JOURNAL OF PLANKTON RESEARCH | VOLUME 17 | NUMBER 11 | PAGES 2117-2130 | 1995
© Oxford University Press
research-article |
Effects of different natural regimes of temperature and food on survival, growth and development of Artemia monica Verrill
1Marine Science Institute, University of California Santa Barbara, CA 93106, USA 2Department of Biological Sciences, University of California Santa Barbara, CA 93106, USA 3Present address: Biological Sciences Center, Desert Research Institute PO Box 60220, Reno, NV 89506-0220, USA
Received on October 30, 1994; accepted on August 3, 1995 Each year, two generations of Artemia monica Verrill develop under different environmental conditions in hypersaline Mono Lake, California, USA. The first generation develops during spring when food levels are high and temperatures are low and warming slowly. The second generation develops during summer at low food levels and higher initial temperatures which continue to warm. In three experimental treatments, the development, growth and survival of first-and second-generation Artmia were determined under laboratory conditions which tracked the natural temperature and food regimes in the lake. Two food treatments were administered concurrently at low temperatures to first-generation shrimp, representing the high levels usually found during the spring (spring-high-food) and reduced food levels observed during a recent 6 year period of meromixis (spring-low-food). The third treatment of low food and higher temperatures was administered to second-generation shrimp in summer (summer-low-food). The development to adulthood and onset of reproduction occurred 5 days sooner in the high-food treatment than in the low-food treatment of the spring experiment, while development was 2–3 times faster in the warmer, summer-low-food treatment. Under spring-high-food conditions, shrimp had a higher survival to adulthood (46%) and lower daily mortality rate (0.012 day–1) than in the spring-low-food treatment (30% survival and a 0.015 day–1 mortality rate). Survival to adult hood of summer-low-food animals (49%) was similar to that in spring-high-food; however, the daily mortality rate was twice as high (0.029 day–1). While instar-specific length did not vary among treatments, instar-specific weights of juveniles and adults were lower in the summer-low-food treatment than in the other two treatments. Since food in the summer-low-food treatment was lower and tem peratures higher than in the spring-low-food treatment, the lower weights in summer may be explained by food rather than temperature, or by both. The cumulative secondary production of single cohorts was lowest in the summer (0.32 mg dry weight individual–1) due to low individual weights and highest under spring-high-food conditions (1.1 mg dry weight individual–1).