Effects of oxygen, temperature and age on the metabolic rate of the embryos and early larval stages of the Antarctic krill Euphausia superba Dana

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During their developmental descent and ascent, the embryos and early larvae of the Antarctic krill Euphausia superba Dana encounter a range of temperatures and partial pressures of oxygen. Oxygen consumption rates of known age embryos and early larvae were measured at 0 ° C and at partial pressures ranging from 90 to 0% of air saturation. Four of the five stages of embryos (single cell, multiple cell, gastrula, and limb bud) and the larval stages (Nauplius I, Nauplius II, Metanauplius, and Calyptopis 1, the first feeding stage) regulated their oxygen uptake down to 7.3 kPa. Younger stages of embryos and larvae were able to regulate oxygen uptake at lower partial pressures of oxygen than older stages. Embryos close to hatching (twitch) were not good regulators. The oxygen consumption rates of the developing embryos and larvae usually will be independent of the partial pressure of oxygen in the environment. The pattern of oxygen consumption with age was similar to that of many fish: a low respiration rate at fertilization, increasing slowly until the embryos hatch, then a sharp increase at hatching when the larvae begin to swim, with a two-fold variability between the oxygen consumption rates of larvae of the same stage and age determined in different experiments. Embryo metabolism was only 3.45% of the total metabolic demand of all the non-feeding stages. Thus, most of the lipid reserves can be passed on to the larvae for use during development to the first feeding stage. Only the larvae were used in experiments to determine the effect of temperature on oxygen consumption rates. Experimental temperatures were −1,0, and 2 ° C, spanning nearly the full range of temperatures that the larvae encounter in the environment during early development. The effect of temperature on oxygen consumption was not linear. Oxygen consumption rates for the same age or stage larvae at 0 and 2 ° C were the same, and much higher than those at −1 ° C. The metabolism-temperature response suggests that oxygen consumption rates are temperature independent for the Calyptopis 1 larvae in the surface waters, where temperatures are usually > 0 ° C during the summer when these larvae appear.