Environmental dependence of colony morphologies in <i>Labyrinthula</i> species

Labyrinthula species are protistan organisms found across a variety of marine environments whose defining characteristic is the secretion of an extracellular ectoplasmic net. Under certain conditions, colonies form a spatial network of 'tracks' through which cells move bidirectionally. We show that this network morphology depends on the presence of a liquid overlay, with air-exposed colonies exhibiting instead a dense, aggregated morphology. We demonstrate dynamic restructuring between these two morphologies upon addition or removal of the liquid overlay and investigate growth behaviour under varying nutrient conditions. Given the inter-tidal environment of certain seagrass species colonized by Labyrinthula, our results may shed light on the relationship between this organism and its seagrass host, for which it is an opportunistic pathogen associated with seagrass wasting disease.