Importance of a Small Carnivorous Isopod in Energy Transfer

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Abstract
The predatory isopod C. imposita (Barnard) inhabits kelp holdfasts off the west coast of southern Africa. Its energy contribution to kelp bed communities was estimated. Annual production and standing crop were 2229 and 394 kJ m-2 yr-1, respectively (P/B [production/biomass ratio] = 5.56). Consumption (9899), defecation (976) and respiration (1822) rates (kJ m-2 yr-1) were estimated experimentally and their relationships analyzed. The ratios between the various rates of energy transfer were used to characterize the physiological and ecological properties of the population. Assimilation efficiency ranged from 88-98% on a natural diet of syllid polychaetes; gross growth efficiency, net growth efficiency and P/R [production/respiration ratio] were calculated as 15-26%, 55% and 1.02, respectively. The ecological implications of the high assimilation efficiency and low metabolic rates combined with the various energy transfer components are discussed in relation to other members of the kelp bed community. Although C. imposita biomass is less than half that of the commercially exploited rock lobster Jasus lalandii, its energy flow contribution to the community is estimated to be 5 times as great as the lobster''s.