Migration of a marine oligochaete: induction of dispersal and microhabitat choice

Abstract

We present evidence for migration in the asexual phase of the life cycle of Paranais litoralis (Mller), a marine oligochaete that reproduces asexually by fission. Depletion of resources triggers a swimming response by some worms ('migrators'). Migrating worms are longer, thinner and have more segments than non-migrating worms, indicating that migrating worms postpone reproduction. Experiments show that migrators swim more actively than non-migrators, and that this causes them to stay suspended in the water column longer than non-migrators. Worms avoid sediment where resources are exhausted, both when burrowing and when returning to the bottom after swimming. Based on laboratory cultures and field observations, we hypothesize that local depletion of resources is a common phenomenon for P. litoralis, and that migration is important for the persistence of P. litoralis populations.