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Life History and Energy Relations of the Giant Fairy Shrimp Branchinecta gigas Lynch 1937 (Crustacea: Anostraca)

Graham R. Daborn
Ecology
Vol. 56, No. 5 (Late Summer, 1975), pp. 1025-1039
Published by: Wiley
DOI: 10.2307/1936144
Stable URL: http://www.jstor.org/stable/1936144
Page Count: 15
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Life History and Energy Relations of the Giant Fairy Shrimp Branchinecta gigas Lynch 1937 (Crustacea: Anostraca)
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Abstract

The life cycle and energy relations of the giant fairy shrimp, Branchinecta gigas Lynch, in a turbid, aestival lake in western Canada are described for 1972. Hatching of overwintered eggs began when lake sediments thawed in April, at which time salinity was low as a result of snow runoff; hatching ceased after a few days as salt deposits redissolved and salinity of the water incresed. The population, being of almost uniform age, was treated as a single cohort. Larval and post-larval growth in length followed a sigmoid pattern that could be well described by a logistic curve. Maximum growth rates occurring at 3-4 wk of age were 2.54 mm/day for @M @M and 2.95 mm/day for @V @V, representing daily length increments of 11.3% and 10.3%, respectively. Corresponding max dry weight increases were 33% of body weight per day in each case. Average max lengths of 47.7 mm for @M @M and 60.6 mm for @V @V were attained at ages of 40-45 days; max longevity was 60 days. The species is exclusively predaceous for most of its life cycle, feeding primarily upon Branchinecta mackini and Diaptomus nevadensis. Females were estimated to produce three clutches of eggs, with clutch size being proportional to total body length of the @M, and average fecundity in 1972 was calculated at 630 eggs. Measurements of feeding rate and O"2 consumption were made over 24-h periods in the lake and an energy budget was cosntructed for most of the life cycle (46 days) on the basis of logistic growth curves fitted to field data. Males assimilated 67% and @M @M 94% of ingested food, investing 23% and 22% of assimilated energy, respectively, in somatic growth. Molting losses were estimated at 5%-6%, and an extreme estimate of 14% was calcualted to represent nitrogen excretion, on the assumption of strictly carbohydrate and lipid-based metabolism. Maintenance costs were estimated at 58% in @M @M and 47% @V @V. The difference (11.3%) corresponded precisely to the costs of egg production.

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