AN ENERGY BUDGET FOR THE SOUTH AFRICAN ABALONE HALIOTIS MIDAE LINNAEUS

Abstract

Existing data on feeding, growth rate, fecundity, absorption efficiency, respiration and excretion rates in the South African abalone Haliotis midae Linnaeus are converted to energy equivalents and utilised to compile individual energy budgets. About 63% of the energy content of the food consumed (C) is lost as faeces (F) and a further 32% expended on respiration (R). Energy losses in the form of ammonia excretion are negligible, accounting for less than 1% of consumption. Some 5% of energy intake, or 13% of absorbed ration (Ab) is thus available for growth and reproductive output (Pg & Pr). In juveniles (−2,.consumes about 3260 KJm⁻²y⁻¹ algae and has a P/B ratio of 0.46, whereas at Cape Hangklip, on the Cape south coast, the population biomass is_133gm⁻², consumes 8613KJm⁻²y⁻¹ and has a P/B ratio of 0.70. These figures indicate that a high proportion of kelp bed primary production is directly consumed by grazing abalone in areas where populations have not been reduced by human exploitation