The life history and ecological energetics of Neomysis integer (Leach) (Crustacea, Mysidacea)
A survey of the literature revealed the limited quantitative information on the food requirements and food partitioning by mysids. An investigation combining field and laboratory studies was carried out in an attempt to construct energy budgets for the entire life span of Neomysis integer. A population of N. integer in the Ythan estuary, Aberdeenshire, was sampled regularly and analysed during 1977-1978. N. integer in the Ythan has two distinct generations each year; a summer generation which is born in the spring and breeds during the summer and a winter generation which is born during the summer, remains immature through the winter, and breeds in the spring. The main breeding period of N. integer was between April and September. The fecundity of females was related to their length but several other factors (e.g. season, generation) also affect fecundity. Mortality or loss of up to 25% of eggs initially laid in the marsupium was estimated to occur during development. Many N. integer were heavily infested by a colonial protozoa Zoothamnium sp. Several animals were found to be infected by a parasitic nematode Thynnascaris adunca. An unidentified algae found growing on N. integer is also described. Linear relationships were established between; 1) moult uropod length and body length; 2) log body length and log dry weight. These enabled length and dry weight to be estimated from moult measurements. The growth rate of N. integer maintained in the laboratory on a diet of Artemia nauplii was found to be 0.06 mm/day and 0.09 mm/day at 9°C and 16°C respectively. In terms of dry weight the growth was 0.02 mg/day and 0.03 mg/day at 9°C and 16°C respectively. Linear relationships were calculated between body length and log growth factor. Percentage growth factors decreased with animal length but were not affected by temperature. Growth factors ranged from approximately , 14% in juveniles to approximately 3% in adult animals. Linear relationships were calculated between body length and log intermoult period. Duration of the intermoult periods of N. integer increased with animal length but decreased with temperature. Intermoult periods were 4-8 days and 12-16 days for juveniles and adult animals respectively. x Laboratory growth curves were calculated for N. integer and compared to those constructed from field samples. 12. Linear relationships were calculated between log dry weight and log oxygen consumption of Nointeger. The oxygen consumption of similar size animals was found to be higher in summer than in winter. This is discussed in relation to the life history of N. integer. 13. N. integer feeds at high intensity throughout the year, and no seasonal changes were observed in its diet. Detritus, sand grains and harpacticoid copepods appeared most important by volume. 14. The log food intake of N. integer was linearly related to the log of its dry weight. Food intake was affected by temperature. Juveniles and adult animals consumed daily 10-18% and 6-9% of their dry weight respectively. Food intake decreased when animals were about to moult. 15. N. integer appears to search for prey (Artemla nauplii) until it has obtained its maximum ration. If available prey is less than its maximum ration N. integer was able to locate and capture almost all available prey, both in 500ml and 51 experimental volumes. 16. Preliminary filter feeding experiments on 5 species of cultured algae suggested that only when feeding on one species (Cricusphaera oblongata) was N. integer meeting all its metabolic requirements. 17. The dry weight of a moult of N. integer was linearly related to the dry weight of the animal which shed the moult. Moults of juveniles and adult animals weigh about 8% and 10% respectively of the dry weight of the animals which produced them. The calorific values of N. integer showed little seasonal changes; annual mean calorific value of females (4.75 cal/mg dry wt) was significantly greater than that of males (4.62 cal/mg dry wt). The calorific value of moults was 1.28 cal/mg dry wt. 19. The assimilation efficiency of N. integer was calculated to range between 57-65%. 20. To meet its life requirements N. integer ingests approximately 305 and 372 calories at 9°C and 16°C respectively. 21. Energy budgets constructed for the entire life span of N. integer were similar at both 9°G and 16°C; of assimilated food energy 14% was used for growth, 10% for egg production, 3% was lost as moults, 50% was used for respiration and 24% was presumed to be excreted in soluble form. 22. Log gross growth efficiency (%) decreased linearly with weight (expressed as calories). Gross growth efficiency ranged from 20--25% in juveniles to 4-9% in adult animals. 23. All results have been discussed in relation to available information on other mysids or similar size Crustacea.