand, they contained significantly higher quantities of total lipid and saturated FA and, in consequence, higher ratios of lipid:protein, C:N, and saturated:unsaturated FA. All these differences in biomass and chemical composition suggest that the larvae of the Amazon population are energetically better adapted to planktonic food limitation, which likely occurs during riverine downstream transport toward coastal marine waters, also explaining previous observations of much stronger initial starvation tolerance in larvae from the Amazon versus those from the Pantanal. The latter develop in highly productive lentic inland waters, where large body size, an early onset of feeding, and a strong musculature (indicated by a high protein content) should facilitate their role as planktonic predators and allow for fast growth. An initial independence from food (lecithotrophy in the zoea I stage) as well as a preference for oligohaline rather than fully limnic conditions observed in the Pantanal larvae are interpreted as traits that have persisted from an ancestral coastal marine clade. Altogether, consistent ontogenetic differences between shrimps from the Pantanal and the Amazon estuary support the hypothesis that the taxon M. amazonicum comprises a complex of closely related but separate species.

Description: The “brown shrimp”, Crangon crangon (Linnaeus 1758), is a benthic key species in the North Sea ecosystem, supporting an intense commercial fishery. Its reproductive pattern is characterized by a continuous spawning season from mid-winter to early autumn. During this extended period, C. crangon shows significant seasonal variations in egg size and embryonic biomass, which may influence larval quality at hatching. In the present study, we quantified seasonal changes in dry weight (W) and chemical composition (CHN, protein and lipid) of newly hatched larvae of C. crangon. Our data revealed significant variations, with maximum biomass values at the beginning of the hatching season (February–March), a decrease throughout spring (April–May) and a minimum in summer (June–September). While all absolute values of biomass and biochemical constituents per larva showed highly significant differences between months (P 〈 0.001), CHN, protein and lipid concentrations (expressed as percentage values of dry weight) showed only marginally significant differences (P 〈 0.05). According to generalized additive models (GAM), key variables of embryonic development exerted significant effects on larval condition at hatching: The larval carbon content (C) was positively correlated with embryonic carbon content shortly after egg-laying (r 2 = 0.60; P 〈 0.001) and negatively with the average incubation temperature during the period of embryonic development (r 2 = 0.35; P 〈 0.001). Additionally, water temperature (r 2 = 0.57; P 〈 0.001) and food availability (phytoplankton C; r 2 = 0.39; P 〈 0.001) at the time of hatching were negatively correlated with larval C content at hatching. In conclusion, “winter larvae” hatching from larger “winter eggs” showed higher initial values of biomass compared to “summer larvae” originating from smaller “summer eggs”. This indicates carry-over effects persisting from the embryonic to the larval phase. Since “winter larvae” are more likely exposed to poor nutritional conditions, intraspecific variability in larval biomass at hatching is interpreted as part of an adaptive reproductive strategy compensating for strong seasonality in plankton production and transitory periods of larval food limitation.

Description: Palaemonetes zariquieyi, an endemic palaemonid species of shrimp that lives in freshwater and brackish coastal habitats in eastern Spain, shows an abbreviated, non-feeding larval development comprising only three zoeal stages. To identify the endogenous bioenergetic fuel that allows for food-independent development from hatching to metamorphosis, larvae were reared under controlled laboratory conditions, and ontogenetic changes in dry weight (W), elemental (CHN), and lipid composition (total lipids, principal lipid classes, and fatty acids [FA]) were quantified at the onset of each zoeal stage and in the first juvenile. Values of W, C, and H per larva and per mass unit of W decreased throughout the time of larval development, while the N content showed only a weak decline (suggesting strong lipid but only little protein degradation). Correspondingly, directly measured values of total lipids (both in ?g/larva and in % of W) decreased gradually, with neutral lipids (NL) consistently remaining the predominant and most strongly used fraction; sterol esters and waxes were not detected. In contrast to the NL, the fraction of polar lipids (PL) per larva remained stable and, as a consequence, tended to increase as a percentage of total lipids. Likewise, other important lipid fractions such as free FA and cholesterol remained stable throughout the time of larval development. Among the FA, palmitic (16:0), oleic (18:1n?9), linoleic (18:2n?6), and eicosapentaenoic (20:5n?3) acid were predominant, showing a significant decrease during larval development; stearic (18:0), vaccenic (18:1n?7), and arachidonic acid (20:4n?6) were found only in small amounts. Our results indicate that the lecithotrophic development of P. zariquieyi is primarily fuelled by the utilization of lipids (especially triacylglycerides and other NL), which is reflected by a decreasing carbon content. Proteins and PL, by contrast, are preserved as structurally indispensable components (nerve and muscle tissues, cell membranes). The abbreviated and non-feeding mode of larval development of P. zariquieyi may have an adaptive value in land-locked freshwater habitats, where planktonic food limitation is likely to occur. The patterns of reserve utilization are similar to those previously observed in other palaemonid shrimps and various other groups of decapod crustaceans with lecithotrophic larvae. This suggests a multiple convergent evolution of bioenergetic traits allowing for reproduction in food-limited aquatic environments.

