The influence of structure and dynamics of infaunal predator populations on predatory activity: the example of Nephtys hombergii

In an attempt to associate population structure of infaunal predators with the effect of predation in structuring benthic communities, an extensive study was conducted focusing on a population of the predatory polychaete Nephtys hombergii in the Rance estuary (western English Channel). Sampling was designed to study both spatial distributions in abundance and weight throughout the whole estuary (1995), and temporal variations of the predator population on a sublittoral mudflat (1995–1997). The results reveal that large individuals are significantly distributed on intertidal mudflats, while juveniles (G0 and G1 classes) inhabit the whole sublittoral area. Juveniles are dominant throughout the year (>90% of individuals), but are characterized by high mortality rates (70–80%), which are directly responsible for changes in population abundance. Before investigating the effect of predation, the population structure and the spatial distribution of predators must be known, an important step when considering that prey mortality induced by a 1-year-old N. hombergii was about 20% higher than rates observed with adults. Based on the example of N. hombergii, the results underline the necessity of considering the age, the weight structure and the dynamics of the predator population to understand the dynamics of marine communities in a better way.