Pelagic jellyfish have often been considered to be trophic dead-ends, providing little benefit to marine food webs. However, studies have increasingly indicated that both aquatic and terrestrial species frequently consume pelagic jellyfish despite their low energy content. Much less is known about the role that benthic jellyfish play in marine and estuarine food webs, a topic of great importance as benthic jellyfish blooms may occur as a result of anthropogenic activities. In this study, we documented one of the first known instances of predation on the benthic jellyfish, Cassiopea spp., by the polychaete bristle worm, Hermodice carunculata on Abaco Island, Bahamas in March, April, and August, 2014. We conducted feeding trials with Cassiopea using video cameras in a hard-bottom, mangrove-lined tidal creek (150m long, 8m wide) on Abaco. In each feeding trial (N =7), Cassiopea were placed in front of the camera; two daytime feeding trials within three creek locations were conducted, and in one trial, a dead ballyhoo (Hemiramphus brasiliensis) was offered to elucidate whether H. carunculata exhibit a feeding preference between jellyfish and fish. One nighttime feeding trial was also conducted using infrared lighting to document whether bristle worms consume jellyfish at night.
Results/Conclusions
In 5/6 daytime feeding trials, H. carunculata found Cassiopea and began consuming them. The time it took for worms to find Cassiopea varied; worms ranged between 3 and 15 minutes to appear on camera. Between 1 and 5 worms were found to consume an individual jellyfish, and feeding lasted no longer than 30 minutes. Predation on jellyfish appeared haphazard; worms consumed both the oral arms and jellyfish bell. Worms did not consume the dead fish in the daytime trial, instead selecting the jellyfish. This is surprising, as H. carunculata has been found to prefer dead fish over live coral. We also found worm predation in the night trial; one worm began consuming the jellyfish within the first 3 minutes of the trial, and an additional worm began consuming the jellyfish after 8 minutes and 52 seconds of the trial. Most of the worms were observed emerging from the creek bottom, actively swimming towards jellyfish. Though further research is required, H. carunculata may consume Cassiopea jellyfish to acquire venom from nematocysts, influencing which aquatic species can consume H. carunculata. Ultimately, as jellyfish populations increase in response to global environmental change, understanding biotic interactions between jellyfish and other organisms is imperative.