INFAUNAL PREDATION REGULATES BENTHIC RECRUITMENT - AN EXPERIMENTAL-STUDY OF THE INFLUENCE OF THE PREDATOR NEPHTYS HOMBERGII (SAVIGNY) ON RECRUITS OF NEREIS-DIVERSICOLOR (MULLER,O.F.)

Field and laboratory experiments were carried out to examine predatory activity effects of the infaunal polychaete Nephtys hombergii on the recruitment of Nereis diversicolor. Using N. diversicolor juveniles as prey, we tested the effects of (1) the temperature variations on pred atory activity and (2) the predator density (d = 114 and 342 ind. m(-2 )) on prey mortality, on their growth and their escape behaviour. In t he field, N. diversicolor alone (d = 13750 ind. m(-2)), and N. homberg ii (d = 114 and 342 ind. m-2) and N. diversicolor juveniles together w ere enclosed in 15-cm dia. PVC cylinders during 12 weeks, from 7 March to 30 May 1995, in a mudflat of the Rance Estuary. In the presence of the predator, the biomass of N. diversicolor juveniles declined 8-12 X more than in control cylinders, whereas their individual weight was increased. Although it had little effect on the biomass of prey, preda tor density regulated the consumption by N. hombergii. Predation activ ity was minimal, but effective, at a temperature of 7 degrees C, incre ased between 9 and 11 degrees C, and became constant above 11 degrees C. In the laboratory, gradual or sudden temperature variations had lit tle effect on predatory activity of N. hombergii, presumably because t hey were already physiologically active. Reduction in the abundance of infauna may be due to prey emigration as well as predation: beyond th eir mortality, N. hombergii induced, proportional to its density, the emigration of juveniles. The experimental results suggest that infauna l predation, by regulating recruit densities, should be considered in addition to the interactions between adults as a strong force structur ing soft-bottom communities. (C) 1998 Elsevier Science B.V. All rights reserved.