Space occupation by the polychaetous annelid Perinereis cultrifera: Influence of substratum heterogeneity and intraspecific interactions on burrow structure

Spatial analysis, laboratory experiments and field observations in the intertidal zone of La Rance Estuary (northern coast of Brittany, France) of the infaunal polychaete Perinereis cultrifera indicate that the distribution and the abundance of this species appear to be related to the availability of cobbles. Individuals build U-shaped galleries with a surface gutter network protected by a cobble which acts as a roof. The study of spatiotemporal evolution of P. cultrifera burrows showed experimentally that density is important in space-sharing modalities within the sediment. Effects of increased density lead to modifications in the shape and size of the burrows. The absence of connections between burrows, as observed in 'sandwich aquaria' and in resin casts, suggest that the gallery is defended against intruders. The study of the distance between individuals in the laboratory did not reveal a regular distribution pattern. These results probably mean that the area around the burrow opening is not defended and, therefore, does not constitute a territory. Perinereis cultrifera is probably competing for burrow space while food may be shared. Territoriality is certainly the main factor involved in the organization and the spatial arrangements of individuals within a population.