Habitat selection and adult-recruit interactions in Pectinaria koreni (Malmgren) (Annelida: Polychaeta) post-larval populations: Results of flume experiments
The fate of recently settled populations of soft-bottom invertebrates depends not only on dispersal of pelagic larvae by tidal currents but also on other physical ( e. g. resuspension) and biological mechanisms ( e.g. habitat selection and adult-recruit interactions) acting at the water-substratum interface. To assess the relative importance of such processes under megatidal conditions in the Abra alba community of the eastern Baie de Seine (English Channel), flume experiments were conducted on post-larvae of the dominant polychaete species, Pectinaria koreni. Habitat selection by post-larvae of P. koreni was determined in a first set of experiments, where individuals were sowed either on a suitable or on an unsuitable substratum. Once resuspended, post-larvae were given a choice between two highly contrasting treatments with a natural organic-rich muddy sand and a bare flat PVC surface. P. koreni post-larvae were able to leave an unfavourable substratum into which they had initially burrowed and reach a more suitable substrate by drifting (induced by the secretion of mucus) before final settlement. The influence of adults on habitat selection and survival of P. koreni post-larvae was analysed in a second set of experiments, where individuals were sowed onto a suitable sediment with adults (test treatment) or without (control treatment). The presence of conspecific adults induced a high resuspension rate of the post-larvae. Drifting occurred mainly just after the introduction of the current and affected the whole experimental population, regardless of size. Such a response seems to be related to the intense bioturbation caused by the sub-surface deposit-feeding habit of the adults, which alters the boundary-layer flow. In contrast, the presence of adults of Owenia fusiformis, another dominant polychaete of the Abra alba community, led to an enhanced recruitment by a reduction in post-larvae resuspension. In fact, at low shear velocities, dense aggregates of tubes stabilize the sediment and so act as particle traps. Thus, in the megatidal environment of the Baie de Seine, physical conditions and behavioural responses interact and contribute to structuring the benthic community.