ECOLOGICAL EFFICIENCY OF A PELAGIC MYSID SHRIMP; ESTIMATES 

 FROM GROWTH, ENERGY BUDGET, AND MORTALITY STUDIES ' 



Robert I. Clutter^ and Gail H. Theilacker^ 



ABSTRACT 



The net ecological efficiency (yield/assimilated) of a population of Metamysidopsis elongata (Crus- 

 tacea, Mysidacea) is estimated to be 32 %. The gross ecological efficiency (yield/ingested) is probably 

 between 19 % and 29 %. 



Energy use by the field population was calculated from estimates of age specific natural mortality 

 rates and data on growth, molting, reproduction, and respiration. Average growth and molting rates 

 were determined by rearing the mysids in the laboratory. Size specific fecundity was determined from 

 field and laboratory observations. The calorie contents of the mysids, their molts, eggs and larvae 

 were estimated by bomb calorimetry and in part from biochemical composition. The energy used in 

 metabolism was calculated from size specific respiration and data on body composition. 



Biological systems are organized by the flow of 

 energ-y. Trophic structui-e, numbers of steps in 

 food chains, and numbers of conjunctions in 

 food webs depend on the amount of energy 

 passed through populations to other populations. 

 Energy units provide a means of expressing 

 productivity in terms common to all organisms. 

 The energy produced in the breakdown of 

 biomass by organisms is stored as chemical en- 

 ergy in the pyrophosphate bonds of adenosine 

 triphosphate (Horowitz, 1968). The overall 

 thermodynamic efficiency of this process is sim- 

 ilar in all animals, about 60 to 70 '}t according 

 to Krebs and Romberg (1957). It has been 

 suggested (e.g. Slobodkin, 1961, 1962) that the 

 efficiency of energy transfer between popula- 

 tions of animals is also fairly constant. This 

 efficiency is necessarily of lower order because, 

 for example, there are losses involved in syn- 

 thesizing macromolecules, in continually resyn- 

 thesizing proteins that undergo thermal dena- 

 turation, in transforming foodstuff energy into 

 work energy (about 65 ^r efficiency), and in 

 the degradation of energy during the perform- 



' This research was supported in part by NSF Grant 

 GB 7132. 



' Formerly of National Marine Fisheries Service Fish- 

 ery-Oceanography Center, La Jolla, Calif. 92037. 



^ National Marine Fisheries Service Fishery-Oceanog- 

 raphy Center, La Jolla, Calif. 92037. 



Manuscript received September 1970. 



FISHERY BULLETIN: VOL. 69. NO. 1, 1971. 



ance of work. All energy that passes through 

 a population is either lost as heat or passes on 

 to another trophic level. If one assumes that 

 all mortality is caused by predation, the gross 

 ecological efficiency (Phillipson, 1966) of energy 

 transfer through that population is the ratio 

 of the energy yield in mortality to the energy 

 ingested. 



Through laboratory studies of growth, molt- 

 ing, reproduction, respiration, body composition, 

 and energy content, we have constructed an 

 energy budget for the pelagic mysid shrimp 

 Metamysidopsis elongata (Holmes). Various 

 aspects of the distribution, behavior, and pop- 

 ulation biology of this species have been de- 

 scribed by Clutter (1967, 1969) and Fager and 

 Clutter (1968). The energy budget data, to- 

 gether with estimates of natural population 

 mortality rates, are used to estimate net and 

 gross ecological efficiencies for the field popu- 

 lation. 



GROWTH AND DEVELOPMENT 



Metamysidopsis elongata is a member of the 

 Mysidae, a family that is ubiquitous and often 

 very abundant in most of the neritic zones of 

 the world ocean. This species is free-swimming 

 and occurs in shoals and swarms just above the 

 sand bottom in areas where surf is common 



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