Hypoxia interface behavior of the ctenophore Mnemiopsis leidyi

The ctenophore Mnemiopsis leidyi is most widely known as a destructive invasive species of the Black and Caspian seas. Ctenophores are also found endemically in oceans worldwide, where their low oxygen tolerances allow many of them to use hypoxic zones to escape predation and hunt disabled prey. Ctenophores have also been observed in the wild and laboratory conditions associating with the interface of hypoxic and normoxic waters, allowing them to feed on the organisms found there. In order to test the ability of M. leidyi to find oxygen interfaces, a 10 cm diameter X 60 cm tall cylindrical tank was designed with a sharp oxycline (<1cm) in the middle, stabilized by a 1 ppt salinity difference. The hypoxic water was produced by nitrogen bubbling prior to the experiment. We found that animals introduced to the tank under oxycline conditions increased their time spent at the interface by over nearly five-fold versus those in a fully normoxic or hypoxic water. These preliminary results would indicate that M. leidyi preferentially associates with the interfaces of hypoxic zones. As human effects such as overfishing, nutrient enrichment of coastal waters, and invasive introduction continue to rise, the complex interactions of these animals and hypoxic zones will become increasingly important to planktonic and pelagic ecosystems worldwide.