Sand‐Beach Energetics: Importance of the Isopod Tylos Punctatus

Abstract

The isopod Tylos punctatus dominates the supratidal sand—beach communities at a number of locations in southern California and northern Mexico. It feeds on the giant kelp Macrocystis pyrifera, which appears to be the major source of organic input for these beaches. Field measurements on kelp input and on the kelp consumption and assimilation rates of the isopods indicated that the animals were consuming an average of only 4%—5% of the edible kelp input. Assimilation efficiencies were high, however, averaging 64%. Approximately 88% of the assimilated energy could be accounted for by metabolic activity and growth. The beaches investigated appear to be of only minor importance in the degradation of nitrogen compounds (e.g. proteins) to NH 4 + —N and the recycling of this material to the nearshore waters.