Notes: Abstract The dynamics of accumulation and loss of different physico-chemical forms of 106Ru were measured in the euphausiid Meganyctiphanes norvegica. The accumulation of 106Ru was directly related to the concentration of the radioisotope in solution, as evidenced by similar concentration factors for euphausiids in the “low” and “high” activity 106Ru chloride solutions. The chemical form of the radioisotope in solution had a pronounced effect on the uptake, with 106Ru chloride fractions being accumulated at a faster rate than 106Ru nitrosyl-nitrato complexes. Euphausiids lost 106Ru, previously accumulated from the 106Ru chloride complexes, at a faster rate than 106Ru which had been accumulated from 106Ru nitrosyl-nitrato forms. Also, in the case of the 106Ru chloride complexes, the loss rate was inversely proportional to the time allowed for isotope accumulation. The process of molting greatly accelerated the loss of 106Ru from euphausiids, with first molts shed during the loss phase accounting for 70 to 80% of the total 106Ru body burden. When euphausiids accumulated 106Ru from the food chain, the initial-loss rate was rapid due to large amounts of the radioisotope associated with fecal pellets; however, no relationship was found between loss rate and the number of food rations received. Molts from these individuals did not contain 106Ru, thus, loss from euphausiids obtaining this radioisotope through the food chain is mainly due to fecal pellet deposition and other excretion or exchange processes.

Notes: Abstract The effects of temperature and body size on the intermolt periods (molting frequencies) of the North Pacific euphausíid Euphausia pacifica and the Mediterranean forms of Meganyctiphanes norvegica, Euphausia krohnii, Nematoscelis megalops, and Nyctiphanes couchii were studied under controlled conditions in the laboratory. Mean intermolt periods for E. pacifica and M. norvegica were inversely and linearly related to temperature, over temperature ranges which the euphausiids normally encounter in the sea. At higher temperatures there was a tendency for three size groups of M. norvegica to approach a minimum intermolt period independent of temperature. M. norvegica cycled for different time periods between 13° and 18°C molted regularly at mean frequencies which would be expected if the animals had been held constantly at the timeweighted means of the two experimental temperatures. The increase in mean intermolt period per unit weight was faster in small, fast-growing M. norvegica than in large, slow-growing adults. This relationship was corroborated by following the changes in the intermolt period of an actively growing individual N. couchii over an 11 month period. Neither feeding nor the time of year of collection affected the molting frequency as long as temperature and animal weight were held constant. No tendency was found for euphausiids of the same species and/or size, and from the same collection, to molt on the same night. Molting occurred at night 80 to 90% of the time for all species, over the temperature ranges normally experienced by the euphausiids in the sea, and over all animal weights tested. There appeared to be a weakening of the night-time molting rhythm at low temperatures. Although neither temperature nor anímal weight substantially affected the night-time molting rhythm, both affected the mean intermolt period. Therefore, both temperature and body size apparently act together to adjust the length of the intermolt period of each individual in increments of whole days, but they exert little control over time of molting within any 24h period. No information was obtained regarding the factors which specify night-time molting over daytime molting within any 24 h period; however, regulation of certain hormone activities is probably involved.