Cryptic life stages in scyphozoan jellyfish: Larval settlement preferences of the South American sea nettle Chrysaora plocamia

- This is the first study on settlement preferences of planulae from the scyphozoan jellyfish Chrysaora plocamia.
- Chrysaora plocamia planulae displayed clear settlement preferences for specific colours, i.e., red and green.
- Fine-scale microhabitat preferences may enhance polyp survival and may be important within the context of jellyfish blooms.

Bloom forming jellyfish have received considerable attention over the past years. And while the eye-catching medusa is well studied, little is known about its small, inconspicuous and hard to find polyp-counterpart. In fact, so hard to find that polyps of most scyphozoan species have not been detected in their natural habitat. Considering the important roles polyps may play in jellyfish bloom formation, identifying the criteria for planulae to select suitable microhabitats that warrant the well-being and survival of polyps is a key issue. In order to find clues on the characteristics of natural habitats of Chrysaora plocamia polyps, settlement preferences of planulae were determined in a laboratory study. The settlement density, geotaxis and colour preferences were assessed, using a three-dimensional substrate that provided settlement areas of different orientation, levels of shelter and colours. Planulae exclusively colonized horizontal surfaces in an upside down position, tended to settle in sheltered areas and showed significant preferences for green and red substrates. If planulae of the jellyfish C. plocamia display similar preferences in the field, polyps should be found on protected substrates that provide overhangs, small caves, crevices or roof-surfaces, and green or red substrates, like stipes and blades of macroalgae, or crustose coralline algae.