Energy transformation by the supralittoral isopod Ligia dilatata Brandt

Abstract

Energy flow was studied through a population of the supralittoral isopod Ligia dilatata Brandt, which inhabits kelp debris cast up on rocky shores. Mean annual standing crop ( B ̄ ) and production ( P) were estimated from field data to be 422 and 1582 kJ · m −1 of shoreline, respectively, giving a P B ̄ ratio of 3.7. Population consumption (C), egestion ( F), and respiration ( R) rates (123258, 88395, and 5194 kJ · m −1 · yr −1, respectively) were estimated from laboratory experiments. Energy lost through urinary excretion and DOM was considered to be negligible and was not estimated. Various efficiency ratios are used to characterize energy flow through the population: absorption efficiency ( (C−F) C ) is 28.3%, assimilation efficiency ( (P + R) C ) is 5.5% and gross growth efficiency ( P C ) a very low 1.3%. The ecological implications of the fast consumption and egestion rates coupled with low assimilation and growth efficiences are discussed, showing that L. dilatata must be regarded as energy transformers returning large amounts of suspended detritus to adjacent aquatic ecosystems.