Creature of the Month- Comb Jelly
By: Alexandrya Robinson, UHM MOP Student
If you take a dive into an estuary, you might be dipping into the same area as a comb jelly. Despite the word ‘jelly’ in their name, these organisms are not “jellyfih”, but actually ctenophores. The comb jelly’s unique comb plates, which they use to move up and down in the water, refract light in the water column and create the iconic appearance of a glowing rainbow along the oval body of the organism. Some species also bioluminesce at night! There are over 100 species of comb jelly that inhabit the ocean, many of which have been extant for over 500 million years. Although species of comb jellies can be found in every ocean on Earth, non-native species can sometimes travel to other bodies of water and become invasive there.
The adaptable nature of the comb jelly allows it to colonize multiple areas of the ocean. They are carnivores, feeding primarily on zooplankton and salps. Although sometimes phytoplankton can also be found in the digestive tract of comb jellies, but their presence is most likely due to the feeding style of the organism. Comb jellies take in food by pumping water into the opening at the bottom of their bell and catching prey with specialized cells that are adhesive, called colloblasts, coating the inner tentacles. Unlike the cnidarians (including true jellyfish) the tentacles of the comb jelly do not sting.
When swimming, the comb jellies flare out two lobes to which the tentacles are attached in order to collect even more food until they are covered, at which point the lobes are taken into the body. Comb jellies are typically constant feeders, although in areas with poor nutrient availability, comb jellies can reduce their physical size to require less food, allowing them to survive in suboptimal environments- even in highly polluted waters. In these low nutrient environments, comb jellies have also been known to cannibalize their young.
Full-grown comb jellies can ingest other juvenile and adult comb jellies. Mature comb jellies reproduce by releasing both male and female gametes during the summer months. According to the Chesapeake Bay Program, some species of comb jelly reach sexual maturity within two weeks, and a 2012 study published in Biology Letters found that one species, Mertensia ovum, was capable of reproducing while still in the larval stage. In some cases, low salinity does impact this sexual maturity. The hermaphroditic nature of the comb jellies allows even a single jelly to populate a whole new area on their own, which is another advantageous adaptation, and one that makes them especially insidious as an invasive species. Comb jellies are lots of fun to see, but be mindful! These ctenophores are incredibly delicate and can easily break apart if removed from the water.