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The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (44000 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.

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.

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We investigated the nutritional vulnerability of Zoeae I of the spider crab Maja brachydactyla in experimental treatments with differential periods of starvation. As response variables, the moulting and survival rates, the point-of-reserve-saturation (PRS), the point-of-noreturn (PNR), dry mass, elemental composition (carbon, hydrogen, nitrogen; CHN), hepatopancreas lipid vacuoles and activities of digestive enzymes were measured. Average median time spans when 50% of the larvae reached PNR or PRS (PNR 50 and PRS 50 ) 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 previous starvation periods of < 7 d resulted in a re-establishment of the lipid vacuoles, indicating successful capture and ingestion of food, but this did not necessarily allow for completing the moulting 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.

Pleuroncodes monodon, an important fishery resource and key species in the Humboldt Current Large Marine ecosystem, has a prolonged reproductive period from winter until end of summer, and during this time females incubating their embryos are exposed to seasonal variation in food availability and in temperature. Additionally, in order to ensure successful reproduction and survival of embryos, changes occur in the main internal reserves and/or sources of energy of P. monodon. The aim of this study was to determine the extent of seasonal variation (winter vs summer) in the lipid content and fatty acid composition of ovigerous females and their embryos. The results show that a higher percentage of saturated and polyunsaturated fatty acids are found in females in winter. Similarly, the composition of fatty acids in embryos found here indicates that winter embryos have more saturated fatty acids and essential fatty acids (C18:2n6cis, C18:3n6 and C22:6n3) than do summer embryos. According to PCA analysis of fatty acid profile, samples from summer may be distinguished into two isolated groups with conspicuous variations in fatty acids profile of embryo and hepatopancreas. While in winter, the opposite pattern occurs in the fatty acid profile of embryo and hepatopancreas. These variations may be related to relevant physiological processes (reproduction and growth) and of their ontogeny (development and survival of offspring). Seasonal variation in the lipid content and composition of fatty acids of P. monodon could directly impact this species’ reproduction and survival and subsequently could have consequences on the food web and fishery exploitation.

Pleuroncodes monodon is an important fishery resource and key species from the Southeastern Pacific. During its prolonged reproductive period (from February to December), ovigerous females are exposed to seasonal variation in environmental factors (e.g. temperature and food availability), with higher levels of these environmental parameters during summer and lower in winter, and must adjust their biochemistry to ensure their own survival and that of their embryos. The aim of this study was to analyse seasonal changes in the biochemical composition of ovigerous females and their eggs. The data show that the content of lipids, proteins and organic matter in the hepatopancreases of females was significantly higher in winter than in summer.Similarly, the lipid content of the eggs was significantly higher in winter than in summer, yet the protein content of the eggs had the opposite pattern with greater values found in summer. Consistent with the 'reproductive energetic model', the initial and final energy produced by the hepatopancreas showed significant seasonal variations, whereas female investment in egg production (in absolute values) did not show significant seasonal differences. The seasonal differences observed in the biochemistry, organic matter and energy content of the female hepatopancreases may be related to the storage of energy for growth and reproduction. Furthermore, the seasonal variation in the content of lipids, proteins and energy in eggs is likely related to embryogenesis and larval hatching in function with environmental conditions. Seasonal variation in the biochemical composition of P. monodon has direct effects on the marine food web and also upon fisheries.

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