Food-dependent migratory behavior of benthic harpacticoid Heterolaophonteminuta: An experimental approach and...

Benthic harpacticoid copepods are usually patchy distributed forming short-lived aggregations at small spatial scales. They also regularly emerge from the sediment to the water column and then resettle, concentrating in food-rich microhabitats. The trophic relationships with their prey are among the most plausible explanations for these migrations, but the specific regulatory mechanisms are still unclear. The resettling behavior of the harpacticoid Heterolaophonte minuta under no-flow conditions was investigated. The experiments were carried out in 12-well settling chambers with azoic sediments in the wells. One half of the wells contained diatom cultures as a food source. At the start of the experiment, an equal number of crustaceans were placed in half of the wells, and the chambers were filled with sieved seawater to mimic a flood tide. After 24 h, the harpacticoids left the no-food wells and were concentrated in the food-rich wells, resulting in two-to threefold greater densities in the algae-treated wells than in the no-food controls. This result was similar among all the experiments irrespective of the algal culture used and the initial number of crustations. Two simple models were proposed to simulate this migratory behavior. The first model assumed the food-dependent emergence rate, while movement and resettlement are nonselective random processes; the second model assumed the equiprobable emergence, but harpacticoids are able to search for diatom-rich cells for selective settling. Both models were able to satisfactorily reproduce the experimental results, whereas the former model performed slightly better and faster. Both mechanisms are not mutually exclusive and may contribute to meiofaunal dispersal, but in high-energy intertidal habitats, trophic-dependent emergence with passive dispersal by water flow seems to be more realistic.