Description: The morphology of the first three zoeal stages of Hippolyte leptocerus (Heller, 1863) are described and illustrated in detail from laboratory-hatched material. The ovigerous females were collected on the Alfacs Bay, Ebro Delta, Spain (Western Mediterranean). The early larval stages (ZI, ZII, ZIII) showed the anterolateral margin of carapace with denticulations, a median tubercle behind rostrum, scaphocerite segmented distally (only ZI and ZII), exopodal seta at the maxillule and pleonite 5 with a pair of dorsolateral spines. The morphology of the first three zoeal stages of H. leptocerus is typical of species with an extended larval development. Morphological characteristics of the genus Hippolyte are discussed.

Description: The “brown shrimp”, Crangon crangon (Linnaeus 1758), is a benthic key species in the North Sea ecosystem, supporting an intense commercial fishery. Its reproductive pattern is characterized by a continuous spawning season from mid-winter to early autumn. During this extended period, C. crangon shows temporal variations in offspring size and biomass (Urzúa et al. 2012). Shrimps were periodically (January-September, 2009) sampled from a population living in the lower Elbe estuary, North Sea (54º03’-54º04’N; 8º18’-8º24’E; ca 13 m depth). In the laboratory, we quantified seasonal changes in dry weight (W) and carbon content (C) of early-stage eggs and newly hatched larvae. Relationships between biomass data and conditions of temperature and food concentration prevailing during the early life-history stages (oogenesis, embryogenesis, larval hatching) were analysed and modelled.Our data revealed significant seasonal variations, with maximum values of W and C at the beginning of the reproductive season (January), decreasing values throughout spring (April-May), minima in summer (June-August), and a slight increase thereafter. While the absolute values of biomass per offspring showed highly significant differences (P 〈 0.001), the relative composition (% W) remained similar throughout the reproductive period. According to generalized additive models (GAM), environmental factors affecting the early phases of the reproductive cycle exert significant effects on offspring condition: the C content per egg showed a highly significant negative relationship with day length (r² = 0.40; P 〈 0.0001), a weak positive relationship with temperature (r² = 0.09; P 〈 0.05), and a weak negative relationship with food availability (phytoplankton biomass; r² = 0.12; P 〈 0.05) at the time of beginning oogenesis. The C content per larva was positively correlated with the embryonic carbon content shortly after egg laying (r² = 0.60; P 〈 0.001) and negatively with the average incubation temperature during the period of embryogenesis (r² = 0.35; P 〈 0.001). Water temperature (r² = 0.57; P 〈 0.001) and phytoplankton biomass (r² = 0.39; P 〈 0.001) at the time of hatching were negatively correlated with larval C content at hatching. “Winter larvae” hatching from larger “winter eggs” showed higher initial values of biomass compared to “summer larvae” originating from smaller “summer eggs”. This indicates carry-over effects persisting from the embryonic to the larval phase. Intraspecific variability in larval biomass is interpreted as part of an adaptive reproductive strategy compensating for strong seasonality in plankton production and transitory periods of larval food limitation.