AN ENERGY BUDGET FOR THE SOUTH AFRICAN ABALONE HALIOTIS MIDAE LINNAEUS

Existing data on feeding, growth rate, fecundity, absorptionefficiency, respiration and excretion rates in the South Africanabalone Haliotis midae Linnaeus are converted to energy equivalentsand 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 lossesin the form of ammonia excretion are negligible, accountingfor less than 1% of consumption. Some 5% of energy intake, or13% of absorbed ration (Ab) is thus available for growth andreproductive output (Pg & Pr). In juveniles (<100mm)this is all allocated towards somatic growth, while in adultsan increasing proportion of production is expended on reproductiveoutput. Although feeding, respiration and excretion rates allincrease with temperature the proportions of energy allocatedto the various components of the energy budget appear to beconsistent. Population energy budgets are calculated from densityand size distribution surveys at two study sites. At MarcusIsland, on the Cape west coast, the population has a standingstock of 82 g (wet flesh weight) m^–2,.consumes about 3260KJm^–2y^–1 algae and has a P/B ratio of 0.46, whereasat Cape Hangklip, on the Cape south coast, the population biomassis_133gm^–2, consumes 8613KJm^–2y^–1 and hasa P/B ratio of 0.70. These figures indicate that a high proportionof kelp bed primary production is directly consumed by grazingabalone in areas where populations have not been reduced byhuman exploitation (Received 16 March 1987;