Limits of Nematoscelis megalops in the northwestern Atlantic in relation to Gulf Stream cold core rings. II, Physiological and biochemical effects of expatriation

Abstract

Nematoscelis megalops, a cold water euphausiid commonly found in Northwestern Atlantic Slope Water, is frequently transported in the cores of Gulf Stream cyclonic rings into the Sargasso Sea. The inner core made of cold Slope Water gradually assumes physical and biological characteristics of the surrounding Sargasso Sea. These changes gradually lead to a localized extinction of this species in the core of the ring. Samples of N. megalops taken from the same ring at 6 and 9 months after its formation show a weakened physiological and biochemical condition. Deterioration of ring individuals is evidenced by an increase in body water content and a reduction in total body lipid, carbon, respiration rates, and nitrogen relative to Slope Water individuals. By 6 months it appears that ring N. megalops must supplement food intake by metabolizing some of their body protein and by 9 months they appear to use lipids as well. A shipboard starvation experiment involving 40 Slope Water individuals showed that physiological and biochemical states similar to those found in individuals from the 9 months old ring could be duplicated in 4 days of complete starvation.