Selective settlement of deep-sea canyon nematodes after resuspension — an experimental approach

Abstract

Dispersal processes are known to influence dynamics of marine benthic communities. It has been argued that as a result of nematodes being small in size and lacking pelagic larvae, it is unlikely that they are able to disperse actively over wide geographical ranges. Nematode dispersal is therefore assumed to be predominantly driven by water currents entraining resuspended sediments containing nematodes. Three different types of substrates combined with sediment (algae, bacteria, and sulphides) and two different controls (empty and azoic sediment) were offered to a nematode community sinking through the water column in three independent, simultaneously running replicated experiments. Selective settlement of nematodes was observed whilst descending in the water column under ex-situ experimental conditions using samples collected in the Whittard canyon at 812m of water depth. Significant differences in nematode community structure between treatments suggest that different nematodes are attracted by different substrates. They may colonise suitable patches selectively when descending in the water column, but whether they are attracted by food or by other attractants, such as pheromones or other chemical signals, is still unclear. High abundances of the chemosynthetic, mouthless nematode Astomonema found in the canyon study area over medium-scale distances (10–100m) contribute to the idea that resuspension events enable dispersal of nematodes over larger distances, after which active settlement can occur through chemical attraction.