Infaunal predation regulates benthic recruitment: an experimental study of the influence of the predator Nephtys hombergii (Savigny) on recruits of Nereis diversicolor (O.F. Müller)

Abstract

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 predatory activity and (2) the predator density ( d=114 and 342 ind. m −2) on prey mortality, on their growth and their escape behaviour. In the field, N. diversicolor alone ( d=13750 ind. m −2), and N. hombergii ( d=114 and 342 ind. m −2) and N. diversicolor juveniles together were 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× more than in control cylinders, whereas their individual weight was increased. Although it had little effect on the biomass of prey, predator density regulated the consumption by N. hombergii. Predation activity was minimal, but effective, at a temperature of 7°C, increased between 9 and 11°C, and became constant above 11°C. In the laboratory, gradual or sudden temperature variations had little effect on predatory activity of N. hombergii, presumably because they were already physiologically active. Reduction in the abundance of infauna may be due to prey emigration as well as predation: beyond their mortality, N. hombergii induced, proportional to its density, the emigration of juveniles. The experimental results suggest that infaunal predation, by regulating recruit densities, should be considered in addition to the interactions between adults as a strong force structuring soft-bottom communities.