Migration of a marine oligochaete: induction of dispersal and microhabitatchoice

We present evidence for migration in the asexual phase of the Life cycle of Paranais litoralis (Muller), a marine oligochaete that reproduces asexuall y by fission. Depletion of resources triggers a swimming response by some w orms ('migrators'). Migrating worms are longer, thinner and have more segme nts than non-migrating worms, indicating that migrating worms postpone repr oduction. Experiments show that migrators swim more actively than non-migra tors, and that this causes them to stay suspended in the water column longe r than non-migrators. Worms avoid sediment where resources are exhausted, b oth when burrowing and when returning to the bottom after swimming. Based o n laboratory cultures and field observations, we hypothesize that local dep letion of resources is a common phenomenon for P. litoralis, and that migra tion is important for the persistence of P. litoralis populations.