Population dynamics and energy budget for a population of Donax variabilis(Say) on an exposed South Carolina beach

Donax variabilis is widely distributed over the lower half of the shore at Waites island on the South Carolina coast. Densities peaked at almost 12 00 0 individuals m(-2) at spawning, which also coincided with a concentration of the population in a narrow strip at mid-tide level. Following this, the population almost disappeared from the shore until late in the year, when n umbers of small individuals started to appear. Evidence for a second, autum n spawning was equivocal. Mean annual biomass over the lower part of the be ach was low (6.45 kj m(-2)) but P:B very high (6.74) and in addition, gamet e output accounted for another 86.6 kj m(-2) y(-1), equivalent to 64% of to tal production. The evidence also suggested that the majority of the popula tion was effectively semelparous, but the population reproductive strategy was classified as one of restraint rather than reckless. The productivity m akes a significant contribution to neighbouring land and nearshore systems. (C) 1999 Elsevier Science B.V. All rights reserved.