Predatory copepods can control nematode populations: A functional-response experiment with Eucyclops subterraneus and bacterivorous nematodes

A classical functional-response experiment was conducted in order to test the potential of copepods as predators of free-living nematodes. The cyclopoid copepod Eucyclops subterraneus scythicus readily fed oil the two offered bacterivorous nematode species, Panagrolaimus sp. and Poikilolaimus sp. In nature, the investigated organisms are members of a very simply structured community occurring in floating microbial mats in the chemoautotrophic groundwater ecosystem of Movile Cave, Romania. At different prey densities, the copepod's feeding rates followed type II functional responses. Within 20 ruin, the maximum number of consumed nematodes was 25.8 Panagrolaimus sp. or 37.5 Poikilolaimus sp., corresponding to 28.7 % and 31.1 % of the predator's average dry weight. Within 24 h, the predator's mean consumption corresponded to 264.4 % of its own dry weight. Using the estimated copepod feeding rates and known population growth rates of the mat's nematodes, we calculated that E. s. scythicus has the potential to top-down control exponentially growing nematode populations. This study is the first attempt to quantify a predator-prey relationship between coexisting copepods and nematodes at the population level and sheds light on a trophic link that could be relevant in many marine, limnic, and semi-terrestrial habitats.