Microalgal biofilm induces larval settlement in the model marine wormPlatynereis dumerilii

Abstract

ABSTRACTA free-swimming larval stage features in many marine invertebrate life cycles. To transition to a seafloor-dwelling juvenile stage, larvae need to settle out of the plankton, guided by specific environmental cues that lead them to an ideal habitat for their future life on the seafloor. Although the marine annelidPlatynereis dumeriliihas been cultured in research labs since the 1950s and has a free-swimming larval stage, specific environmental cues that induce settlement in this nereid worm are yet to be identified. Here we demonstrate that microalgal biofilm is a key settlement cue forP. dumeriliilarvae, inducing earlier onset of settlement, and enhancing subsequent juvenile growth as a primary food source. We tested the settlement response ofP. dumeriliito 40 different strains of microalgae, predominantly diatom species, finding thatP. dumeriliihave species-specific preferences in their choice of settlement substrate. The most effective diatom species for inducingP. dumeriliilarval settlement were benthic pennate species includingGrammatophora marina,Achnanthes brevipes, andNitzschia ovalis. The identification of specific environmental cues forP. dumeriliisettlement enables a link between its ecology and the sensory and nervous system signalling that regulate larval behaviour and development. Incorporation of diatoms intoP. dumeriliiculture practices will improve the husbandry of this marine invertebrate model.