An Estimate of Production and Consumption Rates in the Spiny Lobster Panulirus homarus on a Shallow Littoral Reef off the Natal Coast, South Africa

Abstract

Production and consumption rates were studied in a population of the spiny lobster Panulirus homarus (Linnaeus) inhabiting an isolated reef. Estimated mean production rate (P) (comprisJng somatic tissue, unliberated gonadal products and exoskeleton) was 47.6 kJ nr2y-' or, in terms of dry mass, 2.lg m-*y-' (P/B : 0.42). Mean gonadal output (G) was 9.8 kJ m-'y-' of which egg production comprised about 90 /Q. Nevertheless, total production rate (PS G) was approximately equal in the sexes suggesting that the slower growth rate and lower value for P i n females is directly proportional to energy loss by egg production. The energy lost through moulted exuviae (conventionally assigned to excreta (U) in the energy budget) was determined using the same basic method as for determination of Pand amounted to 28.1 kJ m2y-'. On the basis of the consumption rate of flesh of the mussel Pema pema in captive lobsters (the principal food organism of P. homarus) it was estimated that the reef population consumed 1070 W m-2y-'. The food in the form of mussels on the reef was substantially in excess of the requirements of the lobster population although an unknown proportion may be physically unavailable.