Sediment selection by juvenile Arenicola marina

Abstract

Juveniles of the benthic polychaete Arenicola marina migrate until they recognise a substratum suitable for settlement. As in a number of marine invertebrates, inter- and intra-specific interactions are of importance in selecting a habitat, and specific chemical factors are involved. This study focuses on the sediment preferences of larvae and juveniles and includes an assessment of both the positive and negative chemical cues. The data confirm an attraction of juvenile conspecifics to each other during settlement in a gregarious type of positive response, whereas a negative response to sediments that have been populated by adult A. marina exists. Attraction and larval settlement were induced by a number of synthetic chemicals, including fatty acids, amino acids and tripeptides, and by Rhodomonas sp. and Nephtys hombergii populated sand. Aquatic fish food (Tetra-Marine, commercial trout diet) enriched sediment induces settlement at a similar range; this suggests that settlement can be induced non-specifically by water soluble compounds, which may indicate organically enriched and therefore potentially favourable sites for settlement. In A, marina, brominated aromatics (e.g. 3,5-dibromo-4-hydroxybenzoic acid) inhibit settlement and function as negative cues in a similar way to those described for terebellid polychaetes. Negative cues may be more important than positive cues and their role in substratum choice by invertebrate larvae has been underestimated.